Post by thread:[EE]: Bulb Life -- Burned out bulb resurected

I have been having a problem with the light fixture in my kitchen going through bulbs fast (bulbs lasting about a month). This fixture uses the more expensive, large diameter bulbs. When the last one went out, I did not replace it right away. Several days later, it came back to life! Since then, it has gone out several times (for 2-7 days) but has, so far, always come back to life. I have measured the voltage in the socket during one of the bulb's dead periods and verified that there is power in the socket (117v). I imagine that somewhere in the bulb is an intermittent short. The room is air conditioned so temp does not vary that much (except when the bulb is on:) Another strange thing: Three times now, when other bulbs have gone out in this fixture, the glass bulb separates from the metal socket while the light is on and drops to the table below! So I guess my question is "Should I be concerned that this fixture is haunted?". Should I call Bill? (Maurry - not Gates) --BobG {Original Message removed}

I would guess that the fixture is trapping heat from the bulb and overheating it. {Quote hidden}> -----Original Message----- > From: Robert E. Griffith [spam_OUTbobTakeThisOuTJUNGA.COM] > Sent: Monday, July 16, 2001 11:15 AM > To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU > Subject: Re: [EE]: Bulb Life -- Burned out bulb resurected > > > I have been having a problem with the light fixture in my > kitchen going > through bulbs fast (bulbs lasting about a month). This > fixture uses the more > expensive, large diameter bulbs. When the last one went out, > I did not > replace it right away. Several days later, it came back to life! > > Since then, it has gone out several times (for 2-7 days) but > has, so far, > always come back to life. > > I have measured the voltage in the socket during one of the > bulb's dead > periods and verified that there is power in the socket (117v). > > I imagine that somewhere in the bulb is an intermittent > short. The room is > air conditioned so temp does not vary that much (except when > the bulb is > on:) > > Another strange thing: Three times now, when other bulbs > have gone out in > this fixture, the glass bulb separates from the metal socket > while the light > is on and drops to the table below! > > So I guess my question is "Should I be concerned that this fixture is > haunted?". Should I call Bill? (Maurry - not Gates) > > --BobG > > -----Original Message----- > From: pic microcontroller discussion list > [PICLISTKILLspamMITVMA.MIT.EDU]On > Behalf Of Jinx > Sent: Saturday, July 14, 2001 9:54 PM > To: .....PICLISTKILLspam.....MITVMA.MIT.EDU > Subject: Re: [EE]: Bulb Life > > > Ha ha! They don't want to educate you, they want > > to keep you as stupid as possible and buying as many > > bulbs as possible. Evil empires are like that! ;o) > > -Roman > > Appropriate then that this is posted under an [EE] Evil Empires > tag. What truth is there really to planned obsolescence ? Any > proven examples ? Light bulbs and tyres spring to mind as > products widely believed to be "improvable" > > btw, as I travel around I pop into the odd electrical wholesaler > and always leave a copy of my bulb life web page and some > comments from the list (anonymous of course) about extending > filament bulb life. Had a few "ooohs" from counter staff as they > realised the implications > > -- > http://www.piclist.com hint: To leave the PICList > EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

What does the loose neutral do to make the bulb burn out faster? --BobG -----Original Message----- From: pic microcontroller discussion list [KILLspamPICLISTKILLspamMITVMA.MIT.EDU]On Behalf Of Jim Sent: Monday, July 16, 2001 1:43 PM To: RemoveMEPICLISTTakeThisOuTMITVMA.MIT.EDU Subject: Re: [EE]: Bulb Life -- Burned out bulb resurected A loose white wire (neutral) will make the bulb go out fast... ----- Original Message ----- From: "Don Hyde" <spamBeGoneDonHspamBeGoneAXONN.COM> To: <TakeThisOuTPICLISTEraseMEspam_OUTMITVMA.MIT.EDU> Sent: Monday, July 16, 2001 12:13 PM Subject: Re: [EE]: Bulb Life -- Burned out bulb resurected {Quote hidden}> I would guess that the fixture is trapping heat from the bulb and > overheating it. > > > -----Original Message----- > > From: Robert E. Griffith [RemoveMEbobTakeThisOuTJUNGA.COM] > > Sent: Monday, July 16, 2001 11:15 AM > > To: PICLISTEraseME.....MITVMA.MIT.EDU > > Subject: Re: [EE]: Bulb Life -- Burned out bulb resurected > > > > > > I have been having a problem with the light fixture in my > > kitchen going > > through bulbs fast (bulbs lasting about a month). This > > fixture uses the more > > expensive, large diameter bulbs. When the last one went out, > > I did not > > replace it right away. Several days later, it came back to life! > > > > Since then, it has gone out several times (for 2-7 days) but > > has, so far, > > always come back to life. > > > > I have measured the voltage in the socket during one of the > > bulb's dead > > periods and verified that there is power in the socket (117v). > > > > I imagine that somewhere in the bulb is an intermittent > > short. The room is > > air conditioned so temp does not vary that much (except when > > the bulb is > > on:) > > > > Another strange thing: Three times now, when other bulbs > > have gone out in > > this fixture, the glass bulb separates from the metal socket > > while the light > > is on and drops to the table below! > > > > So I guess my question is "Should I be concerned that this fixture is > > haunted?". Should I call Bill? (Maurry - not Gates) > > > > --BobG > > > > -----Original Message----- > > From: pic microcontroller discussion list > > [EraseMEPICLISTMITVMA.MIT.EDU]On > > Behalf Of Jinx > > Sent: Saturday, July 14, 2001 9:54 PM > > To: RemoveMEPICLISTEraseMEEraseMEMITVMA.MIT.EDU > > Subject: Re: [EE]: Bulb Life > > > > > Ha ha! They don't want to educate you, they want > > > to keep you as stupid as possible and buying as many > > > bulbs as possible. Evil empires are like that! ;o) > > > -Roman > > > > Appropriate then that this is posted under an [EE] Evil Empires > > tag. What truth is there really to planned obsolescence ? Any > > proven examples ? Light bulbs and tyres spring to mind as > > products widely believed to be "improvable" > > > > btw, as I travel around I pop into the odd electrical wholesaler > > and always leave a copy of my bulb life web page and some > > comments from the list (anonymous of course) about extending > > filament bulb life. Had a few "ooohs" from counter staff as they > > realised the implications > > > > -- > > http://www.piclist.com hint: To leave the PICList > > RemoveMEpiclist-unsubscribe-requestspam_OUTKILLspammitvma.mit.edu> > > > > -- > > http://www.piclist.com hint: PICList Posts must start with ONE topic: > > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > > > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

At 01:58 PM 7/16/01 -0400, you wrote: >What does the loose neutral do to make the bulb burn out faster? Normal wiring in US and Canadian residences looks like this.. 120VAC o-------x <----------x | | [100W bulb] | N | | o--//---x 240VAC | | [500W load] | | | o-------x <----------x 120VAC See what happens to the 100W bulb if the neutral connection is flakey? Best regards, =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Spehro Pefhany --"it's the network..." "The Journey is the reward" RemoveMEspeffTakeThisOuTspaminterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

I may not have a clue, but my guess would be that the problem is mechanical. I would suggest swapping one of the sockets with a standard replacement from a hardware store.. There are several possible issues, the most likely of which is that the socket is expanding / contracting in such a way that it is applying torque to the glue holding the bulb in the base.... I have seen intermittent lamps resulting from cheaply made sockets where there was an unused switch leaf. I guess it was easier to disable the switch leaf than to manufacture without it....Every time the socket warmed up, the leaf bent because there was no knob to hold it in place... My guess is that if the sockets were all installed at the same time, they are the same make. probably same production lot. Probably made in some totally unknown factory in a remote location. The rest of the lot are probably scattered throughout the known world... Just some thoughts, probably erroneous, but maybe worth a try. Best of luck, Martin At 03:30 PM 7/16/01 -0400, you wrote: {Quote hidden}>Thanks for the suggestions. Here are some facts: > >* The bulbs are incandescent, not halogens. >* The fixture is hanging from the ceiling, 3 bulbs, each with a metal >reflector above it - looks like plenty of ventilation to me. >* Each socket is rated for 100w. >* All three bulbs that separated were 60w. >* We have used 60w and 100w bulbs - failure rate is about the same. >* The mysterious off again / on again bulb is 100w. >* Thermal shutoff cannot explain mysterious bulb because it will not light >even when fixture has not been used for hours and I measured the voltage in >its socket while it was not working. > >--BobG > >{Original Message removed}

part 1 6995 bytes content-type:text/plain; charset=us-ascii I have had this exact same problem with an outside fixture, and turned out to be thermal in nature. I improved the ventilation of the fixture, and bent the bulb mount away from the thermal barrier and the problem went away for good. (For some reason the bulb was hovering about a 1/4" from the insulator. I increased this to about an inch.) Scott Martin Baker <mbaker@OPTIME To: EraseMEPICLISTspamspamBeGoneMITVMA.MIT.EDU INC.COM> cc: Sent by: pic Subject: Re: [EE]: Bulb Life -- Burned out bulb resurected microcontrolle r discussion list <PICLIST@MITVM A.MIT.EDU> 07/16/01 03:46 PM Please respond to pic microcontrolle r discussion list I may not have a clue, but my guess would be that the problem is mechanical. I would suggest swapping one of the sockets with a standard replacement from a hardware store.. There are several possible issues, the most likely of which is that the socket is expanding / contracting in such a way that it is applying torque to the glue holding the bulb in the base.... I have seen intermittent lamps resulting from cheaply made sockets where there was an unused switch leaf. I guess it was easier to disable the switch leaf than to manufacture without it....Every time the socket warmed up, the leaf bent because there was no knob to hold it in place... My guess is that if the sockets were all installed at the same time, they are the same make. probably same production lot. Probably made in some totally unknown factory in a remote location. The rest of the lot are probably scattered throughout the known world... Just some thoughts, probably erroneous, but maybe worth a try. Best of luck, Martin At 03:30 PM 7/16/01 -0400, you wrote: {Quote hidden}>Thanks for the suggestions. Here are some facts: > >* The bulbs are incandescent, not halogens. >* The fixture is hanging from the ceiling, 3 bulbs, each with a metal >reflector above it - looks like plenty of ventilation to me. >* Each socket is rated for 100w. >* All three bulbs that separated were 60w. >* We have used 60w and 100w bulbs - failure rate is about the same. >* The mysterious off again / on again bulb is 100w. >* Thermal shutoff cannot explain mysterious bulb because it will not light >even when fixture has not been used for hours and I measured the voltage in >its socket while it was not working. > >--BobG > >{Original Message removed} part 2 8188 bytes content-type:application/octet-stream; (decode) part 3 154 bytes -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

At 03:05 PM 7/16/01 -0400, you wrote: >I am embarrassed to say that I do not get it. What's the 500w load in your >diagram? In your scenario, is the faulty neutral at the breaker box or at >the lamp? Where I drew the // lines in it (below). The 500W load might be other lights, whatever. The important thing is that it is higher current draw (lower impedance) than the lamp. If the neutral is broken entirely, then the voltage will divide across the two loads. Assuming (for simplicity) the two loads are resistive, and that the 100W lamp is R = 144 ohms, the 500W load is 28.8 ohms (fixed for simplicity), then the 100W bulb would see 240 * (144/(144+28.8) = 200V. Obviously it won't last very long at all! If the loads on either side of the neutral are exactly balanced, then there will be no obvious ill effects from breaking the neutral. >Every outlet/lamp fixture in my house has 3 wires - what I typically think >of as 'line', 'ground', and 'neutral'. Ground and neutral are at the same >potential and 'line' is +-120vac. I think of ground as an alternate return >path to ground in case the line is accidentally exposed. I have never quite >understood why ground and neutral should be electrically isolated. It's a safety issue. The safety ground is not supposed to carry current except under fault conditions. Typically something like the housing of a clothes washer is connected to ground. Imagine if it was connected to neutral and the neutral went open (you don't have to think about the other line to see this..) all of a sudden the metal housing is at 120VAC (in series with the internal motor or whatever), which will happily fry you without getting much voltage across it. >So you are saying that with a faulty neutral, a 120vac appliance with see >240vac? It can see anything between close to zero to close to 240, depending on how imbalanced the loads are. But a flickering (to dim) could just be a bad connection in series with the load. Flickering (to more brightly) pretty much nails it down to being a bad neutral. Best regards, {Quote hidden}> >120VAC >o-------x <----------x > | | > [100W bulb] | >N | | >o--//---x 240VAC > | | > [500W load] | > | | >o-------x <----------x >120VAC =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Spehro Pefhany --"it's the network..." "The Journey is the reward" RemoveMEspeffKILLspaminterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Thanks for the detailed explanation. That clears it up for me. --BobG -----Original Message----- From: pic microcontroller discussion list [PICLISTSTOPspamspam_OUTMITVMA.MIT.EDU]On Behalf Of Spehro Pefhany Sent: Monday, July 16, 2001 4:17 PM To: spamBeGonePICLISTSTOPspamEraseMEMITVMA.MIT.EDU Subject: Re: [EE]: Bulb Life -- Burned out bulb resurected At 03:05 PM 7/16/01 -0400, you wrote: >I am embarrassed to say that I do not get it. What's the 500w load in your >diagram? In your scenario, is the faulty neutral at the breaker box or at >the lamp? Where I drew the // lines in it (below). The 500W load might be other lights, whatever. The important thing is that it is higher current draw (lower impedance) than the lamp. If the neutral is broken entirely, then the voltage will divide across the two loads. Assuming (for simplicity) the two loads are resistive, and that the 100W lamp is R = 144 ohms, the 500W load is 28.8 ohms (fixed for simplicity), then the 100W bulb would see 240 * (144/(144+28.8) = 200V. Obviously it won't last very long at all! If the loads on either side of the neutral are exactly balanced, then there will be no obvious ill effects from breaking the neutral. >Every outlet/lamp fixture in my house has 3 wires - what I typically think >of as 'line', 'ground', and 'neutral'. Ground and neutral are at the same >potential and 'line' is +-120vac. I think of ground as an alternate return >path to ground in case the line is accidentally exposed. I have never quite >understood why ground and neutral should be electrically isolated. It's a safety issue. The safety ground is not supposed to carry current except under fault conditions. Typically something like the housing of a clothes washer is connected to ground. Imagine if it was connected to neutral and the neutral went open (you don't have to think about the other line to see this..) all of a sudden the metal housing is at 120VAC (in series with the internal motor or whatever), which will happily fry you without getting much voltage across it. >So you are saying that with a faulty neutral, a 120vac appliance with see >240vac? It can see anything between close to zero to close to 240, depending on how imbalanced the loads are. But a flickering (to dim) could just be a bad connection in series with the load. Flickering (to more brightly) pretty much nails it down to being a bad neutral. Best regards, {Quote hidden}> >120VAC >o-------x <----------x > | | > [100W bulb] | >N | | >o--//---x 240VAC > | | > [500W load] | > | | >o-------x <----------x >120VAC =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- = Spehro Pefhany --"it's the network..." "The Journey is the reward" KILLspamspeffspamBeGoneinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- = -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Yes they like the dark...ha ----- Original Message ----- From: "Robert E. Griffith" <EraseMEbobEraseMEJUNGA.COM> To: <@spam@PICLIST@spam@spam_OUTMITVMA.MIT.EDU> Sent: Monday, July 16, 2001 8:14 AM Subject: Re: [EE]: Bulb Life -- Burned out bulb resurected > I have been having a problem with the light fixture in my kitchen going > through bulbs fast (bulbs lasting about a month). This fixture uses the more > expensive, large diameter bulbs. When the last one went out, I did not > replace it right away. Several days later, it came back to life! > > Since then, it has gone out several times (for 2-7 days) but has, so far, > always come back to life. > > I have measured the voltage in the socket during one of the bulb's dead > periods and verified that there is power in the socket (117v). > > I imagine that somewhere in the bulb is an intermittent short. The room is > air conditioned so temp does not vary that much (except when the bulb is > on:) > > Another strange thing: Three times now, when other bulbs have gone out in > this fixture, the glass bulb separates from the metal socket while the light > is on and drops to the table below! > > So I guess my question is "Should I be concerned that this fixture is > haunted?". Should I call Bill? (Maurry - not Gates) > > --BobG > > {Original Message removed}

IIRC, The National Electric Code specifically prohibits using a common neutral between the two phases. With the neutral's only tied together at the service panel you avoid a very dangerous situation when a neutral goes open outside the service panel. ___ 120VAC | |-----------x <----------x | S | | | | V | [100W bulb] | | C | N | | | E |-----------x 240VAC | | | | P |-----------x | | A | N | | | N | [500W load] | | E | | | | L |-----------x <----------x --- 120VAC Paul ========================================= Paul Hutchinson Chief Engineer Maximum Inc., 30 Samuel Barnet Blvd. New Bedford, MA 02745 spamBeGonephutchinsonKILLspamimtra.com http://www.maximum-inc.com ========================================= -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> IIRC, The National Electric Code specifically prohibits using a common > neutral between the two phases. I don't believe this is true. When I wired my woodworking shop I installed several 12/3 w/gnd lines from the service panel to outlet boxes containing 2 GFI's each. I used separate (not ganged) 20A breakers to drive each phase (one on red wire, one on black). In the outlet box the neutral (white) was shared by both GFI's and the RED and BLACK conductors each drove one GFI. The electrical inspector specifically said this was a fine way to do it. Also, the copy of the NEC that I have also contained no prohibition that I could find against this. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) > With the neutral's only tied together at the service panel you avoid a very {Quote hidden}> dangerous situation when a neutral goes open outside the service panel. > > ___ 120VAC > | |-----------x <----------x > | S | | | > | V | [100W bulb] | > | C | N | | > | E |-----------x 240VAC > | | | > | P |-----------x | > | A | N | | > | N | [500W load] | > | E | | | > | L |-----------x <----------x > --- 120VAC > > > Paul > > ========================================= > Paul Hutchinson > Chief Engineer > Maximum Inc., 30 Samuel Barnet Blvd. > New Bedford, MA 02745 > .....phutchinsonspam_OUTimtra.com > http://www.maximum-inc.com > ========================================= > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> > IIRC, The National Electric Code specifically prohibits using a common > > neutral between the two phases. > > I don't believe this is true. > > When I wired my woodworking shop I installed several 12/3 w/gnd lines from > the service panel to outlet boxes containing 2 GFI's each. The neutral is rated at one size smaller than the power carrying conductor. So, if the two 110 outlets are rated to carry power equal to what the neutral is rated than this configuration will work (30 amp neutral rating on 12/3 basically rating the outlets at 15 amps each). I am surprised that the inspector allowed this on an industry outlet such as a woodshop that normally requires a full 20 amps per outlet. I use this configuration all the time when wiring houses. The bedroom circuits are under rated because they may carry a clock, TV, or a lamp... normally all low power items. Pulling a three wire saves money because the bedrooms are normally the furthest from the panel. Jim -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

At 05:23 PM 7/16/01 -0400, Paul Hutchinson wrote: >IIRC, The National Electric Code specifically prohibits using a common >neutral between the two phases. Not correct! Specifically, kitchen receptacles in homes are wired with 2 phases and a neutral: this allows 2 breakers (ganged) to feed a single duplex receptacle so that plugging a toaster and an electric frying pan into the top and bottom of a single receptacle does not trip a breaker. The local inspectors test for this by measuring the voltage between the 2 hot terminals on each kitchen receptacle: if they do NOT measure 230Vac, it fails the test. Industrial wiring shares the neutral between the 3 phases for most 120V outlets and for area lighting. You tend to find dedicated neutrals only on special outlets such as those dedicated for computers and such. dwayne Dwayne Reid <TakeThisOuTdwayner.....TakeThisOuTplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 17 years of Engineering Innovation (1984 - 2001) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> > > IIRC, The National Electric Code specifically prohibits using a common > > > neutral between the two phases. > > > > I don't believe this is true. > > > > When I wired my woodworking shop I installed several 12/3 w/gnd lines from > > the service panel to outlet boxes containing 2 GFI's each. > > > The neutral is rated at one size smaller than the power carrying conductor. > So, if the two 110 outlets are rated to carry power equal to what the > neutral is rated than this configuration will work (30 amp neutral rating on > 12/3 basically rating the outlets at 15 amps each). I am surprised that the > inspector allowed this on an industry outlet such as a woodshop that > normally requires a full 20 amps per outlet. I use this configuration all > the time when wiring houses. The bedroom circuits are under rated because > they may carry a clock, TV, or a lamp... normally all low power items. > Pulling a three wire saves money because the bedrooms are normally the > furthest from the panel. > > Jim 12/3 neutral is 12 gauge (the one-size-smaller rule doesn't kick in until you get to higher sizes, typical AL 4 (maybe AL 6) or bigger) and thus is rated for 20A. Also, neutral current worst case is when you have an unbalanced load: ie: drawing 20A on one leg and nothing on the other. I guess the thinking is that the probability of a badly unbalanced load goes down when the guage goes up. This makes sense as long as the load is the sum of a relatively large number of small loads. The idea breaks down if you have just a few high power single phase loads. A (partially) contrived example (something similar to this actually happened to me!): A showerhouse at a summer camp. 5 20A outlets in the boys half on one leg 5 20A outlets in the girls half on the other leg All the girls turn on their 2000W hair dryers at the same time, while the guys are shaving with their 5W shavers.... Now you got quite a big neutral current! Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Why couldn't you have the two circuits in the kitchen on the same phase as long as they each have a 15-amp breaker back at the box? Surely the single phase could handle the combined 30-amp load, so what's the advantage of having them on different phases? I would think that any 240v appliance in the kitchen would need it's own circuit, so its not for the combined 240v. The book I used when wiring my kitchen showed alternating the circuits of the 3 wire BX so that each box had only one circuit. Wait a minute; maybe I just figured it out. When there is load on both circuits, if the circuits are 180 degrees out of phase then the current on the common neutral would tend to cancel - creating a smaller current load on the neutral wire. If they were in phase, the current on the neutral would be the sum of the two circuits so it would have to be rated for the sum of the two circuits (30-amps). Is that it? Here's a somewhat related question. In my basement, I have a chop saw on a 15-amp circuit that blows occasionally when the saw starts. If the wire on this circuit is thick enough, can I replace the 15-amp breaker with a 20-amp breaker? What gauge is rated for 20-amp? It is a short run to the box and it runs through conduit - not bx, so maybe I could just pull the heavier wire if I need to. There was originally a 240v circuit in this conduit. Along the conduit are 120v receptacles and a single 240v receptacle. I do not know whether they shared any wires. Could they - legally? Can you put 120v receptacles on a circuit that is also used as half of a 240v circuit? In the box, a 240v breaker is just two 120v breakers with a bar connecting them so that if one trips, they both trip. --BobG {Original Message removed}

At 10:51 PM 7/16/01 -0400, Robert E. Griffith wrote: >Wait a minute; maybe I just figured it out. When there is load on both >circuits, if the circuits are 180 degrees out of phase then the current on >the common neutral would tend to cancel - creating a smaller current load on >the neutral wire. If they were in phase, the current on the neutral would >be the sum of the two circuits so it would have to be rated for the sum of >the two circuits (30-amps). Is that it? Got it exactly! >Here's a somewhat related question. In my basement, I have a chop saw on a >15-amp circuit that blows occasionally when the saw starts. If the wire on >this circuit is thick enough, can I replace the 15-amp breaker with a 20-amp >breaker? What gauge is rated for 20-amp? My first attempt at fixing this would be to pull heavier wire to the saw but staying with the 15A breaker. Here is why: if the wire is too small, the voltage at the saw is too low and the saw takes too long to come up to speed. The breaker will handle surge currents only for a limited amount of time. Because the saw is still drawing too much current when that time limit is up, the breaker trips. 12 AWG is the standard wire size for 20 Amps. But in your case, I'd try pulling 10AWG wire in. If the 15A breaker still trips, then go for the 20A breaker. But the heavier wire may just fix the problem. dwayne Dwayne Reid <TakeThisOuTdwaynerKILLspamspamplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 17 years of Engineering Innovation (1984 - 2001) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> [broken neutral] Where I drew the // lines in it (below). The > 500W load might be other lights, whatever. >>> 120VAC >>> o-------x <----------x >>> | | >>> [100W bulb] | >>> N | | >>> o--//---x 240VAC >>> | | >>> [500W load] | >>> | | >>> o-------x <----------x >>> 120VAC I've seen this up close. Thought the story might amuse you. I live in southern California. Four years ago, a storm blew through with _major_ wind storm damage. Electric utility people were totally overwhelmed. Our neighbor asked me if I knew what might be wrong with their power. Certain appliances would only work if they had "enough" light fixtures turned on, etc. Weird behavior through-out the house. I knew that residential wiring frequently puts one phase on the light fixtures and the other phase on the wall outlets. So I suspected the neutral right away. Breaker panel seemed OK. Then I looked up. Electric feed is overhead with steel messenger cable twisted with two insulated wires. Each insulated wire is one phase from the pole mounted transformer. Steel messenger cable is used to carry cable tension and for the neutral return. (Roughly balanced phases, so neutral carries lower current, so steel is "OK", and they save money on wire.) Wind had broken the steel messenger cable; insulated phase cables were still intact. But things would work if loads were reasonably well matched on both power phases. Mismatch loads on the two phases and things behaved erratically. I did a temporary repair. I used rope around the feed cable bundle tied to the entrance pipe to take up the physical strain on the cable. Then I used a car jumper cable to reconnect the ends of the broken steel messenger wire. Problem solved. It was that way for 3 days until the local electrical utility repair crew could get to it. Repair guy fixing it appreciated the kludge. And I did get my jumper cable back. Lee Jones -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Hi Bob, many of those 3-light fittings are NOT suitable for larger bulbs. The socket itself might be ok but the fitting won't take the total watts heat. My 3-light kitchen fitting gets over 85 degrees C (yes I have a infrared thermometer) with 60w bulbs in it. When your bulb goes on/off intermittantly the filament has failed. Broken filament. You're relying on luck to make it connect. :o) Also, the symptom of the bulb separating glass from the metal cap is a sure symptom of excessive heat, fatiguing the solder that holds them together. I guess your kitchen lights are on a lot, and it gets hotter in there than other rooms, and you have 3 larger bulbs as kitchens need a lot of light. Try 2 compact fluoros in there, will reduce the heat to almost nothing, and give good light. My kitchen now has them. :o) I also suggest checking the temperature of your home light fittings, you might be surprised how dangerous they are, most wiring cables are rated at 85'C and my lights were at that temperature or higher... -Roman Robert E. Griffith wrote: {Quote hidden}> > Thanks for the suggestions. Here are some facts: > > * The bulbs are incandescent, not halogens. > * The fixture is hanging from the ceiling, 3 bulbs, each with a metal > reflector above it - looks like plenty of ventilation to me. > * Each socket is rated for 100w. > * All three bulbs that separated were 60w. > * We have used 60w and 100w bulbs - failure rate is about the same. > * The mysterious off again / on again bulb is 100w. > * Thermal shutoff cannot explain mysterious bulb because it will not light > even when fixture has not been used for hours and I measured the voltage in > its socket while it was not working. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> I have been having a problem with the light fixture in my > kitchen going > through bulbs fast (bulbs lasting about a month). This > fixture uses the more > expensive, large diameter bulbs. When the last one went out, > I did not > replace it right away. Several days later, it came back to life! > > Since then, it has gone out several times (for 2-7 days) but > has, so far, > always come back to life. > > I have measured the voltage in the socket during one of the > bulb's dead > periods and verified that there is power in the socket (117v). You do not say what sort of socket it is, but if it is a bayonet one I would suspect the spring in one of the contacts is broken or lost tension due to heat (possibly from using too high wattage bulb for the fitting? :)) Even if it is a screw fitting the contact spring may have similar problems. The other possibility is the wire in the back of the socket is only just touching the pin, and replacing the bulb disturbs the socket enough to make good enough contact for it to work until the heat corrodes the wire at the point of contact again. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

----- Original Message ----- From: "Robert E. Griffith" <.....bobRemoveMEJUNGA.COM> To: <RemoveMEPICLISTspamBeGoneMITVMA.MIT.EDU> Sent: Monday, July 16, 2001 10:51 PM Subject: Re: [EE]: Bulb Life -- Burned out bulb resurected > Why couldn't you have the two circuits in the kitchen on the same phase as > long as they each have a 15-amp breaker back at the box? Surely the single > phase could handle the combined 30-amp load, so what's the advantage of > having them on different phases? I would think that any 240v appliance in > the kitchen would need it's own circuit, so its not for the combined 240v. > > The book I used when wiring my kitchen showed alternating the circuits of > the 3 wire BX so that each box had only one circuit. > > Wait a minute; maybe I just figured it out. When there is load on both > circuits, if the circuits are 180 degrees out of phase then the current on > the common neutral would tend to cancel - creating a smaller current load on > the neutral wire. If they were in phase, the current on the neutral would > be the sum of the two circuits so it would have to be rated for the sum of > the two circuits (30-amps). Is that it? Yep, that's it. > Here's a somewhat related question. In my basement, I have a chop saw on a > 15-amp circuit that blows occasionally when the saw starts. If the wire on > this circuit is thick enough, can I replace the 15-amp breaker with a 20-amp > breaker? What gauge is rated for 20-amp? It is a short run to the box and > it runs through conduit - not bx, so maybe I could just pull the heavier > wire if I need to. 14 guage wire --> 15 AMPS 12 guage wire --> 20 AMPS 10 guage wire --> 30 AMPS > There was originally a 240v circuit in this conduit. Along the conduit are > 120v receptacles and a single 240v receptacle. I do not know whether they > shared any wires. Could they - legally? Can you put 120v receptacles on a > circuit that is also used as half of a 240v circuit? In the box, a 240v > breaker is just two 120v breakers with a bar connecting them so that if one > trips, they both trip. I believe that this is legal. However, if you have any 240V loads, then you MUST have a ganged breaker. Actually, interally most 240V breakers are not just two 120V's with a bar between them. In the olden days this was more likely true. Now the bar is generally just cosmetic. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

----- Original Message ----- From: "Roman Black" <spamBeGonefastvid@spam@spam_OUTEZY.NET.AU> To: <TakeThisOuTPICLISTspamMITVMA.MIT.EDU> Sent: Tuesday, July 17, 2001 5:43 AM Subject: Re: [EE]: Bulb Life -- Burned out bulb resurected {Quote hidden}> Hi Bob, many of those 3-light fittings are NOT suitable > for larger bulbs. The socket itself might be ok but > the fitting won't take the total watts heat. > > My 3-light kitchen fitting gets over 85 degrees C (yes > I have a infrared thermometer) with 60w bulbs in it. > > When your bulb goes on/off intermittantly the filament > has failed. Broken filament. You're relying on luck > to make it connect. :o) Also, the symptom of the bulb > separating glass from the metal cap is a sure symptom > of excessive heat, fatiguing the solder that holds them > together. I guess your kitchen lights are on a lot, > and it gets hotter in there than other rooms, and you > have 3 larger bulbs as kitchens need a lot of light. So, if the bulbs can't stand the heat they should stay out of the kitchen? {Quote hidden}> Try 2 compact fluoros in there, will reduce the heat > to almost nothing, and give good light. My kitchen > now has them. :o) > > I also suggest checking the temperature of your home > light fittings, you might be surprised how dangerous > they are, most wiring cables are rated at 85'C and > my lights were at that temperature or higher... > -Roman > > > Robert E. Griffith wrote: > > > > Thanks for the suggestions. Here are some facts: > > > > * The bulbs are incandescent, not halogens. > > * The fixture is hanging from the ceiling, 3 bulbs, each with a metal > > reflector above it - looks like plenty of ventilation to me. > > * Each socket is rated for 100w. > > * All three bulbs that separated were 60w. > > * We have used 60w and 100w bulbs - failure rate is about the same. > > * The mysterious off again / on again bulb is 100w. > > * Thermal shutoff cannot explain mysterious bulb because it will not light > > even when fixture has not been used for hours and I measured the voltage in > > its socket while it was not working. > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Bob Ammerman wrote: > > When your bulb goes on/off intermittantly the filament > > has failed. Broken filament. You're relying on luck > > to make it connect. :o) Also, the symptom of the bulb > > separating glass from the metal cap is a sure symptom > > of excessive heat, fatiguing the solder that holds them > > together. I guess your kitchen lights are on a lot, > > and it gets hotter in there than other rooms, and you > > have 3 larger bulbs as kitchens need a lot of light. > > So, if the bulbs can't stand the heat they should stay out of the kitchen? Ha ha ha! Or... "Why do women have smaller feet than men?" All in fun, ;o) -Roman -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> > > Why couldn't you have the two circuits in the kitchen on the same phase as > > long as they each have a 15-amp breaker back at the box? In the kitchen is not a problem. A phase to phase short is very exciting and can be more potentially fatal. An electrican that expects 120 in a kitchen box could get into something he would rather not have. Keeping a 120 v box single phase is not a hard thing to do. Its basically electrical edicate. > between them. In the olden days this was more likely true. Now the bar is > generally just cosmetic. > The bar makes sure that one leg of a 240 v cct. does not remain hot when the other side shorts out. True, taking the bar off makes two single 110 breakers, but never supply 240 with two SP not tied together Jim -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> > between them. In the olden days this was more likely true. Now the bar is > > generally just cosmetic. > > > > The bar makes sure that one leg of a 240 v cct. does not remain hot when the > other side shorts out. True, taking the bar off makes two single 110 > breakers, but never supply 240 with two SP not tied together Right, _never_ supply 240 without both legs simultaneously broken. When I said the 'bar was cosmetic', I was implying that in most modern breakers, the actual tying mechanism is inside the breaker, and the bar has no function other than to indicate to the user that the handles are tied. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

----- Original Message ----- From: "Jim" <RemoveMEjimEraseMEspam_OUTCPCEMA.COM> To: <@spam@PICLISTRemoveMEEraseMEMITVMA.MIT.EDU> Sent: Wednesday, July 18, 2001 3:54 PM Subject: Re: [EE]: Bulb Life -- Burned out bulb resurected > > When I said the 'bar was cosmetic', I was implying that in most modern > > breakers, the actual tying mechanism is inside the breaker, and the bar > has > > no function other than to indicate to the user that the handles are tied. > > > So if you take a bar off of a DP breaker, both sides will still trip? I believe so, with most modern breakers. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistserv@spam@mitvma.mit.edu with SET PICList DIGEST in the body