Post by thread:[EE] RCD trips on bulb failure... Was Dumb mistak

On 24 April 2006 12:04, Howard Winter [SMTP:spam_OUTHDRWTakeThisOuTH2Org.demon.co.uk] wrote: > That's odd! I've heard of MCBs tripping, due to the vapourised filament causing a current surge (usual > solution is to use a C-rated MCB rather than B-, which has a greater short-term overload capability), but I > can't see why an RCD should trip. Are these low-voltage halogens? I wonder if it's possible that the > electronic "transformer" is doing some sort of load-shedding to the Earth conductor? Howard, I was brought up in a house with a 30mA RCD which was fitted in about 1984.(Prior to that we had a 'fault voltage circuit breaker'). The RCD has frequently 'tripped' when ordinary filament bulbs have blown, and, to my great shame, I have never asked the question that you pose. Our installation is single phase (L&N plus local earth electrode). I have Googled a bit and I see that Phil and I are part of a detectable minority who experience this phenomenon. 'Fred' in this thread has a theory: http://www.ureader.co.uk/message/10 16262.aspx. FWIW, in our case we have power to a number of outbuildings, all through the single RCD, and some 30+ years old. I wonder whether, in damp weather conditions we are living with a 'permanent' leakage which is close to, but below the trip level of the RCD. This would effectively increase our susceptibility to the transient effects that Fred suggests. Richard.

Richard, On Mon, 24 Apr 2006 23:54:23 +0100, Richard Stevens wrote: > Howard, > I was brought up in a house with a 30mA RCD which was fitted in about > 1984.(Prior to that we had a 'fault voltage circuit breaker'). The RCD has > frequently 'tripped' when ordinary filament bulbs have blown, and, to my > great shame, I have never asked the question that you pose. Our > installation is single phase (L&N plus local earth electrode). I have > Googled a bit and I see that Phil and I are part of a detectable minority > who experience this phenomenon. > 'Fred' in this thread has a theory: http://www.ureader.co.uk/message/1016262.aspx. That's an interesting thread - thanks! I think the Common Mode explanation has legs - the way an RCD detects a current imbalance, together with the wiring connected to it, could all contribute to a trip when a very fast current spike occurs. > FWIW, in our case we have power to a number of outbuildings, all through > the single RCD, and some 30+ years old. I wonder whether, in damp weather > conditions we are living with a 'permanent' leakage which is close to, but > below the trip level of the RCD. This would effectively increase our > susceptibility to the transient effects that Fred suggests. It would have to be a pretty small permanent leakage - you've only got 30mA to play with, and that's the maximum spec. Most actual devices trip at rather less than that. I used to have a mains cable that plugged in in the kitchen, then went out through the window frame to the shed 10 feet away, then on down the garden to the garage, 150 feet away. One day I plugged it in via an RCD Adaptor, which tripped instantly. Got out my trusty multimeter and measured the leakage to Earth: 1.8Amps! I disconnected the run to the garage and it was OK thereafter, but it just shows how much leakage you can get if there isn't an RCD to detect it. Nowhere enough to blow a fuse or MCB, but a lot more than you'd want to pay for if it was connected permanently, not to mention the possibility of personally becoming part of the circuit... Cheers, Howard Winter St.Albans, England

> One day I plugged it in via an RCD > Adaptor, which tripped instantly. Got out my trusty multimeter and > measured the leakage to Earth: 1.8Amps! I > disconnected the run to the garage and it was OK thereafter, but it just > shows how much leakage you can get if > there isn't an RCD to detect it. Nowhere enough to blow a fuse or MCB, OK, help me out here, I'm in the USA and our acronyms are different. RCD = Residual Current Detector? Would that be the same as our GFI (Ground Fault Interrupter)? MCB = Master Circuit Breaker? Mechanical Circuit Breaker? Cheerful regards, Bob

On 25 April 2006 17:56, Bob Blick [SMTP:.....bblickKILLspam@spam@sonic.net] wrote: > OK, help me out here, I'm in the USA and our acronyms are different. > > RCD = Residual Current Detector? Would that be the same as our GFI (Ground > Fault Interrupter)? Residual Current Device. According to my reading, yes. > MCB = Master Circuit Breaker? Mechanical Circuit Breaker? Miniature Circuit Breaker. These are the things we see on domestic distribution boards where previously we would have seen fuses. (In UK and Western Europe. Can't speak for the rest. )

Bob, On Tue, 25 Apr 2006 09:56:24 -0700 (PDT), Bob Blick wrote: {Quote hidden}> I'd said: > > One day I plugged it in via an RCD > > Adaptor, which tripped instantly. Got out my trusty multimeter and > > measured the leakage to Earth: 1.8Amps! I > > disconnected the run to the garage and it was OK thereafter, but it just > > shows how much leakage you can get if > > there isn't an RCD to detect it. Nowhere enough to blow a fuse or MCB, > > > OK, help me out here, I'm in the USA and our acronyms are different. > > RCD = Residual Current Detector? Would that be the same as our GFI (Ground > Fault Interrupter)? > > MCB = Master Circuit Breaker? Mechanical Circuit Breaker? As Richard said, Residual Current Device (similar to your GFCI I believe): http://www.tlc-direct.co.uk/Images/Products/size_3/WYWRS63SLASH2.JPG and Miniature Circuit Breaker: http://www.tlc-direct.co.uk/Images/Products/size_3/WYNSB32.JPG And here's an example of where they go, a split-load Consumer Unit - MCBs installed in the left (green) half are protected by the RCD in the middle, those on the right are not: http://www.tlc-direct.co.uk/Images/Products/size_3/WYNHRS12SLX.JPG Cheers, Howard Winter St.Albans, England