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'[EE]: Fuse box'
2007\03\01@215832 by John Chung

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One of the fuse on my MCB is causing the main circuit
breaker to trip. Here is the problem. The *fuse* to
the gate can be turned on for about 15 mins. After
that the main circuit breaker trips. I hooked off the
live and neutral wires from the auto gate box. Still
trip immediately after I switch on again. So I gave a
cool down period of 4 hours again. The same cycle
happens.

There are 2 possibility that I have accounted for.
1) The wiring to the GATE to faulty! Still can't
explain the 15 mins delay....
2) The fuse switch to the gate is faulty! 15 mins
delay? Not sure on this.

I don't have any other possible clues.
Guys do you have any other suggestion?

John



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2007\03\02@071734 by Howard Winter

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John,

On Thu, 1 Mar 2007 18:58:31 -0800 (PST), John Chung wrote:

{Quote hidden}

Circuit breakers (at least the ones here in the UK) have two tripping mechanisms:  Magnetic, which responds to a gross overcurrent, such as a
short-circuit, incredibly quickly, and Thermal, which responds to small overcurrent conditions on a time/current basis that is supposed to track
overheating of cables, so the larger the overcurrent the quicker it will trip.  There are different versions with different time/current trip graphs, but
let's say that a 10% overcurrent will trip in an hour, a 100% overcurrent in 10 seconds, etc.  Fuses have a different shaped graph, so it's possible for a
fuse to survive while an upstream circuit breaker trips.

So from what you say it looks like you are overloading the circuit, but not by much!  That's why it's tripping - as for what's causing it I think you need
to measure the current, and then find out where it's going.

Cheers,


Howard Winter
St.Albans, England


2007\03\02@163019 by Recon

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John Chung wrote:

>One of the fuse on my MCB is causing the main circuit
>breaker to trip.
>
Is this your home or shop main circuit box you are talking about.  is
the main CB a GFI type?
It is VERY unusual to see this. Against code in some places.

>Here is the problem. The *fuse* to
>the gate can be turned on for about 15 mins. After
>that the main circuit breaker trips. I hooked off the
>live and neutral wires from the auto gate box. Still
>trip immediately after I switch on again. So I gave a
>cool down period of 4 hours again. The same cycle
>happens.
>  
>
another problem might be The total current draw on each circuit is not
enough to trip their own breaker or fuse but the total of all circuit
will trip the main CB.
example 18 circuits each having a 15 amp CB  the main CB is 100 Amp.
Just 12 circiuts drawing 8 or 9 amps each will total 96 to 108 amps and
cause the main CB to trip. being it is warm  it will trip again if you
try to reset it right away.  If you wait for it to cool and then reset
it, the process will start over.


{Quote hidden}

2007\03\02@203712 by Rich

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Could there be a current leak from hot to ground through a low resistance,
like moisture perhaps?

{Original Message removed}

2007\03\03@121516 by John Chung

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Howard,
{Quote hidden}

 This is very informative. Need to read more about
this when I can find the reference manual. The info
should be applicable in my country,Malaysia. We are
apart of the colonies. Btw I have concluded that the
wiring in my house has gone bad. I cut the wiring to
the load and still tripping....

Regards,
John



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2007\03\03@121534 by John Chung

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--- Recon <spam_OUT556reconTakeThisOuTspamcharter.net> wrote:

> John Chung wrote:
>
> >One of the fuse on my MCB is causing the main
> circuit
> >breaker to trip.
> >
> Is this your home or shop main circuit box you are
> talking about.  is
> the main CB a GFI type?
> It is VERY unusual to see this. Against code in some
> places.
The MCB is for the house

{Quote hidden}

 The MCB is not warm at all. Room temperature. I did
more wire hacking and cut the wires to the porch
lights. Still trips. Looks like the cabling to the
porch and the auto gate is a major problem. I believe
somehow the wiring from the MCB to the porch is a
problem... Must be bad wiring and now has finally
cropped up after many years of stay in my current
house.

Thanks guys.
John



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2007\03\03@134523 by Bob Axtell

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John Chung wrote:
{Quote hidden}

Before you decide your wiring is bad....

Make sure that the connections to the power box are VERY tight.

Once in Georgia, I built a house where the wiring was acting strange,
and it turned out to be that when the power company connected their
big wires to our meter, they failed to tighten them properly.

Symptoms were: intermittent loss of power, strange noises in the walls,
unable to dry clothes properly, lights going up and down, etc, and circuit
breakers tripping for no reason, etc.

Finally I examined the meter connections and caught it ARCING one night,
and called the power company. They had to replace the power meter, which
had been damaged by the arcing and sputtering.

--Bob Axtell

Vitaliy wrote:
{Quote hidden}

2007\03\03@171409 by Dave Lag

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John Chung wrote:
{Quote hidden}

Unless I'm drawing an incorrect picture in my head I don't understand
why you disconnect downstream wiring , still have the original problem
(MCB = Main Circuit Breaker?) yet point to the downstream wiring as the
problem?

2007\03\03@173651 by peter green

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face

> One of the fuse on my MCB is causing the main circuit
> breaker to trip. Here is the problem. The *fuse* to
> the gate can be turned on for about 15 mins. After
> that the main circuit breaker trips. I hooked off the
> live and neutral wires from the auto gate box. Still
> trip immediately after I switch on again. So I gave a
> cool down period of 4 hours again. The same cycle
> happens.
>
> There are 2 possibility that I have accounted for.
> 1) The wiring to the GATE to faulty! Still can't
> explain the 15 mins delay....
> 2) The fuse switch to the gate is faulty! 15 mins
> delay? Not sure on this.
>
> I don't have any other possible clues.
> Guys do you have any other suggestion?
firstly where are you, conventional wiring practice varies hugely

secondly can you post some photos of your setup somewhere.

is the connection to the gate really a fuse or is it some kind of cuircuit breaker, if the former are you sure it is actualy a fuse that is in there and not some other metal object.


2007\03\04@095907 by John Chung

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{Quote hidden}

 Some ascii art.

  load ------ XXX -----  MCB.

 XXX - marks the cut.
 

 Now that I have cut it and TRY to on the switch the
MCB trips*Which still has about 8 metres of cabling
from the MCB to the disconnected point*.The cables
happen to run outside of the house under the soil.

From my understanding some of the cable must have
gone bad. One of the fuse switch is tied to the house
lights. The house lights work fine BUT when I switch
on the switch to the porch the MCB trips. I must
explain better next time.

Thanks for the correction.
John








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