mcb tripping

[nabby68]

i have an mem 2000 cu and the problem i am having is on the power circuit side. my mcb (rates at 32amps) keeps tripping even with everything disconnected and nothing at all plugged in. i do not have an rcd so am i right in saying that the fault cannot be current leakage to earth? by the way the tripping intermittent and sometimes it trips the mains switch.

i have noticed also that today, as it is a particular damp and wet day were i live and i am having a few damp issues on the property, that it is tripping quite regular but still intermitent, and yet the other day, which had followed a particular hot and sunny week, that it didnt trip once!

am i being paranoid or could the damp conditions be causing this or could it be quite simply a faulty mcb??

 

[andy]

just because there is no RCD doesnt mean there is not an earth leakage. also, you say it trips the main switch? unless this is an RCD or MCB (unlikely to be an MCB) then it will not trip. when it trips, is the disc in the meter spinning fast then (almost) stop when the MCB trips? you should get an electrician round to test since it could be a serious fault

 

[Screwi]

It could still be a circuit on the rcd side - the mcbs only break the positive - the neutral and earths arnt broken by the mcb - so, say if a neutral touched an earth or visa versa - it would still trip the rcd - even with the mcb switched off!

 

[Hacman]

Get a spark to check it with a megger.

We had a problem like this on a council house. Everything off of circuit, still had a fault.

It turned out to be mice that had nibbled down the insulation, causing a short but not a dead one. Every so often the breaker would go but you could not time it as it could go for hours.

By using a megger we found a breakdown in the insulation.

I suspect that is what has happened here.

 

[nabby68]

hi everyone, thanks for your replies i do have access to a continuity tester so i will test for that first. by the way, what i thought to be the mains switch is in fact an rcd.

so the process of elimination would be to do a continuity test first/

 

[andy]

hi everyone, thanks for your replies i do have access to a continuity tester so i will test for that first. by the way, what i thought to be the mains switch is in fact an rcd.

so the process of elimination would be to do a continuity test first/

you need an insulation tester. continuity will not pick up certain faults. and if you think that you can do it with a continuity then you shouldnt be doin the testin

 

[nabby68]

could someone therefore give me a quick crash course on testing insulation and resistance?

 

[andy]

could someone therefore give me a quick crash course on testing insulation and resistance?

EDITED: bad idea....

 

[breezer]

could someone therefore give me a quick crash course on testing insulation and resistance?

NO

since you do not understand the previous statement, you would not know what you are looking for. besides in your case i dont think it would be crash, more of a bang

i suggest you get several quotes, there may be more that is wrong

 

[nabby68]

thanks andrew

 

[pdcelec]

You could test the insulation resistance with an insulation resistance tester and this would tell you whether there is a problem with the insulation of the circuit.

 

[nabby68]

thanks also pd

 

[mapj1]

A proper insulation test applies 500volts DC to the wiring, and measures the curretn flow, with all loads removed. This is not something to be done by the unsure !
If a defective circuit is found, it is sub-divided until th fualty section is identified.
However, you might be able to see something with a multimeter on megohms, between N and E and L and E measured with the circuit isolated.
The probelm is some faults require serious voltages (not a meter battery) to make them show up.
AS the trip that fires is an RCD, it could well be an N-E fault, and if its protecting sockets then only 30mA of leakage is requred to trip it.

 

[nabby68]

ok thanks to eneryone who has replied. here is an update of the problem.
removed all the fittings from the power circuit and put all the cables in chock blocks to try and discount defective fittings. no luck.

so then i disconnected one socket at a time and then re-connecting and between each time seeing if it tripped the mcb. i found that at one particular socket as soon as i touched both earths together with the power connected then this tripped the mcb, but it was not immediate. there has been a damp issue on this wall where the socket is.
now i'm thinking that if it was an earth leakage problem then shouldnt the mcb trip straight away?
and further to my original post, it is not an rcd but a mccb.

 

[andy]

ok thanks to eneryone who has replied. here is an update of the problem.
removed all the fittings from the power circuit and put all the cables in chock blocks to try and discount defective fittings. no luck.

so then i disconnected one socket at a time and then re-connecting and between each time seeing if it tripped the mcb. i found that at one particular socket as soon as i touched both earths together with the power connected then this tripped the mcb, but it was not immediate. there has been a damp issue on this wall where the socket is.
now i'm thinking that if it was an earth leakage problem then shouldnt the mcb trip straight away?
and further to my original post, it is not an rcd but a mccb.

an earth leakage will only trip an MCB if there is a high current. i.e big spark when you touch them. however, itll only take 30mA to trip the RCD