garage electrics

[peter privett]

Hi everyone, a bit of advice if you will.

 My garage whiich is approx 20 mtrs from the house, is served by armoured cable from house to garage main switch  which has RCD & 32 amp mcb serving the sockets  and a 5amp for lighting.

All has worked well, until yesterday when a peculiar problem appeared.

Looking at the main switch, the sockets to the right side of this switch are working as they should,

but the sockets to the left, if radio is plugged in, no problem, but plugging in anything heavier trips the main switch in the HOUSE????

what is puzzling me is if there is a fault on this section of wiring,

  (A)  why doesn't it trip the switch in the garage

  (B) why doesn't it  trip the mcb marked garage in the house, why the main RCD switch

I have a socket tester and all sockets in thouse and garage are reading OK!

Your help will be really appreciated.

 

[leesparkykent]

looks like you have a neutral earth fault on fixed wiring or an appliance.

 

[Lurch]

(A) What rating (mA) are the RCD's? Probably no discrimination.

(B) Because the fault is between earth and one of the live conductors (phase/neutral) and is of a sufficient enough current to trip the RCD but not of such a magnitude that the MCB operates.

I have a socket tester and all sockets in thouse and garage are reading OK!

All that does is tell you the wires are in the right holes, not that it is all OK.

Basically you need proper test equipment to identify exactly where the fault is, which would be brought by an electrician who you should call to locate/repair the fault.

 

[leesparkykent]

The neutral earth fault doesn't necessarily have to be within the garage but could be on any circuit thats protected by the same RCD as the distribution circuit to the garage. If the fault is of sufficiently high resistance so that normal use of the faulty circuit generates <30mA to earth, when the higher current also passes through the fault this may be enough to trip the RCD.

 

[peter privett]

thanks guys, looks like it is going to need some serious lookig at.

But! i'm still a bit puzzled, the fact the thing trips when a heavier tool is applied to the left hand side sockets, does this imply the fault must be on that side.

because as I have said there is no reaction when tools are plugged into the right hand side?

 

[Andy™]

the fault is usually (but not always) on the RCD that trips, but it could be on any circuit on any side

 

[Lurch]

Not necessarily, the fault might not even be in the garage. It just means that that section of wiring allows enough current to flow through the fault to operate the RCD.

 

[peter privett]

Oh dear,  could it be said that the rcd in the house is not strong enough, (replace with one that is less sensative)

 

[leesparkykent]

Oh dear,  could it be said that the rcd in the house is not strong enough, (replace with one that is less sensative)

NO WAY! The RCD is doing what its supposed to....Get an electrician with the correct test equipment in to find the fault and normal service will be resumed.

 

[Andy™]

do NOT go round replacing RCD's, its most likely to be a fault and the RCD is doing what its supposed to and keeping you safe

its also possible that its the RCD thats faulty, but either way, the RCD rating will not change

 

[peter privett]

Please excuse my lay-mans interpration of this fault....the current from the right sockets runs through the same armoured cable as the left hand sockets,and does not trip the rcd, so surely this points to the fault being on that left hand circuit??

 

[Lurch]

No, it doesn't work like that. There are parallel resistances in the circuit, so some current will flow here and there as dictated by the resistances of the cables and connections. The fault may be in the left hand leg of sockets, but it could actually be anywhere.

Just because you plug something in there and the RCD operates does not mean that is where the fault is. You might find that plugging a higher load into the other leg of the socket circuit will also operate the RCD, or the other RCD, or both, or each one alternately.

 

[peter privett]

Ok guys, good advice...I will get an electrician in. many thanks!