the whole lighting and socket circuit goes off.


Postby DIY1975ELECTRICS » Tue Jul 02, 2013 11:35 am

At work we work in a small office, but at times when we plug the hoover in or switch on the lioght or even if the whole 7 computers are on the whole circuit goes off. The breakers don't trip. An electrician said it could be overload there is 10 lights in one switch but that should not effect the whole supply.

Can anyone tell why the whole supply is going off, we have to put the supply back on from the isolator which is next to the fuseboard.
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Postby ericmark » Thu Jul 04, 2013 1:05 pm

I will start by quoting a rather basic regulation:-
[quote]314.1 Every installation shall be divided into circuits, as necessary, to:
(i) avoid hazards and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Section 537)
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation
(v) mitigate the effects of electromagnetic interferences (EMI)
(vi) prevent the indirect energizing of a circuit intended to be isolated.[/quote]
There has been due to this a rethink on what a circuit is. We had got into a rut and thought only about the overload device be that fuse or MCB but clearly from the above regulation we have also to consider the RCD as producing circuits.

The office fault could be either RCD or MCB/Fuse tripping with the current (MCB/Fuse) quite easy to measure how much is used but with 7 computers mine rated 0.5 - 1 amp then only a 7A load and unlikely a 13A socket supply would be feed from a 6A MCB so unlikely the amount of power used.

So more likely the RCD is tripping. The computer likely has a device to stop spikes these often leak power to earth this is limited to 3.5mA max but using a filtered extension lead this could be greater and most RCD's trip between 15mA and 30mA so 7 computers could be a 24.5mA leakage even without extension leads with filtered sockets.

Also spikes caused by turning on equipment can tip the balance.

Likely just one computer where the filter network is faulty and any spike just takes it over the top. I would use my PAT tester to measure the leakage on each PC in real terms should be less than 1mA and if above then needs repairing. Likely that means new power supply fitted.
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Postby DIY1975ELECTRICS » Thu Jul 04, 2013 4:54 pm

can it also be a earth leakage ?
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Postby ericmark » Thu Jul 04, 2013 11:26 pm

As I had thought I had said most likely an earth leakage.

Earth leakage and be roughly split into two.
1) Designed leakage
2) Fault leakage

In an ideal world one should declare the designed leakage but this is not the case in reality so the electrician has to decide how many items can be fed from one circuit with a blind fold on. I would not expect a problem with 7 computers but even without a fault there could still be a problem with high design leakage.
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Joined: Fri Oct 02, 2009 8:49 pm
Location: Mold, North Wales.


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