non-RCD circuit tripping RCD

[EFLImpudence]

You have missed the point.

 

[very_pointy_ears]

You have missed the point.

So it would seem.

If a ring is reasonably balanced and the cable and breaker are of suitable ratings, what have I missed?

 

[EFLImpudence]

Saying you should not have a socket on a 6A circuit because someone may plug in more than 6A is the equivalent of saying you should not have more than two sockets on a 32A circuit because someone may plug in more than 32A - not valid.

 

[very_pointy_ears]

Ah that, yes I understood that point - and now I get your joke

 

[winston1]

Having a separate switch up there to enable/disable the feature has been usefully convenient a few times. I agree that there's no need for two switches up there, but it all came down to what was available at the time and it does no harm.

You have a plug up there which a far better isolator than a switch. You also have a free socket on the end of the flying lead which is also a better isolator than a switch.

 

[winston1]

Saying you should not have a socket on a 6A circuit because someone may plug in more than 6A is the equivalent of saying you should not have more than two sockets on a 32A circuit because someone may plug in more than 32A - not valid.

Not at all. One socket on a 6 amp circuit is much more likely to overload the circuit, than say 20 on a 32 amp circuit.

 

[EFLImpudence]

Not really, when it's above a kitchen wall unit and being used for a very small light.

 

[JohnW2]

Not at all. One socket on a 6 amp circuit is much more likely to overload the circuit, than say 20 on a 32 amp circuit.

It obviously 'depends' upon the circumstances. The most common context is that of a socket in the roof space on a lighting circuit, more-or-less dedicated to use with a wallwart (e.g. for a TV amplifier) - and I don't think that anyone sensible would believe that it was in any way 'likely' that a large load would ever be plugged into that.

In any event, the whole point of OPDs is to protect cables if an excessive current flows - and that is no less true of a 6A circuit than of a 32A one. With any sockets circuit, the designer has no choice but to make 'reasonable assumptions' about what loads might be plugged in - but safe in the knowledge that the OPD is there should those assumptions ever prove to have been incorrect.

Kind Regards, John

 

[winston1]

It obviously 'depends' upon the circumstances. The most common context is that of a socket in the roof space on a lighting circuit, more-or-less dedicated to use with a wallwart (e.g. for a TV amplifier) - and I don't think that anyone sensible would believe that it was in any way 'likely' that a large load would ever be plugged into that.

Wives in lofts object to the dirt and drag vacuum cleaners up there.

 

[JohnW2]

Wives in lofts object to the dirt and drag vacuum cleaners up there.

Obviously not impossible, but I still think very unlikley - particularly if, as discussed so many times before, the socket is suitably labelled and/or steps are taken to frustrate removal of the usual load.

In any event, if all that fails, most vacuum cleaners are unlikely to significantly overload a 6A circuit for an appreciable period of time.

Kind Regards, John

 

[ericmark]

An RCD detects an imbalance between line and neutral, this happens when current finds it way to earth, it obeys the simple rules of ohms law, so higher the voltage then the more current flows.

So with the line wire the voltage is around 230 volt so few volts up or down makes no difference in how much current flows to earth.

With the neutral however with nothing switched on it is exactly the same voltage as earth, so 0/what ever = 0 so no current flows. However when you put a load on the neutral the resistance in the cable means the voltage raises slightly, so 5/166Ω = 0.030 amps so with just a 166Ω leakage path the RCD will trip when the volt drop = 5 volt.

Common example is the toaster with a bit of damp bread stuck in it. With nothing running no RCD trip, even using the toaster it uses less than 5 amp so trip stays in, however use the kettle and the load is higher so also more volt drop so RCD trips, leading one to think the kettle is at fault, not the toaster.

Main problem is many items only switch the line, there is no switch on the neutral, so something not being used could cause the problem.

So step one is unplug everything you can, not just switch off as switch may not switch neutral, unplug all you can, is the fault still there, if it is then look at FCU with switches, could be them, immersion heater specially. Also any outside light look for water ingress. This is why out side lights should have double pole switching.

It may not be a neutral, but seems likely it is.

 

[ban-all-sheds]

Wives in lofts object to the dirt and drag vacuum cleaners up there.

Give it a rest, Winston, your arguments are pathetic.

 

[ericmark]

Give it a rest, Winston, your arguments are pathetic.

He is right, mine will drag the vacuum cleaner (should really call it an air volatility cleaner) into the loft to suck up cobwebs, however the cleaner has a long hose and long lead so not plugged in within the loft space, so makes no difference.

Also even if it was plugged into lights with no RCD why would that cause the RCD to trip? Likely a loose neutral wire some where and/or a neutral earth fault.

 

[EFLImpudence]

Now the weird thing is that this circuit is not on the RCD protected side (single RCD CU).

Has anyone addressed this part of the OP.

That should not happen, so something else is not as it should be or as stated.

 

[JohnW2]

Has anyone addressed this part of the OP. That should not happen, so something else is not as it should be or as stated.

I would think that the OP's UPS, which he now thinks he had identified as the culprit, has an N-E fault, and that switching on other things (even if not protected by the same, or any, RCD) could then be the last straw in terms of causing an RCD trip?

Kind Regards, John