Breaker sensitivity?

abenn · 3 Aug 2015

I know there's a sub-forum for overseas electrics, but since there's more people viewing here and my question is a general one, I'm posting here first:

I'm staying at a relative's house in Bangkok, and the main circuit breaker is forever tripping -- probably at least once a day, and always when someone switches off a light, not always the same light. Air conditioning compressors automatically stopping and starting don't ever seem to cause a trip. Looking at it, I see that the breaker has a sensitivity adjustment knob that is set at 5mA; from other posts in this forum it would seem that 30mA is a more-normal value in the UK, so I've suggested to my hosts that they might be better off changing the setting to 10mA (the next available setting) for a start. The settings go up to 25mA, plus a 'Direct' setting.

The voltage here is 220. Is my advice safe?

bernardgreen · 3 Aug 2015

It would be safer to discover what is causing the 5 mA leakage that is tripping the breaker. Setting the breaker to 10 mA may not be unsafe but 10 mA through a human body could be fatal. RCDs do NOT prevent electric shocks. They only reduce the duration of the electric shock to a duration that is less likely to cause irrevocable damage to the person's body.

ericmark · 3 Aug 2015

When I lived in Algeria I had to re-thing on earthing the same with Falklands and Hong Kong. Not only the climate but also grond conditions mean our standards in the UK can't be always applied abroad.

Also 5 mA seems rather low, try buying just a 10 mA here in UK and both hard to find and expensive. The MK 10 mA offered by TLC costs £92 so to get a 5 mA would be near impossible. Also in this country adjustable versions can't be used by ordinary persons so only place I have seen them is on portable generators.

So I question if really 5 mA? Could it be 50 mA? Likely you could do away with the whole RCD for years without anyone being injured but also it could happen next week. So yes I would in my own house be happy with a 100 mA RCD but in my own house I know the earth loop impedance and likely hood of direct contact, I would not however fit a 100 mA RCD to some one else's house instead of 30 mA as no idea of earth loop impedance or how they treat the electrics.

So I would leave it to the locals as too many things different to UK and last thing you want is for some one to get injured.

bernardgreen · 3 Aug 2015

ericmark said:
as too many things different to UK

Somewhere in or near Thailand a hostel had electric showers where Neutral and Earth were combined with the water pipe to feed the shower and only the Live was by wire.

abenn · 3 Aug 2015

I suspected that might be the answer I'd get. I think you're saying the speed of the disconnect is probably more important than the trigger current, but I have no way of telling what that is with this locally-manufactured breaker. The reason for the leakage is a puzzle to me, for the trips seem to be triggered by several different light switches in different rooms -- but randomly. We might use the same light switch for days on end without tripping the breaker.

It seems strange to me (a layman with some understanding of electrial theory, but not of installation practice) that the problem never seems to happen when fans etc. are switched on or off, or unplugged from the nasty American-style 2-pin sockets that prevail here. So what could it be about the light switches? All the lights are circular fluorescent tubes; could that cause an issue.

Ericmark, there's no ambiguity about the markings in the rotary switch on the breaker, though I have no way (and don't intend to get that involved) of knowing its accuracy. The standard of electrics here is such that we actually have a breaker for our electric shower heater inside the shower cubicle! So, other than suggesting they get a qualified electrician to look at things -- which I doubt they'll bother to do -- I'll keep my nose out of it.

endecotp · 3 Aug 2015

Are the light switches metal or plastic?
What happens if you turn them off with an insulated glove or similar?

JohnW2 · 3 Aug 2015

endecotp said:
Are the light switches metal or plastic? What happens if you turn them off with an insulated glove or similar?

Interesting thought - but if there were enough current leaking by that route to trip even a 5mA RCD the person would feel it, and I would have thought that the OP would have mentioned it if people were getting shocks/tingles from the switches!

Kind Regards, John

ericmark · 4 Aug 2015

abenn said:
from the nasty American-style 2-pin sockets that prevail here.

then I will assume 120 volt between lives? The USA system even in USA has many different methods of wiring. Split phase is common where unlike us small pole mounted transformers are used in the street for domestic supplies rather than our much larger centralised transformers. A ground fault circuit interrupter

Wikipedia said:
In North America, GFI receptacles can be used in cases where there is no grounding conductor, but must be labeled as "Ungrounded". An ungrounded GFI receptacle will trip using the built in Test button, but will not trip using a GFI test plug, because the plug tests by shorting a small current from line to the non existent ground.

Wikipedia said:
In the United States, the American Boat and Yacht Council requires both GFCIs for outlet and Equipment Leakage Circuit Interrupters (ELCI) for the entire boat. The difference is GFCIs trip on 5 mA of current whereas ELCIs trip on 30 mA after up to 100 ms. The greater values are intended to provide protection while minimizing nuisance trips.

I do not understand the USA system, but clearly it is different from ours and 5 mA is used.

abenn · 4 Aug 2015

The light switches are plastic, and nobody has ever felt a tingle so far as I know -- and I've been the one that's caused the trip on at least one occasion.

The system here has every appearance of being the American system, with overhead distribution and small pole-mounted transformers. But that, I suppose, is no guarantee that it is.

Without a locally-qualified electrician on site it's now clearer to me that there's so many variables that nothing can be assumed. So thanks for the contributions, but I'm going to leave things alone and let my host get professional advice if he wants to.

Just out of interest though, how can a GFCI ever trip if there's no ground connection (as per the Wiki quotation)?

bernardgreen · 4 Aug 2015

abenn said:
Just out of interest though, how can a GFCI ever trip if there's no ground connection (as per the Wiki quotation)

The Live and Neutral pass in opposing directions through a current transformer, if the current in the Neutral is not the same as the current in the Live then the current transformer creates an output current on a third winding. This output current is proportional to the difference between Live and Neutral. If the difference exceeds the rated maximum difference then the current from the transformer is enough to trip the mechanism.

JohnW2 · 4 Aug 2015

abenn said:
Just out of interest though, how can a GFCI ever trip if there's no ground connection (as per the Wiki quotation)?

As bernard has said, residual current devices will trip whenever the L and N currents differ by more than the specified amount (5mA, 30mA or whatever), due to some of the L current returning directly to earth/ground, rather than through the N conductor. Even if there is no earth/ground connected to the socket/outlet, there might be other earthed things nearby (water pipes etc.) - so if a person were to simultaneously touch L and that water pipe (or whatever), if enough current flowed through the, the device would trip.

Kind Regards, John

abenn · 5 Aug 2015

Thank you. That explains it clearly enough for me.

JohnW2 · 5 Aug 2015

abenn said:
Thank you. That explains it clearly enough for me.

You're welcome.

Kind Regards, John

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Breaker sensitivity?

Similar threads