breaker response time

I'd try just replacing the breakers on the problem circuits first - they should trip at something like 5ma where the mains trip at 30ma? fault current.

Reply to
clare
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(Nice call on RCD.)

------------------------ One of the important questions about an electric power system is how it handles a hot-to-ground short - a ground fault.

In the US the fault current is carried on the ground system to the service where it goes across the required neutral-ground bond to the service neutral and back to the supply transformer. This is an all-metal path that can supply the high current to trip a breaker. An earth connection is not allowed to be used because it can not reliably carry a high current. (What is the current if you connect 120V to a ground rod that is a code-compliant 25 ohms-to-earth?)

In parts of the UK the neutral is earthed at the supply transformer but not elsewhere. There is no N-G bond at the building. That means the fault current return is through the earth, which will not reliably trip a breaker. I think that is why RCD main-breakers are used - the earth fault return current will trip an RCD. That may be why this system has RCDs. The only number I have seen for an RCD trip is 30 mA. That seems like it would be subject to nuisance trips. It is also the number I have seen for RCDs protecting people - seems too close to the can't-let-go current.

In the US, as most of us know, GFCIs to protect people trip at 5 mA. There are GFIs to protect equipment that trip at 30 mA. And AFCIs include a ground fault trip, I think always at 50 mA.

------------------------------- The pictures show devices in series. Likely the top unit is an ordinary over-current breaker and the bottom one is only an RCD.

Likely a large main breaker in the center (that is how it is marked), fed from the bottom, feeding 2 - RCD-protected feeders.

------------------------------ A 63 A (67?) 220V 3 ph feed is equivalent to about a 190 A split-phase service here.

------------------------------ Would be a good idea for the OP to google the breaker information to find specs and instructions.

----------------------------- As a warning - the service may only be about 150 A. But a short on the service wires before the breaker can have a current of thousands of amps

- would be very unpleasant.

------------------------------ And this newsgroup is mostly US, though we humor some foreigners from north of the border. Happy to answer questions, but would have helped for the OP to say he is in Thailand, especially on a question like this.

Reply to
bud--

There are so many wires in the sub panel. How do I find the neutral for the particular breakers? The breaker boxes in the US have bus to which all the neutral and ground wires connect to. Not this box. So, where are the neutral wires? And I heard that three phase circuit shares neutral wire. That makes things more complex.

Even for the breaker boxes in the US, how to find out which neutral wire goes with which breaker?

Reply to
Lenny Jacobs

You follow the hot wire from the breaker back to the incoming cable and find the white neutral wire that's with it, that's how you figure it out in the US. In your case, that RCD breaker has 4 wires going through it, with one labeled "N" doesn't it? I don't have the spec sheet for the breaker, but it seems pretty obvious to me that would be the neutral.

But does any of this really matter? It sounds like you have a serious safety problem, one that could be lethal, the fault you have must exceed 100ma, isn't it time to hire an electrician and get it fixed?

Reply to
trader_4

As I have said earlier, I did ask an electrician about the tripping. He just shrugged and said it's due to moisture. No need to fix it. Indeed, during dry season, there is no problem even when all the four problematic breaker are flipped up.

Reply to
Lenny Jacobs

Neutrals are not really tied to a breaker except for that RCCB and that is all of the neutrals on that feeder. You do need to keep track of the neutral for each outgoing cable but it is only important when you are disconnecting it and you want to keep the ungrounded conductors grouped so you can assure they are on different phases.

Reply to
gfretwell

With that much fault current this is probably more than a little moisture. I bet you have boxes filling up with water. I would start with a visual inspection of all of your outdoor fixtures and junction boxes. You might also have some splices underground that are not waterproof. Without actually looking at your installation it is hard to guess from half way around the planet. ;-)

Reply to
gfretwell

I suspect it'd take more than just visual inspection. I see some above-ground junction boxes. Not sure if there are underground junction boxes. I do have an underground junction box for phone line. How to keep water from getting into underground junction boxes? I have no clue.

Reply to
Lenny Jacobs

In the US, one can buy cables that have hot, neutral, and ground wires all in a sheath. It's very easy to tell which hot goes with which neutral. Here, people use separate wires. They maybe black, red, green, blue, etc. How to figure out which two wires go with which breaker? Impossible, I think.

Reply to
Lenny Jacobs

You don't really keep the water out, you just use waterproof splices. They are typically a crimp splice in a silicone filled tube. Above ground you just be sure they are arranged to drain and that the conductors are not near the bottom of the box or touching the sides.

Reply to
gfretwell

Perhaps plant "umbrella plants" over the jboxes?????

Reply to
clare

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