On 14/07/2017 08:46, wrote:
On Thu, 13 Jul 2017 19:10:54 -0600, bud-- wrote:




3 phase. It is not unusual on large services out there in 220v land


(Nice call on RCD.)

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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.

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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.

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

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

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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.

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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.

I poked around on the Legrand catalog and found his switch gear. It is
63 amps, the top one is a 3 pole breaker, the bottom one is an RCCB
(RCD in Europe) That particular one is 100MA so it is not protection
for personal in any sense. You are dead by the time that sucker trips.
It is exactly what you say. It just detects a serious ground fault and
trips the main.

http://www.legrand.com.au/products/e...ion/tx3-rccbs/

If you poke around a little you will see all of that stuff in the
picture. That is an Australian site so Thailand is probably in their
marketing area.

Yes. It does say 100 mA on the breaker.