House DB main switch

**Leecatt** · 26-Feb-14, 06:44 AM

Originally Posted by Sparks

Keep looking, if I find the time i will get it. Main switches must isolate all Live as well as the Neutral. In a single phase installation that means double pole: SP+N, Isolator or ELCB can serve as main switch, whichever is used must be indicated on the COC as well. You may have a SP CB before the main switch often the case when the ELCB is the main switch. For a 3ph supply, surprising to almost all, you are supposed to use a 3ph 4pole isolator, 3pole+N or 3phELCB. It is in the regs but i am afraid I do not know exactly where. If I get a chance I will look for you. A sub DB may be fed from a SPCB but the DB must have a DP as main switch which is also specified in the regs.

In a single phase system you may have a combination of a circuit breaker and an earth leakage instead of an earth leakage with integrated overload protection.
However where this earth leakage is used as the isolating device for the db then it must also isolate power to the accompanying circuit breaker which will then be mounted on the load side of the earth leakage.
Should you wish to remove various circuits from the earth leakage circuit then an additional isolating device must be installed before the earth leakage.
At this point the accompanying circuit breaker may be installed on the supply side or the load side of the earth leakage.

See SANS 10142-1:2009 6.8.1
6.8.1 Circuit-breakers used as main or local switch-disconnectors, A circuit-breaker that is used as a main or local switch-disconnector (see
6.9.4) shall comply with the relevant requirements of a standard given in clause 4 for switch-disconnectors, or, alternatively, a switch-disconnector
shall be positioned on the supply side of the circuit-breaker.

**mikilianis** · 04-Mar-14, 09:09 AM

In the case of a single phase circuit I would use a SP+N as the main isolator and then install a ELCB omitting to connect the the lighting circuits on the ELCB for safety.Then again the difference between domestic and industrial D.B.s need to be considered.Using an ELCB as a main switch I have had whole production lines come to a standstill through nuisance tripping (night watchmans kettle)

**AndyD** · 04-Mar-14, 11:28 PM

I think you have a very valid point. I consider any installation, even domestic, that uses a single RCD as a main switch to be poorly designed. The nuisance factor is far too high if there's ever a leakage fault. I don't understand why it's still the norm nowadays when you can purchase a half decent RCD for afew hundred bucks so splitting the load between 2 or 3 RCD's wouldn't break the bank.

On several jobs recently we've had a specification for RCBO's on every circuit. I had to import them myself because nobody within a thousand Km stocks them. They've been using these in many countries for several years now but every wholesaler I spoke to hasn't even heard of them.

Click image for larger version.

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**Leecatt** · 05-Mar-14, 07:23 AM

Originally Posted by AndyD

I think you have a very valid point. I consider any installation, even domestic, that uses a single RCD as a main switch to be poorly designed. The nuisance factor is far too high if there's ever a leakage fault. I don't understand why it's still the norm nowadays when you can purchase a half decent RCD for afew hundred bucks so splitting the load between 2 or 3 RCD's wouldn't break the bank.

On several jobs recently we've had a specification for RCBO's on every circuit. I had to import them myself because nobody within a thousand Km stocks them. They've been using these in many countries for several years now but every wholesaler I spoke to hasn't even heard of them.

Unfortunately I cannot make much out as the picture is extremely small.
Is it possible to post a larger version?
What is that above the circuit breakers?

**ians** · 05-Mar-14, 07:30 AM

This would confuse the local sparkies. I assume this is a pic of a DB used in the USA not in SA by the colour code. Black live and blue neutral with an exposed bussbar at the bottom. My kind of DB nice and neat.

**Leecatt** · 05-Mar-14, 07:50 AM

Originally Posted by Slow Blow

Does the main switch on a single phase DB have to be single pole, single pole and neutral or double pole, I ask this as there seem to be some confusion amongst a lot of local electrical CoC providers in Cape Town.

The db must be protected by a double pole disconnecting device that disconnects both the live and neutral.
If there is no integrated overload protection in the disconnecting device then a circuit breaker may be installed on the load side of the disconnecting device.
See SANS 10142-1:2009 section 6.9

**AndyD** · 05-Mar-14, 02:08 PM

Originally Posted by Leecatt

........What is that above the circuit breakers?

Originally Posted by ians

This would confuse the local sparkies. I assume this is a pic of a DB used in the USA not in SA.......

It was just a picture showing RCBO'S for the benefit of anyone uncertain what they are. t's not my handywork (my panels are far neater than that

) the DB shown is actually a UK 17th Edition compliant one, each socket and light circuit MCB has two wires because they generally use 32A ring circuits.

RCBO

**Dave A** · 05-Mar-14, 09:23 PM

A residual-current circuit breaker with overload protection (RCBO) combines the functions of overcurrent protection and leakage detection.

With thanks to Wikipedia.

**AndyD** · 05-Mar-14, 10:35 PM

Thanks Dave, forgot about wikipedia momentarily. Basically they're the size of an MCB, well at least the more recent versions are, the older ones are quite a bit taller than an MCB but same width. You fit one for each circuit being supplied from the DB and they provide earth leakage protection as well as overload protection to each individual circuit. The bonus is that an earth leakage fault just causes tripping of the guilty circuit and not the entire premises.