Three phase consumer unit - how to use with RCDs

[Agroshield]

Could one of the electrically-astute people please advise me?

This is not for use in the UK, so I am looking for good practise rather than strict compliance with a particular set of regulations.

Is it possible to use a three-phase consumer unit with RCD breakers? How?

I plan to buy a consumer unit with a three pole incoming switch and three pole busbar feeding single way MCBs for lights, air conditioning, cooker, water heater, etc. (I know I have to balance the demand among the three phases).

What I do not understand is how I can feed an RCD breaker off the busbar (RCD breaker is two pole, requiring a neutral connection - used for ring mains).

I can feed one single RCD if I put it at the end of the line and shorten the busbar by one unit. I can run the neutral wire into the space vacated by the cut-off busbar.

What I do not know is how to set it up with more than one RCD, as further shortening of the busbar to open a neutral connection for the second RCD will remove the live feed from the first one.

Any advice is greatly appreciated. Thanks.

 

[brightspark]

single phase rcbo fit in the 3 phase db and theres a neutral lead on them that conects to the comon neutral bar they take the place of a single pole mcb here http://www.rselectricalsupplies.co....9d16806_8471?gclid=CML89ZCgl8UCFcoJwwodIhsAnA the white lead goes to the earth bar . just make sure your breakers match the 3 phase board

 

[dobbslc]

As above^
Don't start cutting bus bars to fit 2 pole mcb's not designed for the board, you'll end up with a cross phase blow up!
Single pole rcbo's are the way to go and will mean if you get a fault on one circuit it'll trip only that one out and not the whole board.
I should think most countries will have decent 3 phase switch gear available.
Where is it going?

 

[awemawson]

All my 3 phase boards have 3 phase RCDs as their main switch. Most are 30mA ones, but the one that feeds the CNC machine had to be 100mA due to the nature of the load (18.5 kW and 7.5 kW spindle drives on the big lathe)

 

[dobbslc]

Needing a larger 100ma rcd would be due to the earth leakage a big set of motors and the associated control gear produce.
You can also get time delayed one's (S type) for use with inverter controlled motors as well.

 

[brightspark]

this will give u the idea .theres 3 phase breakers fitted and single pole breakers in board . then a comparison of rcbo and mcb together that fit in

 

[awemawson]

In my case it's the high frequencies involved in the two large inverter drives giving a high leakage current by capacitive coupling. The motors, although 'rather special' in that they cost an arm and a leg, are only three phase at the end of the day like any other. Meggaring them when isolated gives no discernable leakage at DC or 50 Hz

The orange boxes in the picture are the huge inverter drives and the main spindle motor is in the other picture with a 2 foot ruler for comparison !

 

[brightspark]

what size board are u after and wheres your location

 

[Agroshield]

Don't start cutting bus bars to fit 2 pole mcb's not designed for the board. Where is it going?

Thanks for the advice. I will not be blowing anything up. It is for use in Ghana. The stuff is available but of dubious quality.

 

[brightspark]

Thanks for the advice. I will not be blowing anything up. It is for use in Ghana. The stuff is available but of dubious quality.

what size board u after

 

[Agroshield]

what size board are u after and where's your location

Thanks for your advice. I have now read up about RCBOs and can see that are what I need.

There are 18-way ones with 100A 3-pole incomer, fully populated with single pole MCBs on a certain auction site for £55. They are MCG brand (which seems to be viewed with disdain by serious sparkies).

I am after something of similar size off a more respected manufacturer and at reasonable cost. I am in NW London.

 

[brightspark]

the one in my picture is a 12 way if only using single phase breakers or 4 no 3 phase breakers. its only a month old and was a temp supply on a job and taken back out

 

[dobbslc]

Don't touch MCG!
They are total ****e!

 

[Agroshield]

Don't touch MCG!

I had gathered that from a brief search. Can you perhaps recommend one or more reasonably-priced alternative brands? Thanks.

 

[brightspark]

hager .mk wylex . crabtree ,as for the price thats negotiable depending on what percent discount u get from the wholesaler. if u go for mk electrifix has the most comprehensive amount of boards and the price is good