Removing single phase RCD??

[jimboallen]

Hi All.

I have another question for you. I suppose its really a 'is it legal to' question as its a business setup providing power to customers via 16amp sockets.

Please refer to the picture attached, at the moment, 3 phase comes in on the right, into a 3 phase RCD, then the 3 phase goes off into its own MCB. A single phase is taken off the top of the 3phase RCD and feeds a single phase RCD, then into 4 single phase MCBs and then down to the sockets.

My question is, would I be able to and would it be OK to do away with the single phase RCD. To do this I would like to take a single phase off the bottom of the 3 phase RCD and go straight into the 4 single phase MCB's.

The reason for this is we need more space in each box to fit meters. each meter is the size of a single phase RCD and we need to fit 4 on the rail.

Obviously we would ensure the 3 phase RCD was the same amperage as that of the single phase one and we understand that if any single socket trips the RCD we would loose the 3 phase socket (fitted just out of view on the bottom right).

Is there any logical or regulatory reason why we cant do this?

Thanks in advance

James

 

[SimpleSimon]

My experience with three phase is limited so bear with me, but wouldn't it cause an imbalance as the RCD is only detecting one phase as oppose to three?

 

[yellowvanman]

Doesn't matter if there is a current imbalance on the RCD, as long as the currents go in and out through the RCD on the phases and neutral it won't trip.

In effect the picture is showing the single phase circuits having 2 x 30mA RCDs in series, so if there is a fault on the single phase sockets either RCD could trip, it'll be a race between them. So even with what you've got you could get the 3phase RCD tripping before the single phase RCD.

So I'm thinking what you are proposing will not degrade the protection you have already.

Just one note also, your 3 phase MCB is a 'B' type whilst the single phase ones are 'C' types so you could get the 3 phase MCB tripping before the single phase ones, if your supplying motors etc.

 

[jimboallen]

Ok Thanks for that, so in theory it should work.


Yellowvanman....The single phase is fed from the top of the 3phase RCD is it not and therefore does not pass through the 3 phase RCD just the single phase one.

 

[yellowvanman]

Sorry, I was thinking the black cables were the incoming.

Your theory still works.

 

[jimboallen]

Thanks for the help yellowvanman.


If anyone else could just confirm to or against on the regulations front that would be very helpful. I personally see no reason why it cant be possible now, and having looked at the diagram on the RCD it shows all 3 phases travelling through the RCD coil separately so I should have figured that out before, but I would like to have conformation on whether it would be above board to run like that.

Thanks again
James

 

[SimpleSimon]

Again I don't see a problem Regs wise but wait for a few more to reply.