Bringing single phase off three phase board

[NCSPARKY]

Hi all, new to this thread and just looking for some views.

I have today attended a industrial unit which is being converted into small individual offices. An electrician has previously been here and has taken 3 individual sub mains from the existing three phase consumer unit to single consumer units with main switch and RCBOS in each office which are being fed off C63 MCBS. They have asked me to sign off this work (which has been carried out poorly so would need "tidying" up a bit) and also wants me to continue the install. I haven't looked into the existing install too much and am unsure whether to carry out the works, what is everyone's views on running single phase boards in this method?

If I carry out the work I was thinking of replacing 3 phase board with a 6 way Ryefield board and then supplying each different office off of each 63a fuse depending on loads and then maybe one single phase board for the communal circuits.

Any feedback more than welcome.

Thanks CN

 

[westward10]

It isn't ideal as selectivity probably isn't being achieved but it isn't the end of the world there must be millions of circuits configured like this in the UK.

 

[snowhead]

The very first issue to sort out is why didn't the first Spark finish and sign it off?
Is it because the customer is a nightmare or maybe hasn't paid for the initial work or wouldn't pay for a Ryefield?

 

[NCSPARKY]

It isn't ideal as selectivity probably isn't being achieved but it isn't the end of the world there must be millions of circuits configured like this in the

The very first issue to sort out is why didn't the first Spark finish and sign it off?
Is it because the customer is a nightmare or maybe hasn't paid for the initial work or wouldn't pay for a Ryefield?

I dont know the ins and outs but he was supposedly very unreliable and they got rid. He's work was pretty "shoddy" so can believe them, but who knows.

 

[pc1966]

As @westward10 says you won't get any decent selectivity between MCBs but for many cases it has been "good enough".

A Ryefield board would be much better in that respect, but if you have a low final Zs and high-ish MCB let-through there is some risk of the fuse going on a fault which is more trouble to fix than resetting the MCB.

Again, depending on the sub-mains and supply characteristic it might be worth looking to see if a 50A or 63A D-curve MCB is viable to balance meeting 5s disconnect and having a touch higher selectivity, but typically a fuse is simply better for that job.

If it is OK just now and no other reason(s) to modify the set up I would be tempted to leave it.

 

[NCSPARKY]

As @westward10 says you won't get any decent selectivity between MCBs but for many cases it has been "good enough".

A Ryefield board would be much better in that respect, but if you have a low final Zs and high-ish MCB let-through there is some risk of the fuse going on a fault which is more trouble to fix than resetting the MCB.

Again, depending on the sub-mains and supply characteristic it might be worth looking to see if a 50A or 63A D-curve MCB is viable to balance meeting 5s disconnect and having a touch higher selectivity, but typically a fuse is simply better for that job.

If it is OK just now and no other reason(s) to modify the set up I would be tempted to leave it.

Thanks for your reply, I do agree.

they have also run these through a single check phase meters, which again for me a neater and better set up would be to have these in the intake cupboard, install ryefield then nice metal trunking work with isolators and check meters. but then again this would be fairly pricey so client might not go for it!!

 

[westward10]

Does the three phase board only do these submains.

 

[NCSPARKY]

Does the three phase board only do these submains.

maybe a couple of lighting circuits and I think 2 small radials.

 

[westward10]

I would personally leave it, a Ryfield or MEM Exel replacement would be consideral expense plus a replacement would/may require additional rcd protection for the small power and lighting. Should you sign it off this would depend as to the extent you can visually verify the circuits for compliance, if couldn't trace and inspect 100% of the circuits then personally I would not.