Carrying out a refurb on old panel boards, worried about discrimination.

[pc1966]

If it really has to be a MCCB board then you are probably as well giving up on the idea of selectivity on the sub-main to incoming fuses, and just got for the basic model rather than trying to fiddle with the fancy electronic settings to try and walk the line between the MCCB/fuse on the supply side and the MCB/MCCB on the sub-DB side.

 

[johnwicklover]

If it really has to be a MCCB board then you are probably as well giving up on the idea of selectivity on the sub-main to incoming fuses, and just got for the basic model rather than trying to fiddle with the fancy electronic settings to try and walk the line between the MCCB/fuse on the supply side and the MCB/MCCB on the sub-DB side.

Thank you for suggestions and the links, I will have a look through them.

There are 6 single phase submains and 2 three phases - submain. Unfortunately I don't know the exact loads at this time.

The bus bar chamber idea sounds good but they want an upgrade to 6 way MCCB panel board. Like you said the fuses probably won't blow but circuit breakers are easily switched on. The MCCB will be more expensive but the school will have to swallow it.

 

[pc1966]

You might want to check the main fuse, as that is quite a lot of sub-mains coming off 3*100A for example, so if they turn out to be 160A or more then you have an easier job.

I had a go at the Schneider on-line tool but it seems broken for me today

I would concentrate on getting tolerable MCB/MCCB selectivity using the short-delay aspect of the fancy MCCB, that way in most cases the selectivity falls back to incoming fuse and final MCB, and that is probably no problem.

Yes, a sub-main fault might not open the MCCB before the incoming fuse, but that is a lot less likely than some final circuit/appliance giving them grief.

If you can find out loads and the PFC & PSCC at each DB just now it would help to decide how well the whole system would work.

 

[johnwicklover]

You might want to check the main fuse, as that is quite a lot of sub-mains coming off 3*100A for example, so if they turn out to be 160A or more then you have an easier job.

I had a go at the Schneider on-line tool but it seems broken for me today

I would concentrate on getting tolerable MCB/MCCB selectivity using the short-delay aspect of the fancy MCCB, that way in most cases the selectivity falls back to incoming fuse and final MCB, and that is probably no problem.

Yes, a sub-main fault might not open the MCCB before the incoming fuse, but that is a lot less likely than some final circuit/appliance giving them grief.

If you can find out loads and the PFC & PSCC at each DB just now it would help to decide how well the whole system would work.

Yeah, that's a good point. I will get the main fuse confirmed.

I might be able to get the loads confirmed as well.

Thanks.