Feeding 250 amp 3 phase board direct from buzz bar need isolatir

[westward10]

Yes I have to agree, you need to have a chat with your boss and explain that at the moment this maybe outside the scope of your competence and you need some guidance and assistance. I think you may also need to bear in mind that he, assuming it is a he has not really thought this through. This isn't routine domestic work as you have realised and the reality from a piece of paper can be a harsh lesson.

 

[Lintay]

I mean an mccb/switch fuse thx

 

[westward10]

Thx for constructive advise darkwood hence why I'm querieing the design.
So could I come straight off the bus bar into dist-board and double up the tails?or will I need to replace the main switchwith a fused switch aswell? Thx

You can come direct from the busbar but your conductors need to be at least 95.0, have you ever worked with this size of conductor.

 

[Lintay]

Yes I have to agree, you need to have a chat with your boss and explain that at the moment this maybe outside the scope of your competence and you need some guidance and assistance. I think you may also need to bear in mind that he, assuming it is a he has not really thought this through. This isn't routine domestic work as you have realised and the reality from a piece of paper can be a harsh lesson.[/QUOTE

 

[Lintay]

If the isolator feeding the busbar has 100amp fuses in could I then feed the dist board directly with 35 mm tails and downrate the dist-board switch to a 100amp mccb.
If my boss is adamant about using the isolator I will still need to use 35 mm tails anyway is that right ?
Thx for advise

 

[Lintay]

You can come direct from the busbar but your conductors need to be at least 95.0, have you ever worked with this size of conductor.

No

 

[westward10]

Yes you could although the main switch at the board is not likely to be an mccb but an EN60947-3, 125A isolator.

 

[Lintay]

Yes you could although the main switch at the board is not likely to be an mccb but an EN60947-3, 125A isolator.

So downrate the the dist- board switch to 125. Amp?
If he's adamant about not changing the isolator or dist- board all I need to do is feed the isolator with 35 mm tails which feeds the dist- board with 35 mm tails which don't route through the bus bar chamber as long as the fuses feeding the bud ad are 100amp

 

[Darkwood]

Sorry earlier I'm sure you said the busbar was fused at 200amp, now are you saying 100amp? It changes alot of the advice or are you suggesting derating them which is unwise as it strangles the future use of the busbar plus you need to assess the demand existing.

 

[Lintay]

Sorry earlier I'm sure you said the busbar was fused at 200amp, now are you saying 100amp? It changes alot of the advice.

Yes I'm thinking now it's 100amp sorry

 

[Darkwood]

I think tbh you need to know exactly what is existing, you cannot design a system by guessing what's existing, like I said earlier, small mistakes cost big in this side of the industry.

 

[Lintay]

I think tbh you need to know exactly what is existing, you cannot design a system by guessing what's existing, like I said earlier, small mistakes cost big in this side of the industry.

If the fuses are 100amp can I feed the dist board directly with 35 mm tails thx

 

[Darkwood]

Yes but you have to look at the bigger picture here, can the fuses be uprated again ie.. is the cable big enough to do so, you want to avoid forcing limitations on future additions, they may just have 100amps because of the low demand but fitted a 200amp system for expansion, we lack the info to give you a true informed reply but your boss really should have done all this and supplied you with the correct gear to start with with which I have my doubt he has.

 

[Lintay]

Yes but you have to look at the bigger picture here, can the fuses be uprated again ie.. is the cable big enough to do so, you want to avoid forcing limitations on future additions, they may just have 100amps because of the low demand but fitted a 200amp system for expansion, we lack the info to give you a true informed reply but your boss really should have done all this and supplied you with the correct gear to start with with which I have my doubt he has.

Maybe he couldn't get a 100amp dist-board hence why he got the isolator?but then the cost in price is a huge difference?But he had said to use 25mm tails.il have to run through the design with him tomorrow,thx for the advise really appreciate it.
I only started new job last week so had to make sure I knew what I wax on about before speaking to him.thx

 

[Toneyz]

what 250A D.B. have you been provided with ?

 

[Lintay]

what 250A D.B. have you been provided with ?

Will check in the morning

 

[westward10]

Try and be open with your boss about your lack of experience with this.

 

[Lintay]

I told him first day on the job, but he was the one who designed it and ordered bits

 

[LeeH]

Tri -rated?

Probably be ok but the ratings are based on 90degC remember with tri.

 

[Darkwood]

Probably be ok but the ratings are based on 90degC remember with tri.

You raise a good point but tri rated still has a higher capacity at 70c plus we do not know the switchgear, the busbar will be ok for 90, I install this stuff all the time and you can maintain the 90c ratings if you choose the correct gear, otherwise it's pointless making it.