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

[Lintay]

I'm working in a warehouse and replacing the old fuse boards with a new 3 phase board.
The board will be sitting directly above the buzz bar im not sure if I need to put in an isolator in between them to isolate the 3 phase board?
Thx

 

[buzzlightyear]

pic would be nice.

 

[Lintay]

pic would be nice.

View attachment 35545

 

[Lintay]

The isolator on the left would be feeding the board but is it needed as there's an isolator feeding the buzz at thx

 

[Lintay]

Buzz bar

 

[Darkwood]

Depends on the rating of the dist-board switch disconnector, the tails you use and what fuses protect the busbar (buzz bar?).

You could always upgrade the dist' board to have a front end MCCB switch/fuse as oppose to a disconnector.

 

[Lintay]

Dist- board switch is 250amp, and the fuses which protect the busbar are 200amp.was gonna use 25 mm tails.thx

 

[buzzlightyear]

whats with the adaptable box next to the main isolator ,32 mm pvc conduit

 

[Lintay]

Lighting controls for new led lighting

 

[Lintay]

The isolator load tails will route back through the bus bar into dust-board

 

[Darkwood]

I take it your not usually doing this kid of work given the questions?, you have 2 options here, fit an mccb rated at the tails you wish to use or upgrade the tails so that they are rated to the busbar O/L protection (200amps), the latter been the cheaper but you need to check it will fit on your switchgear, if not you can parallel 2 smaller tails up.

Why do you have a 250amp disconnector in the board costing a lot more than a standed 100amp 4 pole disconnector if you only intend to use 25mm tails, what is the designed demand on the dist board?

 

[westward10]

25.0 conductors contained are not rated at 100A anyway for a triple pole supply.

 

[Lintay]

I'm usually doing domestic work but now work for a new employer. He's gave me a 100 amp isolator to feed from the bus bar to then feed the dist-board,my boss has supplied all the materials.
So if the dis-board main switch was 100amp I could connect tails direct to busbar?
Thx guys

 

[Darkwood]

25.0 conductors contained are not rated at 100A anyway for a triple pole supply.

Tri -rated?

 

[westward10]

Tri -rated?

Or BS7211.

 

[Darkwood]

The isolator load tails will route back through the bus bar into dust-board

No you won't be doing this, the bussbar chamber is not a through route for circuits be they submains or final circuits, you do not need this isolator anyway there are other options I have mentioned already, it does seem your are quite inexperienced in this area, I would suggest and judging from your questions that you bring someone in who has the experience here and work alongside so your can get the valuable experience yourself, the design is totally wrong, your unaware of the relevant regulations which will limit your options here, please take this as constructive advice, errors in this kind of work can be very costly and good, compliant design is crucial here.

 

[buzzlightyear]

can you not use the trucking for the swa cable for the led cable. or use the did board .

 

[westward10]

I'm usually doing domestic work but now work for a new employer. He's gave me a 100 amp isolator to feed from the bus bar to then feed the dist-board,my boss has supplied all the materials.
So if the dis-board main switch was 100amp I could connect tails direct to busbar?
Thx guys

When you say isolator is it fused at 100A. If so you need at least 35.0 conductors to and from it. Have you got additional busbar clamps, I hope you are not going to pair up from existing clamps.

 

[Darkwood]

I'm usually doing domestic work but now work for a new employer. He's gave me a 100 amp isolator to feed from the bus bar to then feed the dist-board,my boss has supplied all the materials.
So if the dis-board main switch was 100amp I could connect tails direct to busbar?
Thx guys

Im sorry to say this but seems your boss has designed this wrong too, I cannot understand why with a modern distribution board that he hasn't fitted a 100amp mccb front end device in the dist board to allow for reduced tails, all the isolator etc is extra work and wasted space, either this or we don't have the full story here, I'm still lost with the design.

PS - you will need to protect your tails for overcurrent if your not fitting 200amp rated (as stated protects the busbar) tails direct to the 250amp disconnector.

 

[Lintay]

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