Distribution Board Rating

[Jeffmo65]

Hi , quick question , in my thoughts requires a quick answer
160amp fused switch feeding existing Hagar panel board fine no problem with that
My superior wants to install a new 125amp rated DB fed from same switch ?
I don't I would want to see a board rated at 160amp or above
Thoughts please

 

[Jeffmo65]

Just so you don't think I'm an idiot . I have installed many bus chambers and designed and installed many panels including ATI panels changeover panels . This was a general question about wether I was loosing it or not as we do work for a number of large supermarket chains and if he isn't going to listen to me then what's the point of my position . I've always installed panels at the fuse rating as a matter of course and as Tony says rectum protectum . Your replies have been very helpful and my boss is due a few lessons maybe and a nudge to read his regs? . Cheers again boys/ girls

 

[Darkwood]

In essence Darkwood that is exactly the answer I was wanting to get to . Yes I agree with you about terminations on the existing switch . The existing cable according to drawings are 35mm . So what you are maybe theoretically proposing is i
1. Main incomer switch feeding busbar
2. Switch for existing fed from bus
3. Switch for new DB fed from bus
so another 2 switches required plus bus chamber and standard let's say 125amp Schneider DB .
This is the right way to me . To him is another matter . I am currently the QS for the company and come from a commercial/ light industrial background , my boss ? You've guessed it . He still has QS STATUS so he can sign for it then . Cheers Darkwood

There is another thread selling a 200amps busbar 750mm and 160 amp switch at a very good price, maybe you want to check it out, you can get cheaper poor quality tat but you will learn quickly that its not worth it in the long term and yes thats the way you should design it if using common upstream isolator, you could as ENG stated cut several hundrend quid off the cost by running a second supply from the 160 sw/f to a 125/100 sw/f and protect your second board correctly but this isn't what would be classed as good design practice but does achieve compliance at a lower cost, alternatively change the 125amp main switch for a 125amp mccb if the brand has the option?

PS 160amp on 35mm cable sounds wrong, are you sure the fuses haven't been de-rated in the 160amp switchgear? What cable and install method isthe existing?

 

[Jeffmo65]

Basically Darkwood the switch fuse is directly next to the cut out and the main panel existing is directly above it . From the photos it is all ran in Galv trunking so would imagine supply side of switch D/I tails and singles from topside to panel . Can't answer on the fuse size but as fitted drawings state 160 . Cheers .

 

[Engineer54]

35 mm on 160A supply, that's got to be right on the limit, depending on the cable and installation method, but i've nothing here to check/confirm...

 

[Darkwood]

Even tri-rated 35mm is going to be a push IMHO without looking it up, I would have thought 50mm tri- as a minimum but I cannot look it up right now, and it is the existing so not your direct concern but may be a point to look into and to be brought up if it doesn't comply, this is why I asked if they had been derated when you said 35mm....

 

[jp1976]

Eng I havnt designed anything this is an existing supermarket with existing distribution connected and yes your right about the design aspect . However someone far more worthy than me has done this previous . This scenario is an add on which I am arguing with my gaffer about . In essence I see the bussbar as just a link of copper so therefore the fused switch device is there to protect the sub feed and the links through the DB . I appreciate that some maths wizard will whistle of some equation about withstand and PSCC and all that which would be fine . But trust me my boss would look at it and throw it in the bin cos he wouldn't understand it . The design with regards to bussbar chamber I had thought of . Costs prevail unfortunately . Thanks guys

I have the easiest solution, if you don't agree or like It, tell your boss to do it himself your well within your rights.

 

[Jeffmo65]

It may well come to that . I have to sleep at night after all

 

[Engineer54]

50mm conductors would be my starting point when considering a 160A OCPD!!

 

[dansk]

Just a shame these contracts aren't your own. Good luck I hope you get your result.

 

[Jeffmo65]

Thanks to everyone who posted on my thread today . It is good to know that we all share the same ethos . There will always be debate between good people and that in itself promotes good standards . I will stand by my laurels until someone can prove to me that good practice is wrong and doing things on the cheap is right .
Cheers Guys/ Gals