supplying sub main from a 3pole mcb?

[D Skelton]

Don't pass up on the job, get a local contractor to split the job with you. Earn and learn.

With regards to discrimination issues, this was highlighted perfectly quite recently on a periodic we were doing up on the Thames. My apprentice shorted out the terminals of a switch in an awkward position with his voltage indicator. It was a switch fed by a sub db fed by a sub db fed by a sub db fed by the main panel. The short took the main 125A MCCB out which in turn took half the ship out.

Bad design leads to bad situations.

 

[Leesparkykent]

Don't pass up on the job, get a local contractor to split the job with you. Earn and learn.

With regards to discrimination issues, this was highlighted perfectly quite recently on a periodic we were doing up on the Thames. My apprentice shorted out the terminals of a switch in an awkward position with his voltage indicator. It was a switch fed by a sub db fed by a sub db fed by a sub db fed by the main panel. The short took the main 125A MCCB out which in turn took half the ship out.

Bad design leads to bad situations.

Maybe the OP should ask you, as your not to far.

 

[ipf]

Besides, it is an AC firm. I come across them regularly and invariably it's a case of throwing SY's in instead of SWA's or conduit. Most are excuses for electricians and the installations are badly designed.

 

[Darkwood]

Your certificate will stipulate designed by your contractor to which he will sign for the design...you can bring up any concerns regarding discrimination been partial at best but your lack of experience may be your downfall in making a strong case and to answer any questions put to you...

As long as they are willing to sign off the design then your only the installer so don't pass up on the job ... IMHO poor design, but bring it up as a query and not a challenge to their design if they are comfortable signing for it then so be it... as for milling machines and lathes, this is my area and you'd be surprised how much diversity can exist depending on what they are using them for and whether the machines are ever fully loaded ... the mcb's may be artificially high to allow for inrush on motors as an example an 11kw DOL motor may require a 63(c)mcb to allow for start-up but will never pull more than about 22amps and that will on be if it ever got stretch to its limits.

This is why commercial and Industrial gets very complicated very fast and indepth knowledge of most systems is a must to be able to evaluate the existing demand of a DB ... or just put an data logger to measure demand over a busy period....but that can be expensive and can price you out if you have to hire the unit.

 

[Motty]

After an almost sleepless night worrying about it, I will go back to the contractor and highlight concerns (strictly no plagiarism - I will tell them I have consulted the heavyweight sparks!)

I could'nt expect another firm to come in seeing as the money side of things isn't exactly lucrative to say the least - The MD reckons "it'll only take a day mate" ... (Existing DB MCB, connections to & new DB, 6x supply cables, 6 x isolators & Condensor connections, testing etc) so its priced on a wing and a prayer as it is, and technically I only have a days' labour at subbie rate. I'm just glad I went in before to look at it on my own time before I was committed. He also wanted me to take sole charge of the EIC so hence when I saw the design I started to worry ... With the best will in the world I'll think I'll give this one a miss. Once again I am thankful for your frank and very informative opinions, and will tread more cautiously in the future, and within my limits ...

cheers

 

[Engineer54]

Diversity: The AC I am assuming no diversity as the offices are internal cubicles inside a metal clad building - the condensors are not permitted to be sited outside (landlords restriction) so will be generating heat inside the warehouse and making it even warmer, so the AC will probably spend 3 months on full cooling 12 hours a day.

You're having a laugh here aren't you, never heard anything so ridiculous for a hell of a long time now!! Even if the compressor units were allowed outside these tiny AC units, in what sounds like open cubicles in a large open space building, would be knocking their guts out trying to cool/heat a vast open area. They would have been far better off installing sized AHU's and ducting to cool/heat such areas.... This is a AC installation company, ....Pull the other leg it's got bells on!! lol!!

Why is it we never get the full story in the OP's??

 

[Darkwood]

After an almost sleepless night worrying about it, I will go back to the contractor and highlight concerns (strictly no plagiarism - I will tell them I have consulted the heavyweight sparks!)

I could'nt expect another firm to come in seeing as the money side of things isn't exactly lucrative to say the least - The MD reckons "it'll only take a day mate" ... (Existing DB MCB, connections to & new DB, 6x supply cables, 6 x isolators & Condensor connections, testing etc) so its priced on a wing and a prayer as it is, and technically I only have a days' labour at subbie rate. I'm just glad I went in before to look at it on my own time before I was committed. He also wanted me to take sole charge of the EIC so hence when I saw the design I started to worry ... With the best will in the world I'll think I'll give this one a miss. Once again I am thankful for your frank and very informative opinions, and will tread more cautiously in the future, and within my limits ...

cheers

Well only you know your limits and whether to pass it on, if they expected you to sign for the design of the install too then thats when I personally would have said no, if they want it done their way for whatever reason that's fine as long as they sign for design then they are the ones who will be challenged come any issues in the future that may arise and not you. I've seen plenty of these firms and knowing my stuff I tell them straight my way or not at all - if they want to cut corners my name doesn't go on the design and I am merely the installer.