Cable Sizing for Switchgears

[kwired]

The engineering lead requested that the engineer size the cable to the load. Cost could be one of the 'good reason' but there may be others.

Would it kill anybody for him to tell us his reason?? It very likely is not top secret information. So far all we have is essentially "because that is what was asked for". It is already too late for cost, other than to withhold the difference from payment to the contractor, and he may still agree to that over making changes as it may cost him even more to change something that otherwise doesn't seem have anything wrong with it.

 

[weressl]

Would it kill anybody for him to tell us his reason?? It very likely is not top secret information. So far all we have is essentially "because that is what was asked for". It is already too late for cost, other than to withhold the difference from payment to the contractor, and he may still agree to that over making changes as it may cost him even more to change something that otherwise doesn't seem have anything wrong with it.

Hmm...I wonder from what information did you determine that it is too late. The Contractor may have not even seen the package as it seems to be in the design phase.

 

[kwired]

Hmm...I wonder from what information did you determine that it is too late. The Contractor may have not even seen the package as it seems to be in the design phase.

OK I give up. I checked OP's profile and he says he is an engineer - he probably installed nothing and is in fact part of designing something.
If he would have said "I am designing a cable installation..." instead of "I sized a cable...":ashamed1:

I initially took it to be a contractor ran 2000 amp conductors and the engineer told him they did not need to be that large - if that were the case I could not understand why it would matter at that point other than cost (which somebody has already endured at the install stage) or possibly available fault current issues.

 

[petersonra]

my guess is the project lead told him to do it differently and he wants one of us to say that the project lead engineer is wrong and it should be done his way.

 

[anbm]

its actually an emergency switchgear........ fed from another 480 V switchgear / Emergency generator by means of an ATS.

What is the size of breaker that feeds this ATS/emergency switchgear? Size your conductors according to that breaker size. That would be the safe way, I believe.

 

[jim dungar]

If the phase conductors are oversized, what does that do to the grounding conductor? How about the ability to terminate the conductors into the ATS lugs? Lets no forget that the conduit may need to be larger, and so it may not fit in the space allocated for it.

Ampacity of busbars in switchgear and switchboard does not usually affect its pricing, but physically replacing it can be expensive once all of the pipe and wire has been installed and the building finished. Therefore it is not uncommon to purchase oversized gear if there is even a slight possibility of future expansion, but costs do need to be controlled, so the easier to replace equipment is not oversized.