wire size

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clayton

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at my workplace they are installing a new switchgear panel. rated at 2000, amps 480 3ph
ok, they are pulling 4 sets of 350kcmil to supply it, is this big enough?, I was under the impression that 350 was only large enough for 350amps, with 3 conductors in the raceway. (ther are 4 seperate 3" conduits) anyway what are your thoughts on this.
:p
 
Re: wire size

Just because the switchgear is rated at 2000A does not mean that it has to be supplied with 2000A. The conductor size is based on how much current is actually expected and the over current protection on the other end.
 
Re: wire size

they is ibew, the total of the switches is also 2000amp, so i guess this is comparable to the situation in the breaker panel correct.?

thanks for your replys.
 
Re: wire size

What has to happen first is the performance of a service calculation, to determine the amount of load that these conductor will be called upon to carry. Then you select the conductor sizes.

A 350 MCM copper is only good for 310 amps (75C column). So four of them would only be good for 1,240 amps. You can use a 2000 amp switchboard to serve a load of 1,240 amps. However, a 2000 amp main breaker (or set of breakers adding up to 2000 amps total protection) cannot be used to protect conductors that are only good for 1,240 amps.
 
Re: wire size

Originally posted by charlie b:
However, a 2000 amp main breaker (or set of breakers adding up to 2000 amps total protection) cannot be used to protect conductors that are only good for 1,240 amps.
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If this is a service than a set of breakers adding up to 2000 amps total protection can be used as the protection per 230.90(A) exception 3 as Ryan has mentioned.

I am not sure we are talking about a service though.

The opening post says:

at my workplace they are installing a new switchgear panel. rated at 2000, amps 480 3ph
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This could be a large subpanel. :)
 
Re: wire size

Originally posted by iwire:If this is a service than a set of breakers adding up to 2000 amps total protection can be used as the protection per 230.90(A) exception 3 as Ryan has mentioned.
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I see what you and Ryan are saying. If this switchboard is a service, and if it has a main breaker set for 2000 amps, that would be a violation. But if it has no main breaker, and has no more than six feeder breakers that add up to 2000 amps, and if the calculated load is less than 1,240 amps, then this is acceptable.

But it still must start with a calculation of the load. Clayton: Do you have any information about the service calculation?
 
Re: wire size

no, charlie i dont, this gear is fed from a 13.8kv to 480 transformer ungrounded delta, ill try and get more info tomorrow. and i think there are only 4 disconnects, with blanks for 2 more, actually being used but ill check again, thanks guys , for the reference too,
Oh, to me this would be a service, it is being installed to feed a chiller, a laser, and i believe some other super high output light that is supposedly super hot white light, very interesting stuff. can't remember but its like some 75k watt light,
thanks again.
 
Re: wire size

As to it being a service or not, where is the service point?

As an example I worked at a large facility and the service point was at our property line, from there we had feeders (4160 volt) to many different buildings and structures, not one of these buildings had a "Service"

Service Point. The point of connection between the facilities of the serving utility and the premises wiring.
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Re: wire size

ok, the utillity comes into a seperate building(just for the purpose of distribution), then branches to all the additional buildings,
the installation in question, comes from the 13.8 substation in my building to a transformer and finally to the switchgear.
so i take it then to mean the substation,on is are all feeders?

[ October 26, 2004, 07:38 PM: Message edited by: clayton ]
 
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