600 amp service 277/480 volt

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KING-CMO31

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I have been asked to look at a bigger scope of electrical work for a customer. They are looking to add 2 600 amp panels roughly 650 ft away from the existing gear room. In looking into this further I am having trouble defining the proper wire size and voltage dropp for this distance. Again i have just been asked to look at the job so just reaching out to see of anyone here has done this type of project before. THANKS
 
Two major factors for VD is actual load and how much VD is acceptable.

600 amp overcurrent device on the conductors doesn't necessarily mean you will see 600 amps and/or could be that you might see that kind of current but only for short time when a motor starts or something like that. So most the decisions here will be based on how much VD is able to be tolerated and not so much on code requirements. You do need minimum conductor ampacity of 600 or whatever size next size up rule will allow to meet NEC though.

Other question is do you have enough capacity wherever it is you are supplying this from?
 
You may want to price out several options for them and let them choose. Like Kwired said the million dollar question is what current to use for the calc. I would consider "worst case" to be like 80% of 600 amps as it is very unlikely you will have more than that if its NEC compliant. But even that may be high. I find HVAC loads are typically about 66% of MCA's. My quick and dirty rule of thumb is actual peak demand is 40-50% of NEC calculated. OF course there are exceptions going both ways so you really have to get a feel for what the loads and diversity is.
 
electrofelon said:
You may want to price out several options for them and let them choose. Like Kwired said the million dollar question is what current to use for the calc. I would consider "worst case" to be like 80% of 600 amps as it is very unlikely you will have more than that if its NEC compliant. But even that may be high. I find HVAC loads are typically about 66% of MCA's. My quick and dirty rule of thumb is actual peak demand is 40-50% of NEC calculated. OF course there are exceptions going both ways so you really have to get a feel for what the loads and diversity is.
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I did a project at a school a few years ago, new heat pump system for entire facility with 9 larger compressor units. They were installed in a location that definitely was best to run a feeder to that location to supply them all, don't recall the exact load calculation, but do remember decided to go with 600 amp feeder, so it was likely at least over 400 amp calculation or even under 400 but not by much. This based on max nameplate loads. These were variable rate compressors with a VFD in each unit. I never been there to see what they draw during extreme cold, which is probably when they would have been loaded the most, but it was July or early August when we got them running and they ran them hard at first just to bring the temp down in the building and to see how they performed, though it was not occupied by students and teachers yet. I bet a 200 or 250 amp feeder breaker would have held for no more than they were drawing at that time, but maybe not during a really cold spell.
 
THANK YOU FOR THE REPLY APPRECIATED ALL THE RESPONSES. THEY EVENTUALLY WANT TO RUN FOR (4) 300 AMP MACHINES, WHICH I KNOW THE 300 AMP IS MAX MOST LIKELY WILL BE USING 275-280 AMPS AT FULL CAPACITY
 
kwired said:
Two major factors for VD is actual load and how much VD is acceptable.

600 amp overcurrent device on the conductors doesn't necessarily mean you will see 600 amps and/or could be that you might see that kind of current but only for short time when a motor starts or something like that. So most the decisions here will be based on how much VD is able to be tolerated and not so much on code requirements. You do need minimum conductor ampacity of 600 or whatever size next size up rule will allow to meet NEC though.

Other question is do you have enough capacity wherever it is you are supplying this from?
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Yes. It is old gear room and they have 2 600 amp open slots. MAX load need per 600 amp is most likely 500-550 amps
 
KING-CMO31 said:
Yes. It is old gear room and they have 2 600 amp open slots. MAX load need per 600 amp is most likely 500-550 amps
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Having slots and having capacity are not necessarily the same thing. Does whatever you are coming from have an extra 1000-1200 amps capacity to give? Maybe the gear does, but at same time maybe the transformer and or service/feeder supplying it needs to be upsized?
 
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