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AssuredElectrical, Master Electrician
Category: Electrical
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Experience:  Contractor-42+ Years in the ElectricalTrade
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# We are working on a datacenter build-out using a 400 amp 480v

We are working on a datacenter build-out using a 400 amp 480v three phase service from the electric company, and would like to know the following:

Is there 400 amps available on each phase?

If using step-down transforms inside of ups's/pdus is the available power once it is stepped down to 120v really 4x the amperage?

For instance 480v @ 400 amps x 3 phases = 1200 amps @ 480v

1200 amps @ 480v x 4 (to go down to 120v) = 4800 amps @ 120v or 2400 amps @ 240v

AssuredElectrical :

Welcome. My name is XXXXX XXXXX would be glad to assist.

AssuredElectrical :

The 400 amps, is just that 400 amps. It is not per phase but total. When wiring on 3 phase, you are required to balance the load on each phase so you have uniform phases. But it still equals 400 amps total load If you have 3 phase equipment, it will draw less amperage so each phase is less than it would be if single phase.

AssuredElectrical :

Now, on the 120 volts, if you use transformer to step the voltage down, the 120 volt side will pull 4 times the 480 side approximately. So if you have 100 amps of 120 volt through transformer then the 480 side only sees approx 25 amps.

Customer:

Gotcha, makes sense now

AssuredElectrical :

Using transformers on a higher voltage system allows for a much smaller service than if you had it at 120/240

Customer:

So, on the first question it's just a total load of 400 amps, so you would balance the load and maybe have max ~ 133amps on each phase?

AssuredElectrical :

That is correct. Usually on 3 phase, you have 3 phase equipment connected so pretty much balances itself out.

AssuredElectrical :

Using the transformer for lighting etc, then you get 4 times the power

Customer:

Perfect

Customer:

So would it make sense to use a 250kw generator on this service?

AssuredElectrical :

for 400 amps at 480 volts? generator is 3 phase 480?

Customer:

Ya

Customer:

Looks like from using a calculator it's probably around 300-325 amps @ 480 3 phase depending on power factor

AssuredElectrical :

Ok, the 400 amps at 480 volts is close to 330kw, depends on your power factor.

AssuredElectrical :

Yes, you were writing while I was, lol

Customer:

ok cool :)

AssuredElectrical :

Just Let me know if anything is needed further

Customer:

I think just one more, they will be running it from a CT box from the power company approx. 150 feet to where our main panel will be, what gauge wire would be used for this? and would it make more sense to run it paralleled?

AssuredElectrical :

Only need 4/0 copper , so I do not see any real benefit of trying a parallel feed.

AssuredElectrical :

The length is not an issue with the 480 comes to around 1.3% drop and you are allowed 3%

Customer:

Great, thanks for all of your time, I appreciate it!

AssuredElectrical :

you are most welcome, glad to assist

Customer:

Have a good day!