Advice needed - maxed out 100 amps 3-phase , no electrical knowledge

[ludo8]

Hi everyone,

I need some help to determine what my electrical needs are. I hope some of you can share some of your knowledge with me.

I have outgrown my 100 amp 3-phase service, as my computer servers are pulling 2000 watts each continuously and remain at full load 24/7.
I have tried to do basic calculations such as 208x100x1.73 = 35984 watts --> 28787 usable watts to stay at 80% usage of the 100 amp service line.
However I am only able to power nine computer servers (18000w) instead of the projected 14 servers. Am I missing something??

I am using a L5-30 30 amp single phase 208v PDU and the meter is telling me I'm using 17 amps with 2 servers plugged into it. I have 4 of these running.


I found a few new locations that offer 200 amp 208v 3-phase, or 200 amp 480v 3-phase.

My question is:

If I have 200 amp 208v 3-phase service.

1) How many amps would a 3 phase 30 amp (24-derated) PDU pull at full load? 24 amps out of 200 = 176 amps remaining?
Or is it 72 amps out of 200 used, due to 24 amps being used on each Line?

If I have 200 amp 480v 3-phase service..

2) Does that mean I could potentially have 400 amps of 208v service? How would I maximize this to power as many servers as I could safely fit?


I would like to get it right this time and find a location with enough power for me to grow in the future. Thank you for taking the time to provide some advice, it is fully appreciated.

 

[petersonra]

The best suggestion I think we can give you is to have a qualified electrician look at it. Just because you have a 400 amp main breaker in your panel, does not mean that the service can supply 400 amps continuously or even 80% of 400 amps. If you really need 400 amps your electrician will have to talk to the electrical utility that supplies the building and make sure the Transformer outside is actually able to supply that much current on a continuous basis. Often the utility Transformers are significantly undersized as it as it relates to the calculated load or the rating of the main breaker, because the utility has many years of experience and they know that you normally don't run everything at the same time.

 

[ptonsparky]

As above plus you need to have an electrician ensure the loads are balanced across all three phases. Your math isn't quite right when you are adding the single phase loads if they are applied properly across a three phase system.

 

[Smart $]

...I have tried to do basic calculations such as 208x100x1.73 = 35984 watts --> 28787 usable watts to stay at 80% usage of the 100 amp service line.
However I am only able to power nine computer servers (18000w) instead of the projected 14 servers. Am I missing something??

I am using a L5-30 30 amp single phase 208v PDU and the meter is telling me I'm using 17 amps with 2 servers plugged into it. I have 4 of these running.
...

You are making a 1Ø to 3Ø math error. Your 208V PDU amps do not add up arithmetically on your service. Would have to use vector math to get fairly accurate and even that may not be all that accurate if these PDU's are SMPS. However, a fair approximation can be had with basic math.

Balanced units, i.e. one each connected A-B, B-C, and C-A, drawing 17A each, can be calculated 17A×1.732=29A. If you have one additional unbalanced unit, add 17A to the connected lines. If you have two unbalanced units, add 17A to the two fewer-connected lines and 29A to the most-connected line.

Two examples of 4 units...

3 balanced units, 208V, 17A each = 29A on each line
Add one unbalanced unit = 46A on two lines, 29A on the third

All 4 unbalanced but paired on lines (e.g. 2 units A-B and 2 units B-C) = 58A on one line, 34A on the other two.

What matters is the line with the highest number.