3 phase w/ 'high leg' & PDU selection (input circuit question)

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VTdude12

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Hello all! New to the board as I'm in need of some electrical advice.

A little background, I'm in the process of moving into a new building that has 3 phase electricity. Confirmed today that is 'high leg'. My main question is: I have been shopping around to PDU's to hook-up some computer equipment to and want to be sure it is compatible with the electricity service in my building! So confusing!!! :)

Here are the specs on two PDU's I'm looking at:

#1
Input Circuit: 200-208V 30A 3 phase Delta
Load Capacity: 8646VA @ 208V 3 phase
Input Connection: NEMA L15-30P

Questions about PDU #1... Will this PDU be compatible? With the NEMA L15-30P there are 4 prongs on the plug. X/BLACK (phase a?) + Y/RED (phase b - high leg?) + Z/ORANGE (phase c?) + G/GREEN (ground?). Are my notes here correct?

#2
Input Circuit: 208V 60A 3 phase Delta
Load Capacity: 17.3kVA @ 208V 3 phase
Input Connection: IEC309 3 Pole, 4 wire, 250VAC, 60A


Questions about PDU #2... same as above.

Any info would be greatly appreciated!
 
The high leg delta is a true delta in terms of the voltages among the three line wires. It differs from a pure delta or a wye only in that the grounded conductor (neutral) is not electrically in the center of the wye secondary nor the corner of the delta.

The specification of the input as delta implies but does not absolutely guarantee that the unit does not make any connections to the neutral, and does not care about the actual voltages from each of the line conductors to ground.

The latter part is where the uncertainty comes. If there are, for example, MOVs for surge protection from each line to neutral or to ground, then the higher voltage from line to ground on the high leg could cause problems.

More important, however, is that the spec calls for 208V line to line, which would be seen with a 208Y/120 supply, and your high leg delta has 240V from line to line.

Also the high leg input may well mean that the output is also offset to ground, so if your "load capacity" figure refers to the available output, you may have to make sure that all of your loads are also compatible with high leg delta.

Normally all 120V loads are fed from the A-N-C winding of the delta transformer bank and the B line is only used along with A and C to feed 240V delta loads.

That potentially puts some severe restrictions on what you can do with the output of the PDU. It is very unlikely that your computer equipment will be happy with that supply.

If you are only going to use 120v loads, you have no need for a three phase PDU.
If your computer equipment expects 208V line to line you are simply in trouble unless you add a transformer or two or three to the installation.
 
VTdude12 said:
Thanks for the quick reply!

As an FYI, all devices being plugged into PDU work on 200-240v. Does that change anything?

Sorry - 3 phase novice here!
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Wouldn't matter what you plug into the LOAD side of the PDU, what GD is saying is that your PDU is stating 208V max, you are going to give it 240V. That is of enough concern to get something IN WRITING from the PDU supplier that it will be OK with that.
 
Essentially you will take in 240V single phase (L-L) or 3 phase (L-L-L) and you will have plugs out to your equipment at 240V L-L. Similar to a European voltage arrangement, but I would suggest you get one that is UL listed.

Some data centers are using the European voltage arrangement for higher efficiency of power supplies and smaller branch circuits, so there are plug strip manufacturers that make that type of product.

FWIW, a PDU is a term that APC uses for plug strips, but in reality a PDU in the data center market is a combo transformer / panelboard (or SWBD) distribution piece of equipment, unless you listen to the sales pitch from APC or an APC wannabe. APC is now Schneider for several years but they still use the APC name in the plug strip market.
 
ron said:
Some data centers are using the European voltage arrangement for higher efficiency of power supplies and smaller branch circuits, so there are plug strip manufacturers that make that type of product.
Click to expand...

Thanks Ron!

Can you fire off a few of the manufacturer's names by chance? Been looking around for a 240v 3phase compatible product, but haven't had any luck...
 
Do you need 3-phase? Virtually no modern computer equipment does. You might be better off with a 208/120 2-pole feed (NEMA L14-xx type connector) and forget about the high leg. APC and Eaton both make PDUs/plug-strips that will work.

(I'll save discussion of PDU for another time :).)
 
zbang said:
Do you need 3-phase? Virtually no modern computer equipment does. You might be better off with a 208/120 2-pole feed (NEMA L14-xx type connector) and forget about the high leg. APC and Eaton both make PDUs/plug-strips that will work.

(I'll save discussion of PDU for another time :).)
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It's not that I need it... it's already available in the building I'm looking at leasing and what to make most efficient use of the power available (I have a lot of equipment). :ashamed1:
 
You may not have as much current available on the high leg as the other two. (You didn't mention, but I think we're all assuming 120/208/240 high-leg delta supply.)

Come at the problem from the other direction- how much power do you need? Is that available at all or without using the high-leg? If it is, forget the high-leg.

Another question is whether the high-leg is supplied as part of an "open delta", if that's the case, forget about using it for non-3-phase loads (i.e. motors or delta-connected transformers).

Another option is to use a delta-wye transformer to create a 208/120v system and use more standard power distribution. That's added cost for the transformer but might simplify other things.

Have you had a licensed electrician look at the service and discuss you needs?
 
zbang said:
You may not have as much current available on the high leg as the other two. (You didn't mention, but I think we're all assuming 120/208/240 high-leg delta supply.)

Come at the problem from the other direction- how much power do you need? Is that available at all or without using the high-leg? If it is, forget the high-leg.

Another question is whether the high-leg is supplied as part of an "open delta", if that's the case, forget about using it for non-3-phase loads (i.e. motors or delta-connected transformers).

Another option is to use a delta-wye transformer to create a 208/120v system and use more standard power distribution. That's added cost for the transformer but might simplify other things.

Have you had a licensed electrician look at the service and discuss you needs?
Click to expand...

Thanks zbang! Yes, I am talking with an electrician and he's been telling me the different options I have. Just wanted to come on here and see any/all other ideas :dunce: really appreciate how responsive everyone is here!

FYI, when looking at the service today with a meter we saw the following:

Phase A-B = 240
Phase B-C = 240
Phase A-C = 240

Phase A-Neutral = 120
Phase B-Neutral = 208
Phase C-Neutral = 120

With that said, looking at the PDU I linked... am I wrong to think that since it uses a L15-30P plug which is 4 wire (hot-hot-hot-ground), then I'd connect A-B-C-panelground, and that should supply 240v power through the 30a 3pole breaker we'd install in the panel :?
 
Welcome to the forum!

Jraef said:
Wouldn't matter what you plug into the LOAD side of the PDU, what GD is saying is that your PDU is stating 208V max, you are going to give it 240V. That is of enough concern to get something IN WRITING from the PDU supplier that it will be OK with that.
Click to expand...

THIS!

The 2 PDUs you have are made for 3ph 208V input voltage... 3ph 240V input may very well be too high. or it may be okay.
 
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