Phase reversal on "single phase" 208 data center receptacles

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hugbobandcarol2

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Broomfield, CO USA
Contractor installed "single phase" 208V receptacles inconsistently resulting in the intelligent rack-mounted power distribution units (PDUs) in falsly indicate power input -- 120V single phase rather than 208-240V.

On the particular receptacles connecting their L1-L2 pins to the "A" and "C" phases the contractor sometimes installed L1 to "A" instead of "C" and L2 to "C" instead of "A". Resulting in: A-B; B-C and A-C rather than A-B; B-C and C-A (or L1-L2; L2-L3 and L1-L3 instead of L1-L2; L2-L3 and L3-L1).

Thus one indicator light is on rather than two. This also causes the intelligent web-based power calculations (and thus capacty limit status) to be wrong.

The contractor is refusing to correct the miswiring stating that it should not make any difference.

Is there a standard indicating that the wiring should be A-B; B-C and C-A (or L1-L2; L2-L3 and L3-L1)?
 
The single phase 208 volt receptacle, in a Twistlok, is "L6" plus the amperage. 208 volt,1 phase, 20 amp is an L6-20 outlet. 208 volt, 1 phase, 30 amp is an L6-30 outlet.

Look at the outlet configuration for the designation. The two outlets above have no neutral at the outlet. They are single phase, 2 wire plus ground (three conductors).

Any two hot lines make single phase. There's no difference between A-B, A-C, B-C. Phase only makes a difference for three phase motor loads, it reverses rotation. In this, your contractor is correct. Each hot is 120 volt to ground, 208 line to line. You cite a polarity reversal that has no effect in your application.

If your PDU outlet strip shows 120 instead of 208, you may have brought a neutral conductor to it (0 volts to ground).

There are some 2 wire, plus neutral, plus ground (four conductor receptacles) but they are very non standard. If you had that you would have a bad spec.

This is very easy to check. Look at the outlet for the designation (L6-20, L6-30), then stick a voltmeter into it to see the voltages supplied at the outlet. That will determine the next step.
 
You have me lost. If it is single phase why do you talk about all three phases?

Even if it were three phase, I doubt phase sequence is important on this type of load.
 
Single phase loads are not uncommon on 3 phase systems especially 208. It sounds like eihter the voltage indicator is bad or a neutral is connected which would profuce 120 as expected. Simple enough to test with voltmeter.
 
Are they redundant PDU's? If each set is not connected to the same phases, it may cause a problem, or you may have one phase that is dead (blown fuse or other) that may be causing the issue.
 
Actually it does make a huge difference. Liebert factory duplicated the problem with several new units: connecting the Hubbell pin/sleeve or twist lock's L1 terminal to the "A" leg and L2 to the "C" leg not only makes the internal logic illuminate 1 lamp (defines 120V, single phase), but causes the effective voltage, current and power draw reports to be grossly wrong. Then rotating the connections to L1 to the "C" leg and L2 to the "A" leg makes everything work perfect. We are trying to get reports out of the switching power supplies in the IT chassis to indicate what 'work' the power supply has to do to produce the correct DC output buss on the network and computer devices. The resulting voltage/current across L1-L2 is significantly different when an "out of phase" connection is made, causing the power converter confusion.

What I am looking for is a NEC drawing of how they state the 3 phases should be utilized for this type of power. All the various IT chassis installation manuals specify terminating the L1 and L2 terminals to A-B; B-C and C-A.

Are you aware of such documentation?
 
The PDU load would have to be added to the system in a balanced manner. If the PDU requires 208 single phase, it will have to be happy and work with any combination of A-B, A-C, B-C at the L1, L2 terminals. If you are applying 208 at the L1, L2 terminals and the voltage display says "120 volts", the issue is obvious.

Care to post an equipment model or online document reference. PDU could mean anything from UPS, isolating transformer, to a simple rack box with smaller branch circuit breakers, multi outlet strip, and integrated monitoring. Is the PDU offering DC at the output, or just offering a place to plug in 208 volt AC cords?
 
How would we know which phase is A,B,C, from the POCO?
You need 208v single phase = 2 hots and a ground.
Your equipment has no way of knowing which phase is A,B,C; you would need to know what the phase/rotation is at the Liebert plant then!
 
hugbobandcarol2 said:
Contractor installed "single phase" 208V receptacles inconsistently resulting in the intelligent rack-mounted power distribution units (PDUs) in falsly indicate power input -- 120V single phase rather than 208-240V.

On the particular receptacles connecting their L1-L2 pins to the "A" and "C" phases the contractor sometimes installed L1 to "A" instead of "C" and L2 to "C" instead of "A". Resulting in: A-B; B-C and A-C rather than A-B; B-C and C-A (or L1-L2; L2-L3 and L1-L3 instead of L1-L2; L2-L3 and L3-L1).

Thus one indicator light is on rather than two. This also causes the intelligent web-based power calculations (and thus capacty limit status) to be wrong.

The contractor is refusing to correct the miswiring stating that it should not make any difference.

Is there a standard indicating that the wiring should be A-B; B-C and C-A (or L1-L2; L2-L3 and L3-L1)?
Click to expand...

There COULD be single phase loads where phasing presents a problem, ex. single phase static switches used in redundant UPS supplied power supplies. Since the Contractor is dumb&blind as to how his installation is utilized, it is prudent to keep phasing consistent, but unless it is SPECIFIED, I think he is off the hook.
 
sameguy said:
How would we know which phase is A,B,C, from the POCO?
You need 208v single phase = 2 hots and a ground.
Your equipment has no way of knowing which phase is A,B,C; you would need to know what the phase/rotation is at the Liebert plant then!
Click to expand...


Which phase is A, B, or C according to the POCO is not really that important. You can call them X,Y,Z or 1,2,3 or Adam, Bob, Charlie if you wish. What is important with equipment that may be sensitive to which phases you have is the relationship between them. You know to start with there is only three, so pick a name for each one and keep it consistant beyond that point.
 
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