Identifying phase in a three phase environment

We have a computer room with a couple dozen racks. Each racks has three phase power running to it hardwired from our UPS. Each rack has a PDU that brings out the three pairs (phase 1-2 -> 208V, phase 2-3 -> 208V and phase 3-1 -> 208V). The neutral is not pulled from the UPS to the racks. All loads are single phase.

So far so good. recently we started to see one of the phases with a higher load on it than the others. Our attempts to balance the loads only skewed it more which lead us to find out that the electrician wired the phases inconsistently to the racks. In some racks phase 1-2 on the UPS side is actually on the 2-3 outlet group, etc. Figuring this out is extremely time consuming and dangerous to our data integrity (it means rooting around in the back of the racks, adding or removing loads and monitoring the meters on the UPS in a live environment.

Since the computer room is in production use, we do not have the luxury of switching everything off and tracing the wires.

Is there a device / method that would let us trace the phases from the panel to the rack without having to de-energize everything?

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DarinTCHSenior CyberSecurity EngineerCommented:
I would expect to see a neutral with a three phase scenario
You can buy a DMM digital multimeter at some home depot type stores it's possible that it might not cover commercial voltage if you buy a low-end one that's designed for homeowner scenarios
In addition to testing the voltage you also sound like you have issues tracing the wires
Usually at this level of importance production systems and production Racks it might be more cost-effective to call in a commercial electrician who probably has the equipment on his truck they can readily test the scenario for you

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Officially, I'm with Darin. Hire a Pro.
If you are reasonably good at these sorts of things, something like a "fox-n-hound", should work (please read the Reviews and Q&A for a better idea if it fits your needs).

Grainger has a good selection, for a better idea of what's out there (make sure it handles LIVE  220v, and will send the signal as far as you need it to go).


Greenlee might be worth a look also.
EirmanChief Operations ManagerCommented:
The voltage difference between ground (Nuetral) and any phase (Live) is about 220 Volts.
The voltage difference between any phase and the same phase somewhere else on the rack is about 0-2 Volts.
The voltage difference between any two phases about 400 Volts,

Thus, with an ordinary test-meter (multimeter), it is easy to determine whether two pieces of equipment
are on the same or different phases (i.e. near zero or near 400 volts).

Set your test-meter to 500 AC Volts.
Assuming your three phases are called L1 L2 & L3 ....
Connect one lead of your test-meter to L1 on your main fuseboard.
Then with a long wire on the other lead of the test-meter go around your rack room
and carefully touch all the live cables/connections.
You will immediately see if you have touched a L1 phase or a different one.
Label each piece of equipment with a L1 tag/marker where the voltage reads near zero.

Do the same with L2 on the fuseboard.
This should be quicker, as you will not have to test equipment already marked with a L1 tag.
Label each piece of equipment with a L2 tag/marker where the voltage reads near zero.

Logically, all remaining equipment must be L3 and should be labelled as such.
(You can do a L3 voltage test to confirm you have not made mistakes earlier on L1 & L2 tests).

Job done ..... and no downtime!

(This job would be completed more efficiently and safely with two people).
You can also use more sophisticated meters, such as .....

Go to a good electrical wholesaler and take advise.
Buy suitable labels/tags so you can mark equipment and cables with their appropriate phase.
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Danny ChildIT ManagerCommented:
Don't mess with 400v.  Jack, you dead.

Get your electrician back in.  He can probably tell by visually inspecting the cable routes to your distribution board.
DarinTCHSenior CyberSecurity EngineerCommented:
so did we help?
did you hire someone

remember this could be dangerous - so that was the thrust of many comments

besides understanding PHASE - you also seemed to be tracing wires - a very different request

if  you still looking for more info - wikipedia has the basics
but the main point is that 3 phase is commercial and heavy load
so even though you are on the smaller side of commercial you may or may not have a 4-wire system
if so the 4th wire could be your neutral - in a lower voltage system
otherwise the neutral may not exist in higher voltage systems thus 3-phase o r 3x the power of a single phase system which have both phase and a neutral line

again most electrians could have a look see and answer these points rather easily
EirmanChief Operations ManagerCommented:
The solution I provided involved lateral thinking and was one of my best (and most unique) contributions.
It was also the only suggestion that provided a practical, working solution.

Other comments were theoretical and safety orientated.
DarinTCHSenior CyberSecurity EngineerCommented:
suggest split of points between Darin and Eirman
both provided a practical answer
suggested toolset
some safety
and additional concerns
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