3-phase used for 1-phase (split-phase) power

[SRK]

Hello, I live in a warehouse that has two main circuit panels: one is split-phase (1-phase) which powers most of the 120v electricity in the warehouse, and a second panel that is 3-phase (once used for shop equipment likt a compressor and lathe)-they are located in opposite sides of the building. Instead of running new electrical conduit through the warehouse, I want to use this 3-phase circuit panel for

120v outlets, lights, etc., and I have researched that I am dealing with a 3-phase situation refered to as "Delta Wild Leg 240v." I have 3 hot wires (A, B(wild) & C), I can run all my 120 stuff off A to neutral or C to neutral.

I have these questions:

1) Should I just pull the 3 phase circuit panel and disconnect the B cable, install a single phase panel in it's place and I am good to go?! 2) Just continue to use the 3-phase circuit panel and only use lines A and C to Neutral for 120/220v applications and leave open/free/unused the "Wild Leg" B line. It leaves me with less connecitons, but I can probably make due.

It seems a bad idea to remove this 3-phase power (since I hear it is expensive to install), but then it seems strange to leave unused circuit breaker sections of a circuit panel...

Does anyone have any recommendations? Thanks in advance.

-SRB

[RBM]

I don't see any reason to replace the panel, Just VERIFY that the wild leg is "B" and make sure the panel is marked clearly as a Delta, then just use A and C as you planned

[John Grabowski]

You should confirm that there is a neutral in the three phase panel. It is not uncommon to have a three phase delta panel without a neutral conductor. If so then go ahead and use phases A and C for your 120 volt circuits. If it isn't already identified, it is a good idea to mark the outside of the panel indicating the high B phase.

[W. Wells]

In my area in NC we have a "high leg" on the 3 phase. One of the wires have higher voltage than 120. I would check to see if you have this. I have had electricians here that did not realize it until I told them. I think it goes up to 140V on one wire. One electrician told me he burned a bunch of record players in a bar by knowing this fact.

[Speedy Jim]

As others said, leave the existing panel in place. After you verify that there is a (GROUNDED) Neutral, plug in breaker(s) as needed.

But before you do any of this, you had better contact the utility and find out what the current (no pun) billing arrangements are. If your (puny?) load is all that will be on the service, they may object to continue provisioning the service.

If some one else is *still* using and paying for this service, you have other problems to iron out.

Jim

[SRK]

Hello, First, thanks to everyone that responded.

I have already tested the voltage for each hot line, so I am sure as to which line (the "B" line) is the Wild Leg. Since this is the first time I have come into contact with a Delta system (although I have done enough electrical wiring in the home to feel comfortable around electrical installations), I just needed to make sure I wasn't operating outside of safety limits.

It is interesting to me how three-phase comes into the warehouse, and at the main breaker (just after the meter), two hot lines are split off, so that 2 hots (A, B) plus a Neutral go to one 120/220v panel and three hots (A, B, C) and a Neutral go to another 120/208/120v panel. Of course, there is also a main grounding cable running off to a water pipe as well.

I don't think there will be any problem with my utility, as the warehouse is rated commercial/residential, and if there ever is a problem...well, I'll just go and adjust the Delta system.

But, I do have a follow up question: In both my circuit panels, the ground connector bar is not connected to the Neutral Connector bar. I was reading up on my electricity configurations and I saw mentioned how the Main Circuit Panel should have it's Grounding Connecter Bar connected to the Neutral Connector Bar (and to NOT do this in any subpanels). Is this correct? While the wiring in this warehouse is grounded to metal electrical boxes in some places and in other places there are grounding copper lines to electrical conduit that is attached to the Main Circuit Panel. The 3-phase circuit panel does NOT have the Grounding Bar connected to the Neutral Bar.

Thanks again.

-SRK

[John Grabowski]

Since you have a main breaker the neutral and the ground are probably bonded there or possibly in the meter. The two electrical panels therefore should NOT have the neutral and ground bonded together. The ground and neutral must remain separated.

[Jeff]

If you use 3 phase power for 120V applications then you should try to balance the load on each of the phases. If you don't then the neutral may float above ground a few volts. Another point is you don't have 240V available. There is 208V between any two of the hot legs because they are only 120 degrees out of phase with each other. Many motors are rated to run on either voltage be sure to check if 208 is ok if you are going to use a

240V appliance.

The real advantage of running 3 phase motors is that they are drawing constant power and so run smoother than 2 phase motors where the power goes to zero 120 times a second. Same for generators. That is why you always see high voltage lines in groups of three.

[Speedy Jim]

No. He doesn't have a 120/208V WYE service. This is a DELTA service with 240V between each leg. The C.T. of one transformer is grounded, giving 120V to either side.

He can not "balance" loads because he can only connect to that one transformer winding with the C.T.

This is a totally different situation than the common 120/208 WYE.

Jim

[Thomas D. Horne, FF EMT]

Jeff wrote: > If you use 3 phase power for 120V applications then you should try to > balance the load on each of the phases. If you don't then the neutral > may float above ground a few volts. Another point is you don't have > 240V available. There is 208V between any two of the hot legs because > they are only 120 degrees out of phase with each other. Many motors > are rated to run on either voltage be sure to check if 208 is OK if > you are going to use a 240V appliance. >

Jeff The custom on Usenet is to post your reply below any quoted part of the message you are replying to. This makes it easier for everyone else to follow the conversation.

"According to the IEEE Dictionary, a neutral conductor is the conductor with an equal potential difference between it and the other output conductors of a 3- or 4-wire system. Therefore, a neutral conductor is the white/gray wire of a 3-wire 120/240V single-phase or 4-wire 120/208V or 277/480V three-phase wye-connected system. Figure 250-7

Since a neutral conductor can only originate from a 3-wire single-phase or 4-wire wye system, the white wire of a 2-wire circuit or the white wire from a 4-wire 120/240V three-phase delta-connected system isn't a neutral conductor ? it?s a grounded conductor." Mike Holt website.

It is apparent that you do not know the difference between delta and wye connected three phase power. When the utility provides three phase delta power the transformers; or, more rarely, the three windings of a single transformer; are connected with each end of the secondary winding connected to the end of another transformers secondary winding. None of the transformers / windings are connected to the grounded conductor at the end of it's winding. Instead one of the transformers / windings is center tapped and the grounded conductor is connected at that center tap. This A to C phase transformer is often larger than the other two because it must carry all of the 120 volt loads in the premise served. The output voltage of each transformer across it's entire winding is in fact 240 volts. The voltage between the grounded conductor that is connected to the A to C transformer center tap and the conductor that is connected to the B phase of this service will be higher than the voltage from A to Ground or C to ground. that is why that phase is called the wild or stinger leg. The US NEC requires that the phase with the higher voltage to ground be marked with orange markings at all accessible points in order to warn of this higher voltage to ground. NO load is connected between the grounded conductor and the B phase because the voltage on the B phase is approximately 208 volts to ground.

[Bob Vaughan]

Dont't forget about Open Delta, where instead of 3 transformers connected in a delta configuration, with the center point of one winding grounded, the utility cuts corners, and only provides 2 transformers, with one leg (A-C) being center tapped, and the other (A-B) being the wild leg. The third (B-C) connection between the wild leg and the other end of the center tapped winding is omitted.

This configuration is frequently provided where there is a small requirement for 3 phase power, but not enough to justify (in the eye of the utility) a full delta service. It is not as stable as a full delta, and some equipment dosen't like it (broadcast transmitters, etc..)

Another service is Corner Grounded Delta, where instead of having one transformer center tapped, one corner of the delta is grounded. This configuration does not allow for any split voltages (120/240, 240/480), everything is phase-phase.

Oh, and thinking back to the original question, which is already on the cutting room floor.. He could add a single-phase subpanel, tapped from the 3 phase panel, and avoid the worry about accidently connecting to the wild leg.