Single Phase Service to Three Phase Equipment

[Michael53]

To try and make a long story short, after being told by the Utility they could provide a 277/480 3P 4W 400A service, and my purchasing all the equipment, I'm now told I can only have a 480 Single phase service rated at 200A.

My first panicked thought is to return the three phase equipment for single phase. However after investigating the return/restocking fees, that's not really practicle. Also, single phase 480 equipment appears to be special order and I'm sure it commands a premium.

I'm afraid I know the answer to my question, but would really like to hear comments/suggestions from you. Is there any way possible to legally use the three phase equipment supplied by single phase 480?

This is a new service and all loads will be single phase.

 

[jim dungar]

Have never heard of a single phase 480V service, except for street lighting

 

[dkailiuli]

When I need to power a 10HP 480/3/60 motor with 480/1/60, I use a 20HP rated variable frequency drive. Others use roto phase converters. I'm not sure what your equipment is, but it's a thought. Hope it helps.

 

[ActionDave]

Have never heard of a single phase 480V service, except for street lighting

Not common here in my neck of the woods but not unheard of either for running irrigation. And there is one wildcat gas drller that runs his whole system off of 480V single phase. Both cases are rural settings with no three phase service available, and both use roto-phase converters.

 

[ActionDave]

.I'm afraid I know the answer to my question, but would really like to hear comments/suggestions from you. Is there any way possible to legally use the three phase equipment supplied by single phase 480?

Sure, rotary phase converter or a VFD that can convert single phase to three phase.

This is a new service and all loads will be single phase.

Umm... confused here. Why do you need three phase?

 

[broadgage]

I suspect that the O/P means that whilst the loads are single phase, that the service equipment and switchgear is intended for 480 volt 3 phase, and that they want to know can this equipment be utilised for a single phase service.

To which the answer is possibly, but it probably cant be fully utilised.
Presuming that the panel is intended for 3 phase, 4 wire service at 277/480 volt, then I believe that it could be utilised for single phase 2 wire 480 volt.
Connect the supply to any 2 busbars, A and B for sake of argument.
The connect 2 pole 480 volt breakers to A and B only.
The C phase breaker spaces can not be used.

If the supply is single phase 3 wire at 240/480 volt, then also connect the neutral to the neutral busbar. 240 volt loads can then also be supplied from single pole breakers between A or B and the neutral.

 

[Jraef]

I'm a little concerned about the statement "all loads are single phase" combined with "Also, single phase 480 equipment appears to be special order and I'm sure it commands a premium".

If your original intent was to have a 480/277 3 phase 4 wire system, and "all loads are single phase", then that would typically mean that your loads are likely 277V rated, i.e. 480 to neutral.

If the PoCo has provided you with "480V single phase", in my experience this is because in far flung rural areas, it's too expensive for them to run 3 phase lines out there. That will USUALLY mean then they are giving you a single MV line, where they connect a transformer from line to ground on the primary, as in an open delta corner grounded system, and give you a single phase pole pig that provides you with 480V on the seconrdary, line to line. In that case, you will NOT have 277V to a neutral, unless you yourself create it. In other words you need to more accurately determine the WORKING voltage of your single phase loads before you start buying more stuff here.

 

[Michael53]

Broadgage you?re correct. I want to know if the 3 phase equipment can legally (per NEC) be connected single phase. Yes, if I can use the 3 phase equipment, I'll utilize A and C phases. All CB?s in the system are rated 277/480V. There are no neutral loads.

Here?s the scenario. Remember this was to be 3 phase service, and will be supplying 480V roadway lighting and IT equipment. So I have a 400A 3 phase disconnect in an enclosure with a transocket attached to the outside for metering. I?m considering using A and C phase with fuse reducers down to 200A. The load side of the disconnect goes to another outdoor enclosure which houses a 400A I-Line panel. The I-line sub-feeds both a 200A lighting contactor controlling a 200A roadway lighting panel and an IT panel used for monitoring roadway conditions and operating several assorted types of IT equipment. All branch circuits are 480V for distribution purposes only. These circuits travel quite a distance and are tapped and transformed to 240V single phase for IT. (Saves the cost of a conductor)

Originally the POCO offered the 3 phase because they thought a housing development was going in soon. The builder folded and now the Utility will only provide the single phase 480. (Unless I want to pay for the plant to bring 3 phase to the site? I don?t) Caveat #2 is that since the 240/480V is a single phase corner ground? and is used primarily for roadway lighting circuits, they want to limit the ampacity to 200A, unless I pay and sign a waiver. I can do what I need to do currently with 200A, but was designing for future loads.

If you contact Square D or Siemens and ask about single phase 480V equipment, you?ll learn it?s not an off-the-shelf item. More costs.

Jraef? There are no neutral loads. Where IT picks up and taps the 480V circuit, an MPZ is set with a ground rod provided to establish a separately derived system.

There is a lot more to all of this? but I?ve already written more than most will read. I apologize for the lengthy response. Any thoughts, ideas, suggestions or recommendations are very much appreciated. I?m really looking for someone to agree with me and say the installation is acceptable, but mainly I don?t want anyone to get hurt and won?t install this system as I?m proposing if anyone sees a safety issue with it.

 

[jim dungar]

Someone is mixing systems.
To have a corner ground you must have a 3-phase system.
You may have a 'phase grounded' 480V 2-wire single phase or a center tapped 240/480V 3-wire service.

Per its listing, you can supply a 3-phase I-Line bus stack with only 2 'phases'. You just need to purchase breakers with the appropriate connections (the most common are A-C)

 

[Jraef]

The issue is going to be on your circuit breaker equipment. If the breakers are what are called "slash rated" for 480/277V, then you cannot use it on 480V that is not technically 277V potential to ground. You must use breakers that are fully rated for 480V phase-to-phase, no "slash" in the nameplate.

 

[Michael53]

Jraef and Jim... to leave no stone unturned, if I'm mistaken and the service will be 240/480 single phase... (or if I can get it) would the "slash rated" CB's be acceptable seeing as the 240V on one leg would be less than the 277V rating of the 277/480 volt CB's?

 

[jim dungar]

If you are using I-Line breakers the slash rating is not important, as the 2-pole are all fully rated devices.

 

[Smart $]

Jraef and Jim... to leave no stone unturned, if I'm mistaken and the service will be 240/480 single phase... (or if I can get it) would the "slash rated" CB's be acceptable seeing as the 240V on one leg would be less than the 277V rating of the 277/480 volt CB's?

Yes, if in fact a grounded 240/480 service.

 

[Michael53]

Thank you Gentlemen, I have a good idea how I'm going to handle this now. Have a good weekend.