120/240V 3 Phase 4 Wire

[ASG]

I have a space I'm working on which is 240/120V 3Ph 4W 200A. I have never worked with this kind of service before. Do I have 200A available even on the phase that has no neutral associated with it? In other words, if I need any L6-20R receptacles, can I use that non-neutral leg and have 200A available on that leg?

 

[zbang]

No, you can only use the high/wild/3rd leg for 3-phase loads. Well, you could depending on the actual feed configuration (open or closed delta), but it's usually a bad idea. Further, depending on how the PoCo built the service, that 3rd leg might not be even rated for the full 200 amps, sometimes a smaller transformer is used to create the 3rd leg based on fewer 3-phase loads.

Search the forums here for "high leg delta", there's a lot of info.

 

[texie]

As zbang said. Most POCOs build these as open delta with the high leg supplied by a smaller transformer as they usually intend for the high leg to be used with limited 3 phase loads. As long as you don't over do it you can use the high leg with another leg to supply 240 1 phase loads. Do not ever supply 120/240 loads from the high leg. But keep in mind if you do that you will need straight rated 240 breakers-not 120/240 rated breakers.

 

[ASG]

So it sounds like I should almost just treat it like a single phase service but if I have some HVAC equipment that operates at three phase, I can do it.

 

[winnie]

To add to what zbang says, there are enough different flavors of this sort of service that you need to ask the the power company.

You can have a source that is a balanced delta that simply happens to have a grounded center point on one of the legs. These can be used like any balanced 3 phase service, and you can tap 240V single phase loads between any of the 3 legs. Not infrequently with these setups, what gets limited is the maximum load on the grounded terminal; these are really made for 240V l-l loading with incidental l-n 120V loads.

Or you can have what is essentially a 120/240V single phase service with a small 'stinger' to supply incidental 3 phase loads.

Or you could have some sort of blend between the two.

Only the power company can tell you in detail what sort of loading the service can reliably support.

-Jon

 

[tom baker]

And remember you can not use slash rated breakers ie 120/240, you must use full rated breakers, 240, due to the 208. Slash rated is only listed at 120 to ground.
The POCO want the high leg on a different phase than the NEC requires. And you only have to phase high leg with orange when the neutral is present.