High Leg Delta

[Seven-Delta-FortyOne]

As far as the voltage goes, it will be the same between any two hot legs, regardless if one is the high leg.

High leg only comes into play with H-N circuits.

Generally. YMMV. I have not covered all possible scenarios, etc.

 

[LarryFine]

Yes, capacity issues considered, L-L loads may be served by any two lines.

 

[jim dungar]

From what I understand it would be better if it's a closed Delta vs Open.

It all depends on the sizing of the transformers and the amount of loading on A and C.

Also be aware that many electronic controls want to see no more than 120V to ground even when they do not use neutrals.

 

[electrofelon]

It all depends on the sizing of the transformers and the amount of loading on A and C.

Also be aware that many electronic controls want to see no more than 120V to ground even when they do not use neutrals.

I have always been paranoid about this, but never found it to be the case. My main client has Labs with high leg Delta and I've connected all sorts of stuff line to line with one being the high leg, and never had a problem.

 

[winnie]

Guys, this is an old thread that was resurrected with a new (related) question.

Hello guys
While everyone's on the subject of hi leg delta ...and not to change the subject but....
Any reason why we can use a single phase circuit (2 hot, 1 eq ground) to power our ductless splits at a restaurant renovation with a dated distribution system that were doing
One leg would be the 210 volt hi leg and the other would be A or C

There are 3 issues to address
1) Does the service have the necessary capacity on the high leg? Some high leg services are designed for a small 3 phase load on an otherwise single phase service, and don't really have the capacity for high leg single phase loads. Other services might have lots of unused capacity on the high leg
2) Does the service come from an open delta transformer? If so, then you shouldn't place a single phase load across the open jaw.
3) Does the load itself have any voltage to ground limits. The example of a L-L load with L-G voltage limits is a VFD. The surge suppression in the VFD is connected L-G and will fry if don't use a balanced supply. Your mini splits are likely rated for 240V L-G but you must confirm this.

Jonathan

 

[jim dungar]

I have always been paranoid about this, but never found it to be the case. My main client has Labs with high leg Delta and I've connected all sorts of stuff line to line with one being the high leg, and never had a problem.

Line to Ground connected filters and surge devices are the usual issues.