3p/4w 120/240 delta w/208 high leg

[booter]

I work for an electric utility in Texs. In a recent conversation with a coworker, he made a comment that I found to be untrue.
We were talking about an upcoming job involving the installation of a 3 phase/4 wire, 120/240 w/208 high leg, delta service. We have long been encouraging customers to accept 3 phase/4 wire, 120/208 wye services to better keep our primary distribution system balanced. This coworker commented that the electricians here are balancing what they can on the 4 wire delta services by taking the 208v(high phase) and a 120v phase to a single phase 240v appliance(hot water heater,etc.) rather than both 120v phases to produce 240v. I said that I had never seen that done and that the only high leg load I had ever seen was associated with three phase load.
I also question whether it is acceptable according to NEC to use the high leg in this manner. Any comments would be appreciated.

 

[roger]

Re: 3p/4w 120/240 delta w/208 high leg

I have always used the high leg in any phase to phase single phase loads.

Do not confuse these 240 V loads with 120/240 V loads such as a dryer, which would utilize a "neutral" connection.

FPN: Most do not consider the grounded conductor of a delta a neutral.

Roger

 

[charlie]

Re: 3p/4w 120/240 delta w/208 high leg

Booter, it is common for the EC to make use of the B phase by going from either A or C phase to the B phase (higher phase to ground). This is legal and recommended so the panelboard may be more completely utilized. See Roger's post for more information. A 120/240 volt, 3 phase, 4 wire panelboard would have all the 3 phase slots filled with 3 phase circuit breakers then a blank for every 3rd slot if it wasn't done this way.

Electric utility engineers will usually ask for the loads broken into 1 phase and 3 phase for sizing their service drops and transformers. This method doesn't work! See above for the reason.

BTW, what do you do for the utility?

 

[BAHTAH]

Re: 3p/4w 120/240 delta w/208 high leg

Booter, What your co-worker describes is a common application. This is one reason for the Slash rating of circuit breakers such as 120/240V for use one circuits where the phase to phase voltage does not exceed 240V and the phase to neutral or gcc does not exceed 120v. A 240v rated breaker would be required for connection on a circuit that is phase to phase 240v only with no gcc. Generally if you order a panelboard with a specified breaker layout the manufacture will block the bus at all b-phase positions that are not utilized for 2 or 3-pole breakers, on loadcenters it is up to the installer to properly install the panel with respect to the use of b-phase.