Corner grounded delta services

[daddio]

We recently visited an industrial plant to look at upgrading some old distribution equipment. They have a 230-volt corner-grounded distribution system feeding various machines. I haven't ever run into this before.

The 2002 NEC says that the grounded conductor has to be identified as such (200.6,7), that it cannot be opened by a circuit protection device(240.20). Article 408.16(E) says that we cannot use Delta circuit breakers in panelboards.

I'm confused as to weather we should provide 3-phase panelboards with the grounded circuit conductor run to one of the phase busses or a single-phase panelboards with the grounded circuit conductor run to a "neutral bar", and whether the 3-phase loads should be served with 3-pole or 2-pole circuit breakers.

If anyone can shed some light on this topic I would really appreciate it.

 

[don_resqcapt19]

Re: Corner grounded delta services

First, a "delta breaker: is an obsolete breaker. It was a 3 pole breaker that had only 2 poles connected to the panel bus. The third pole had both line and load terminals. It was used where there was only one or 2 three phase loads on a 120/240 3 phase, 4 wire system. The wild leg was only connected to the "delta breaker", and the other two hots were connected to the panel bus.
You can use either 2 pole or 3 pole breakers on a corner grounded delta system. If you are using 3 pole fusible disconnects, you must install a "dummy" fuse for the grounded leg. To avoid future confusion I would use 3 phase panels and breakers. There are too many electricians who don't really understand the corner grounded system and they may be confused by a 3 phase system with single phase panles and 2 pole breakers. If you do use single phase panels and breakers, you must make sure that they are suitable for use on a corner grounded system.
Don