If the high leg is B, then sharing the neutral on A and C is normal.

Think of it this way, this service is a basic single phase plus the high leg. Everything with A and C are treated the same way as single phase.

 

It's just in a wye three phase system I would not share neutrals on any phase for branch circuits. Code states they must be on a breaker together.

 

With Y connected system, I always share neutrals. Around here, handle ties are not required (by local code).

 

My local utility rarely uses high leg services any more. They use to be somewhat common for small commercial businesses that had a very limited 3 phase load.
Neutrals were shared sometimes. Unlike single phase services where the phases are 180 degrees out of phase with each other , in 3 phase they are out of phase by 120 degrees, and when sharing neuts the current isn't fully cancelled out when using two phases.

 

In a Y connected system, yes, they are 120º out of phase but in a ∆, the phase that the neutral is on is 180º, just like single phase. Ø to Ø is 120º, but Ø to neutral is 180º.

 

very good point thank you. I guess I will keep searching for the ghost.

 

Completely normal and allowed by code.

 

So, if you put a 120v load on B leg the factory sealed smoke would escape. Look for a drawing of a high leg delta. You should understand then. On a high leg delta "B" phase is 208volts to ground.

 

I understand the high leg part. I have never seen an a and c phase share the same neutral for separate branch circuits.

 

Draw out the transformer connections...you will see that A and C are connected to a single transformer winding that has a center tap. This part of the 4 wire delta system is exactly the same as a standard 120/240 volt system and there is no problem of sharing the neutral other than the common means of disconnect (breaker handle tie) required by 210.4(B).

 

Please define "strange occurances". Any type electrical system can give problems due to a long list of situations: loose connections, overloads, shorts, ground faults, equipment failure and many other possibilities.