Multiwire BC loads

[MNSparky]

I was reading my "Mike Holt Changes to the NEC - 2017 edition" and 210.4(C) Ex 2 was discussed. It clearly states in that book that it is acceptable to have line to line and line to neutral loads on the same multiwire BC where all ungrounded conductors are opened simultaneously by the OCPD. Pg 57 if you have the book.

Ive been told in the past by an AHJ that I can't do this due to "mixed loads". He didn't want the two ungrounded conductors to be unbalanced. I've never been able to prove him wrong as the actual wording in 210.4(C) Ex 2 infers, IMO, that line to line loads that use a neutral (like a clothes dryer or range) are acceptable. It doesn't say anything about mixed loads.

My question in the past was in reference to attic air handling units in residential applications. We do these a lot, where a house with boiler heat wants AC as well. The HVAC contractor puts a condenser outside on the ground and runs their lineset to the attic to a 240v air handler. My question is why can't I run a multiwire branch circuit to the attic and supply the air handler and the required 120v service lighting and receptacle off that same MWBC? There's a disconnect at the air handler so the service tech shouldn't have to shut off the circuit to service, thus loosing the lights and receptacle. Am I missing something?

 

[iwire]

The inspector is wrong.

 

[infinity]

My question in the past was in reference to attic air handling units in residential applications. We do these a lot, where a house with boiler heat wants AC as well. The HVAC contractor puts a condenser outside on the ground and runs their lineset to the attic to a 240v air handler. My question is why can't I run a multiwire branch circuit to the attic and supply the air handler and the required 120v service lighting and receptacle off that same MWBC? There's a disconnect at the air handler so the service tech shouldn't have to shut off the circuit to service, thus loosing the lights and receptacle. Am I missing something?

That would be code compliant.

 

[electrofelon]

I agree with the others. I have found it is very common for people to think that you can't "tap off a 240 circuit" for a line to neutral load. I think I used to believe that one myself years ago.

 

[Smart $]

+1

 

[MNSparky]

Sounds good, thanks guys. I couldn't come up with a reason why I couldn't do it, but when an AHJ says I can't it puts doubts in my head. He never gave me a code article because it wasn't a correction, it was just part of a conversation I had with him.

 

[JFletcher]

Would you need GFCI or AFCI breakers for those lights/receptacle by the 2014 or 2017 NEC? Also, if you were over 20A OCPD, how would you tap into the circuit to power the light and receptacle?

 

[MNSparky]

Would you need GFCI or AFCI breakers for those lights/receptacle by the 2014 or 2017 NEC? Also, if you were over 20A OCPD, how would you tap into the circuit to power the light and receptacle?

In most cases I wouldn't need AFCI or GFCI protection because the lights and receptacles go in unfinished attic spaces. The air handler usually only draws around 1-2 amps so we run a 15a ckt for it. Plenty of room for a couple keyless fixtures and a service recep.

There are cases when they stick the air handler in a closet or something. In those cases I'd have to run two BCs and AFCI protect the light and receptacle, if I'm required to put them in. Most times they do that there are already lights and receptacles in the area.