OK to use common from a different circuit for HAI UPB Aux Switch?

[pgray007]

I have a 5 gang box with 3 "slave" switches from a 3-way, and 2 regular switches. The loads for the 3-ways all come into this box, and are fed from 3 other boxes. Running between the master and slave switches I have a wire with red, black, and neutral. I'm using HAI HLC switches, where the "Auxillary/slave" switch doesn't actually control any load, and just communicates with the "master" to do anything.
 
I've connected the black wire between the loads for the 3-ways in the 5-gang and the black wire in the "traveller" bundle, so that my master switch effectively controls the load independent of the aux switch. My problem is that in this configuration, my slave switches use all the wires from the circuit (ground, neutral, traveller) and I don't have a common from that circuit, since I'm using the black wire to actually control the load.
 
I can tap into a common wire from the 2 "normal" switches in the box, but wanted to check if that's kosher before doing so since they're all on different circuits.
 
Thanks!

 

[Desert_AIP]

In a standard (non automated) install, all neutrals (white) in a box are wired together, regardless of the circuits.
They also all connect back to the same bus bar in the circuit breaker panel.
 
I do not know the exact code, but I think it's safe to say it's OK.
 
It will certainly work electrically.

 

[tmbrown97]

I'd love to hear from an electrical contractor on this one - but my understanding is that it's a complete no-no. In my house, if the circuits are different, the neutrals are not tied together in the box (easy way to tell when the boxes have power from different circuits).  Of course if it's several lights on the same breaker, then all the neutrals will be tied together.  That said, I've heard of it being "OK'd" by one switch manufacturer...
 
Point of clarification - if you mean different circuits as in different banks of lights controlled by different switches but on the SAME breaker than absolutely no issue - but if they're totally separate breakers than my understanding is that it's not allowed, but will work anyway.

 

[pgray007]

My problem is not with the neutrals, I have those for each circuit. Rather it's for the common wire, which does nothing other than power the blue light on the switch and allow it to signal the master switch. I've tapped another common from the same box and it all works, but if that's not kosher I'd be interested in redoing it the proper way.

 

[Desert_AIP]

I'm not an electrician but I did stay at a Holiday Inn once.

I gooned it up.
Correction to what I posted above.
All the grounds go together and neutrals from separate circuits on separate breakers remain split.

That still doesn't answer the OP of course.

 

[az1324]

If the other hot is on the same breaker, ok.  Otherwise, if you put all the master switches in the 5-gang wouldn't it solve your problem, aside from requiring derating?

 

[mcelectric]

I am an electrician and you can't tie all commons(neutrals) together, only the grounds.  You need to clairify how you are wiring the switches. Not sure what you are calling a common and  traveler.  Hai switches only need power and a common.

 

[pipeman]

In my experience all neutrals are tied to the same bus, except GFI and ARC Fault breakers.

 

[wuench]

I am no electrician either..
 
The neutrals may all be tied to the same bus, but if you tie neutrals from multiple circuits together (shared neutrals) in a box, the power from one circuit can use a neutral from another wire for a return path.  So you run into issue where you can shut off a breaker to a box and still have power running through that box or a box downstream from the other circuit via the neutral, which is a hazard (although I thought it was allowed by code is some jurisdictions).  So you may need to shut off multiple circuit breakers to turn off power to a box which can get pretty confusing.  It is best to keep neutrals on different circuits isolated from each other.  Preferably it is best to not have multiple circuits in a box period, if you can avoid it, IMHO.
 
For the OP, I think you can use whatever power wire you want as long as the corresponding neutral(s) are used (avoiding shared neutrals). Just be aware that that switch and any downstream boxes will be on that breaker.  You need to do your calcs for that circuit and make sure it isn't going to be overloaded.  If these are all on the same circuit then you shouldn't have an issue. 
 
I am unclear why you need a traveler for a slave switch with UPB. With Insteon you just need to run power, neutral, and ground.  You don't need a traveler so that is usually capped off, as the protocol just handles that.

 

[az1324]

Because upb slave switches do not have plc transceivers they are dumb like lutron slave switches.

 

[RAL]

The neutrals may all be tied to the same bus, but if you tie neutrals from multiple circuits together (shared neutrals) in a box, the power from one circuit can use a neutral from another wire for a return path.  So you run into issue where you can shut off a breaker to a box and still have power running through that box or a box downstream from the other circuit via the neutral, which is a hazard (although I thought it was allowed by code is some jurisdictions). 

 
I think the main issue with shared neutrals is for potential overloads, causing a fire hazard.  The neutral wire of each circuit needs to carry the same current as the hot wire.  If you tie neutral wires for different circuits together in a junction box, they will share the current load for all of the circuits and things should balance out - at least in theory, but not always in practice.
 
With separate neutral wires, if there is a failure in the neutral wire for the circuit, say because it breaks or is cut, the devices on that circuit will stop working because there is no return path for the current and the fact that there has been a failure becomes obvious.
 
But when neutrals for different circuits are tied together, a failure in one of the neutral wires will not cause the devices on that circuit to stop working, since another return path is available via the other neutral.  The remaining neutral now needs to carry the current for both circuits, causing a potential overload condition on the neutral wire, but not on the circuit breaker. And that creates the fire hazard.

 

[tmbrown97]

There's also a situation that used to be allowed for in code (not sure it still is or not) where a neutral can be shared by two circuits as long as they're on opposite phases and IIRC the breakers are supposed to be tied together.  I saw firsthand what happened when a neutral came loose in one of the boxes - basically the Neutral went hot and all the kitchen appliances that were plugged into that circuit got fried with close to 220V.

 

[RAL]

There's also a situation that used to be allowed for in code (not sure it still is or not) where a neutral can be shared by two circuits as long as they're on opposite phases and IIRC the breakers are supposed to be tied together.  I saw firsthand what happened when a neutral came loose in one of the boxes - basically the Neutral went hot and all the kitchen appliances that were plugged into that circuit got fried with close to 220V.

 
Yes, I once lived in a house that had a circuit like that.  A double pole breaker was in the main panel, with 14-3 run to the second floor, where one side was used for outlets in one room and the other side for a second room.
 
If you lose the neutral, you're in trouble if the loads on each side aren't close to being balanced.