Switches and Neutral

[MilspecCQB]

This is an electrical wiring question. Skip to the bottom for the meat of the question.

So I've had a bit of a learning experience of late. I picked up two of the GE 45609 On Off switches. I've learned that these switches, and just about every other On/Off switch out there plus some of the more advanced dimmers such as the magnetic and electronic, all need a separate neutral. I've also learned that unless you home was built by Nostradamus' cousin or maybe built in the last couple years with this explicit functionality in mind, you're not going to have a separate neutral in the switch box.

So here's what I did, I talked to an electrician, scoured the forums for other options, considered returning them. What I finally did was cut some huge holes in my perfectly good wall after I found the junction box for one of the switches and realized how close I was.

So what I have are a porch light and a foyer light both on the same circuit. I ran a new Romex 14-2 from the junction box in the foyer light and tied into the neutral from that light. I then jumped that neutral over to the porch light on the same circuit. These now both work great.

So here's the question, I have a third switch in that gang box. This switch controls a driveway light attached to the eave of the roof. The problem for me is that this switch is on a different circuit. I have to cut a separate breaker for this switch when I work in the gang box. If I pick up another GE on off switch, can I tie into the same common neutral from the other circuit or do I have to run a separate neutral from that circuit for this switch?

[aschwalb]

So here's the question, I have a third switch in that gang box. This switch controls a driveway light attached to the eave of the roof. The problem for me is that this switch is on a different circuit. I have to cut a separate breaker for this switch when I work in the gang box. If I pick up another GE on off switch, can I tie into the same common neutral from the other circuit or do I have to run a separate neutral from that circuit for this switch?

I am not an electrician but I am an electrical engineer so take this as friendly advice and not certified... 

Electrically the neutral wire are all connected to the same buss in the panel so it shouldn't matter.  Assuming this breaker is in the same panel as the others. 

[MilspecCQB]

Assuming this breaker is in the same panel as the others.

It is. This is what a friend told me, but I'm not sure how much I trust his advice. Thanks Aschwalb.

[garrettwp]

Yes, as long as the breakers are in the same panel, all neutrals should be tied together. If you look in the gang box where the switches are, the neutrals should be tied together. Just tap from there. 

- Garrett

[intveltr]

You can get away with that, but I suspect this would be against building code in most countries.  Sharing a neutral between two different breaker groups makes it possible to exceed maximum rated current on that wire without tripping the breakers.  In your case (if I understand correctly) you are only using the new neutral wire to power the GE switches, not the lights themselves (they have their own "proper" neutral), so you should be ok.

[PurdueGuy]

If you don't want to mix neutrals, what about moving the light to the same circuit as the other switches?  (it might be more difficult if the is a 3-way or more).

That being said, I to am NOT an electrician, and I don't know what the code says about an unused wire in the wall.  At the very least, you'd need to cap it off.

[oTi@]

[...] can I tie into the same common neutral from the other circuit or do I have to run a separate neutral from that circuit for this switch?

Separate neutral (i.e. the one that goes with the hot for that circuit).

If it's incandescent lighting (and within the proper wattage range) have you considered putting a GE 45612 dimmer in? Or a Leviton VRS05 switch. They don't need a neutral.

The GE would presumably look better, given that you already have GE's. Also, on the GE, you could change the ramp rate to simulate on/off behavior, if you wanted to.

[kkl]

So here's the question, I have a third switch in that gang box. This switch controls a driveway light attached to the eave of the roof. The problem for me is that this switch is on a different circuit. I have to cut a separate breaker for this switch when I work in the gang box. If I pick up another GE on off switch, can I tie into the same common neutral from the other circuit or do I have to run a separate neutral from that circuit for this switch?

I tried that, mixing the hot/line from one circuit with the neutral from another circuit (terminating in the same load center).  It caused my breaker to trip immediately.  Perhaps I wired something wrong, but that was my experience.  The house is new and was inspected to the current electrical code.

[oTi@]

It caused my breaker to trip immediately.

Regular breaker, or GFCI?

[intveltr]

Regular breaker, or GFCI?

Good point...  this will likely happen if the two circuits having their Neutrals connected are on different GFCIs. 

[kkl]

It caused my breaker to trip immediately.

Regular breaker, or GFCI?

Definitely not GFCI, but now that I went back and looked closer at the breaker, I realized that they are the newer Arc Fault Circuit Interrupters (AFCI).  I think that explains my result and should give hope to the OP.

[silvereagle2208]

When I was installing Z-Wave switches that involved circuits that contained GFCIs, I discovered that I could not install a Z-Wave switch downstream of a GFCI.  If I tried to do so, the GFCI tripped immediately when I turned the switch on.  What I ended up doing was to split the neutral and run one leg to the GFCI.  The other leg served the Z-Wave switch and the downstream circuits.   That meant the the Z-Wave switch and the downstream switches were no longer protected by the GFCI, but it was a choice that I had to make.  I ended up installing another GFCI later in the circuit to protect an outlet located later in the circuit.  Before I installed the Z-Wave switch, the initial GFCI was able to protect this outlet.

[Catman]

<snip>

So here's the question, I have a third switch in that gang box. This switch controls a driveway light attached to the eave of the roof. The problem for me is that this switch is on a different circuit. I have to cut a separate breaker for this switch when I work in the gang box. If I pick up another GE on off switch, can I tie into the same common neutral from the other circuit or do I have to run a separate neutral from that circuit for this switch?

I have no idea where in the world you are, but I ran into a similar issue here in the UK.  In my case, there is a porch light and a hall light, contained in one switch box, but fed form different lives and with different neutrals.  By consumer unit is divided in two with the main breaker bang in the middle. The breaker for the hall light was on the left of that, the porch light on the right.

When I coupled the neutrals (using the porch neutral) all was well until I turned on the hall light, whereupon it all went dark (and quiet) as the main break tripped.

I have been informed by a moderately reliable source that the neutrals are split in that kind of consumer unit.  The intention of having two lights close together running from (to) different sides, is that you have a greater chance of having at least one light working so you can see which breaker has blown (IYSWIM).

So if your case is like mine, you'll need another neutral.

HTH

C