Simply Automated Switches & Sharing Neutrals

[DIYHO]

The reason for having to do this is because the remote box does not have power coming into it from the same circuit. So I am using the white as hot to bring power from the same circuit, and tying the neutral into the other circuit that is in the box.

This is from the original post. Indeed two circuits are involved.

I don't understand the reason for this post, but it would be much appreciated if you would not take my posts out of context.

I have wired everything up, but in order to get the USR to work, I was forced to use the neutral as hot in the 3 cond. traveler wiring for several switches and using an available neutral in the remote electrical box. The reason for having to do this is because the remote box does not have power coming into it from the same circuit. So I am using the white as hot to bring power from the same circuit, and tying the neutral into the other circuit that is in the box.

Now I know that sharing neutrals is generally frowned upon unless the circuit is designed from the beginning that way. That said, is this type a setup really a "shared neutral" and is it a NEC code violation. This is the method recommended by SA for getting power from the same circuit to the USR, however they did not note the neutral tie in had to be on the same circuit like the hot does.

 

[apostolakisl]

The key point is "MUST be powered from the same circuit breaker", this implies that neutral is also from the same circuit. In this case, the wiring would be perfectly acceptable to the NEC. The problem occurs when the neutral is NOT from the same circuit, which is what I thought this whole discussion was about..........

Yes, that is what it is about, however as I already noted in a previous post, the docs make a specific point to say the hot must be on the same circuit, they don't make the same clear distinction with the neutral. Then they go on to explain how you can get a hot feed into the remote box that already has another neutral available by using one of the travelers. I would assume here that if there is already a viable neutral available in the remote box, then there probably is also a hot, just not one from the same circuit. Perhaps I am misreading it, but that is how I understand what was written after reading it many, many times.

They don't mean that the hot from the other circuit is hot, that goes without saying. They mean that the neutral from the other circuit can become hot if it were to become disconnected somwhere on the path back to the panel. The path of the electricity is supposed to be hot to switch, to load, to neutral, to city ground. If you cut the neutral after the load and after it has joined in with the other branches of that neutral (and by after I mean as you travel from load back to the panel), those branches will be hot with the current that has passed through the load and is looking for ground. If all of the switches on that circuit are "off" the neutral will not be hot. The more switches that are on and the more current the loads draw, the more current that will be available at the neutral. Unlike a true hot, this neutral turned hot, will not pop a breaker if you short it to ground becuase it has the resistance to flow from the load.

If you disconnect the neutral in a box returning from the load, put a multimeter on it and and touch the other side of multimeter to ground. Turn the switch on and you will see it is now hot. The difference between this hot and the real hot, is the current will be limited by the load. Nonetheless, it will shock you, I speak from experience here.

If it just so happens that this neutral turned hot is crossed with a hot from the other phase, you will have a voltage of 240 accross. This is what can happen if you plug the hot from one phase and the neutral turned hot from the other phase into the same load. Now you have an overcurrent risk at the load with fire hazard.

 

[IndyMike]

DIYHP,

Again I apologize. I was trying to clear confusion and apparently crated more.

Confusion point 1: The following schematic from SA does NOT propose that you tie the neutrals from two different circuits together. The connection to the right hand side of the schematic are "Optional" (shown dotted). The section dealing with this also clearly specifies that the HOT must be from the same breaker.

Quite from the installation guide:
OPTIONAL: In some multi-way circuits there may not be an 'always hot’ wire available in both junction boxes, requiring use of one of the wires in the traveler Romex to provide a hot
connection to the other junction box, or possibly the hot wire of an adjacent switch in the same junction box as the remote USR. All hot power wires used MUST be powered from the
same circuit breaker

LARGE CAUTION against using hot feeds from different circuits.

If a neutral wire is available in the remote USR junction box (e.g. neutral wire from a power feed to an adjacent switch), other than the white wire in the traveler Romex or the white neutral wire going up to the load/lights, then the white neutral wire in the traveler Romex maybe re-labeled (as black, typically with black electrical tap on white wire insulation at both ends) and used to carry power (hot) from the master switch junction box over to the USR to enable the blue LED function.

Confusion point #2: Remote switch supplied wit 120V by branch A while using a neutral from a separate branch.

This one is a bit stickier and the reason for all of the discussion.

1) Both the SA schematic and DIYHP's schematic clearly show the US40 remote being supplied by 120V from Branch A with a neutral from "somewhere".
2) The SA instructions do not place any restrictions on the source of this neutral.
3) DIYHP has done the work to make sure that this neutral is associated with a branch on the same phase (i.e. if the neutral is lifted the switch cannot see 240V - phases in series).

This is a bit of a gray area. If you examine the "Intent" of the NEC code:

1) The neutral must be sized to properly handle load currents.
2) Multi Wire Branch circuits (MWB) using a single neutral and opposite phase 120V legs are allowed due to the current cancellation that occurs in the neutral. A number of additional requirements apply and (as of 2008) a double pole breaker must be used.

The bottom line intent of the code - ensure that the neutral is properly sized - it's not protected by a breaker.

For those interested, Stubbie has a nice descriptive post (with graphics) over at diychatroom: Stubbie: Sharing Neutrals

Stubbie did a masterful job of illustrating why branch circuits on the same phase should not share a common. The illustration is a violation of rule 1) above (excessive current on the common). I have not been able to find a code section that specifically disallows a shared neutral connection as long as the neutral is properly sized.

As SA (and others) have stated, the US40 remote is not a LOAD device. It presumably contributes an insignificant current to the neutral. As a result, rule 1) should not be violated.

I, and many others, have been trained that shared neutrals (except for the MWB configuration) are an extremely bad thing. For loaded devices they are. This has been pounded into us to the extent that we've accepted it as "Code" - I can't find evidence of that, but then I'm about 35 years out of date. At the moment, I can't see where this specifically violates NEC code.

The real problem here may be yours inspector. Chances are he will have a similar mindset and, if he catches it, will reject the configuration out of hand. You can choose to explain the configuration (this may be hard) or switch the re-tasked wire back to a neutral connection (eliminate the other neutral at the remote) and give up the LED. Your choice.

IM

 

[apostolakisl]

Like Indy Mike Says.

If you have two hots returning on the same neutral, you could potentially carry double current on the neutral. For example, two 15 breakers feeding two 14 gauge hot leads would be returning on a single 14 guage common. What that means is that you could have up to 30 amps on that 14 gauge wire without popping the breaker. That :lol: ain't enough!

 

[IndyMike]

Like Indy Mike Says.

If you have two hots returning on the same neutral, you could potentially carry double current on the neutral. For example, two 15 breakers feeding two 14 gauge hot leads would be returning on a single 14 guage common. What that means is that you could have up to 30 amps on that 14 gauge wire without popping the breaker. That :lol: ain't enough!

Lou,

That is part of what I said...

I'm sorry, but I'm still not making myself clear. Two 120V supplies (same phase) using LOAD devices and the same neutral can cause excessive current on the neutral. I don't believe that's the case with DIYHP's configuration.

The distinction here is that the US40 remote switch is not a LOAD device in the conventional sense. If it contributes an insignificant amount of current to the neutral, NEC code has not been violated (so far as I can tell).

 

[DIYHO]

DIYHP,

Again I apologize. I was trying to clear confusion and apparently crated more.

No worries. I just wanted to make sure people were clear that the SA docs were not suggesting tying neutrals together from two different circuits. At the same time I wanted people to be clear that what I have is not tying two neutrals together from different circuits, nor is it a multi-wire branch circuit.

Confusion point 1: The following schematic from SA does NOT propose that you tie the neutrals from two different circuits together. The connection to the right hand side of the schematic are "Optional" (shown dotted). The section dealing with this also clearly specifies that the HOT must be from the same breaker.

Quite from the installation guide:
OPTIONAL: In some multi-way circuits there may not be an 'always hot’ wire available in both junction boxes, requiring use of one of the wires in the traveler Romex to provide a hot
connection to the other junction box, or possibly the hot wire of an adjacent switch in the same junction box as the remote USR. All hot power wires used MUST be powered from the
same circuit breaker

LARGE CAUTION against using hot feeds from different circuits.

If a neutral wire is available in the remote USR junction box (e.g. neutral wire from a power feed to an adjacent switch), other than the white wire in the traveler Romex or the white neutral wire going up to the load/lights, then the white neutral wire in the traveler Romex maybe re-labeled (as black, typically with black electrical tap on white wire insulation at both ends) and used to carry power (hot) from the master switch junction box over to the USR to enable the blue LED function.

Yes. As far as I understand it, the only "load" being returned by the remote on the common of the other circuit is whatever is necessary to power the blue LED when the lighting load attached to the master switch is powered down. The remote switch is incapable of carrying a load, which would be the reason why there is no provision for grounding on the USR.

Confusion point #2: Remote switch supplied wit 120V by branch A while using a neutral from a separate branch.

This one is a bit stickier and the reason for all of the discussion.

1) Both the SA schematic and DIYHP's schematic clearly show the US40 remote being supplied by 120V from Branch A with a neutral from "somewhere".
2) The SA instructions do not place any restrictions on the source of this neutral.
3) DIYHP has done the work to make sure that this neutral is associated with a branch on the same phase (i.e. if the neutral is lifted the switch cannot see 240V - phases in series).

This is a bit of a gray area. If you examine the "Intent" of the NEC code:

1) The neutral must be sized to properly handle load currents.
2) Multi Wire Branch circuits (MWB) using a single neutral and opposite phase 120V legs are allowed due to the current cancellation that occurs in the neutral. A number of additional requirements apply and (as of 2008) a double pole breaker must be used.

The bottom line intent of the code - ensure that the neutral is properly sized - it's not protected by a breaker.

Agreed, when we are talking about two discrete circuits sharing a single common.

There are no multi-wire branch circuits in my house, and power distribution has been split up almost to the point of absurdity (33 circuits for 1500 sqft). In fact, the master and remote switch in this discussion controls a single 6" recessed can that will end up housing a 8-11 watt LED lamp. The entire lighting circuit that this master/remote switch is on will most likely never see 100 watts of total load, even when all the lights on the circuit are fully energized. The other circuit feeds living room receptacles, so naturally the load can vary, however the majority of the receptacles will never be used given their location.

As SA (and others) have stated, the US40 remote is not a LOAD device. It presumably contributes an insignificant current to the neutral. As a result, rule 1) should not be violated.

I, and many others, have been trained that shared neutrals (except for the MWB configuration) are an extremely bad thing. For loaded devices they are. This has been pounded into us to the extent that we've accepted it as "Code" - I can't find evidence of that, but then I'm about 35 years out of date. At the moment, I can't see where this specifically violates NEC code.

The real problem here may be yours inspector. Chances are he will have a similar mindset and, if he catches it, will reject the configuration out of hand. You can choose to explain the configuration (this may be hard) or switch the re-tasked wire back to a neutral connection (eliminate the other neutral at the remote) and give up the LED. Your choice.

I am with you and everyone else here, hence the reason for my hesitation about using the neutral of the USR remote in this fashion.

What I had hoped to get out of this thread was discussion on the potential problems/safety issues of this setup, if the setup was even legal, and to get enough information together to intelligently explain the setup to the building department (assuming it is legal), and get them to sign off on it before the inspection even occurs. This way, it doesn't really matter what the inspector thinks is a violation or not, as long as I have the approval of the building department.

I've got a much better picture now of what is going on, however I am still uncertain if I have a complete grasp on the potential problems that might arise from such a setup. I suppose it might also help to be able to quote code and demonstrate how the setup is not violating it. I think in order to do this, a better understanding of how the switch functions internally is probably needed.

 

[Isbrant]

Is it possible to add everything from circuit 2 to circuit 1? I am not very knowledgeable about wiring so I don't know if it is possible or practical but it would be another way to solve your problem.

 

[apostolakisl]

With regards to the above wiring diagram I am going to call the left feed box 1, and the right box 2.

I have noticed now that the dotted line means "optional". If the neutral comming off the load is only optionally connected to box 2 neutral, then there must be a path back to neutral in box 1. That path has to be the "remote 1" wire becuase there is no way either of the other two wires could be neutral (one is directly connected to box 1 hot and the other is directly connected to the hot side of load).

It looks like the wire connected to "led 1" & "led 2" may be simply there to light leds when the load is on. Seems like that is the only option to make the switches work without co-mingling circuits (using only 2 inter-box wires).

You might be able to skip the "remote 1" wire and have the fixture work, but this would make the "optional" neutral mandatory and would result in co-mingled circuits. In other words, it might physically work, but be of questionable safety.

 

[DIYHO]

I ran some multi-meter tests last night by breaking the "shared" neutral on the circuit the USR neutral is tied into. Here are the results.

Circuit 1 (C1) = lighting circuit, the one that contains the US2-40 master switch and light load.

Circuit 2 (C2) = receptacle circuit, the one that the USR-40A neutral is tied into.

Broke the C2 neutral at the first Jbox directly outside the subpanel, tested various configurations with circuits on and off (switched at subpanel), and with the light load on and off

1) C1- OFF, C2 - OFF

• 1.5 mV
• 0.000 µA

2) C1- OFF, C2 - ON

• 315 mV
• 0.078 µA

3) C1- ON, C2 - OFF

• US2-40 light load ON
  • 346 mV
  • 0.096 µA
• US2-40 light load OFF
  • 48.5 mV
  • 0.016 µA

4) C1- ON, C2 - ON

• US2-40 light load ON
  • 305 mV
  • 0.076 µA
• US2-40 light load OFF
  • 316 mV
  • 0.078 µA

Verification Step

5) C1- ON, C2 - OFF

• US2-40 light load ON + other light loads on same circuit
  • 335 mV
  • 0.094 µA
• US2-40 light load OFF + all but one other light load off
  • 47.5 mV
  • 0.016 µA

Note: With respect to comments concerning GFCI, you can see the test values for current are well below the 5 mA tripping threshold of your typical GFCI.

Attached is pic of sub-panel and and test location, and again the exact wiring setup for the switches.

Green arrow points to C1 in sub-panel
Blue arrows point to C2 & C3. which have 1 - USR-40A (each in different JBoxes) powered by C1, but has the USR neutral tied into C2 & C3 neutral.
Blue arrow at the bottom 2 gang jbox shows location for multi-meter tests.