Can sharing neutral with other circuits cause comm issues?

[langenet]

Yes, you are correct. In the panel, all neutrals are tied together.

Robert

[Uncle Michael]

Am I mistaken about the neutrals all being tied together??

No, you are correct. But when a circuit is in use, there is current flowing through the hot wire and the neutral. That is what the neutral is for. It completes the circuit. You can easily test it with a multi-meter. When a switch is in the on position, both sides of the load will be hot.

I'm not well enough acquainted with the theory to know how the current flows through the buss bar, but I presume that the neutral from the main provides the dominant path for the return current, while the neutrals on the other circuits do not offer a return path to the main power line, so are not energized by one another.

[Uncle Michael]

It helps me to think of it like it's a form of plumbing. Imagine a water reservoir in the attic and a drain in the basement. If the sink and the tub in one bathroom share a drain line, then water will flow in the shared drain if either one of them has a faucet on. But a sink in another room, with a separate drain line, will not have water in the drain if the faucet is off, even though all the drains are connected in the basement.

[logbuilder]

You might be right, I have no formal training in electricity theory.

However, it seems to me you are describing how DC flows rather than AC.

Hopefully someone who knows this stuff will chime in and straighten us out.

[Uncle Michael]

it seems to me you are describing how DC flows rather than AC.

I readily admit the analogy is not exact. The point is, the potential of an AC circuit is higher on the 'hot' side than the neutral side. By sharing a neutral between two circuits, you are providing two 'hot' sides at high potential connected to the neutral buss at a lower potential through the one shared neutral wire. Yes, the current is alternating, not direct, but it flows from high potential to low potential. In that regard it is analogous to water flowing down hill. If there were no current flow through the neutral wire, it wouldn't be needed. If there is current flow, then there has to be a potential difference between the load and the neutral buss.

If you want to verify the situation, just measure the voltage to ground from the neutral wire and the hot wire at an active load like a light fixture. (You could also try touching the terminals, but I wouldn't recommend that. )

[lj502]

Just looking inside a panel says it all, all neutrals are tied together and to be real all hots on each phase are tied together also albeit with a breaker to limit the current for safety. If all these switches and whatever were not "all" tied together nothing would work as is.

I think the answer is hook it up.

John

[logbuilder]

Just looking inside a panel says it all, all neutrals are tied together and to be real all hots on each phase are tied together also albeit with a breaker to limit the current for safety. If all these switches and whatever were not "all" tied together nothing would work as is.

I think the answer is hook it up.

John

The 'lines' on each phase are tied together with breakers for isolation/safety. But the phases are not tied together in any way. That is why we used to use phase couplers.

[lj502]

Absolutely, but question was about sharing neutral, also called common for a reason, just one big wire with many branches.

John

[Burrington]

The electrical code requires that the neutral buss (and therefore all the neutral wires) be connected to ground. That way you can not be electrocuted by coming in contact with a neutral wire and having your body complete a circuit to ground. That's where the term "Neutral" comes from, because it is neutral with respect to ground. By doing that, a breaker is not required on the neutral wire. The actual point of connection to ground is different between the Canadian and US electrical codes - each has it's advantages.

If the neutral was not grounded, a short to ground would not trip the breaker, it would simply electrify the grounded enclosure which is of course dangerous.

Most homes have a 120/240v panel. That consists of 2 legs of 120v (called L1 and L2) with a common neutral (N) (total 3 wires coming in from the power company). So between L1 & N is 120v, and between L2 & N is 120v. However the AC cycle on L1 is 180 degrees (1/2 cycle) out of phase with L2. That makes the voltage between L1 & L2 240 volts. So an appliance that requires 120v can be connected between either L1 & N, or L2 & N. An appliance that requires 240v is connected between L1 & L2.

Circuits in a house are often wired using 2 hot wires and a common neutral to serve multiple 120v devices. That's the case that started this thread. One hot wire (red) comes from L1, the other hot wire (black) comes from L2, and the white wire connects to Neutral. In this configuration, the amperage is shared by the 3 wires. Say L1 has 12 amps load connected, and L2 has 8 amps load connected. The L1 will carry 12 amps, the L2 will carry 8 amps, and the neutral will carry the difference of 4 amps. Example 2: L1 load is 15 amps, L2 is 0 amps means that Red will have 15 amps, black will have 0 amps, and neutral will have 15 amps. The advantage of this type of circuit is that it uses a single 4 wire cable (L1, L2, N, Gnd) for 2 circuits, vs 2 individual 3 wire cables (L1, N, Gnd + L2, N, Gnd) for a saving of 2 wires.

Important safety aspect to this system!! For this to work safely, one hot wire must be on L1, and the other must be on L2. If both are on the same leg, it will appear to work properly, but the neutral will be carrying the total current from both legs - a guaranteed fire hazard!!!! Further, these circuits MUST be wired with a single handle breaker that shuts off both legs. That prevents an electrified neutral as noted above.

Hope that helps...

[mrceolla]

Thank you all for your input. I understand the safety concerns with sharing neutral after I researched it a bit. I guess it is somewhat common in kitchens:

https://www.nachi.org/forum/f19/tie-...reakers-69661/

https://diy.stackexchange.com/questi...hare-a-neutral

The two circuits involved in any neutral sharing in my house are on different phases so it should be safe. I have a few of those double-switch breakers in my box (two tiny switches instead of one large one) which has something to do with this neutral sharing. Either way, I think we've determined earlier that the neutral sharing is not the cause of my communications problem.

I'm still somewhat confused about exactly how the powerline Insteon signals travel. And I'm not sure what to try next in trying to solve this.

[Uncle Michael]

Do not confuse a tandem breaker with a double pole breaker. They are not the same.

A tandem breaker allows two breakers in the typical space occupied by a single breaker. Both of the circuits on a tandem breaker are on the same leg.

A double pole breaker looks like two single breakers with their handles joined together. It couples two identical breakers, one on each leg of a split phase panel.

https://www.thespruce.com/tandem-bre...eakers-1152748

[mrceolla]

Do not confuse a tandem breaker with a double pole breaker. They are not the same.

Well, I'm not exactly sure what I've got going on here. It's a 40 yr old house. I've attached a pic of my breaker box. The circuit boxed in red is the one I'm having problems with. The PLM is on #18 according to the bottom label.

[Uncle Michael]

The circuit boxed in red is the one I'm having problems with. The PLM is on #18 according to the bottom label.

If I'm counting correctly, it appears that the problematic circuit is on the opposite phase to the PLM. That would certainly support the argument that you may need better phase coupling.

[mnsandler]

[/COLOR]
Well, I'm not exactly sure what I've got going on here. It's a 40 yr old house. I've attached a pic of my breaker box. The circuit boxed in red is the one I'm having problems with. The PLM is on #18 according to the bottom label.

Mike, have you performed some of the diagnostics we disc previously. I didn't see any posts with your results.

[Burrington]

Mike is correct - the PLM is on the opposite leg from the problem circuit, so it could be a phase coupling problem. One easy way to check is to compare communication test results with and without your electric oven turned on and heating. The big element in the oven (or the dryer if that's easier) is a very low resistance bridge between the two phases. If you get better communication test results with the oven on than you do with it off, you have a phase coupling problem. This phenomenon also explains why sometimes things work great and then they don't - depends whether a 240v device was running or not... Ovens, Air Conditioners, Clothes dryers, and electric water heaters are the most common 240v appliances.

For future reference your breakers are as follows (as per the yellow label, not the numbers on the panel):
Leg 1 = Breakers 1,2,5,6,9,10a,10b,13,14a,14b,17,18
Leg 2 = Breakers 3,4,7,8,11a,11b,12,15,16,19,20a,20b

Safety related issue #1: if I understand correctly, you said breaker 4 and 6 are wired with a common neutral. If so, that should be a double-pole breaker (one handle for two breakers like the ones on the left side). That's what prevents someone from turning off only one leg and leaving live wires in the circuit as you found out (fortunately without injury...). I can't tell if they are 15 or 20 amps, but be sure to replace with the exact same rating. If changing the breakers isn't in your abilities/ budget, please at minimum mark your yellow label in big bold print to show that those two breakers need to be shut off in conjunction with one another. Something like "Danger!! Common neutral - shut off both breakers"

Safety issue #2: Please pull the cover off your panel and check each of the tandem breakers (10, 11, 14, 20) to see if any of those are wired as a common neutral. If you see a red wire on any breaker, it is likely wired that way. As explained in a previous post, that configuration requires the neutral (white) wire to carry the total current of both breakers which is double what its rated for and is an extreme fire hazard. If so, get an electrician in asap to correct it.

Question: Do you have an Insteon filter on your HomeSeer computer, monitor, printer, etc? If not put one on it. You could unplug your audio equipment and use that filter to test it. Use a power bar into the filter and plug everything into the power bar except for the PLM which must be direct into the wall. I have never seen a computer that wasn't killing the PLM's Insteon signal level (about 0.5v out to the powerline instead of 5v). So there's no signal left to get to the rest of the house. If the signal out of the PLM is low, it may not make it to the first dual-band device to get repeated nor phase coupled.

Let us know what you find from the above tests.