Induced Current???

Thread Starter

Dan Pressman

Joined Apr 19, 2017
19
I just wired two new 15 amp circuits to my breaker box with a duplex breaker. I used 14-3 wire and put the red wire to one breaker and the black to the other.

When testing the circuit with only one of the two breakers (the black wired one) on I saw 120vac between between white and black but 67vac between white and red. It reversed when I switched which circuit breaker was on.

I think this is simply and induced current in the off wire and I should not worry am I correct?
 

dcbingaman

Joined Jun 30, 2021
495
Place a load on both breakers. And retest. Loads can be anything, toaster oven etc. Test under load, with DMM you will probably find it is working fine. You are most likely observing some kind of bleed through as the impedance of most DMM's is very high, this will prove or disprove that.
 

dcbingaman

Joined Jun 30, 2021
495
Though this has nothing to do with what you are observing I would also go with 12-3 wiring. Even at 15Amp breakers, it is simply a better choice and not much more cost. The other benefit of using 12-3 if you want to go to a 20A breaker in the future you can with no worries. Be sure to use 20A outlets as well. If you already have everything installed don't sweat it. This is just a suggestion for future wiring.
 
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dcbingaman

Joined Jun 30, 2021
495
I just wired two new 15 amp circuits to my breaker box with a duplex breaker. I used 14-3 wire and put the red wire to one breaker and the black to the other.

When testing the circuit with only one of the two breakers (the black wired one) on I saw 120vac between between white and black but 67vac between white and red. It reversed when I switched which circuit breaker was on.

I think this is simply and induced current in the off wire and I should not worry am I correct?
Oops, now that I have reread your post what you are doing is very dangerous!

Consider this, say your first load on red wire is 10 Amps and on the black wire is another 10 Amps. They must come back on the neutral wire at 20 Amps! That is way to much current on a 15 gauge wire! This is a serious fire hazard! You want all the current on either the black wire or red, do not use both! That way the current on the neutral wire is equal and opposite that of the hot wire and the circuit break can do its job properly.

WARNING: Please do NOT wire it up like that or you could have a fire hazard condition!
 

MrAl

Joined Jun 17, 2014
8,547
I just wired two new 15 amp circuits to my breaker box with a duplex breaker. I used 14-3 wire and put the red wire to one breaker and the black to the other.

When testing the circuit with only one of the two breakers (the black wired one) on I saw 120vac between between white and black but 67vac between white and red. It reversed when I switched which circuit breaker was on.

I think this is simply and induced current in the off wire and I should not worry am I correct?
Yes it is most likely induced because the wires are so close within the cable sheathing.
Sometimes meters will pick up AC voltages too that are not really there.
If you follow the loading test you should be able to see better results.
Note that some switches and breakers can have a small about of leakage current too and the sensitive meter (probably 10 megohms input impedance) can pick this up too.

As to the wire gauge, it also depends on the length of the run. The code is usually 12 gauge for 20 amps but if it is a very short run then 14 gauge may work ok. It's all about voltage drop with maxim,um load. If you loose too much voltage it is not good and the wire may overheat. If it is a very long run then 12 gauge wont be good enough for 20 amps either you'd have to go to 10 gauge.
15 amps is good for a lot of things. 20 amps is good for the kitchen, and in fact multiple 20 amp circuits.

What amazes me is that many hotels in the area have microwave ovens in the rooms. Microwave ovens can easily draw 12 amps. With all rooms using ovens i wonder if they all updated their wiring to handle that as normally a room has just a couple lamps and a LCD television.
 

dcbingaman

Joined Jun 30, 2021
495
The proper way to wire two separate 15 Amp circuits:
Each circuit (15 amp breaker) needs to have it's own designated 15 or 20 gauge wire both hot and neutral period. Each circuit also needs its own ground wire for safety and the ground wires should not be shared between circuit breakers for the same reasons.

You should NEVER use 14-3 where one circuit uses the red and neutral and the other uses the black and SAME neutral! This causes both circuits currents to combine in the neutral carrying more current that it is rated for!

Hope that makes sense.
 

MaxHeadRoom

Joined Jul 18, 2013
23,903
Oops, now that I have reread your post what you are doing is very dangerous!

Consider this, say your first load on red wire is 10 Amps and on the black wire is another 10 Amps. They must come back on the neutral wire at 20 Amps! That is way to much current on a 15 gauge wire! This is a serious fire hazard! You want all the current on either the black wire or red, do not use both! That way the current on the neutral wire is equal and opposite that of the hot wire and the circuit break can do its job properly.
In N.A., If you have two 10a 120v circuits each on L1 & L2 and they share the same neutral, the current in the neutral will be zero.
 
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Thread Starter

Dan Pressman

Joined Apr 19, 2017
19
In N.A., If you have two 10a 120v circuits each on L1 & L2 and they share the same neutral, the current in the neutral will be zero.
Max

Max

Since I used a duplex beaker (two minis in one slot) they are not out of phase.

DCBINGERMAN YOU ARE RIGHT!!!!!

THANK YOU THANK YOU THANK YOU!

I had often done this with 2 adjacent breakers which is ok. BUT NOT WITH A DUPLEX. I SHOULD HAVE KNOWN BETTER in fact I do but did not think about it.

THANK YOU THANK YOU THANK YOU.
 

Thread Starter

Dan Pressman

Joined Apr 19, 2017
19
dcbingaman

Once again thank you. I will of course fix MY mistake.

But I could not sleep - My wiring was an add-on to a sub-panel in my workshop. But as I lay in bed Ikept thinking about the Main panel with 8 duplex breakers the licensed electrician installed when the house was built 6 years ago. I quietly got out of bed so as not to alarm the wifey and opened the main panel up.

At first look all is ok as he put the two black wires each from two different 14-3 or 12-3 cables into one duplex breaker and the two reds into the ADJACENT duplex breaker. Therefore the neutral wire would in the case of two 15 or 20 amp loads see a net of zero amps as they are out of phase.

In the morning I will carefully double check that the blacks and the reds are correctly wired to adjacent breakers (i.e. make sure that the black from cable A goes to an ODD duplex breaker and the red goes to an EVEN).

Thank You one more time for catching this hopefully I have convinced you that I have fully absorbed your lesson with my checking of the main panel.

BTW My understanding (from my pop who wrote books on Power Supplies) was that this is called an Edison Circuit. He convinced me years ago that it was safe if wired correctly and as I said I have done it before in another house. But now seeing it in practice and how easy it is to make a mistake like I did or accidently run the black and the red both to an even or odd breaker makes me think this requires extra vigilence.
 

MrAl

Joined Jun 17, 2014
8,547
Any single circuit should have its own hot wire, neutral wire, and ground wire.
The usual colors are black for hot, white for neutral, green or bare for ground. Sometimes gray for neutral.
When you use red it indicates either hot or switched hot, or possibly for a three way switch.
Because of the varied use of the red (and other colors) wire it is a good idea to label (at both ends) it as to what it is actually being used for in that actual application. That way there can be no confusion and no electric shock.
Bx cable usually uses the sheathing as the ground. Romex is the usual go to cable, but Bx is required in some rough duty installs. The codes in your area may vary.
 

dcbingaman

Joined Jun 30, 2021
495
dcbingaman

Once again thank you. I will of course fix MY mistake.

But I could not sleep - My wiring was an add-on to a sub-panel in my workshop. But as I lay in bed Ikept thinking about the Main panel with 8 duplex breakers the licensed electrician installed when the house was built 6 years ago. I quietly got out of bed so as not to alarm the wifey and opened the main panel up.

At first look all is ok as he put the two black wires each from two different 14-3 or 12-3 cables into one duplex breaker and the two reds into the ADJACENT duplex breaker. Therefore the neutral wire would in the case of two 15 or 20 amp loads see a net of zero amps as they are out of phase.

In the morning I will carefully double check that the blacks and the reds are correctly wired to adjacent breakers (i.e. make sure that the black from cable A goes to an ODD duplex breaker and the red goes to an EVEN).

Thank You one more time for catching this hopefully I have convinced you that I have fully absorbed your lesson with my checking of the main panel.

BTW My understanding (from my pop who wrote books on Power Supplies) was that this is called an Edison Circuit. He convinced me years ago that it was safe if wired correctly and as I said I have done it before in another house. But now seeing it in practice and how easy it is to make a mistake like I did or accidently run the black and the red both to an even or odd breaker makes me think this requires extra vigilence.
Correct, in this situation you are probably ok. I was not sure how you where using the 'red' wire within the 14-3 cable. If sending one to L1 and the other black to L2 you are most likely ok. Some high inductive circuits though will not have a 0 phase shift between the voltage and current, and can vary from 0 to 90 degrees. So they will not cancel out in the neutral, but they should in theory still be current subtracting in the neutral.
 

dcbingaman

Joined Jun 30, 2021
495
In N.A., If you have two 10a 120v circuits each on L1 & L2 and they share the same neutral, the current in the neutral will be zero.
That is correct. I got from the TS initial reading he was simply using the red wire of the cable for the second circuit both using L1. Not that the circuit was connected to the L2. His pictures cleared that up well.
 

dcbingaman

Joined Jun 30, 2021
495

dcbingaman

Joined Jun 30, 2021
495
dcbingaman

Once again thank you. I will of course fix MY mistake.

But I could not sleep - My wiring was an add-on to a sub-panel in my workshop. But as I lay in bed Ikept thinking about the Main panel with 8 duplex breakers the licensed electrician installed when the house was built 6 years ago. I quietly got out of bed so as not to alarm the wifey and opened the main panel up.

At first look all is ok as he put the two black wires each from two different 14-3 or 12-3 cables into one duplex breaker and the two reds into the ADJACENT duplex breaker. Therefore the neutral wire would in the case of two 15 or 20 amp loads see a net of zero amps as they are out of phase.

In the morning I will carefully double check that the blacks and the reds are correctly wired to adjacent breakers (i.e. make sure that the black from cable A goes to an ODD duplex breaker and the red goes to an EVEN).

Thank You one more time for catching this hopefully I have convinced you that I have fully absorbed your lesson with my checking of the main panel.

BTW My understanding (from my pop who wrote books on Power Supplies) was that this is called an Edison Circuit. He convinced me years ago that it was safe if wired correctly and as I said I have done it before in another house. But now seeing it in practice and how easy it is to make a mistake like I did or accidently run the black and the red both to an even or odd breaker makes me think this requires extra vigilence.
One easy way to verify you are using the second leg, just check the two circuit breaker outputs with a meter going from the red to black, if they truly are separate legs you will get 240VAC. Make sure you meter can handle the voltage before you do the measurement. If they are not separate legs you will get 0V.
 
I know how 67 V occurs in a system. Ran into it before and it;s confusing to the unititiated.

Datasheet: https://www.farnell.com/datasheets/1668819.pdf

Take a power line filter used in some devices like computers with switching power supplies:
From the above datasheet:

1631026660120.png

If that ground on the right hand side somehow is not connected to a real ground, what it's connected to will see ABOUT 12 of 120 VAC. A capacitor is modeled as an ideal capacitor, a series resistor and a parallel resistor. This particular filter does not have a max leakage current to ground spec, but it;s generally a few mA.

if that ground point is not grounded, you get a "resistive-like" divider at about 1/2 the voltage.

I saw it happen in an defective duplex outlet and an outlet strip.

The outlet strip.
One of the grounds was severed, so that (60 VAC) voltage was applied to downstream outlets to their ground connections through one of the downstream devices.

So, if you have a parallel printer and a computer talking to one another that use ground as a reference, you have a problem. 5V logic doesn't like 60 VAC. Serial ports is another problematic connection. This was a test-jig that was sparking..

Outlet
This case was a little harder to diagnose. We had 420 Pass & Seymour outlets in the building and any one of them could be bad. The design of the outlet was such that the ground connection was purely mechanical between brass and plated steel.
When you took the outlet apart, you could see the arc marks.

Some outlets worked, some didn't. So, what happened is that poor design and manufacturing tolerances allowed one of the grounds to "let go" when to plugs were used in the same outlet.

Not my decision, but what we did was:
a) Replaced all lab outlets from white to brown.
b) Determined what hall outlets were on lab circuits - put a red label on them.
c) Replaced hall outlets that were bad and not on lab circuits and labeled them green.
(D buffer would not then ruin a lab experiment)
d) Offices with computers got their outlets replaced.
e) Anything else was a test before use and replace if necessary.

I had a neat little device which was eventually stolen that was like a 3 neon light outlet tester with a fourth light that detected if the ground resistance was <2 ohms and it lit under that condition.

The tester was plugged in an an IEC power cord was plugged in. You wiggled the IEC cord and if the light went out, the outlet was bad.

One of the outlet strip problems destroyed a computer under warranty. The other baffled a PHD and PHD candidate for 40 hours during the weekend. I had the problem identified within 5 minutes when I came to work on Monday.
I changed the outlet on the strip where something was plugged in and fixed it later.

So, it's a real, dangerous but baffling condition.
 
I've never seen dual single position mini-breakers before. They, in theory, should have separate neutrals.
When a 240 breaker is used to power two 120V outlets in the US, the difference current flows in the neutral.
two 10A loads, 1 on L1 and one on L2 means 0 neutral current. You can't read the sign on your DVM.

Now for some other odd stuff on panels

Categories: main lug and main breaker
The main lug panel has no breaker for all of the circuits; A main breaker panel does.
A main breaker panel must be used when the # of circuits exceed (I think the number is 6).
The main breaker rating can be anything higher or equal to the feed.
You can feed with a 60A breaker in the main panel and have a 200A breaker in the sub-panel.

Main breaker panels need a ground bar kit and must have the N-Ground link removed. Usually a screw to use it as a sub-panel. where grounds and neutrals are kept separate.

Sub-panels in a "detached structure" require another ground rod.

Switch loops
See: https://www.finehomebuilding.com/project-guides/wiring/wiring-a-switch-loop

New switch wiring should be 3-wire w/ground, so that there is a neutral in the box. Capped if not used.

Old wiring says to tapethe white wire black to show it's a live wire.
 

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dcbingaman

Joined Jun 30, 2021
495
I know how 67 V occurs in a system. Ran into it before and it;s confusing to the unititiated.

Datasheet: https://www.farnell.com/datasheets/1668819.pdf

Take a power line filter used in some devices like computers with switching power supplies:
From the above datasheet:

View attachment 247450

If that ground on the right hand side somehow is not connected to a real ground, what it's connected to will see ABOUT 12 of 120 VAC. A capacitor is modeled as an ideal capacitor, a series resistor and a parallel resistor. This particular filter does not have a max leakage current to ground spec, but it;s generally a few mA.

if that ground point is not grounded, you get a "resistive-like" divider at about 1/2 the voltage.

I saw it happen in an defective duplex outlet and an outlet strip.

The outlet strip.
One of the grounds was severed, so that (60 VAC) voltage was applied to downstream outlets to their ground connections through one of the downstream devices.

So, if you have a parallel printer and a computer talking to one another that use ground as a reference, you have a problem. 5V logic doesn't like 60 VAC. Serial ports is another problematic connection. This was a test-jig that was sparking..

Outlet
This case was a little harder to diagnose. We had 420 Pass & Seymour outlets in the building and any one of them could be bad. The design of the outlet was such that the ground connection was purely mechanical between brass and plated steel.
When you took the outlet apart, you could see the arc marks.

Some outlets worked, some didn't. So, what happened is that poor design and manufacturing tolerances allowed one of the grounds to "let go" when to plugs were used in the same outlet.

Not my decision, but what we did was:
a) Replaced all lab outlets from white to brown.
b) Determined what hall outlets were on lab circuits - put a red label on them.
c) Replaced hall outlets that were bad and not on lab circuits and labeled them green.
(D buffer would not then ruin a lab experiment)
d) Offices with computers got their outlets replaced.
e) Anything else was a test before use and replace if necessary.

I had a neat little device which was eventually stolen that was like a 3 neon light outlet tester with a fourth light that detected if the ground resistance was <2 ohms and it lit under that condition.

The tester was plugged in an an IEC power cord was plugged in. You wiggled the IEC cord and if the light went out, the outlet was bad.

One of the outlet strip problems destroyed a computer under warranty. The other baffled a PHD and PHD candidate for 40 hours during the weekend. I had the problem identified within 5 minutes when I came to work on Monday.
I changed the outlet on the strip where something was plugged in and fixed it later.

So, it's a real, dangerous but baffling condition.
This simple tester from Lowes/HomeDepot and other stores will verify all your wiring is correct including ground:

1631040847368.png
 
These testers are not made equal. This one https://www.sperryinstruments.com/en/p/HGT6520/Stop-Shock-II-GFCI-Outlet-Circuit tests for a ground resistance <10 ohms.

The fault I had might not be detected with the Southwire @dcbingaman
tester.

Incidently, what I did to those testers is to glue a bubble level to them. I can level the outlets before the plate goes on.

I have an Ideal Suretest outlet analyzer and I'm not sure it would detect the ground issue that I had. The output is numeric.


I have two Ethernet wiring testers. One checks for wiring errors, but it can't check for intermittent connections. That tester just has a battery and bicolor LEDs. You can flex the ends of the cables and the LED would go out if that pair was intermittant.
I was able to make a simple remote too, but haven't upgraded it for 4 pair.

The next level is a qualification tester which I don't have.
 

Thread Starter

Dan Pressman

Joined Apr 19, 2017
19
Thank you to EVERYONE!

But why is int NOT correct to wire the neutrals as in the lower diagram where it says "Incorrect neutral wiring for multi-current circuit"
 

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