High resistance reading neutral to equipment ground

[RRonke]

I get resistance readings from .1 ohm to 98 ohms when testing neutral to equipment ground in a customer's house. I was testing because his 4' wide curved plasma arc
TV and two plug in surge protectors were ruined when plugged into the recept. behind the TV. Found hot wire fell out of receptacle when I removed it (a stabbed in connection). I wanted to make sure equipment ground was good but neutral to ground tested at 47 ohms. But when a extension cord was used to test to a "good" ground that tested at .1 ohm to neutral, all receptacles and this one tested at .1 ohm. He's asking me to make sure his replacement TV won't go up in smoke. I think that as long as the equipment ground is good the surge protector should have a place to dump to and the loose hot wire could have caused problems but I did not see any signs of arcing on the hot wire that was not connected good. I don't think the 47 ohms reading should be a worry but I'd like some opinions. I have never run into this in 22 years of wiring maybe because I have never tested a bunch of receptacles like this.

 

[hillbilly1]

Kinda sounds like a high resistance neutral issue. Might be a good idea to check the panel neutrals and main neutral. A loose hot would not have fried the tv. A loose main neutral would.

 

[suemarkp]

Is this a multiwire branch circuit? What ruined the tv the first time? A high neutral to ground resistance could be a poor splice on either any upstream grounds or neutrals.

Do you have a meter that can put more current on that connection? Grounding checks that pass with a milliamp tester can fail much easier when a high current tester is used because just one whisker of wire is all a low current test needs to pass. Look for some sort of bonding meter tester.

If MWBC check all the upstream neutrals.

 

[ActionDave]

Equipment ground is not going to protect the tv. Surge protector is not going to dump anything to the EGC, they don't even need an EGC to work.

What kind of voltage readings do you get line to neutral, line to ground at the tv recept with a load on the circuit?

 

[kwired]

Was test with circuit off? Any load on that neutral can change what you read. If from a properly wired sub panel you will possibly have neutral current on at least the feeder portion of the tested path.

 

[RRonke]

Kinda sounds like a high resistance neutral issue. Might be a good idea to check the panel neutrals and main neutral. A loose hot would not have fried the tv. A loose main neutral would.

Thanks hillbilly. I did a break and make on all panel neutrals to eliminate any loose or oxidized connections but did not check the main neutral. I will check it next.

 

[RRonke]

Is this a multiwire branch circuit? What ruined the tv the first time? A high neutral to ground resistance could be a poor splice on either any upstream grounds or neutrals.

Do you have a meter that can put more current on that connection? Grounding checks that pass with a milliamp tester can fail much easier when a high current tester is used because just one whisker of wire is all a low current test needs to pass. Look for some sort of bonding meter tester.

If MWBC check all the upstream neutrals.

Thanks Suemarkp. I did check all upstream neutrals and all were solid bonded. I will research what a bonding meter is all about and see if I can get a hold of one as a next potential step.

 

[RRonke]

Equipment ground is not going to protect the tv. Surge protector is not going to dump anything to the EGC, they don't even need an EGC to work.

What kind of voltage readings do you get line to neutral, line to ground at the tv recept with a load on the circuit?

I will need to load the circuit and check voltages. I did not run that test. Maybe I'm missing something here but I was sure the MOVs shorted to the equipment grounding wire. Thanks for the reply.

 

[RRonke]

Was test with circuit off? Any load on that neutral can change what you read. If from a properly wired sub panel you will possibly have neutral current on at least the feeder portion of the tested path.

I did test with the circuit off and it was not a multi wire circuit. Appreciate the idea and will make sure to use it for future trouble shooting.

 

[Fred B]

That loose hot would not blow up the TV, (bad but I don't think the issue, might be indicator of past work quality). I'd be checking (as others indicated) for a dropped primary neutral at main or sub panel, before even trying to plug in the new TV. It's been suggested in past that such events would "take out" the most expensive item first.
Check voltages L1-L2, L1-N, L2-N, L1 and L2 TO G. It also could have been a transient event at the POCO if all test show good. Your variations in R for your N-G measurement at receptacle can be effected by many factors including what else is plugged in on the circuit. Test at main source.

 

[ptonsparky]

I don't have brand new TVs but my older ones say 120-240 volt. Even my monitors say 100-240.

 

[ActionDave]

I will need to load the circuit and check voltages. I did not run that test. Maybe I'm missing something here but I was sure the MOVs shorted to the equipment grounding wire. Thanks for the reply.

Surge protectors are a blob of semi conductor material that don't do anything till the voltage gets high enough to turn them into full conductor material.

https://www.extremetech.com/computing/50086-surge-suppressors-anatomy-lesson/7

Although all commercial device-level surge suppressors connect in the same way–you plug the surge suppressor into a wall outlet, then plug your computer or peripherals into the surge suppressor–the active components inside the suppressor may actually be connected in parallel or series with your computer.

A series-connected surge suppressor acts as a roadblock. The surge must travel through the suppressor on its way to your computer. The suppressor removes or smoothes out the surge on its way so, in theory, no dangerous voltages are left to harm your equipment.


A parallel-connected surge suppressor is connected in parallel to your computer, across the leads of the power line just as is your computer. The suppressor works by shorting out (or shunting) the surge, routing its high voltage directly from hot to neutral, before the surge voltage on the power line rises to a point at which is can damage your computer.

Engineers design parallel-connected surge suppressors so they only conduct electricity (and thus generate that short circuit) only for the duration of the overvoltage of the surge. As soon as voltage falls back to normal, the surge suppressor removes the short circuit, at least if all goes well. Most surge protectors are parallel, and most engineers would recommend the parallel design.

 

[kwired]

I don't have brand new TVs but my older ones say 120-240 volt. Even my monitors say 100-240.

Most from past 20-25 years probably do. Some the newest ones maybe truly are plug and play, some the older ones maybe need to change a switch to match the voltage range you are connecting to.

 

[Strathead]

I did test with the circuit off and it was not a multi wire circuit. Appreciate the idea and will make sure to use it for future trouble shooting.

No, form your description, i.e. not a multiwire branch circuit the loose or open neutral is next level up feeder. Just read neutral to ground in the panel. I recently was in a facility where the installer failed to put the link between the main and the service so no neutral. 3000A service. the system was so balanced that I read 30 amps of flow between the neutral and ground. There was 550 to 600 amps flowing through each phase, and that is with no neutral at all.

 

[RRonke]

Surge protectors are a blob of semi conductor material that don't do anything till the voltage gets high enough to turn them into full conductor material.

https://www.extremetech.com/computing/50086-surge-suppressors-anatomy-lesson/7

Thanks for the education!

 

[RRonke]

No, form your description, i.e. not a multiwire branch circuit the loose or open neutral is next level up feeder. Just read neutral to ground in the panel. I recently was in a facility where the installer failed to put the link between the main and the service so no neutral. 3000A service. the system was so balanced that I read 30 amps of flow between the neutral and ground. There was 550 to 600 amps flowing through each phase, and that is with no neutral at all.
I did check the neutral to ground in the panel with multimeter and it tested at .1 ohm. I believe I'll see if the neutral main is tight in the panel and if it is I'll check the meter can next.

 

[RRonke]

That loose hot would not blow up the TV, (bad but I don't think the issue, might be indicator of past work quality). I'd be checking (as others indicated) for a dropped primary neutral at main or sub panel, before even trying to plug in the new TV. It's been suggested in past that such events would "take out" the most expensive item first.
Check voltages L1-L2, L1-N, L2-N, L1 and L2 TO G. It also could have been a transient event at the POCO if all test show good. Your variations in R for your N-G measurement at receptacle can be effected by many factors including what else is plugged in on the circuit. Test at main source.

Thanks Fred. Sounds like a good systematic way of testing. If it was a transient I don't understand why within a week it blew up a second surge protector and then the TV. I'll call the power company to see if there have been any other problems in that area.

 

[Fred B]

Thanks Fred. Sounds like a good systematic way of testing. If it was a transient I don't understand why within a week it blew up a second surge protector and then the TV. I'll call the power company to see if there have been any other problems in that area.

Had just that issue, I called armed with the test data from the described testing and they came almost immediately and found a dropped neutral by the POCO transformer.

 

[RRonke]

Had just that issue, I called armed with the test data from the described testing and they came almost immediately and found a dropped neutral by the POCO transformer.

Thanks for the input Fred. I'll be going back out tomorrow and meeting with POCO at meter to check connections at that point.

 

[RRonke]

Thanks Fred. Sounds like a good systematic way of testing. If it was a transient I don't understand why within a week it blew up a second surge protector and then the TV. I'll call the power company to see if there have been any other problems in that area.

I followed your testing recommendation L1-L2, L1-N, etc. and voltages between phases were only .2 volt apart. I also pulled the meter out of the can to check for loose connections and all connections were tight. The owner settled for a Siemens FS140 whole house surge protector to deal with any transients from POCO. I offered to run a dedicated line to his plasma arc to eliminate the 47 ohms reading of neutral to ground since all circuits I tested that were direct such as bathroom and kitchen showed no resistance neutral to ground but he said no. His expensive audio system survived the event despite it being plugged into the same receptacle but it was protected by a APC surge protector rated over 3000 joules and then into a Panamax MR4000 power management device. Still dont know how I could get a high reading of neutral to ground ranging from 33 to 98 ohms to ground at different devices when all voltages checked out. The new TV is installed by Best Buy with their recommended surge protector and owner opted for 6 year extended warranty.Thanks for your ideas and thanks for everyone else who shared their thoughts. If I find anymore about my original question I will definitely post it.