[Rav]

I'm in the process of changing non-GFCI receptacles in our unfinished basement, bathrooms, and kitchen to be GFCI receptacles.

Today I started looking at one particular receptacle on circuit 3. The voltages were what I expected: between hot and neutral and hot and ground were in the 120V range, and between neutral to ground zero. But after I turned the power off, I did a resistance test and was surprised by the results. (I'm using a Fluke 114 multimeter.) If I'm misunderstanding what resistance readings I should expect to see, then I will be glad to be corrected. Here's what I'm seeing:

          [U]Expected[/U]     [U]Seeing[/U]
H to N    Infinite     10 ohms
H to G    Infinite     18 ohms
N to G    0 ohms        9 ohms

Is my "Expected" column correct? I re-checked some of the other receptacles I've been working on. Those on circuits 2 and 3 showed the odd resistance readings, though the GFCI receptacles I've installed on those circuits are working fine and a plug-in outlet circuit tester shows normal. The GFCI receptacles I've installed on a number of other circuits all have the expected readings.

There is an ongoing question as to whether circuits 2 and 3 are an MWBC, since at least for a certain distance from the panel they share the same cable. I was planning on having an electrician check these circuits at some point, since I'd like to have AFCI breakers installed on them, and I'm not going to do that myself. Would being an MWBC have anything to do with these odd resistance readings?

I'm concerned about these readings, and I'm not sure what my next step should be. Should I get an electrician in to investigate this? Thanks.

 

[gregzoll]

Why are you reading Resistance? No one reads resistance when working on electrical circuits, to install new outlets, switches or fixtures. As long as you have connected everything correctly, just flip on the breaker and move on to the next project.

 

[Rav]

Why are you reading Resistance? No one reads resistance when working on electrical circuits, to install new outlets, switches or fixtures. As long as you have connected everything correctly, just flip on the breaker and move on to the next project.

Initially I was just checking continuity, as a sanity check. I only expected continuity between neutral and ground and was surprised when it showed continuity between H-N and H-G. I was concerned that continuity between the latter two indicated a possibly serious wiring problem (leakage, short, bad connection at panel). If it doesn't then I'm very glad to hear that, though I'd at least like to understand why.

 

[jbfan]

The hot to neutral reading could be light bulbs or appliances still plugged into the circuit.

 

[gregzoll]

Initially I was just checking continuity, as a sanity check. I only expected continuity between neutral and ground and was surprised when it showed continuity between H-N and H-G. I was concerned that continuity between the latter two indicated a possibly serious wiring problem (leakage, short, bad connection at panel). If it doesn't then I'm very glad to hear that, though I'd at least like to understand why.

Overkill. All that you need to do is to connect, go flip back on the breaker and then check to make sure that it tests and resets. If you want to check to make sure it has voltage, if not resetting, you would have to place your meter in 200 vAC mode and then check Red lead to Black, Black lead to White.

I have only had one GFCI outlet that was bad at install. It was a cheap pick bin one that my wife had picked up for me at the local Menards. Only way that I found out that it had a current leakage problem, was that the LED nightlight we have in the bathroom, was still lit up after tripping the outlet test button.

 

[Rav]

The hot to neutral reading could be light bulbs or appliances still plugged into the circuit.

AHA! So even though the circuit power was off, and even though they were all turned off, things such as light bulbs and appliances can still add a load to the circuit, and add resistance to the circuit? I hope I understand now. Anyway, I just physically disconnected everything from that circuit that I could, and re-tested, and sure enough, hot to neutral and hot to ground now read infinite resistance. It turned out to be two particular places where things had been plugged in: A light bridge with six CFLs, and a multi-receptacle surge protector with a phone, answering machine, and fan plugged into it. So it now looks safe for me to continue. Thank you.

 

[joed]

Turned off light bulbs won't add anything. Any device that has a remote or clock will not truly be turned off and thus add resistance. Any wall wart powered device will not be truly turned off.

 

[Know A Little]

Why are you reading Resistance? No one reads resistance when working on electrical circuits, to install new outlets, switches or fixtures. As long as you have connected everything correctly, just flip on the breaker and move on to the next project.

Actually

Everyone SHOULD BE reading resistance and the USA is behind the ball on this.

In commercial installations we perform insulation resistance test all the time (aka MEGGER, typical test voltage 1000 VDC).


To the OP as noted by others you are most likely reading through some equipment connected to the circuit.

If the resistance was that low at 9 VDC (test voltage of your meter) you would trip the GFCI when it is connected, heck your should have tripped the CB if the low resistance was not from a piece of equipment.

 

[gregzoll]

Actually

Everyone SHOULD BE reading resistance and the USA is behind the ball on this.

In commercial installations we perform insulation resistance test all the time (aka MEGGER, typical test voltage 1000 VDC).


To the OP as noted by others you are most likely reading through some equipment connected to the circuit.

If the resistance was that low at 9 VDC (test voltage of your meter) you would trip the GFCI when it is connected, heck your should have tripped the CB if the low resistance was not from a piece of equipment.

Incorrect. No one has a need to check resistance when putting in switches, outlets, lights, etc.. MegOhm tests would not do anything for the homeowner. They are rarely done, unless it is by a utility when they are checking their service lines for problems.

Even we never did MegOhm tests, unless it was a piece of equipment or Shorepower cables, which only the E1 did, because if he screwed up, he was the only one answering to the higher ups.

 

[Jim Port]

Just another thread where anyone that does something different than Greg is wrong. Maybe he should open up www.gregsays.com.

 

[al_smelter]

Read the very first word in post #6. And that, folks, is why it wasn't an unnecessary or 'stupid' test.

 

[Jim Port]

While not commonly done, thre is no harm in testing, especially before the drywall goes up. Way easier to replace a damaged cable than ripping out drywall looking for the issue.

 

[Know A Little]

Incorrect. No one has a need to check resistance when putting in switches, outlets, lights, etc.. MegOhm tests would not do anything for the homeowner. They are rarely done, unless it is by a utility when they are checking their service lines for problems.

Even we never did MegOhm tests, unless it was a piece of equipment or Shorepower cables, which only the E1 did, because if he screwed up, he was the only one answering to the higher ups.

And there sir you show your total lack of understanding of electrical testing and safe wiring practices.

With the implementation of AFCI breakers insulation resistance testing will become the norm.

I

 

[ddawg16]

I like using resistance to test ckt's....especially new ckt's.

You can do it without power...

And it's a fast way to 'measure' the health of a line.

 

[Know A Little]

I like using resistance to test ckt's....especially new ckt's.

You can do it without power...

And it's a fast way to 'measure' the health of a line.

Or you could wait for it to go bang

 

[ddawg16]

Or you could wait for it to go bang

I don't like 'bangs'......especially in my direction

 

[pdxoregon]

And if you have an old school Biddle megger a great way to build up muscles in one arm. :wink2:

 

[AllanJ]

You can do it without power.

You must turn off power before doing resistance/continuity checks, otherwise you will blow out the meter.

 

[Know A Little]

You must turn off power before doing resistance/continuity checks, otherwise you will blow out the meter.

Is that a helpful hint or based on experience?:surprise:

 

[ddawg16]

You must turn off power before doing resistance/continuity checks, otherwise you will blow out the meter.

Unless you have a Fluke....