SPD & N/G Bond

[George Stolz]

I have noticed in two different buildings now, that when I check for resistance between neutral and ground using the audible setting on my DMM, it rings intermittently. As in enough conductance to ring for a second, then the resistance increases for a second quieting the meter, and so on.

Is it safe to say that this is normal with a TVSS or SPD in the system?

 

[petersonra]

I have noticed in two different buildings now, that when I check for resistance between neutral and ground using the audible setting on my DMM, it rings intermittently. As in enough conductance to ring for a second, then the resistance increases for a second quieting the meter, and so on.

Is it safe to say that this is normal with a TVSS or SPD in the system?

there should always be a dead short between N and G.

 

[SG-1]

I do not know what meter you are using George, but some meters will react this way when voltage is present.

 

[George Stolz]

http://www.milwaukeetool.com/test-and-measurement/fork-meter/2205-20

What do you mean by "voltage present"? I am testing between neutral and ground, there is negligible voltage between them.

Bob, what would you suspect with the reading I observe?

 

[iwire]

What do you mean by "voltage present"? I am testing between neutral and ground, there is negligible voltage between them.

4 or 5 volts would not be that odd (depending on distance from bond point) and with my Fluke if AC voltage is present when I do an audible continuity check the tone 'wobbles' at a rate I assume to be 60hz.

Did you check the resistance on the ohm scale?

 

[SG-1]

George, I have a Fluke T-5 1000. It has a continuity/ohm setting. I measured the meters output current that it uses to determine continuity/ohms, at 0.5 mA DC. Now suppose a small AC signal is "present", it could over power the meters own signal adding to it during half the cycle & bucking it during the other half. Which is one reason the instructions say:

To reduce the risk of electric shock for
Resistance, Continuity, and Capacitance
measurements, never use the meter on an
energized circuit.

In most modern meters these functions are protected against a voltage, but voltage could cause the reading to be in error. Next time you are using this feature, check for voltage between the N-G to determine the threshold that causes the buzzer to become intermittent.

Your continuity mode buzzes for 30 ohms or less. Too bad these things are not adjustable. I would be more inclinded to use the ohm scale to measure the N-G bond. If any AC voltage is present at all the ohm reading will probably be unstable.



Steve

 

[George Stolz]

Yeah, that's probably it. It's odd though, because the main reason I detect it is because GFIs tend to go unmarked during rough-in, and the easiest way to find the line is to find a cable with N-G continuity. In that case, there are no energized circuits in the unit, save for a temp GFI that usually is unused while we are in there.

No current flow, the voltage between neutral and ground should be zero, which blows that hypothesis.

However, I'm pretty sure I've tested from N-G at the service and haven't detected the oddity, so it's probably the case. I guess the one thing that has changed in the past couple years is the meter, so it must be the meter malfunctioning causing the odd readings.

Bob, I haven't tested for voltage, but I will Tuesday. The ohm readings are too variable to give a number. The audible fluctuation doesn't sound like 60hz, sounds like 1hz.

 

[chris kennedy]

Low batteries?

 

[Smart $]

...

Bob, I haven't tested for voltage, but I will Tuesday. The ohm readings are too variable to give a number. The audible fluctuation doesn't sound like 60hz, sounds like 1hz.

Not certain about your model meter or modern dmm's in general, but older portable battery-powered meters used only a low dc voltage for resistance testing (for some reason I'm thinking 1.2 volts but that may have been for a particular model)... and the portion being tested is always supposed to be isolated to get accurate readings. The portion you are testing is not isolated, so any outside voltage will definitely throw accuracy out the window.

As for the tone not fluctuating at 60Hz, I see from the link you provided your meter is digital. Many of these meters take samples then average for a display or tone-threshold value. Depending on the sample rate and averaging method the tone could very easily warble at 1 Hz.

JMO

 

[ptonsparky]

It doesnt souund like you are in the boonies but sometimes electric fencers will cause similar problems. Change to a good meter with an analog type display, and watch the display while on voltage scale.