Anybody use voltage drop across a breaker, switch, etc. in troubleshooting or PM?

In one of Fluke's Application Notes it mentions a voltage drop of more than 100mv across a breaker being max. I've found simple 120V single pole light switches that are or were over 100mv. One that I replaced dropped well below the 100mv level.

I have one that is near 400mv that I haven't replaced yet. Even used a IR imager on it. It was a bit warm but not eecessive.

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Bill

Hey Bill,

I have not used the method you mentioned, simply due to not have a specific application at this time. I am visiting all of our switching offices at this time to log with the 435 and perform thermal audits with the Ti25. I did notice yesterday that a breaker was about 20 degrees above ambient. The load will be the same as adjacent breakers, but this was the only one with the temperature difference.

After I have visited all of the sites, I am going to sort through the data and make a punch list of what I feel needs attention. Other than verifying solid connections, the voltage drop across the breaker will be the next step.

Tom

Tom:

I had a post somewhere here where I replaced a double pole 30A breaker on a water heater that was dropping around 150mv. As I remember the new one dropped below 50mv.

I had another post about a overload on a dehumidifier compressor that drew around 6A and was dropping 3.2V which caused it to just keep turning ON/OFF. The output side of the OL had melted insulation on the wires.

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Bill

Hey Bill, I remember those 2 posts. I have not used the voltage drop method yet, I have been keeping an eye on the temperatures using the Fluke 568 IR. And we have been tracking the current loads on the breakers, lots of nuscents tripping. We have many older circuits that were not designed for the loading that PC's and large cooling fans put on them. A coule of weeks ago, We had fault tripping on a GFI 2000 ampere breaker, we could not find the issue. We had a High Voltage Tech. come out and find the GFI fault was coming from the local utility. They found after 2 days of false tripping.

I finally got around to replacing that light switch that was dropping 400mv across it. So the new switch is only dropping 35mv.

Ah! The old switch I discovered is a old mercury type soft switch. Now the question is does a mercury switch ever wear out or are they because of their nature drop more voltage across them?? A mecury switch has been illegal to sell for many years, so not like I can compare to a new one.

An IR image after the change only shows 3-5F cooler temperature.

EDIT:
Can't find anything that states that this type of mercury switch is illegal for sale!

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Bill

My thoughts on the subject is that I was under the impression that the VD was an issue of the electronics in a breaker, not in the stabs on contacts themselves.

What electronics in a breaker??? I never took one apart!

I had a overload on the compressor in my dehumidifier that was dropping 3.2V as I remember. Nothing inside but a bi-metalic disc that flexed when it gets too warm.

Voltage drop can be used to measure the quality of any connection/termination.

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Bill

"Voltage drop can be used to measure the quality of any connection/termination."


Understood, just never utilized that method for checking terminations.

I have to say that I never did either in electronics/electrical work but it's very common check of battery cable connection quality on automobiles.

In electrical work it's more of a quality test than operational test. A breaker, fuse, switch, etc. that you know is working, a voltage drop test will tell how good. The catch is what's good and what's bad or passable? Any voltage drop will cause some heat.

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Bill

I remember you telling me about being able to also use the RELATIVE feature in V mode, and thought to myself,...."Well, ...I don't know." I also remember thinking,..."Never done it before now."


Hi Res V mode with RELATIVE function. I have 'sum tinkering to do. I use REL all the time on benchtop meters, never used in measuring voltage with a handheld.

Men and their toys