Magnettica

I had been to this persons house a week ago to repair the "power going on and off." I checked for line and load voltage at the meter and finally at the main breaker. Everything checked out normal and even the connection to the utility at the service head were crimps so I assumed it was on POCO's end. PSEG shows up, they check there connection at the x-former and they even re-crimp the connection at the service head. Everything is working ok.

I specifically asked the HO's if the breakers were ever in the tripped position.

"No, we just did what the poco told us to do, turn the breaker off and then back on again. After that it's fine but it keeps going off."

I go back there again and notice the 150 amp main is a little warm to say the least. Sure enough, these two little screws on the left that attach the MB to the bus were loose. I tighten them, wait around for a few and flirt with the lady for a little while, and the breaker's no longer heating up.

Surprised to see this happen on a Siemens panel since they are made so well.

Magnettica

I'd also like to add.... the first time I was there the breaker wasn't tripped.

Today, while I was there it did trip.

Difficult to find a problem when everything's working.

Bob Badger

This is sarcasm right?

Magnettica

Siemens are well made I thought.

I know they're a part of the Murray family though

B4T

Do we really want a panel to last (30) years without needing any kind of service?

Seems EVERYTHING breaks down in a few years and needs replacement... why should electrical products be any different?

We do make a nice living fixing these things, in case you forget..

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Jlarson

That problem is the type of thing that would have shown up on a FOP test. That's pretty much my MO on a call like that, check the voltage drop across the breaker and the amp draw on each leg before I go and start tightening or looking for other problems that way I know I fixed the problem.

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Bkessler

I agree, the first thing I do on any job is try and get in the panel to do an fop test. Especially because here in socal it's all zinsco and fpe and bulldogs.

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When ls lunch?

Jupe Blue

FOP? Fall of Potential? What kind of test is this and how do you run one?

nolabama

seimens is good stuff in my opinion

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480sparky

Measure voltage across the breaker.

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In winter, why do we try to keep the house as warm as it was in summer when we complained about the heat?

nolabama

quite a useful test

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“Dammit, Smithers, this isn’t rocket science, it’s brain surgery!”

Jlarson

You measure the voltage drop across a contact or breaker. The higher the resistance the higher the voltage drop. The increased resistance is what causes the heat increase. I attached a visual example of how to do the test.

Attached Files

	Doc3.doc (34.0 KB, 71 views)
	FOP.pdf (30.0 KB, 51 views)

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nolabama

why do you use the milliamp setting for this?

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“Dammit, Smithers, this isn’t rocket science, it’s brain surgery!”

Jlarson

Cause I'm an idiot and meant mV not mA.
Ok I fixed it, all good now.

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B4T

I can't open a DOC file..

Anyone have this in a different format?

__________________
There comes a time when people who volunteer their service need to step back and see if it is better for them to retire. A red flag is when they become "cranky" and lose all sense of reality by making decisions that really don't make any sense..

Jlarson

You don't have word? What about a pdf, I just put that option up.
There isn't much to see, I whipped it up in like 5 minutes.

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B4T

I had to save it on desktop and then it opened..

__________________
There comes a time when people who volunteer their service need to step back and see if it is better for them to retire. A red flag is when they become "cranky" and lose all sense of reality by making decisions that really don't make any sense..

Jupe Blue

Could you give me an example of typical values for this type of test and what would they mean? I understand the higher the resistance would cause a breaker to heat up but what are acceptable values?

For example would a 10 mV drop be significant? Or is the critical matter that the breaker feels hot?

B4T

I just did a GOOGLE and this came up.. who knew..

Paging Brian John... FOP test

__________________
There comes a time when people who volunteer their service need to step back and see if it is better for them to retire. A red flag is when they become "cranky" and lose all sense of reality by making decisions that really don't make any sense..

Jlarson

You should see almost 0 mV across a good contact, I reality 10mV or less is ok for most stuff. I just had a 60 amp QO two pole with 15 amps per leg start tripping, I measured a 33mV drop across A phase. The breaker was hot like, 2nd degree burn hot.

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