Need help diagnosing a panel issue.

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Easiest way to check for poor connections which don't appear the to poor is voltage drop across the connection under load. Load the panel up as much as possible and measure line to load on the same pole and see how many millivolts of drop is across the contacts. Measure each side and if one is way more than the other thats your answer.
 
ptonsparky said:
The VD will be different dependent on loads.
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Yes. And it should be pretty small. My wild guess is a few tenths, tops, with a decent load running (like +25A). With a decent load it won't be zero. It can't be, because the bimetallic strip inside the breaker has to heat up to work. And that creates a little voltage drop. Note that the typical DMM is not going to be really great at measuring small voltages like that. But...

mbednarik said:
Measure each side and if one is way more than the other thats your answer.
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In the OPs case, presuming the loose connection was one one side of the main only, you can measure the FOP (voltage drop literally from top to bottom of the main) on each pole of the main breaker. Even if the DMM is not super accurate, it will very likely be able to tell you a good side from a bad side. If one side shows 0.2V and the other shows 2.7V (with mostly same amount of current on each leg), then like the saying goes... "There's your problem".
 
A FLIR camera would help in some of this situations. I know some are expensive but it would sure be nice to open a panel and see the hot spot before ever even touching anything. I went into our integration area last week and they had a small device that plugged into the charging port of one of our engineer's cell phones. He was looking at a thermal image of some power delay circuits we had designed. Really cool device. I have no idea what is was or cost but I may have to look it up.
 
ptonsparky said:
Even the small thermal scanners you buy at the local Big Box store work. Try one. If nothing else it takes the kids temperature from a safe distance. No need to touch the germ carriers.
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I saw a thermometer yesterday on phacebook that showed 98.6F and had crap all over it and it said something like "I'm feeling much better now that my fever has broken." That image came to mind when I read your post. LMAO [/derail]
 
MD Automation said:
Yes. And it should be pretty small. My wild guess is a few tenths, tops, with a decent load running (like +25A). With a decent load it won't be zero. It can't be, because the bimetallic strip inside the breaker has to heat up to work. And that creates a little voltage drop. Note that the typical DMM is not going to be really great at measuring small voltages like that. But...



In the OPs case, presuming the loose connection was one one side of the main only, you can measure the FOP (voltage drop literally from top to bottom of the main) on each pole of the main breaker. Even if the DMM is not super accurate, it will very likely be able to tell you a good side from a bad side. If one side shows 0.2V and the other shows 2.7V (with mostly same amount of current on each leg), then like the saying goes... "There's your problem".
Click to expand...
Just to point out to those that maybe don't realize it. 0.2 volts x 25 amps = 5 watts of heat will be given up through that resistance. may not sound like a lot but the smaller the point where it is focused the hotter that point will be. There are 7 watt pencil type soldering irons to give you an example of what is possible.

Now in your example of .2 drop on one line and 2.7 on the other, 2.7 x 25 amps = 67.5 watts of heat is being given up somewhere between the points of the measurement.
 
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