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Old 03-02-2008, 02:52 PM   #1
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Question Hot Breaker

Just got a call from our on-call AC tech and I was helping him troubleshoot a hot breaker over the phone and have question about what some of you guys might think?

The condensor is drawing 17A under full load, the breakers above and below the one in question are cold to the touch, I had him check for loose and high resistive connections and discolored bus bars. It seems like a bad breaker but they just don't heat up for no appearent reason, I can usually find something. The breaker is a Cutler Hammer CH230 (2P 30A). When he took the cover off the panel it cooled down and didn't trip anymore. I don't know if the panel is flush or surface mounted I didn't think to ask. He also didn't have a camera to take pictures of what the panel looked like inside and surrounding environment. Monday I'm giving him a new breaker to put in, since I'm already slated for another job (Daytona Bikeweek ).

Any ideas I can I give him to check-out?

I wanted to go to the job but the customer didn't want to pay for me to come out, now I'm curious.

Thanx,

Greg

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Old 03-02-2008, 02:59 PM   #2
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Sounds like a faulty breaker from the factory to me. I'd replace it especially if the load was only 17A and it was tripping.

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Old 03-02-2008, 04:29 PM   #3
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Originally Posted by dowmace View Post
Sounds like a faulty breaker from the factory to me. I'd replace it especially if the load was only 17A and it was tripping.
What he said.

A 2P CH is cheap enough and easy enough to change out.
(It's also common enough to be a truck stock item too)
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Old 03-02-2008, 04:48 PM   #4
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Quote:
Originally Posted by Greg View Post
Just got a call from our on-call AC tech and I was helping him troubleshoot a hot breaker over the phone and have question about what some of you guys might think?

I wanted to go to the job but the customer didn't want to pay for me to come out, now I'm curious.
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Old 03-02-2008, 06:39 PM   #5
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Sure sounds like a bad connection. Is your guy sure the load side isn't AL wire?
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Old 03-02-2008, 06:45 PM   #6
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Did anyone think to put an IR camera or thermometer on it?
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Old 03-02-2008, 06:51 PM   #7
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I have the thermometer and we don not have an IR. I do keep an assortment of CH breakers on my service van but the guy didn't want to pay. Also I'm the on call sparky this week, so I had no problems going out and making overtime.
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Old 03-02-2008, 08:28 PM   #8
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Type ch breakers are pretty reliable , check the connections ahead of the panel especally the meter socket.
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Old 03-02-2008, 08:37 PM   #9
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Type ch breakers are pretty reliable , check the connections ahead of the panel especally the meter socket.
Educate me, how do meter socket connections affect 1 breaker? Also this was a commercial building so no telling how many panels it has.
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Old 03-02-2008, 08:56 PM   #10
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Did he perform a FOP (Fall of Potential) test, this will show if it is the CB the Cb to bu connection? In either case the CB replacement is warranted.


While replacement will happen a good tech should know why he is replacing a device.

Fall of Potential test (FOP)

With any electrical procedures that involve making measurements with energized conductors care must be taken and proper PPE must be worn

Fall of potential is a measurement of voltage drop (VD), in a circuit that is the voltage lost to heating due to resistance in the circuit. To perform this test one measures voltage from the line side connections to the load side connections, the readings are typically in the millivolts range and require load.

For example with a 3-phase Circuit Breaker that is nuisance tripping, measure current (balance loads are beneficial but not necessary), then measure from the line bus to the load conductors (if bare conductor is exposed), for all three phases. If one phase has a higher that average millivolts reading, then try to isolate this issue. Measure from line bus to the Circuit Breaker bus stab, if all 3-phases have millivolts readings that are the same (or close to the same) measure from the bus stab to the load side conductor termination connector (through the Circuit Breaker), if all these readings are close, next take measurements from the load side termination connector to the load conductor. In this case you can determine if it is a line bus connection issue, bad Circuit Breaker or a load conductor termination issue. Any accessible portion of the device can be tested in this method.
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Old 03-02-2008, 10:13 PM   #11
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Voltage drop should be measured anytime nuisance tripping or heating is noticed, but it is sort of meaningless without some standard and I know of none. Does anybody know of any sort of manufactures' specification for voltage drop across a breaker at some level of amps?
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Old 03-02-2008, 11:04 PM   #12
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Check all connections, at the equipment aswell.
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Old 03-03-2008, 10:52 AM   #13
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Quote:
Voltage drop should be measured anytime nuisance tripping or heating is noticed, but it is sort of meaningless without some standard and I know of none. Does anybody know of any sort of manufactures' specification for voltage drop across a breaker at some level of amps?
The readings are more than meaningless, THIS IS A STANDARD TEST IN BREAKER ACCEPTANCE TESTING, though we utilize a test set, DLRO/Ductor/Micro0ohm meter. It is the same theory.

1st Ohms law.
2nd Comparison readings.
3rd Read the above post, it gives some insight to readings.
4th After doing this for a while you can come up with a understanding of what is acceptable.
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Old 03-03-2008, 06:09 PM   #14
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The breaker was changed changed out and I'm assumiong all is well. I printed a copy of the test procedure and gave it to the tech showed him how to do it on a panel on the shelf, haven't heard what the results are yet. Hopefully tomorrow I'll know something.
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Old 03-03-2008, 07:35 PM   #15
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Read the above post? Any voltage drop measured MUST be measured under load, else no voltage drop. So, how much load?

And, any voltage drop measured will probably be in millivolts, so how many millivolts are acceptable? 17 amps producing a .022 volt drop (22 millivolts) is generating about 374 milliwatts. How many watts are too many?
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Old 03-03-2008, 09:03 PM   #16
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Quote:
How many watts are too many
First we are not measuring watts we are measuring FOP FALL OF POTENTIAL/ voltage drop, and yes it is assumed a knowledgeable electrician knows there is NO voltage drop if there is no load.

So (assuming) you have experience with performing this test and therefore have some references, or you can do comparison readings between similar CB's, WITH LOAD. If one has 22 Milli-volts and one had 50 millivolts, the technician is to isolate the VD, is it at the load connection, across the CB or at the CB to line bus. This allows one to understand the problem not just be a parts swapper.


By you thought process why spend money on IR, how much heat is too much heat? through training and understanding it is possible for electricians to improve their understanding of their cjhosen profession.
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Old 03-04-2008, 12:01 AM   #17
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I don't understand if the work is not worth anything to the customer why are you paying for it?
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Old 03-04-2008, 01:12 AM   #18
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Is the wiring copper or al. ?
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Old 03-04-2008, 07:33 PM   #19
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Okay the new breaker is holding. The tech didn't perform the FOP test so no data there. What do you expect for an A/C tech. The wiring was copper, I did find that much out.

Quote:
Read the above post? Any voltage drop measured MUST be measured under load, else no voltage drop. So, how much load?
I'm not sure if that was directed at me but the panel on the shelf was to show the tech where to put the test leads.
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Old 02-13-2009, 09:04 PM   #20
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Brian John ,Thanks for your FOP tip.

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