Breaker causes 40V drop with no load?

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jaggedben

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Northern California
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Solar and Energy Storage Installer
This is a puzzler to me...

A solar system of ours wasn't working because the inverters were not seeing the correct voltage (240V nominal). We sent a guy out and he measured at the terminals of the breaker. One leg was 120V to ground and the other was 80V to ground. L-L voltage was under 200. Voltage in the rest of the panelboard was fine, so he replaced the breaker, and all was well.

Also, inverters had a data connection through the good leg and they record around 25V L-L before the breaker was fixed.

Okay, bad breaker, problem solved. But I want to understand how a voltage drop could show up with no load in this situation, and why the inverters would record a different voltage than a Fluke. Any thoughts?
 
I doubt that it was really a voltage drop. I would expect that the voltage readings were taken with a high impedance meter and the breaker had one open and one closed contact.
 
I have seen a 2 pole GE 60 amp with reduced voltage on one leg.
Have seen FPE 2 pole 100 with reduced voltage on one leg.
An 1 pole 20 amp Square D , QO series with just 60 volts going through it.
All of these were new breakers.
 
JDB3 said:
I have seen a 2 pole GE 60 amp with reduced voltage on one leg.
Have seen FPE 2 pole 100 with reduced voltage on one leg.
An 1 pole 20 amp Square D , QO series with just 60 volts going through it.
All of these were new breakers.
Click to expand...
With or without a load?
 
I saw a bad batch of 2 pole, 30 amp, SQ D NQOB. No load voltage on a new install only dropped five or so volts. It would not make solid with repeated closings. I was doing a lot of them at the time and pulled out at least 20 same that were .5 million ohms closed contact resistance.

Testing it with the customer's load was unthinkable.
 
__dan said:
I saw a bad batch of 2 pole, 30 amp, SQ D NQOB. No load voltage on a new install only dropped five or so volts. It would not make solid with repeated closings. I was doing a lot of them at the time and pulled out at least 20 same that were .5 million ohms closed contact resistance.

Testing it with the customer's load was unthinkable.
Click to expand...
I like to use my heat gun. An old baseboard heater works pretty good too. Sometimes all you need is a 100W light bulb.
 
ActionDave said:
I like to use my heat gun. An old baseboard heater works pretty good too. Sometimes all you need is a 100W light bulb.
Click to expand...

IT load in the data center, live power no load tie in test. Bad breakers should be none. Let's say you exercise the breaker and get the voltage drop close to zero but it fails later. If the customer would find out you detected this problem but let it slip by, honesty would not be the best policy.

Yesterday's job, load tested with an ancient corroded 480 volt heater, simulated a ground fault connecting the 277 v line to the equipment ground through the heater. Three sites in the mine were all 3 phase 480 ungrounded (3 phase 3 conductor) but somehow it had passed previous annual mine grounding surveys. One site the fourth conductor was run to the top if the pole but not brought down the riser. I connected it but half of the path was triplex and the other half corroded EMT EGC.

Load test passed, cold resistance 28 ohms, it powered at 12.3 amps and dropped 4 volts total. It came up 4 volts from an isolated test ground rod, but would have come up the full 277 volts before I connected the EGC in the triplex.
 
__dan said:
IT load in the data center, live power no load tie in test. Bad breakers should be none. Let's say you exercise the breaker and get the voltage drop close to zero but it fails later. If the customer would find out you detected this problem but let it slip by, honesty would not be the best policy.

Yesterday's job, load tested with an ancient corroded 480 volt heater, simulated a ground fault connecting the 277 v line to the equipment ground through the heater. Three sites in the mine were all 3 phase 480 ungrounded (3 phase 3 conductor) but somehow it had passed previous annual mine grounding surveys. One site the fourth conductor was run to the top if the pole but not brought down the riser. I connected it but half of the path was triplex and the other half corroded EMT EGC.

Load test passed, cold resistance 28 ohms, it powered at 12.3 amps and dropped 4 volts total. It came up 4 volts from an isolated test ground rod, but would have come up the full 277 volts before I connected the EGC in the triplex.
Click to expand...
Ohhh. That's a little more involved.
 
JDB3 said:
I have seen a 2 pole GE 60 amp with reduced voltage on one leg.
Have seen FPE 2 pole 100 with reduced voltage on one leg.
An 1 pole 20 amp Square D , QO series with just 60 volts going through it.
All of these were new breakers.
Click to expand...

This would have to be with no load, if not that breaker would melt down.
 
don_resqcapt19 said:
With or without a load?
Click to expand...

Best I recall, it was with a load. The 2 pole GE breaker was when the A/C guy was trying to start up an A/C for the first time. That was my first experience when he pulled out his "Amprobe" (the old black one with the needle & numbers) back in the mid 70's!
After that, in the late 70's (perhaps).
 
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