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50 amp CB Resistance

petehowell

Well Known Member
Anybody know what the resistance across the terminals of a 50 amp P&B circuit breaker should be. I'm chasing a voltage drop issue and trying to see if the CB might be at fault.

Thanks!
 
Suggest you measure voltage drop across the breaker for a more accurate determination of it’s resistance.
 
Anybody know what the resistance across the terminals of a 50 amp P&B circuit breaker should be. I'm chasing a voltage drop issue and trying to see if the CB might be at fault.

Thanks!

Don't think you can measure it with a normal multimeter.

I guess it should be well less than 0.01 ohms (0.5V with 50 amps going though it). I could well be wrong.
Edit:
https://www.mouser.com/catalog/english/101/apac/1794.pdf

so 0.002 ohms for 50 Amp breaker or 0.1 volts over the breaker with 50 amps flowing through it or 0.02 volts with a 10 amp load.


Finn
 
Last edited:
Max 0.002 ohms +/-30% (from the attached datasheet).
 

Attachments

  • W23-W31 breakers.pdf
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Tracing fault

Measuring resistance across a contactor is always a bit problematic especially if the contactor is new with a modern multimeter as they do not have enough drive. An old fashioned AVO moving coil multimeter is far better.
If you have a volt drop you should be able to measure it across the contactor terminals when the contact is closed.
One other method is to switch everything on and leave it for 10 minutes then trace the wiring connections with your hand to see if you have a hot joint as a poor joint will generate heat from the joint resistance.
Also wiggle the wiring at each joint whilst monitoring the voltage.

Good luck on the hunt.

Rob
 
Anybody know what the resistance across the terminals of a 50 amp P&B circuit breaker should be. I'm chasing a voltage drop issue and trying to see if the CB might be at fault.

Thanks!

Be sure to measure resistance at the terminal attach points (one probe on terminal and other on CB lug), as they are also potential resistance points. The screw types can loosen and some faston's can also be loose if they weren't crimped enough at the factory or taken on and off too many times.

Larry
 
I'm more in Walt's camp here. A resistance check could indicate a gross discrepancy within the breaker; but, something else would be difficult to detect with a mA flow from a multi-meter.

I would suggest troubleshooting this like a slow cranking issue. Put the suspected circuit under load (more is better, knowing the amp load even better) Keeping a common reference (neg battery term), measure volt potential at various. progressive points along said circuit. When you find a big delta V, that is the connection/device/lead that needs further attention. Let us know what you find.
 
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