I have a customer who has a 20 amp receptacle on a dedicated circuit. When he plugs his miter saw(15amp draw) in directly into the outlet, it will trip the breaker when he uses it. But if he plugs the saw into the SAME outlet using a 50 foot extension cord the breaker holds. Anybody have a suggestion why this happens???
breaker tripping
- Thread starter otm126
- Start date
- Status
- Location
- Massachusetts
Re: breaker tripping
The voltage drop provided by the extension cord is allowing a "softer" start of the motor.
Just my wild guess.
The voltage drop provided by the extension cord is allowing a "softer" start of the motor.
Just my wild guess.
- Location
- Illinois
- Occupation
- retired electrician
Re: breaker tripping
The impedance of the extra length is limiting the inrush current enough so that the breaker does not trip.
Don
[ January 15, 2004, 05:43 PM: Message edited by: don_resqcapt19 ]
The impedance of the extra length is limiting the inrush current enough so that the breaker does not trip.
Don
[ January 15, 2004, 05:43 PM: Message edited by: don_resqcapt19 ]
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: breaker tripping
All the above + a weak breaker. a 15 amp miter saw should not trip a 20 amp breaker. unless there is alot of saw dust built up in the motor that is causing it to bog down.
All the above + a weak breaker. a 15 amp miter saw should not trip a 20 amp breaker. unless there is alot of saw dust built up in the motor that is causing it to bog down.
Re: breaker tripping
Assumong that the breaker is tripping instantaneously the impedence answer with regard to the extention cord makes sence. However, it may be masking a problem with the breaker. Being a non-continuous load that saw should be able to be used on a 15a circuit. I would plug the saw in to a 15a circuit to see if he still gets a trip. Since the magnetic/instantaneous pickup of both the 15 and 20a breakers most likely are the same if it doesn't trip the 15a breaker then the 20a breaker may have a mag. trip pickup that is on the low side something of which would never be detected with normal applications.
I also understand SqD does have a higher Mag. QO120HM available where higher inrushes are a problem and other manufacturers have them such as the C-H with the a CH120HM breaker.
Assumong that the breaker is tripping instantaneously the impedence answer with regard to the extention cord makes sence. However, it may be masking a problem with the breaker. Being a non-continuous load that saw should be able to be used on a 15a circuit. I would plug the saw in to a 15a circuit to see if he still gets a trip. Since the magnetic/instantaneous pickup of both the 15 and 20a breakers most likely are the same if it doesn't trip the 15a breaker then the 20a breaker may have a mag. trip pickup that is on the low side something of which would never be detected with normal applications.
I also understand SqD does have a higher Mag. QO120HM available where higher inrushes are a problem and other manufacturers have them such as the C-H with the a CH120HM breaker.
- Status