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+-- Thread: Why do you need a 30 amp breaker on a planer with a 15 amp motor? (/showthread.php?tid=7226220)
Why do you need a 30 amp breaker on a planer with a 15 amp motor? - Billbo - 02-22-2016
I'm thinking about getting the Powermatic 15HH planer.
The online manual it says it has a 1 phase, 230 volt, 15 amp, 3 HP fan enclosed motor. But the recommended circuit breaker is 30 amps. I thought the standard formula for breakers was 1.25 X Load (1.25 x 15 amps) which would be 18.75 amps. If so, then a 20 amp breaker/circuit should be O.K.
I currently have a 20 amp 240 volt circuit available in my shop and although I can put in a 30 amp circuit, it would be a LOT of work I'd rather avoid if a 20 amp breaker would do the job.
Any advice/enlightenment on this subject would be appreciated.
Billbor
Smyrna, GA
Re: Why do you need a 30 amp breaker on a planer with a 15 amp motor? - TDKPE - 02-22-2016
The standard formula you're referring to is for the minimum sizing of conductors for a single-motor circuit. The higher ampacity circuit is to protect against nuisance trips on motor start-up, not because it's needed for normal running. Starting (locked-rotor) current is typically 4-8 times the full-load current (FLA) as indicated on the motor's nameplate, and can be determined from the "Code" or "kVA Code" letter on the nameplate - it translates to a multiplier on FLA at the voltage it's configured for, and is likely to be close to 100A.
Modern circuit breakers will trip on either a small overcurrent for a long period of time, or a larger overcurrent for a shorter period of time (inverse-time), and they will operate essentially instantaneously at some even higher current threshold, which is typically 6-10 times their rated ampacity, depending on ampacity, manufacturer, and even the individual breaker, as there is a bit of a tolerance on those parameters.
There's a good chance it will start just fine on a 20A circuit. If it nuisance trips, there are remedies, like a high-magnetic breaker (has a higher threshold for the instant-trip current), and others that aren't worth going into unless and until you can't make it work.
Re: Why do you need a 30 amp breaker on a planer with a 15 amp motor? - Billbo - 02-22-2016
Thanks Tom.
Re: Why do you need a 30 amp breaker on a planer with a 15 amp motor? - BrentDH - 02-22-2016
I have that planer on a 20A breaker - have not had any problems.
Re: Why do you need a 30 amp breaker on a planer with a 15 amp motor? - BobW - 02-22-2016
^^^ Me too!
Re: Why do you need a 30 amp breaker on a planer with a 15 amp motor? - Aram - 02-22-2016
BobW said:
^^^ Me too!
Same deal. No issues.
Re: Why do you need a 30 amp breaker on a planer with a 15 amp motor? - Billbo - 02-23-2016
BrentDH and Aram - thanks for the feedback/inputs.
We've got an anniversary coming up and the Mrs. will be speechless when I tell her I got her a new Powermatic 15HH for out anniversary!
Billbor
Smyrna, GA
Re: Why do you need a 30 amp breaker on a planer with a 15 amp motor? - pprobus - 02-23-2016
Billbo said:
BrentDH and Aram - thanks for the feedback/inputs.
We've got an anniversary coming up and the Mrs. will be speechless when I tell her I got her a new Powermatic 15HH for out anniversary!
Billbor
Smyrna, GA
In that case, you might want to still go ahead and put in that 30 amp line so that you can have heat while you're sleeping out in the shop.
Paul
Re: Why do you need a 30 amp breaker on a planer with a 15 amp motor? - Curlycherry - 02-23-2016
BobW said:
^^^ Me too!
Mine is a 3Hp Grizzly on a 20 Amp breaker and it too runs just fine.
Re: Why do you need a 30 amp breaker on a planer with a 15 amp motor? - TDKPE - 02-23-2016
Aram said:Same deal. No issues.
[blockquote]BobW said:
^^^ Me too!
[/blockquote]I've noticed that Powermatic pretty much always recommends 30A 240V circuits for their 3 hp machines, and I've also noticed (and not just from this thread) that many folks just run them on 20A circuits without problem.
I've run my 3 hp Unisaw (Marathon motor; 12.4 FLA) on a 15A 240V circuit, because I retasked the single basement 15A 120V receptacle circuit to run my saw when I first moved here. Never had a problem, but it's a dual-capacitor motor (which makes a difference in both running and starting current), while PM machines use (or used to use) Baldor motors, which have a higher FLA rating for the same hp rating.
While technically not by the book (12A max for a motor on a 15A circuit), it never tripped. And it now runs on a 20A circuit. And still hasn't tripped on start-up.
