Electical Question (Amps & Phases)

[Steve Canada]

Sweet! Thanks folks I think I've got all the details.

I'm going to inspect the wiring. Glad now that I only used painted OSB on my walls and took pictures of all the wiring before I covered it up! Downer is that the outlet needed is the furthest from the panel...

[Curt Harms]

the short answer is 5HP needs 10 gauge wire, and a 30A breaker. There really is no way to be legal with 12ga 20A breaker... sure you can do it, and a ton of other bogus wiring stuff that would never be permitted or pass inspection, and it will work just fine until your house burns down

I've got 3 5HP machines that I want soooo much to just run on my existing 20A circuits. After 15 hours with the NEC, there's just no way to do it, unless I just choose to ignore the code and wish it true...
Good luck

Even though the motor data plate specifies 20 amps at 230 volts? I thought manufacturer specs trumped NEC data? As long as the 20 amp breaker was functional, I personally wouldn't have heartburn running a motor spec'd for 20 amps on a 20 amp circuit. Remember, a 3 h.p. Unisaw was spec'd for and would run nicely on a 15 amp. circuit. Also, Canada's requirements may be different from the U.S. and local requirements may be different (more strict) than NEC. The best answer IMO--check with local authorities phrasing in hypothetical terms e.g. Can I? What if I?.

[Dave MacArthur]

... The entire process of determining the right wire gauge and circuit breaker for a 5hp motor, according to the NEC, is laid out. Here's the link for you:
Sizing Wires and circuit breakers for 3HP and 5HP shop motor circuits

... There really is no way to be legal with 12ga 20A breaker... sure you can do it, and a ton of other bogus wiring stuff that would never be permitted or pass inspection, and it will work just fine until your house burns down

Answer is still the same Curtis, if the inspector and local area use the NEC as their basis, and it's rare that this isn't the basis. The NEC trumps the motor nameplate--you START with that nameplate, but the NEC then adds safety factors in for the rest of the system including using the wire itself as a HEAT SINK for everything it's connected to. Both circuit breaker and motor builders rely on you following the NEC and being able to dump heat into the wire, and the wire not getting near-boiling (90C!) and causing component damage. There is a place in the analysis where you look at what the nameplate says will actually flow, but it's really just a check at the end and not usually the driving factor.

Despite everyone WISHING to just read the motor nameplate amps and call it a day, despite that working for most cases and houses NOT burning down, it turns out that there IS an entire section of the NEC for proper circuit wiring calculations for motors, and it is what it is. You should click on the link in my thread and read it I took the time to write the thread EXACTLY because there are people like you and me (most of us I'd bet!) who just don't want to believe this stuff has been calculated and written down, and it's NOT the answer we all want.

Seriously, you can pretty much do anything you want and if it works fine and your house doesn't ever burn down, then you'll have been right. BUT... it's unlikely you'd get a circuit permitted if you flat out tell the inspector "this is a dedicated circuit intended to run this 5HP saw". If you're vague and tell him that it's to run various power tools all of which "are less than 20A load", well, he's probably not going to do the calculation and call you on it. This successful "wool pulling over the eyes" does not make it correct though... it just means someone got away with being vague. Sure folks put in 12ga 20A systems, have a permit, and run their 5HP saws on it. I drive 10mph over the speed limit all the time too, and don't get stopped, and "it works", but I'm not going to then claim the real speed limit is 75mph, and I'm not going to tell a person new to driving, "Hey, the real speed limit is 75."

I've got my 5HP saw stop plugged into a 20A circuit right now, and while it's idling at 4A, or slicing up plywood at 7A, or slicing 5/4 hardwood at 8A, for 1 minute at a time, it's doing just fine... I'm pretty sure it would forever. But I know the "right answer", and I know the risk, and I've made that temp decision for myself--and I know I won't have a leg to stand on if I try to get it permitted or I had to deal with an insurance investigator after a fire. So I'll be running a new 10ga 30A circuit real soon...

Hope that helps, it's heinously complex and painful, which is why I try to post to help others in this area when I can.
Dave