Motor rating and circuit

[Scott Rychnovsky]

I have a new (old) tool that has a 20.5-21.5 A 205-230 V motor. It is a continuous duty motor with a nominal 5 hp rating. I assume it need to be plugged into a 30 A 230 V plug rather than the 20 A, 230 V plug I currently have in my workshop?

If I want to try it on the 20 A circuit just to see if it runs, will that damage anything besides throwing the circuit breaker?

Yeah, I need to get an electrician out here to install more power.

Ironically, it has dual pulley drive using 4L pulleys, which are rated for sub-horsepower. I should probably switch them out to A-belts.

Scott

[John McClanahan]

Yes, you will want it on a 30 amp breaker, but it won't hurt anything to test it on a 20 amp breaker.

The power ratings for 4L belts must be from many years ago, with belt manufacturing of the time. From what I remember reading, 1 belt for each 1.5 HP now.


John

[Rod Sheridan]

Scott, is this a commercial or home application?

If the motor will start on the 20 ampere circuit, I would run it that way.

In a home shop your machine will never run at rated load, and if it does it will be for a very short period of time.

For example my 4HP machines rated at 16 amperes are running from a 15 ampere branch circuit..................Regards, Rod.

[Barry Mabery]

Is the motor single phase or 3 phase? Generally, a FLA of 21.5 at 230V would indicate single phase. Remember that the circuit breaker protects the wire, not the device (motor, whatever). A 30 amp circuit, derated 75% is 22.5 amps, so your 5HP motor would be the only device that could / should run on that circuit.

[Scott Rychnovsky]

It is a home application and I do not anticipate putting the motor under much load. It is running a planer that is often equipped with a 2 HP motor, so 5 HP is overkill. I will probably have en electrician install 30 A circuit that I will use with one machine at a time--so I should not overload that circuit. I could downgrade the product with a 3 HP motor, but it probably makes more sense to get more power in my workplace for future tools. :-)

[Keith Hankins]

Ok, 5hp 30A requires 30A rated electric resources. This inlcudes a 30A Plug receptacle, and breaker. Failure to do so will heat that wire and potentially burn your house down.

Now to see if it runs if at 20+A continuous that means it will be significantly higher on start. I'd bet even if the plug worked which it should not as a 20A 220v plug will be diff from a 30A rated one and won't fit. If you wanted to test it, I'd get a length of flex cable and plug it into your dryer outlet. \

If she runs pull the appropriate 10AWG wire and 30A plug/receptacle/breaker.

Good luck, and nothing like an old tool!

[Rod Sheridan]

Ok, 5hp 30A requires 30A rated electric resources. This inlcudes a 30A Plug receptacle, and breaker. Failure to do so will heat that wire and potentially burn your house down.

Now to see if it runs if at 20+A continuous that means it will be significantly higher on start. I'd bet even if the plug worked which it should not as a 20A 220v plug will be diff from a 30A rated one and won't fit. If you wanted to test it, I'd get a length of flex cable and plug it into your dryer outlet.

If she runs pull the appropriate 10AWG wire and 30A plug/receptacle/breaker.

Good luck, and nothing like an old tool!

Incorrect, the motor will only draw enough current to produce as much power as the planer is using.

The OP indicated that the machine is often equiped with a 2 HP motor, in a home shop the planer won't be using a 5 HP motor to full capacity, 2 HP is more than adequate......Rod.

[Rod Sheridan]

Scott, you won't be overloading a 20 ampere circuit with that planer.

As you indicated they also come with a 2 HP motor.

If it starts, don't bother wasting your time on the wiring upgrade, your current consumption is unlikely to be more than 10 or 12 amperes when planing............Rod.

[John McClanahan]

It may start most of the time on a 20 amp circuit, but it may have nuisance tripping at startup from time to time on 20 amps.


John

[Keith Hankins]

Incorrect, the motor will only draw enough current to produce as much power as the planer is using.

The OP indicated that the machine is often equiped with a 2 HP motor, in a home shop the planer won't be using a 5 HP motor to full capacity, 2 HP is more than adequate......Rod.

Sorry, I must have miss read the initial post. I thought it said it was a 5hp 220v motor with a continuous rating of 21+ amps. It that were the case then I would be correct to have the 10awg/30A rated plugs, receptacles, and breakers. A 2hp rated 220 motor would indeed be fine on a 20A breaker. It is important to have the appropriate rated wiring.

[Wade Lippman]

My prediction is that it would run fine if you could get it started, but you will never get it started.
A few years back I saw a Youtube about a maniac who starts his TS with a broomstick. That might work.

[Rick Fisher]

A 5hp planer can easily draw 5hp or more if you let the cutterhead become too dull .. I have seen this in person.

Its a simple process. Take a steak knife, set it on some cheese .. Then place weight on your hand ... heavier and heavier, until the sharp edge cuts through the cheese ..

Then repeat with the knife upside down.. Dull side down ..

I think the biggest risk is with Helical cutterheads.. They can be blunt dull and still leave a decent finish .. A straight knife will tell you its dull much faster..

[Scott Rychnovsky]

The discussion has been interesting. I just want to spin up the cutter (no planing) to be sure everything is working. I agree that the start-up current is the main problem and may trigger the breaker.

The actual planer is a 12" Powermatic 100 with a 3" cutter head. I would be happy with a 3 HP motor, but it was retrofitted with a 5 HP motor (with a maximum draw of 21.5 A--does that make it a 4 HP motor in real life?) I think the only way I could bog it down with a 5 HP motor would be planing old railroad ties. The motor is rated close to a 20 A load, which makes me want to cheat, but it is also a good excuse to power up the garage.

If I do try it on a 20 A circuit, I will let you know the result.

Scott

[Rick Fisher]

I really don't believe the start up current with be an issue.. I would set the magnetic starter to say 19 amps if you can .. call it a day ..

[Mark Walden]

If you have a shop tool that is 110v or 220 the only advantage is you can use smaller wire on the 220v. Some think you will use less electricity or have more power, that is not true.
If you have a 20 amp circuit on 110v you have a hot, neutral, and ground so you have all 20 amps through the hot and neutral. If you have a 220v 20amp you have 2 hot wires a neutral and a ground. So you have 10amps on each hot wire not 20. So all you need is 12/3 wire with ground and a 30amp breaker. Take this from a guy who wired his shop with 10/3 and found out he didn't need it.
Mark Walden