Help with wiring size for 2 post lift?

[Dr_Pippin]

Had a plan for wiring up my 2 post, but a friend just pointed out I might consider a change. My original plan was 10 gauge NM-b for the motor and 12 gauge NM-b for a 20 amp circuit mounted on the post. I finally looked at the motor plate and saw it’s a 3hp motor. A friend suggested instead wiring the motor to the 12 gauge and instead using the 10 gauge for a welder outlet. Going to the ol’ google and searching the wiring requirement for a 3hp motor, I’ve found about five different “definitive” answers on other forums. Can someone give me a sixth definitive answer on if I can run my lift motor on 12/2 Romex with a 20 amp breaker? I feel like this motor plate is missing information.

 

[ratflinger]

Found it. Bucher lists it as a 2.2kw unit, so at 240v you'll pull just under 10a. I'd use 12ga, but that's me.

 

[Dr_Pippin]

Difficult to say since they didn't bother to spec the amp load. A lift motor from Derek Weaver in this size & ETL cert requires a 30a feed. While #10 will handle the amps I believe code says 80%, so you would need #8. You need to go back to the manufacturer and have them provide the amp load so you can size the circuit correctly. Even if it turns out to be only 20a, I'd use #10 only.

Thanks for confirming that not all the necessary info is on the motor plate. This is my first time trying to read a plate, so I didn’t know if I was missing something or if it just wasn’t all there. I’ll call the lift company tomorrow (Advantage).

 

[ratflinger]

Now updated my post.

 

[Dr_Pippin]

Found it. Bucher lists it as a 2.2kw unit, so at 240v you'll pull just under 10a. I'd use 12ga, but that's me.

Thank you for finding and sharing that info. Didn’t occur to me to search for the motor specifically.

I will use 12 ga for the lift, and take my friend’s suggestion of using the 10 ga for a welder outlet. Thank you!

 

[mike93lx]

The NEC requires wiring it based on the nameplate HP rating. A 3hp motor is listed at 17a @ 240v, then you uprate it 125% for wire sizing and get 21a. So that would mean #10 nm-b or #12 thhn in conduit..
The reality is that at a 2.2kw draw, it's not really 3hp, so I expect it would run fine on 12 nm-b, but it's not code compliant



If you want a welder outlet, 10nm-b will work for welders up to about a 50% duty cycle. 12 is good for something like a 35% duty cycle.

 

[Dr_Pippin]

The NEC requires wiring it based on the nameplate HP rating. A 3hp motor is listed at 17a @ 240v, then you uprate it 125% for wire sizing and get 21a. So that would mean #10 nm-b or #12 thhn in conduit..
The reality is that at a 2.2kw draw, it's not really 3hp, so I expect it would run fine on 12 nm-b, but it's not code compliant



If you want a welder outlet, 10nm-b will work for welders up to about a 50% duty cycle. 12 is good for something like a 35% duty cycle.

And this is why I found so many different answers searching online. Thank you. From what you shared, I understand using 12 ga wire for the lift motor doesn’t meet NEC, but seeing as it’ll be the only thing on the circuit and will have very short run times I’m comfortable using 12 ga.

 

[mike93lx]

Make sure you have a disconnect of some sort at the lift. We've seen too many stories of contactors sticking closed and guys unable to shutdown a lift. A 30a dual pole switch is cheap insurance.

 

[TxSteve]

You said it's a 20 amp circuit. 20 amp requires 12 gauge for runs < ~50 ft depending on what's acceptable voltage drop.

I'd use 12/2 and move on. You can use 10 if it will make you feel better - it's only money

 

[Dr_Pippin]

Make sure you have a disconnect of some sort at the lift. We've seen too many stories of contactors sticking closed and guys unable to shutdown a lift. A 30a dual pole switch is cheap insurance.

I’ve got one in hand. Thank you for suggesting.

You said it's a 20 amp circuit. 20 amp requires 12 gauge for runs < ~50 ft depending on what's acceptable voltage drop.

I'd use 12/2 and move on. You can use 10 if it will make you feel better - it's only money

I didn’t know for sure it was a 20 amp circuit. I had to run wires from the sub panel into the attic before I completed drywall, so I ran 10 ga to be sure I was covered no matter what the lift ended up needing. Now I’m considering repurposing that 10 ga for a welder outlet and using the 12 ga for the lift instead of for a 20 amp outlet as I had initially planned. Got a whole bunch of outlets on the wall on the other side of the lift, so don’t know how critical this one would actually be for my regular usage.


And an answer from Advantage Lifts:

Hello,



The motor plate should state the FLA (fully loaded amperage) at 15.9A.

You will need to run a 20A breaker for this.

 

[TxSteve]

I’ve got one in hand. Thank you for suggesting.

I didn’t know for sure it was a 20 amp circuit. I had to run wires from the sub panel into the attic before I completed drywall, so I ran 10 ga to be sure I was covered no matter what the lift ended up needing. Now I’m considering repurposing that 10 ga for a welder outlet and using the 12 ga for the lift instead of for a 20 amp outlet as I had initially planned. Got a whole bunch of outlets on the wall on the other side of the lift, so don’t know how critical this one would actually be for my regular usage.


And an answer from Advantage Lifts:

Sounds like a good plan. Don't waste a 30 amp circuit on a 20 amp draw.

 

[mike93lx]

Following code is hardly a waste

 

[wyliesdiesels]

Found it. Bucher lists it as a 2.2kw unit, so at 240v you'll pull just under 10a. I'd use 12ga, but that's me.

wrong. motor circuit is sized based on HP NOT KW or nameplate amps

3HP requires 21a rated wire so technically #12 NM-b is too small.

 

[wyliesdiesels]

You said it's a 20 amp circuit. 20 amp requires 12 gauge for runs < ~50 ft depending on what's acceptable voltage drop.

I'd use 12/2 and move on. You can use 10 if it will make you feel better - it's only money

the motor is NOT a 20a circuit. thats not even how a motor circuit is sized.

 

[TxSteve]

Following code is hardly a waste

I don't follow. The MFG states a 15.9 amp draw and a 20 amp circuit which requires 12 gauge wire.

 

[mike93lx]

I don't follow. The MFG states a 15.9 amp draw and a 20 amp circuit which requires 12 gauge wire.

That's not how motor circuits are sized under the NEC. The manufacturer is wrong and should stop labeling the motor as 3hp, then

 

[wyliesdiesels]

I don't follow. The MFG states a 15.9 amp draw and a 20 amp circuit which requires 12 gauge wire.

That's not how motor circuits are sized under the NEC. The manufacturer is wrong and should stop labeling the motor as 3hp, then

The NEC FLC table lists 3hp as 17a so a motor with a 15.9a FLA is about right for 3HP.... regardless, if the motor nameplate says 3HP, it needs to be wired with 21a rated wire (17a x 125%)

 

[mike93lx]

The NEC FLC table lists 3hp as 17a so a motor with a 15.9a FLA is about right for 3HP.... regardless, if the motor nameplate says 3HP, it needs to be wired with 21a rated wire (17a x 125%)

You're right, I had the 2.2kw figure in mind from earlier and didn't really think of the 15.9 fla

 

[ratflinger]

@wyliesdiesels - Please explain. The motor is listed on the label as 3hp, but in the pdf I posted the motor is rated at 2.2kw with no mention of HP. If what you say is true (not doubting you) then the motor should be listed as a 4kw. So why the confusion here? Is the motor not really a 3hp or is the rating posted wrong?

 

[mike93lx]

@wyliesdiesels - Please explain. The motor is listed on the label as 3hp, but in the pdf I posted the motor is rated at 2.2kw with no mention of HP. If what you say is true (not doubting you) then the motor should be listed as a 4kw. So why the confusion here? Is the motor not really a 3hp or is the rating posted wrong?

The nameplate matters, a pdf doesnt

 

[TxSteve]

Honest question - I thought the 125% upsizing was for continuous duty use. Is that not right?

I'm surprised the motor plate doesn't have FLA listed...

 

[ratflinger]

The nameplate matters, a pdf doesnt

PDF was from was an official doc from the manufacturer, shouldn't they match?

 

[mike93lx]

PDF was from was an official doc from the manufacturer, shouldn't they match?

No argument there, but we have no control over that

 

[pattenp]

PDF was from was an official doc from the manufacturer, shouldn't they match?

The manufacturer of the lift is not the manufacturer of the motor. The catch is the NEC specifies to use the motor HP if listed on the motor data label to determine supply conductor size. But if the lift manufacturer gives instructions stating required conductor size and overcurrent protection, then that's what you use.

 

[mm08822]

The NEC requires you to size the motor conductors based off a specified amperage listed in table 430.248 found by looking up the stated hp of your motor.

You no longer simply use the motor FLAs from the nameplate.

Once you have the value from the table, add 25% to it to determine wire size.

BTW 1hp = 746watts....2.2kw = 3hp.

 

[pattenp]

Once you have the value from the table, add 25% to it to determine wire size.

I believe the NEC doesn't require the 25% addition if the motor is used in a non continuous application such as a lift.

 

[ratflinger]

The manufacturer of the lift is not the manufacturer of the motor. The catch is the NEC specifies to use the motor HP if listed on the motor data label to determine supply conductor size. But if the lift manufacturer gives instructions stating required conductor size and overcurrent protection, then that's what you use.

The PDF in question was from the motor manufacturer, Bucher Hydraulics. What I don't understand is why a motor rated for 2.2kw requires more power and a larger gauge wire than a 2.2kw load would seem to need. I'm not an electrical engineer.

 

[Metal-Marc]

Following code is hardly a waste

For too many people it is. LoL

 

[mm08822]

I believe the NEC doesn't require the 25% addition if the motor is used in a non continuous application such as a lift.

Agreed. In this case it would be hard to consider it continuous duty. 430.22E allows from 85% to 140% of FLAs depending on motor service rating - which we don't know.

I'd call it good with 12-NM-B. (It's 90C wire anyway. )

 

[TxSteve]

I'd call it good with 12-NM-B. (It's 90C wire anyway. )

And.....we're back where we started. (I would, too)

 

[Norcal]

Honest question - I thought the 125% upsizing was for continuous duty use. Is that not right?

I'm surprised the motor plate doesn't have FLA listed...

To size the circuit conductors you have to use the value listed in NEC article 430 in the table shown in that article for the type motor of being used, plus 125%, NOT the nameplate value. Still out of State until early Friday morning so still don't have access to my code books to make it more specific.

 

[mm08822]

Honest question - I thought the 125% upsizing was for continuous duty use. Is that not right?

I'm surprised the motor plate doesn't have FLA listed...

The footnote in NEC 430.22E states all motors are treated as continuous unless its use meets the exceptions in 430.22E.

Kind of bazzar w/o FLAs on the nameplate. But hey, it's from china.

 

[pattenp]

To size the circuit conductors you have to use the value listed in NEC article 430 in the table shown in that article for the type motor of being used, plus 125%, NOT the nameplate value. Still out of State until early Friday morning so still don't have access to my code books to make it more specific.

I assume you meant times 125%, not plus 125%.

 

[TxSteve]

To size the circuit conductors you have to use the value listed in NEC article 430 in the table shown in that article for the type motor of being used, plus 125%, NOT the nameplate value. Still out of State until early Friday morning so still don't have access to my code books to make it more specific.

I'll be interested in your interpretation based on 430.22(E) Other Than Continuous Duty

 

[beltfeed]

How long is the run for the lift circuit ?

 

[wyliesdiesels]

deleted

 

[600SL]

Make sure you have a disconnect of some sort at the lift. We've seen too many stories of contactors sticking closed and guys unable to shutdown a lift. A 30a dual pole switch is cheap insurance.

Yup, happened to me when my lift was new. Ha sent happened since in 20 years but once was enough.

This is approximately what the switch looks like in the Bend Pak HD9 4 post lift. Hard to believe this thing is rated at 2HP. But it explained a lot.