Motor Sizing and protection help

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Walters

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Berkley County West Virginia
Car lift company installed a new lift and tapped off a circuit sharing other equipment. Lift shuts off at start up because everything is undersized. They installed 12/2 romex, exposed from the motor to a standard none fused disconnect that was sharing other equipment (Tire Machine). Circuit is being feed with #12 copper off a standard GE 20 amp breaker almost 100 feet away. I attached the motor pictures, it does not tell me FLA only max working load amps 24.5 amps.

Off this information I believe I should size the conductors at 125% (30.325 amps) #10 off the 75 Deg.
I believe I should size the breaker at 250% which would be 61.25 amps next fuse size at 70 amps. At start up it showed 65 amps and flashed 80 amps on the wire doing a amp probe.
With the disconnect sharing the other equipment I plan to separate this and let the tire machine have its own 20 amp 2 pole breaker, no disconnect because it has a twist lock plug.

I would like to re-use the standard non fuse disconnect or would I need to install a fused discconet with dual element fuse at 125% (35 amp fuse)

Thanks for reading and your help
 

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Before we even get into voltage drop or the load of the tire machine, this intermittent duty motor has different rules then a continuous duty motor when it comes to selection of conductors and overcurrent/overload protection.

See 430.33(E).

In table 430.33(E) this should fit in the classification driving a pump and says it is a 5 minute duty motor right on the nameplate you provided.

Minimum conductor ampacity to this motor is allowed to be 85% of motor FLC. Since the motor nameplate says 15-18 (I would assume 15 @ 240 volts and 18 @ 208, but lets go with 18 just for worst case scenario) 18 x .85 = 15.3. This motor can be supplied with a 14 AWG conductor.

Then go to 430.33, which allows this motor to be protected from overload by the SC/GF protective device, if it doesn't exceed the that specified in table 430.52 - 175% for time delay fuses and 250% for inverse time breakers.

That motor supplied by 14 AWG conductor can have up to 35 amp time delay fuses or 45 amp inverse time breaker protecting it.

Voltage drop is another issue, but something tells me you have more issues then just voltage drop if you can't start this motor. If the tire machine isn't running at the same time it is not contributing to any problems at that time. Maybe run a temp line to it - possibly even 10 AWG, if it still won't start - there is other problems with the motor itself, but most of these can take a pretty big drop in voltage during starting, it just may cause it to take longer to accelerate to speed is all, and once up to speed current drops and voltage goes back up. I'd be more concerned what that drop does to anything else on the same circuit then how it effects this machine.
 
The shop owner was holding the breaker closed to operate the lift.
I did not spend to much time there, just enough to get some pictures and some information. Tire machine was not on while trying to start the motor for the lift. I also need to verify when I go back that the motor is wired correctly. On the nameplate it says factory wired for 230 volt and the building is 120/208 volt. I was figuring #10 would take the voltage drop also.
so your thinking #10 conductors (safe)
45 amp breaker with Interrupting Rating : 10kA@120V
 
Walters said:
The shop owner was holding the breaker closed to operate the lift.
I did not spend to much time there, just enough to get some pictures and some information. Tire machine was not on while trying to start the motor for the lift. I also need to verify when I go back that the motor is wired correctly. On the nameplate it says factory wired for 230 volt and the building is 120/208 volt. I was figuring #10 would take the voltage drop also.
so your thinking #10 conductors (safe)
45 amp breaker with Interrupting Rating : 10kA@120V
Click to expand...
Breaker should be able to trip whether handle is being held or not.

If this unit is just tripping breaker at start up, you probably just don't have high enough instantaneous trip, but remember NEC says you can go with up to 45 and you only have a 20. However that may not be acceptable with the tire machine to increase the breaker setting if you keep them both on the same circuit though, but maybe try temporarily putting at least a 30 amp breaker in there to see if it allows the motor to start.
 
ok give me a little lesson here if you don't mind? high enough instantaneous trip meaning the 20 amp to a 45 amp breaker correct. I always get confused with the Interrupting Rating of a circuit breaker. The ones in this panel now are all 10K. I remember doing a estimate for roof ice melting last year and I found out I needed to increase the Interrupting Rating of the breaker from a 10K to a 65K I believe. There was a huge increase in the price of the breaker. The higher Interrupting Rating is used for long distance and what exactly if you don't mind?
Thanks again for all your help
 
The interrupting rating has to do with the power company's delivery from the transformer. Distance will lower the AIC however that is not the reason fo the AIC afaik.
 
Walters said:
ok give me a little lesson here if you don't mind? high enough instantaneous trip meaning the 20 amp to a 45 amp breaker correct. I always get confused with the Interrupting Rating of a circuit breaker. The ones in this panel now are all 10K. I remember doing a estimate for roof ice melting last year and I found out I needed to increase the Interrupting Rating of the breaker from a 10K to a 65K I believe. There was a huge increase in the price of the breaker. The higher Interrupting Rating is used for long distance and what exactly if you don't mind?
Thanks again for all your help
Click to expand...
See this document: http://www.cooperindustries.com/con...ircuit_Breakers_Instantaneous_Trip_Region.pdf
 
Walters said:
The shop owner was holding the breaker closed to operate the lift.
....
Click to expand...
That is not possible with any listed breaker made in the last 40 to 50 years. They are of a "trip free" design, which means it will trip, even where the external operating handle is physically held in the on position.
 
A high interrupt rating just means it can take a higher fault current and shoulnd't destroy the breaker when it takes that higher fault current.

Magnetic trip is a fixed setting on common miniature plug on breakers, but does increase as the overcurrent protection rating increases.

That initial surge of current that flows until a field is established in the motor is what will cause magnetic trip to operate if it is not at a high enough setting. Locked rotor is not the same thing, locked rotor is current motor draws after magnetic fields are established but the rotor is not turning.
 
If the owner "holds the breaker" actually has a effect on the operation I'd check the breaker line and load connections. There is at least the possibility of a poor buss connection.
 
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