Motor Amps on Name plate

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Little Bill

Little Bill

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If you have a motor that the nameplate says 230V/115V and the amps say 7/14, would the fact that the actual voltage is 240/120 change the amp rating?
Seems if you do the math that the KW would be 1610 and using 230V, you get the nameplate rating.
But if you use 240V with the same KW, you get 6.7A/13.42A.
Is this the way it would work, or is the nameplate what I have to use?

I'm trying to figure if I can run two motors off of a 20A circuit. These motors are for a swimming pool and spa.
I assume (maybe wrong) that I need to factor in 125% for continuous use since it's possible that these will run for three or more hours at a time.

One is the motor mentioned above 230/115 - 7/14
The other is 230/115 - 9.7/19.4

I will run 240V on a 20A circuit if I can do this.

I just remembered that the 125% is probably already factored in the nameplate, is that correct?
 
430.24- 125% of the largest motor plus 100% of any other motor(s) to size the conductors. The note to Table 430.22(E) states all motors shall be considered as continuous duty unless the nature of the apparatus it drives is such that the motor will not operate continuously with load under any condition of use. The nominal voltage of the motor is to be used (230/115V)- refer to Table 430.248. I believe you'll need to upsize to #10- correct me if I'm wrong.
 
Little Bill said:
If you have a motor that the nameplate says 230V/115V and the amps say 7/14, would the fact that the actual voltage is 240/120 change the amp rating?
Seems if you do the math that the KW would be 1610 and using 230V, you get the nameplate rating.
But if you use 240V with the same KW, you get 6.7A/13.42A.
Is this the way it would work, or is the nameplate what I have to use?

I'm trying to figure if I can run two motors off of a 20A circuit. These motors are for a swimming pool and spa.
I assume (maybe wrong) that I need to factor in 125% for continuous use since it's possible that these will run for three or more hours at a time.

One is the motor mentioned above 230/115 - 7/14
The other is 230/115 - 9.7/19.4

I will run 240V on a 20A circuit if I can do this.

I just remembered that the 125% is probably already factored in the nameplate, is that correct?
Click to expand...

I agree with what others have said so far.

Also remember the rating means that the motor fully loaded with 115/230 applied will be 14/7 amps, not necessarily that you must input exactly 115/230 volts. Chances are your input voltage maybe drops some when the motor is running and loaded.

125% is not factored into amps marked on name plate, that is rated amps at rated speed, voltage and rated load.

Some realities to consider is that these motors likely will not draw their rated current (though the code does not necessarily consider that). I would not recommend fudging with any branch circuit calculations but may consider fudging a feeder calculation if it is really close.
 
rbalex said:
You have no choice. See Section 430.6 (A). Nameplate values are only permitted to be used for overload protection. [Section 430.6(B)]
Click to expand...

I think the nameplate should include rating for overload and fault/short circuit. Would be lees confusing to me!
 
kwired said:
I agree with what others have said so far.

Also remember the rating means that the motor fully loaded with 115/230 applied will be 14/7 amps, not necessarily that you must input exactly 115/230 volts. Chances are your input voltage maybe drops some when the motor is running and loaded.

125% is not factored into amps marked on name plate, that is rated amps at rated speed, voltage and rated load.

Some realities to consider is that these motors likely will not draw their rated current (though the code does not necessarily consider that). I would not recommend fudging with any branch circuit calculations but may consider fudging a feeder calculation if it is really close.
Click to expand...

So you're saying to size the conductors for the larger load, but maybe could get by with smaller OCPD?
 
Little Bill said:
I think the nameplate should include rating for overload and fault/short circuit. Would be lees confusing to me!
Click to expand...
Submit a Proposal for the 2017 NEC. Section 430.6 in some form or another has essentially been around a very long time; i.e., Table ampacities for basically everything but overload, nameplate for overloads.

Section 430.7 details motor nameplate requirements.

I happened to be on CMP11 (1996) when the last major update to the ampacity/motor ratings to the Tables was made. The NEMA representative making the Proposal acknowledged the ampacity ratings were based on the worst motor of any NEMA motor manufactured.
 
680.21(C) only specifies GFCI for single-phase, 120 volt through 240 volt branch circuits, rated 15 or 20 amperes.

680.44 requires majority of Spas to have GFCI protection, exception is if unit is marked and has internal protection or if three phase, over 250 volts, or over 50 amps.
 
Little Bill said:
I think the nameplate should include rating for overload and fault/short circuit. Would be lees confusing to me!
Click to expand...

It has been the way it is since the beginning of time, well maybe not that long.

Motor overload is in 430 part III. It is based on nameplate full load current, but can vary based on service factor of the motor. Can also vary depending on the duty cycle of the motor, starting methods, and other things.

Short circuit and ground fault protection is in 430 part IV. Setting of this depends on type of overcurrent device, and even if that original setting will not allow starting of the motor you are still permitted to increase the setting to certain extent. The more available current from the source the higher the starting current can be in many cases. But put same motor on a longer run of conductors or on a smaller supply and the starting current may be limited by impedance of the supply and or the conductors and will not trip a lower setting breaker in this installation.
 
The only thing the nameplate is good for is for setting the O/L's. Everything else, wire, breaker size comes from the tables.
 
kwired said:
You also need Hp,voltage, phase to know which table to use:happyyes:
Click to expand...
And like you said, the tables have been around since dirt was invented. The issue I have is the advent of all these "special" motors such as the ones found on consumer type air compressors and the like. You end up with wildly oversized conductors because you have to use the bogus HP marked on the nameplate.
 
Another Question Concerning Conductors

Another Question Concerning Conductors

I have another question about wiring the motors. If I decide to feed the two motors and a couple of other small loads with a just one 2-pole 30A GFCI circuit and use #10 wire, would I need to also use #10 to each motor and the other loads.

Let me explain the setup:

There is an 1-1/4" conduit ran from the pool equipment panel to the area containing the pool equipment.

The timer enclosure will not accept 1-1/4" conduit so there is a junction box there to splice the conductors so they can be sent to the timer and other loads.
There is no one load that requires 30A, but all the loads together will need 30A.

So even though #12 would normally be all that is required for each load, would I need to use #10 on to each load since they're protected by a 30A breaker?

It may be easier/simpler to just run two 20A GFCI circuits and use the #12 for everything.
Main reason for a single 30A circuit was so that I could use the timer, which has two timers and clock motors, to control the pool pump, spa pump, and heater.
My plan was to feed the second timer off the load side of the first timer to insure the heater wouldn't be on without the pool pump running.

I think the timer can be fed with two separate circuits, but I might have to change the wiring a bit for the clock motors.
 
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