Small ECM pump conductor sizing

[greenspark1]

Hello,
We're starting to see a lot of ECMs that are variable speed and very low power use. This makes traditional branch circuit sizing tough. For instance, a Grundfos 1/2 HP 115V pump lists a max current of only 2.8A. This is in comparison to the 9.8A listed in the NEC table 430.248, or 5.4 per 430.247. I would like to put 3 of them on a 20A branch circuit. Is it fine to use the actual nameplate/manufacturer data for branch circuit sizing and OCPD sizing? How are others handling these (relatively) new pumps.

 

[petersonra]

what is ecm?

it appears to me to be some kind of vfd. see 430.120-128.

 

[greenspark1]

what is ecm?

it appears to me to be some kind of vfd. wiring and ocpd to a vfd are sized according to 430.120-128.

Electrically commutated motor:
http://www.thomasnet.com/articles/machinery-tools-supplies/ECM-Motors-HVAC-Systems

Here's some examples:
http://us.grundfos.com/products/find-product/magna3.html

Variable speed DC motor.

 

[petersonra]

Electrically commutated motor:
http://www.thomasnet.com/articles/machinery-tools-supplies/ECM-Motors-HVAC-Systems

Here's some examples:
http://us.grundfos.com/products/find-product/magna3.html

Variable speed DC motor.

the point would be that the BC to the drive has to follow different rules than the actual motor.

 

[greenspark1]

Sorry not sure I follow you. BC??

 

[petersonra]

Sorry not sure I follow you. BC??

branch circuit.

you have to provide conductors and OCPD in accordance with 430.120 for the input to the drive.

the chart tells you what the conductors are between the drive and the motor.

 

[kwired]

Hello,
We're starting to see a lot of ECMs that are variable speed and very low power use. This makes traditional branch circuit sizing tough. For instance, a Grundfos 1/2 HP 115V pump lists a max current of only 2.8A. This is in comparison to the 9.8A listed in the NEC table 430.248, or 5.4 per 430.247. I would like to put 3 of them on a 20A branch circuit. Is it fine to use the actual nameplate/manufacturer data for branch circuit sizing and OCPD sizing? How are others handling these (relatively) new pumps.

Table 248 has this information attached to it:"The following values of full-load currents are for motors running at usual speeds and motors with normal torque characteristics. The voltages listed are rated motor voltages. The currents listed shall be permitted for system voltage ranges of 110 to 120 and 220 to 240 volts." I think that disqualifies it from applying to that table, I also don't think they fit into the same classification as the DC motors in table 247, so they are kind of on their own and nameplates is about all you can go by.

I think their use has primarily been OEM specific for the most part and there are not enough of them being used as a general duty motor to warrant NEC making a separate table for this kind of motor, or to incorporate into an existing table should it apply.