Originally Posted by
Roger Frazee
...the actual reason that 5 hp saw in that other thread is not allowed cord and plug is it requires a 5 HP rated single phase 250 volt plug and receptacle ...
Roger, please pardon my ignorance and understand that I'm not trying to challenge what you say. I'm simply trying to improve my understanding.
Following comments are based on my understandings, and I would certainly appreciate corrections where they fall short.
If a 5HP motor requires a 5HP rated plug and socket, by extension, would not a 3HP motor require a 3HP rated plug and socket? Or, for that matter, would not any plug and socket used for a motor load need to be rated for the HP of the motor? The reason I ask is because I do not recall ever seeing plugs and sockets rated for anything other than volts and amps and I've seen no negative comments regarding using power cords/plugs/sockets for 3HP and smaller motor loads.
I understand that switching devices need to be rated for the HP of the motors they control because of the inductive nature of the load and the voltage spikes and/or arcing that occurs when the switch is actuated. But unlike switches, contactors, etc., plugs and sockets are static devices and aren't intended to be used to make/break a circuit. Thus they aren't subject to the same conditions as switches, etc.
After reading your comment concerning 5HP rated plugs and sockets, I made a fast, admittedly incomplete, search of various manufacturers web sites looking for receptacles that were rated for HP in addition to volt/amps. I didn't find any. I found NEMA 6 and L6 devices in both 20 and 30 amp ratings, none of which were rated by the manufacturer in terms of power. Not saying they aren't out there, just that I didn't find any.
I've previously had no qualms about using a 6-20/L6-20 device on a power cord for a 3HP motor (20 amp circuit) and by extension, would have had no qualms about using 6-30/L6-30 devices for a 5HP motor on a 30 amp circuit. In the absence of power rating on the devices, I see no substantiative difference between the two cases.
For any readers not familiar with the designations, NEMA 6/L6 devices are 250 volt 2-pole, 3-wire, grounding devices - IOW, 250 volt single phase grounding plugs and receptacles.
Tom Veatch
Wichita, KS
USA