Anonymous asked in Home & GardenMaintenance & Repairs · 5 months ago

This sounds a bit dangerous for electrical connection?

I have a PD Blower (supercharger) that runs an industrial vacuum. I am upgrading from one that can run on a motors of 5 hp, so long as it has a service factor of at least 1.15 to one that runs on a 7.5 hp motor, so long as it has a service factor of 1.15. My current motor is wired about 25' from the breaker using #10 wire. The receptacle is NEMA 14-30. The breaker is 40 amps, which concerns me, but has never been an issue. This motor runs 4-5 hours per 8 hour shift, 3 days per week for about 3 years now. It is a WEG compressor motor. It is actually rate 6.4 hp with a service factor of 1.0. It is my understanding, that is essentially the same as 5 hp with a SF of 1.15. A lot of these cheap compressors have a 5 hp motor with a SF of only 1.0. The point is the breaker is 40 amps and the receptacle is only 30 amps. The FLA is 23 amps.

The new motor will also be made by WEG. The FLA is 33.3, so maybe it is more efficient? The electrician that wired my first motor in is doing the second. He says 50 amp receptacle and 60 amp breaker, #8 wire. Is he coming in with a low ball price that may be dangerous? I'm thinking pay a few dollars extra for #6 wire, 60 amp receptacle, which is like $60 vs $10 for the NEMA 14-50 and a 70 or 80 amp breaker? I don't want to be voltage starved. A also may see this new system running 5-6 hours in a 10 hour split shift and 4 days per week at some point. I want to do it right, I want to do it heavy duty. If it costs me an extra $200, that's fine.

4 Answers

  • Anonymous
    5 months ago
    Best answer

    Good idea. But his suggestion may be more than adequate. It is possible to convert horsepower into watts and watts into amps. Which yields a theortetical 46.6 amps. Therefore a 50 amp breaker would have little reserve. Similarly, #8 is rated for 50 amps. But it is usual to over rate by 50%.

  • 5 months ago

    Go with the the #6 THHN, the wire is in pipe and the cost is mostly labor. He has the same labor cost to do the job so go to Granger and price the new THHN wire to see if it's really the added cost the electrician said. You can always get your own wire on a spool and then the electrician will lose his material profit for the job. You only need him for the connections, pull your own #6 stranded THHN and only pay him for the terminations if they won't deal with your job properly.

  • Anonymous
    5 months ago

    To satisfy code the overcurrent protection can't exceed the receptacle rating.

    But I think your receptacle amperage rating is a bit irrelevant, a receptacle is a disconnecting means, and to satisfy NEC Section 430.109(F) all disconnecting means have to be Horsepower Rated for the load, and I'm not aware of any NEMA straight blade or twistlock receptacles that are HP rated.

  • 5 months ago

    well what does the nameplate say? #8 is rated for 50 amps but based on typical specs a 50amp receptacle is perfectly fine. you wont know unless you actually look at the motor specs but your electrician looks like hes right on it. fla or full load current is a good estimate on the starting current which all looks within spec. its weird hes putting in a 60amp breakr and not a 50 unless its a typo on your side.

Still have questions? Get answers by asking now.