Three Phase Plugs / Motor Ratings

[BentBierz]

Hello,

I have some three-phase woodworking equipment (two of which are 7.5 HP) that I am powering through a Phase Perfect converter (picture below). The manufacturer recommended just using twist lock plugs/receptacles instead of hardwiring into a disconnect but said I could do either.

I was on the Hubbell website looking at plugs and found that a 3Ø, 30 amp, 250AC plug has a max 3 A/C HP rating with the following footnote: "The horsepower ratings are the phase values." I'm confused by this statement and also don't see other options shown that are any higher than 3 HP.

Any three-phasers or electricians out there that could interpret? Thanks.

 

[alfredeneuman]

Receptacle ratings over 3.5HP are available but the are a pin and sleeve product and expensive (almost prohibitively so).
Can you hardwire the machines?

 

[wyliesdiesels]

Plugs and receptacles for motor circuits must be rated for the same or greater HP as the motor HP rating.

You will not find a standard NEMA twist-lock plug rated for that high amount of HP. As said above, pin and sleeve would be your only option if you must use cord and plug setup.

 

[alfredeneuman]

A pin and sleeve plug generally has a ring around it that mates up with the receptacle that you twist to lock them together. The actual contacts don't move though

 

[Mr. T]

If you aren’t planning to move it often, I’d just hard wire it.

 

[BentBierz]

Receptacle ratings over 3.5HP are available but the are a pin and sleeve product and expensive (almost prohibitively so).
Can you hardwire the machines?

Yes, I can hardwire it and that is certainly an option that I am entertaining. I was just surprised to have an engineer from the manufacturer (Felder) tell me that a twist-lock would be fine and then to see there was a HP component to the equation.

 

[wyliesdiesels]

Yes, I can hardwire it and that is certainly an option that I am entertaining. I was just surprised to have an engineer from the manufacturer (Felder) tell me that a twist-lock would be fine and then to see there was a HP component to the equation.

you know what they say about engineers....

I would never trust an engineer to follow NEC code.

I cant count the times Ive seen architects draw up plans that violated the NEC....

 

[Stuart in MN]

you know what they say about engineers....

I would never trust an engineer to follow NEC code.

I was going to respond by telling the OP about pin and sleeve connectors, but since I'm an engineer I guess I better not.

 

[matt_i]

Everyone is going to go bananas because of NEC. But:

The twistlock will work functionally fine as long as you don't a) overload the amp rating and b) don't unplug it under load.

Real potential for a nasty arc flash that can damage people, the plug or the receptacle if plugged or unplugged under load. The pin & sleeve connectors I have only seen interlocked to a disconnect so that they can only be mated or un-mated when the disconnect is in the OFF position.

 

[W-Cummins]

You can use a 15-50p for 7.5hp it's not a locking plug, but way cheaper than a pin and sleeve plug set.

 

[W-Cummins]

Real potential for a nasty arc flash that can damage people, the plug or the receptacle if plugged or unplugged under load. The pin & sleeve connectors I have only seen interlocked to a disconnect so that they can only be mated or un-mated when the disconnect is in the OFF position.

The design of the pin&sleeve set allows the disconnect under load with the larger pin spacing and also the shroud. I have them with and without the disconnect interlock.


I also have a water proof twist lock setup that is "up rated" to 15hp from 10hp when using the interlock setup, thus making my $$$ extension cord ( not to code
William....

 

[BentBierz]

You can use a 15-50p for 7.5hp it's not a locking plug, but way cheaper than a pin and sleeve plug set.

Thanks...these might be an option. I have also found some 50 amp locking plugs but unfortunately could not find any HP ratings. Seems like HP ratings are an afterthought when listing specs online. I have seen some listings that say that the item has an HP rating but doesn't say what it is...pretty frustrating.

 

[jeffmoss26]

we had some 60 amp 3 phase pin & sleeve connectors at the college for our power distros.

 

[86turbodsl]

I was going to respond by telling the OP about pin and sleeve connectors, but since I'm an engineer I guess I better not.

Same here. I don't follow the NEC 100% either. Those guys are ridiculously ****. There's risk in everything. Trying to stop any sort of problem from ever happening costs $$$ to everybody and is a nuisance. don't get me started on arc-fault breakers the assh*les made me put in my house build.

 

[BentBierz]

I was going to respond by telling the OP about pin and sleeve connectors, but since I'm an engineer I guess I better not.

in my job in the Coast Guard as a commercial vessel inspection branch chief, i have to deal with engineers (naval, mechanical, electrical, P.E.) all the time and currently have two on my staff. Other than an ocassional knuckle head (smart but no common sense), I would rather have more than fewer working for me.

 

[Lightning rod]

OP
THe plug that you found is fine for your application
The rating 3 HP phase rating means that the plug is capable of 3 HP per phase for 9 HP total
Your 7.5 HP 3 ph motor rating will draw approx 20 amps at full load Amps
According to charts. Check the nameplate rating on your motor
Therefore a 30 amp plug will be fine
We used this approach in our factory all the time
Direct wiring is always better of course

https://www.hubbell.com/wiringdevic...geRatingDescription:3+Phase+WYE+120%2F208+VAC

I assume that you have a 208 v 3 ph system which is very common

 

[wyliesdiesels]

OP
THe plug that you found is fine for your application
The rating 3 HP phase rating means that the plug is capable of 3 HP per phase for 9 HP total
Your 7.5 HP 3 ph motor rating will draw approx 20 amps at full load Amps
According to charts. Check the nameplate rating on your motor
Therefore a 30 amp plug will be fine
We used this approach in our factory all the time
Direct wiring is always better of course

https://www.hubbell.com/wiringdevic...geRatingDescription:3+Phase+WYE+120%2F208+VAC

I assume that you have a 208 v 3 ph system which is very common

Most of the plugs and receptacles on your link are either non-grounding 120/208Y or 5-wire.

OP only need 4-wire grounded

 

[Lightning rod]

WD
I did peruse the “PHASE TECHNOLOGIES” website but honestly didn’t open a manual to see details
I should have been more clear in my post in that the webpage illustrated what I used in the factory testlab
If the converter needs just 3 phases and a ground , then 4 wire grounded would be correct
If the converter needs a neutral, then 5 wire would be needed
Maybe the OP can give more detail on his model for a more precise answer
In any event, plugs and sockets can be had for what he is trying to do.
Thanks for the input