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I have a water pump, it works fine. Motor is rated for 115/230 and draws 9.6 or 4.8 full-load amps depending on voltage. Its cord has a plug that appears to be vintage NEMA 10-20, but I'm not certain as I've never seen one before. The receptacle is on its own 30-amp dual-pole breaker, and I verified that the wiring is two hots and a ground.

I want to run this pump from my generator, which is an older 5000 watt Troy-Bilt with standard 240v L14-30 and 120v 5-15/20 receptacles.

The problem: I can't find any adapters for 10-20 plugs anywhere. Is this just because they're obsolete? Or because they're ungrounded and super-dangerous?

Main question: Should I bother making a custom adapter cord for this setup or just upgrade the plug and receptacle to something newer? Is one option obviously better/safer/easier?

Pump motor is a 1986 Dayton 5K658B 3/4HP 115/230 3450 rpm. I found this tech sheet but I'm not 100% sure it's the same model.

nema 10-20 plugdayton pump faceplate

receptacle wiring

Conclusion:

Based on the discussion in the comments, this whole situation is more complex and sketchy than I had anticipated. I have other electrical work I need done so I'm going to add this plug/receptacle to the list and seek professional help.

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    The logic conflict was a NEMA 10 uses a neutral connection with 240v, but when the motor when wired for 120v it couldn't have a 60v mid-point connection. The label confirmed the NEMA 6 was not right. That plug should be a NEMA 6-20 if wired for 240v. So now we need to see what's behind the receptacle to see if it's easy to install. And is it a 120v breaker or a two-pole 240v breaker? Dec 14 '20 at 4:24
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    Pretty clear this thing needs a ground. Plus in any new installation it should be on a GFCI. Dec 14 '20 at 4:28
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    For those that don’t understand how the windings work (60v mid point is not how a dual voltage motor is wired) there are 2 sets of windings. With the windings in parallel the voltage is 120 with the windings in series the voltage is 240. 120v uses neutral and ground by today’s code and 240v uses 2 hot conductors and ground. Would that plug receptacle be safe ? If properly wired it would function for decades more, however if converting I would change to the appropriate 3 wire twist lock , GFCI protection the installation is regulated by the date installed and GFCI protection was not required
    – Ed Beal
    Dec 14 '20 at 14:45
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    GFCI protection was not required at installation and presumably not for a straight replacement. But unlike some other situations (e.g., a kitchen counter receptacle that realistically isn't so close to a sink where "no big deal"), a water pump seems to me to be pretty much a prime application for GFCI to truly improve safety, at least if that water has any chance of being touched by people. Dec 14 '20 at 15:33
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    Prior to the 99 code update the ground and neutral were connected even in sub panels so back then this would have been just fine no difference between the 2 and the reason prior to this you see 3 wire more often. It was only with more recent code changes that changes, I say recent because I started in the 70’s so that method was legal for new construction for over 1/2 the years I have been doing this and as “as built” it is still legal today, note you can update a receptacle without having to add GFCI protection. (Or this is true in all the states I have worked).
    – Ed Beal
    Dec 14 '20 at 17:39
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Is that plug safe, yes when properly wired there is no issue with that plug. What would a best practice be when setting up a direct connection to a generator. Change the plug to the appropriate 3 wire twist lock. The old plug will work but with motor loads vibrations can allow the plug to work out of the receptacle moving the plug from one source to another increases the chance the plug can vibrate out because of the stress on the wire being different.

The only real difference in today’s plug / receptacles is the ground lug each voltage hi / low has the ground lug pointing in or pointing out on twist locks. a 120v 5-15 standard receptacle and plug 120v would work Or a 6-15 240v 15a would also work but there is a higher chance for this plug to fall out, this is why I would suggest twist locks.

If you want to get fancy you could pay more and go to a 4 wire plug that is 120/240 rated but that is a waste because you won’t be changing your motor configuration but some folks have asked me to do this.

Last you are using a 5000w 240v generator, to power a pump with a book value 1657w (book values not nameplate is used for load calculations). I would suggest to put in a simple interlock kit on your panel and an inlet to the panel and you could run your pump, refrigerator, Freezer and some lights off of that generator (my small backup generator is a 5000w welder and it runs all these loads) I turn the other breakers in the panel off and have had this setup for years. The issue I see with that large of a generator is fuel usage when not pumping.

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  • Yes, this might be the thing that finally gets me to add an interlock.
    – meetar
    Dec 14 '20 at 18:48
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    I should mention my primary generator is larger but the 5k welder will run the basics and a TV. I set my pump up for 240v so the load would be balanced when the well kicks in. The fridge and freezer are on opposite legs as they require dedicated circuits but tend to run at similar times even though independent, if the well and both fridge/ freezer kick in at the same time with lights and tv running I hear the generator really pull but it makes it and we don’t loose sync on the tv so the frequency is at least fairly stable. I bring out my bigger generator so I can add heat pumps to the list.
    – Ed Beal
    Dec 14 '20 at 19:32
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The NEMA 10 configurations is a 240v receptacle for appliances that ground via the neutral conductor conductor, and cannot be properly wired to a single pole breaker, and even if wired for 240v as far back as I can recall it was never a legal configuration for that motor anyway.

I would attempt to change the receptacle and cord cap to a NEMA 5-20. The code requires replacement with GFCI's where GFCI's are required*. I wouldn't recommend changing the wall receptacle to a twist lock because the L14-30 configuration to match the generator shouldn't be wired to the existing 20A breaker or fed by the #12 wires probably feeding the receptacle.

A first thought might be that swapping wire for wire to a NEMA 5 which should work, but it's anybodies guess if the wire colors would actually comply with Code. Since it's improperly wired to begin with what colors are present is anybodies guess.

A NEMA 10 should be a white (or grey), and two other colors besides green. A Nema 5 should be a ground (green, bare, or raceway), white (or grey), and one hot (none of the aforementioned colors). There are some minor exceptions, but it is best to determine what you have before going down that path.

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  • *NEC 406.4(D)(3)Ground-Fault Circuit Interrupters. Ground-Fault Circuit Interrupters shall be provided where replacements are made at receptacle outlets that are required to be so protected elsewhere in this code. Dec 14 '20 at 17:40
  • Adding a 20 amp receptacle to a dedicated load of less than 15 a? Really
    – Ed Beal
    Dec 14 '20 at 17:49
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    At least the good side is you got one black, one white, and one bare ground. You are good to go with replacing with a NEMA 5 that matches your generator. Dec 15 '20 at 0:26
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    @meetar, and both the white and black wires are going to that double pole 30? That pretty well confirms it's currently wired for 240V then, so you'd have to use a NEMA 6 if you want to keep it that way. But you may be able to jumper the motor for 120, which would make it easier to use with your generator.
    – Nate S.
    Dec 15 '20 at 0:44
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    You might as well just measure the voltage across all the legs @meetar. That'll be the final arbiter. That'll tell you whether to change to NEMA 5-20 or NEMA 6-20. Dec 15 '20 at 2:17

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