3 wire generators

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leggo

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I installed a manual transfer switch with a 10/3 nm wg from transfer switch to a male outlet box in garage for generator cord set. I come to find out that the 5kw portable generator is older and only has a 20 amp 250v 3 wire outlet instead of the L14-20 locking 4 wire plug. How do I rewire cord set using the 3 prong male plug? Would I use the white insulated conductor instead of the ground that runs through the 10/3 romex? The cord set is a sjoow cord that does have an insulated green wire, but the romex does not. Does that portable generator need to have a ground rod?
Thanks for your help!
 

leggo

Member
I didn't look close enough but what I saw was a 240 volt 20amp duplex that had the two horizontal female ends with a ground on the bottom, just opposite of a standard 15 amp duplex with the verticle female ends. I assume that it is a ground and not some kind of floating neutral.
 

tryinghard

Senior Member
Location
California
leggo said:
I installed a manual transfer switch with a 10/3 nm wg from transfer switch to a male outlet box in garage for generator cord set. I come to find out that the 5kw portable generator is older and only has a 20 amp 250v 3 wire outlet instead of the L14-20 locking 4 wire plug. How do I rewire cord set using the 3 prong male plug?

You change the cord to a 10-4 so you have A, B, N, & GR and you change to cap to be the correct NEMA rating of 30A 4W. The neutral and ground DO NOT bond together in the generator.

leggo said:
...Does that portable generator need to have a ground rod?
Thanks for your help!

No the generator does not require a ground rod or electrode. The generator does need to be bonded this is why you need a 10-4 cable and cap.
 

don_resqcapt19

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Location
Illinois
Occupation
retired electrician
You change the cord to a 10-4 so you have A, B, N, & GR and you change to cap to be the correct NEMA rating of 30A 4W. The neutral and ground DO NOT bond together in the generator.
First, at this point we don't now if it is even possible to convert this generator to a 4 wire system. Some generators are 240 volt only with no center tap to get a grounded conductor. Second, since this is a generator designed for cord and plug connection, it is my opinion that 250.20(B) requires a neutral to ground connection at the generator. Note before anyone says this section does not apply to a generator please read the definition of premises wiring systems in Article 100. Yes, I am well aware that you can buy generators that are designed for cord and plug use that do not have this bond installed by the manufacturer. It is my opinion that the use of power from such a generator is a code violation.
Don
 

hillbilly

Senior Member
don_resqcapt19 said:
Second, since this is a generator designed for cord and plug connection, it is my opinion that 250.20(B) requires a neutral to ground connection at the generator. Note before anyone says this section does not apply to a generator please read the definition of premises wiring systems in Article 100. Yes, I am well aware that you can buy generators that are designed for cord and plug use that do not have this bond installed by the manufacturer. It is my opinion that the use of power from such a generator is a code violation.
Don

I disagree...
I've got to go right now, but I'll have more to follow after I get all of my ducks in a row.:)

steve
 

don_resqcapt19

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Location
Illinois
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retired electrician
I believe my ultimate question is "Can I run 120v loads off of this generator safely?"
I don't know the answer to that question. You will have to look and see if there are 3 or 4 wires comming out of the windings. If there are, then it you may be able to supply 120 volt loads. However if there are only 2 wires comming out of the winding, the generator is 240 only.
Don
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
leggo said:
I installed a manual transfer switch with a 10/3 nm wg from transfer switch to a male outlet box in garage for generator cord set. I come to find out that the 5kw portable generator is older and only has a 20 amp 250v 3 wire outlet instead of the L14-20 locking 4 wire plug. How do I rewire cord set using the 3 prong male plug? Would I use the white insulated conductor instead of the ground that runs through the 10/3 romex? The cord set is a sjoow cord that does have an insulated green wire, but the romex does not. Does that portable generator need to have a ground rod?
Thanks for your help!

My bet is that the 220 volt receptacle you are referring to is set up for just 220 volts. The generator can produce 120 volts ( I am sure there is a 120Volt plug on it but I would not feed 120 volts from the receptacle in question.
 

tryinghard

Senior Member
Location
California
don_resqcapt19 said:
First, at this point we don't now if it is even possible to convert this generator to a 4 wire system. Some generators are 240 volt only with no center tap to get a grounded conductor.

If this generator is 240 volt only it should not be hooked up to 120 volts; I don't think Yogi Berra could-a said it better! :roll:

don_resqcapt19 said:
Second, since this is a generator designed for cord and plug connection, it is my opinion that 250.20(B) requires a neutral to ground connection at the generator. Note before anyone says this section does not apply to a generator please read the definition of premises wiring systems in Article 100. Yes, I am well aware that you can buy generators that are designed for cord and plug use that do not have this bond installed by the manufacturer. It is my opinion that the use of power from such a generator is a code violation.

Do you know if this is this a separately derived system? A portable 5 KVA usually isn't, and I don't believe it's the sole source either at this size, but if it is then the neutral would bond. If a generator is not a separately derived system the neutral bond isn't getting broken therefore it does not need to be re-established. In other words the generator feeder is like a sub-panel feeder and the neutral does not bond -- 250-24(A)(5) & 250-142(B) -- it will be a code violation if it does.

I gotta say now that I've re-read 250-34(A) I think you do need an electrode at the generator to bond its frame because your supplying more than a receptacle and other equipment not mounted on the generator.
 

leggo

Member
Yes the generator does have a 15 amp 120v duplex and a 20amp 250volt duplex, I just wasnt sure if I should try and feed a 10 circuit manual transfer panel by gentran by plugging in a cord into the 20amp 250v duplex that the generator has?
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
leggo said:
Yes the generator does have a 15 amp 120v duplex and a 20amp 250volt duplex, I just wasnt sure if I should try and feed a 10 circuit manual transfer panel by gentran by plugging in a cord into the 20amp 250v duplex that the generator has?

Use your meter first.If you get 120 between its ground/neutral to both ungrounded hots and 240 between them your likely fine.The connection is arguable.If above is the case i would need to know how and where the romex is made up in panel.Is the panel service or a sub ?
 

don_resqcapt19

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Location
Illinois
Occupation
retired electrician
trying,
I gotta say now that I've re-read 250-34(A) I think you do need an electrode at the generator to bond its frame because your supplying more than a receptacle and other equipment not mounted on the generator.
As long as the connections to the load are made with cord and plug connections, there is no requirement for an electrode. The frame of the generator is permitted to serve that purpose.
Don
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Jim W in Tampa said:
Use your meter first.If you get 120 between its ground/neutral to both ungrounded hots and 240 between them your likely fine.
I recommend a solenoid-type tester and not a typical voltmeter.
 

jerm

Senior Member
Location
Tulsa, Ok
I got out the schematics to one of the generacs we installed recently and traced out the lines from the actual source to the plugs. There is a 50a 250v style plug (three wire) and a 15a 125v plug on the chassis. Wire number 22 on this drawing connects the grounded side of the recept to the center tap and to the chassis ground and to the 250v recept grounding.

So in this case, the "neutral" and ground are bonded, and there is 120v available, but it doesn't come with a 4-wire plug built in.

make sense? maybe I can scan this drawing in...
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
jerm said:
So in this case, the "neutral" and ground are bonded, and there is 120v available, but it doesn't come with a 4-wire plug built in.

make sense? maybe I can scan this drawing in...
No need, it makes sense; you have a 3-wire feeder. Technically, you should be using a T/S that switches the neutral.
 

jrannis

Senior Member
jerm said:
I got out the schematics to one of the generacs we installed recently and traced out the lines from the actual source to the plugs. There is a 50a 250v style plug (three wire) and a 15a 125v plug on the chassis. Wire number 22 on this drawing connects the grounded side of the recept to the center tap and to the chassis ground and to the 250v recept grounding.

So in this case, the "neutral" and ground are bonded, and there is 120v available, but it doesn't come with a 4-wire plug built in.

make sense? maybe I can scan this drawing in...


Be very careful!!! The machine he has is very likely straight 240 at that plug. Do not attempt to rewire the alternator output!!
If you just gotta have 120/240 from that generator buy a 240/ 120/240 single phase transformer and derive a neutral from it.
 
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