Just installed a transfer switch for a customer. The 5kw generator supplied by the customer is a Sears model and when I went to test the new system out the lights went dim and then the popping sound no electrician likes to hear happens. Checked the output on the 120/240 4w outlet and it reads 260v line to line and 66v line to ground or neutral. Luckily no electronic equipment was damaged. Anyone have this problem before. I told them to send the Generator back and have it fixed or replaced. This was a first for me.
Incorrect generator output
- Thread starter yetiman
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dbuckley
Senior Member
- Location
- Canterbury, New Zealand
I'd guess there is a lost neutral in the genset prior to the 4W connector. Use a wiggy rather than a DVM and I think L/N voltages will be 0V.
Howard Burger
Senior Member
- Location
- N of Anchrage, AK
Your Sears genny may be OK
Your Sears genny may be OK
I am getting similar voltage readings with my generator and I don't think the Sears genny you worked with is bad. Either that, or both generators need work
The other day at Costco I saw a genny with 'floating neutral' on the box. Research on this forum and web led me to check and see if I might have a bonded neutral in my backup (Generac 5.5kw) genny. I checked the owners manual, and sure enough, neutral was bonded to ground.
So I opened up the genny and found a jumper between the ground screw on one of the Nema 5 recepts and the neutral.
Here are the voltage readings I received before and after removing the jumper:
Before:
Nema 14 recept.: A-B 269; A-N 134; A-G 134; B-N 135; B-G 133
Nema 5 recept, A phase: A-N 136; A-G 135
Nema 5 recept, B phase: B-N 136; B-G 135.
Ideal plug tester in Nema 5 recept. showed two lights, normal.
After removing the jumper:
Nema 14 recept.: A-B 271; A-N 136; A-G 62; B-N 136; B-G 71
Nema 5 recept, A phase: A-N 135; A-G 62
Nema 5 recept, B phase: B-N 133; B-G 72.
Ideal plug tester in Nema 5 recept. showed one lights, open ground.
We have normal voltage a little above 120/240 where I live. I've used the genny (via a 100 amp CH transfer switch) on two occassions for a couple hours each with no problem.
Regarding the hot-ground readings, it looks like the frame of the genny isn't a very good earthing source, and that is why we should use GFI protection on our circuits at construction sites.
My web research came up with the nugget that OSHA requres the generators on work sites to have a ground-neutral bond. I didn't confirm that with any official site, however for temporary power I belive that the G-N bond at the genny should be removed to comply with NEC as a non-sds system. Your Sears generator likely didn't have the bond or you would have gotten a full reading on your hot-ground check.
I found this web site to be informative:
http://members.rennlist.org/warren/generator.html
Hope this information is of use to you.
Your Sears genny may be OK
I am getting similar voltage readings with my generator and I don't think the Sears genny you worked with is bad. Either that, or both generators need work
The other day at Costco I saw a genny with 'floating neutral' on the box. Research on this forum and web led me to check and see if I might have a bonded neutral in my backup (Generac 5.5kw) genny. I checked the owners manual, and sure enough, neutral was bonded to ground.
So I opened up the genny and found a jumper between the ground screw on one of the Nema 5 recepts and the neutral.
Here are the voltage readings I received before and after removing the jumper:
Before:
Nema 14 recept.: A-B 269; A-N 134; A-G 134; B-N 135; B-G 133
Nema 5 recept, A phase: A-N 136; A-G 135
Nema 5 recept, B phase: B-N 136; B-G 135.
Ideal plug tester in Nema 5 recept. showed two lights, normal.
After removing the jumper:
Nema 14 recept.: A-B 271; A-N 136; A-G 62; B-N 136; B-G 71
Nema 5 recept, A phase: A-N 135; A-G 62
Nema 5 recept, B phase: B-N 133; B-G 72.
Ideal plug tester in Nema 5 recept. showed one lights, open ground.
We have normal voltage a little above 120/240 where I live. I've used the genny (via a 100 amp CH transfer switch) on two occassions for a couple hours each with no problem.
Regarding the hot-ground readings, it looks like the frame of the genny isn't a very good earthing source, and that is why we should use GFI protection on our circuits at construction sites.
My web research came up with the nugget that OSHA requres the generators on work sites to have a ground-neutral bond. I didn't confirm that with any official site, however for temporary power I belive that the G-N bond at the genny should be removed to comply with NEC as a non-sds system. Your Sears generator likely didn't have the bond or you would have gotten a full reading on your hot-ground check.
I found this web site to be informative:
http://members.rennlist.org/warren/generator.html
Hope this information is of use to you.
incorrect generator voltage
incorrect generator voltage
The problem is that we had 66v either phase to the neutral point and to ground from the generator.
So a to n = 66v
b to n= 66v
a to gr= 66v
b to gr= 66v
Line to line read 266v
This is from the nema 14 120/240 v rec.
The reading from the 15a 120 rec. read 130v to neutral and ground
My suggestion was this is a generator we should not put into service with the nema 14 receptacle.
incorrect generator voltage
The problem is that we had 66v either phase to the neutral point and to ground from the generator.
So a to n = 66v
b to n= 66v
a to gr= 66v
b to gr= 66v
Line to line read 266v
This is from the nema 14 120/240 v rec.
The reading from the 15a 120 rec. read 130v to neutral and ground
My suggestion was this is a generator we should not put into service with the nema 14 receptacle.
Howard Burger
Senior Member
- Location
- N of Anchrage, AK
agree with dbuckley
agree with dbuckley
I agree that there's something fishy with the N14 recept. I think dbuckley is right about there being a lost neutal on the nema 14. I pulled the box off mine that has the recepts in it to get to the n-g bond, and found that the neutral was daisychained from the Nema 14 to the first N5 and then to the other N5 and then back to the generator (orange wire, couln't believe it). Could be yours is similarily wired and something came loose.
And I checked L/N with a solenoid tester, as dbuckley mentioned, and got 0.
agree with dbuckley
I agree that there's something fishy with the N14 recept. I think dbuckley is right about there being a lost neutal on the nema 14. I pulled the box off mine that has the recepts in it to get to the n-g bond, and found that the neutral was daisychained from the Nema 14 to the first N5 and then to the other N5 and then back to the generator (orange wire, couln't believe it). Could be yours is similarily wired and something came loose.
And I checked L/N with a solenoid tester, as dbuckley mentioned, and got 0.
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