I got a 240 V 3 Phase generator with 3 ungrounded conductors and 1 grounded coming out of the unit. My question is can the grounded wire be hooked to and one of the 3 hot wires to get 120 V. The motor starers he intends to use have 120 V coils. I'm not sure where to hook the other side of the coil to get true 120V with out putting in a transformer. It seems to me the grounded conductor would be used for equipment grounding only. If anyone out there has experience with this kind of system please educate me!!!
GENERATOR SET
- Thread starter sportster
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Re: GENERATOR SET
Yes a name plate would be nice, but this old unit is lucky to have wire numbers on it. From what I understand the wire combination coming out is 4&8 =120V/ 7&6= 120V/5&9=around 170V (wild leg?). The other wire is hooked to the frame of the unit ( equipment ground?) I have not delt with gen sets much so be gentle. Thanks
Yes a name plate would be nice, but this old unit is lucky to have wire numbers on it. From what I understand the wire combination coming out is 4&8 =120V/ 7&6= 120V/5&9=around 170V (wild leg?). The other wire is hooked to the frame of the unit ( equipment ground?) I have not delt with gen sets much so be gentle. Thanks
wirenut1980
Senior Member
- Location
- Plainfield, IN
Re: GENERATOR SET
Sounds like it might be 240 Volt Delta with a stinger leg. Three ungrounded conductors with 240 V between them, grounded at the midpoint between 2 of the legs, 120 V between grounded conductor and the two points between which the midpoint is grounded and 180 V between the third leg and the grounded conductor. Hard to envision without a picture like I am looking at. Why not try to measuring the voltages at the outputs of the generator somehow, or is that not possible?
Sounds like it might be 240 Volt Delta with a stinger leg. Three ungrounded conductors with 240 V between them, grounded at the midpoint between 2 of the legs, 120 V between grounded conductor and the two points between which the midpoint is grounded and 180 V between the third leg and the grounded conductor. Hard to envision without a picture like I am looking at. Why not try to measuring the voltages at the outputs of the generator somehow, or is that not possible?
- Location
- Illinois
- Occupation
- retired electrician
Re: GENERATOR SET
I've never seen a a generator with a "wild" leg. Do they even exist?
I've never seen a a generator with a "wild" leg. Do they even exist?
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: GENERATOR SET
Don I think I had one of those! It just got up and walked right off the job site.
Re: GENERATOR SET
Yes 120/240 3phase 4 wire delta output is available from most any 12 wire generator set.
The wire you describe as grounded to the frame is probably a bonded neutral as opposed to a floating neutral. Bonded neutral is for use with portable sets with convenience outlets and with 4 pole 3 phase transfer switch. Floating neutral is for use where the neutral is not transferred to the generator by the transfer switch (3 pole 3 phase switch. There should be a separate frame ground.
To answer your question, there should be 2 120V L to N leads and one which is about 208 line to neutral. Line to line should be 240 all around.
A 120/208 set may have the voltage increased to get about 220 line to line. Sort of hitting a middle ground between overvoltage on the 120V loads and undervoltage on the 240V loads.
Jim
Yes 120/240 3phase 4 wire delta output is available from most any 12 wire generator set.
The wire you describe as grounded to the frame is probably a bonded neutral as opposed to a floating neutral. Bonded neutral is for use with portable sets with convenience outlets and with 4 pole 3 phase transfer switch. Floating neutral is for use where the neutral is not transferred to the generator by the transfer switch (3 pole 3 phase switch. There should be a separate frame ground.
To answer your question, there should be 2 120V L to N leads and one which is about 208 line to neutral. Line to line should be 240 all around.
A 120/208 set may have the voltage increased to get about 220 line to line. Sort of hitting a middle ground between overvoltage on the 120V loads and undervoltage on the 240V loads.
Jim
Re: GENERATOR SET
What a great resource this form is. I think its a megatron, I will look at it again tonight and post tomorrow. Its kind of a side project a friend of mine roped me into. Yesterday I heard there could be 2 more wires taped of coming out of the gen #1/#10 that would give me a neutral, but I haven't got back to check that possibility out (on the road). Dose that make since to anyone?
If any of you need a friend I will give you this guy. Thanks for the help guys.
What a great resource this form is. I think its a megatron, I will look at it again tonight and post tomorrow. Its kind of a side project a friend of mine roped me into. Yesterday I heard there could be 2 more wires taped of coming out of the gen #1/#10 that would give me a neutral, but I haven't got back to check that possibility out (on the road). Dose that make since to anyone?
If any of you need a friend I will give you this guy. Thanks for the help guys.
- Location
- Illinois
- Occupation
- retired electrician
Re: GENERATOR SET
Jim,
If you connect the 12 lead generator to provide a 120/240 3 phase 4 wire system are the 120 volt loads limited to a small fraction of the generator rating like they are in 3 phase transformers that supply this voltage? I think that a 3 phase transformer is limited to 5% of the transformer rating for the 120 volt loads.
Don
Jim,
If you connect the 12 lead generator to provide a 120/240 3 phase 4 wire system are the 120 volt loads limited to a small fraction of the generator rating like they are in 3 phase transformers that supply this voltage? I think that a 3 phase transformer is limited to 5% of the transformer rating for the 120 volt loads.
Don
Re: GENERATOR SET
The load on the generator winding is limited by the amperage rating at whatever voltage you have it connected. This is as far as I know anyway.
We have utility power which is setup like this, but it is supplied by an open wye/open delta transformer bank of pole mounted transformers. So we want the emergency power to match the utility. I have never worried about trying to balance the load any more than it is balanced for the utility. It is impossible to balance it anyway since you cannot load the high voltage line to neutral leg with 120V loads. No problems with these small 50-60kW generators.
The limitation I think you might be referring to is for a dry type transformer where the heating is more of a problem. We bought a wye wound set and wanted to step up the voltage to 240 for running the larger motors especially. The transformer manufacturer only recommended the transformer for supplying the 3 phase loads, not center tapped to supply a neutral to get 120 out.
Jim
The load on the generator winding is limited by the amperage rating at whatever voltage you have it connected. This is as far as I know anyway.
We have utility power which is setup like this, but it is supplied by an open wye/open delta transformer bank of pole mounted transformers. So we want the emergency power to match the utility. I have never worried about trying to balance the load any more than it is balanced for the utility. It is impossible to balance it anyway since you cannot load the high voltage line to neutral leg with 120V loads. No problems with these small 50-60kW generators.
The limitation I think you might be referring to is for a dry type transformer where the heating is more of a problem. We bought a wye wound set and wanted to step up the voltage to 240 for running the larger motors especially. The transformer manufacturer only recommended the transformer for supplying the 3 phase loads, not center tapped to supply a neutral to get 120 out.
Jim
Re: GENERATOR SET
I went online and got drawing, but still have questions. It is a 12 lead unit Magna One 75 KW 277/480V 113 amp. I hooked T7-T1=L1 T8-T2=L2 T9-T3=L3 and T4-T5-T6-T10-T11-T12. This is a low volt wye set up. Is the 4 5 6 10 11 12 connection neutral. I get 0 ohms from this terminal to the frame of the unit. I'm not sure about hooking the other side of the motor starter coil to it. I can get 120V from L1, but need to hook the other side. The motor starter does work when jumpered to that terminal, but is that a correct installation? Thanks for all your help!
I went online and got drawing, but still have questions. It is a 12 lead unit Magna One 75 KW 277/480V 113 amp. I hooked T7-T1=L1 T8-T2=L2 T9-T3=L3 and T4-T5-T6-T10-T11-T12. This is a low volt wye set up. Is the 4 5 6 10 11 12 connection neutral. I get 0 ohms from this terminal to the frame of the unit. I'm not sure about hooking the other side of the motor starter coil to it. I can get 120V from L1, but need to hook the other side. The motor starter does work when jumpered to that terminal, but is that a correct installation? Thanks for all your help!
pierre
Senior Member
- Location
- Westchester County, New York
Re: GENERATOR SET
CCJersy
Your a dairy/vet - how did you learn your electrical backround?
CCJersy
Your a dairy/vet - how did you learn your electrical backround?
Re: GENERATOR SET
Hi Pierre,
Generally by keeping a farm going for the last 30 years. Had a couple physics courses in college, but that was a long time ago.
I guess it is mainly what a person is interested in that sticks to your brain over the years!
This and other forums are great too.
Jim
Hi Pierre,
Generally by keeping a farm going for the last 30 years. Had a couple physics courses in college, but that was a long time ago.
I guess it is mainly what a person is interested in that sticks to your brain over the years!
This and other forums are great too.
Jim
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