jimwalker
Senior Member
- Location
- TAMPA FLORIDA
Can a 4 square box have 2 switches ,one on 120 volts other on 277 ? both ran in 600 volt mc
120 volts 277 volts
- Thread starter jimwalker
- Start date
- Status
pierre
Senior Member
- Location
- Westchester County, New York
Re: 120 volts 277 volts
404.8(B) Voltages Between Devices.
The voltage between the devices cannot exceed 300 volts.
A barrier can be installed in that box, and make it code compliant.
404.8(B) Voltages Between Devices.
The voltage between the devices cannot exceed 300 volts.
A barrier can be installed in that box, and make it code compliant.
bphgravity
Senior Member
- Location
- Florida
Re: 120 volts 277 volts
I have never seen a 4 square box equipped with a permanent barrier for this purpose. Do they make such a thing?
I have never seen a 4 square box equipped with a permanent barrier for this purpose. Do they make such a thing?
- Location
- Massachusetts
Re: 120 volts 277 volts
Oh yeah they make them, we use them when we have more than 1 phase of 277 lighting in a switch box.
Question, with a 120 and a 277 circuit in a box is there always more than 300 volts between switches or just when we have different phases?
I am thinking with 120 and 277 volt circuits both from the same phase you would only have 157 volts between switches. Is this a correct assumption?
Oh yeah they make them, we use them when we have more than 1 phase of 277 lighting in a switch box.
Question, with a 120 and a 277 circuit in a box is there always more than 300 volts between switches or just when we have different phases?
I am thinking with 120 and 277 volt circuits both from the same phase you would only have 157 volts between switches. Is this a correct assumption?
- Location
- Massachusetts
Re: 120 volts 277 volts
AGAIN
AGAIN
Re: 120 volts 277 volts
120 volts and 277 volts are derived from two different sources. They are both in reference to ground. They are allowed to occupy the same enclosure without a barrier. (less than 300v between energized conductors) However neutrals, if present, must be indentified differently to indicate they are from two different sources.
120 volts and 277 volts are derived from two different sources. They are both in reference to ground. They are allowed to occupy the same enclosure without a barrier. (less than 300v between energized conductors) However neutrals, if present, must be indentified differently to indicate they are from two different sources.
- Location
- Illinois
- Occupation
- retired electrician
Re: 120 volts 277 volts
derwith,
Since both the 120 and 277 volt systems are referenced to a common point, there is voltage between the systems ungrounded conductors. The voltage between A phase on the 120 volt system and B or C phase on the 277 volt system is ~359 volts.
Don
derwith,
Since both the 120 and 277 volt systems are referenced to a common point, there is voltage between the systems ungrounded conductors. The voltage between A phase on the 120 volt system and B or C phase on the 277 volt system is ~359 volts.
Don
Re: 120 volts 277 volts
Don,
Both the neutral of the 120 volt system and the neutral of the 277 volt system are at ground potential. There is 120 volts to ground and there is 277 volts to ground. 120 minus 277 is 157. That is the maximum difference between ungrounded conductors.
The 120 volt to ground circuit has either 240 volts single phase or 208 volts if three phase between ungrounded conductors. The 277 volt to ground circuit has 480 volts three phase between ungrounded conductors. It is 277 volts to ground whether using phase A, B, or C.
With a box containing two switches and one is 120 volts and the other is 277 volts, two 480 volt between ungrounded conductors would not be there.
I believe the 300 volt limitation is specifically to allow 277 volt switching.
Don,
Both the neutral of the 120 volt system and the neutral of the 277 volt system are at ground potential. There is 120 volts to ground and there is 277 volts to ground. 120 minus 277 is 157. That is the maximum difference between ungrounded conductors.
The 120 volt to ground circuit has either 240 volts single phase or 208 volts if three phase between ungrounded conductors. The 277 volt to ground circuit has 480 volts three phase between ungrounded conductors. It is 277 volts to ground whether using phase A, B, or C.
With a box containing two switches and one is 120 volts and the other is 277 volts, two 480 volt between ungrounded conductors would not be there.
I believe the 300 volt limitation is specifically to allow 277 volt switching.
- Location
- Illinois
- Occupation
- retired electrician
Re: 120 volts 277 volts
derwith,
If you want to find the actual voltage between the A phase of the 120 volt system and the B phase of the 277 volt system you must use vector addition because these two votlages (vectors) are 120? out of phase. The 157 volt difference only applies when the 120 and the 277 voltages are both of the same phase. Any time there is a combination of phases, the voltage between the two will be ~359 volts and require a barrier per 404.8(B).
Don
derwith,
If you want to find the actual voltage between the A phase of the 120 volt system and the B phase of the 277 volt system you must use vector addition because these two votlages (vectors) are 120? out of phase. The 157 volt difference only applies when the 120 and the 277 voltages are both of the same phase. Any time there is a combination of phases, the voltage between the two will be ~359 volts and require a barrier per 404.8(B).
Don
bphgravity
Senior Member
- Location
- Florida
Re: 120 volts 277 volts
I always wondered what that slot in the plaster ring was for.
I always wondered what that slot in the plaster ring was for.
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
Re: 120 volts 277 volts
They are also used to satisfy 725.55 for seperation of line voltage and low voltage. If you notice, plastic boxes have them as well.Originally posted by bphgravity:
I always wondered what that slot in the plaster ring was for.
jimwalker
Senior Member
- Location
- TAMPA FLORIDA
Re: 120 volts 277 volts
Thanks everyone.We now can handle this and be code compliant
[ September 13, 2004, 05:49 AM: Message edited by: jimwalker ]
Thanks everyone.We now can handle this and be code compliant
[ September 13, 2004, 05:49 AM: Message edited by: jimwalker ]
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
Re: 120 volts 277 volts
Bryan: In your picture it looks like the both switches are on the same phase and therefore wouldn't require a seperator.
Bryan: In your picture it looks like the both switches are on the same phase and therefore wouldn't require a seperator.
Re: 120 volts 277 volts
Don,
My math and logic of the previous post is wrong. Thanks for pointing that out Don.
Here is another thought. Since there are two separately derived systems wouldn't there be no voltage between them except for incidental capacitance and inductance from the wiring system?
Wouldn't this would be true regardless if the systems are single phase or three phase.
Don,
My math and logic of the previous post is wrong. Thanks for pointing that out Don.
Here is another thought. Since there are two separately derived systems wouldn't there be no voltage between them except for incidental capacitance and inductance from the wiring system?
Wouldn't this would be true regardless if the systems are single phase or three phase.
- Location
- Illinois
- Occupation
- retired electrician
Re: 120 volts 277 volts
derwith,
While they are separate systems, they share a common reference point...the grounding electrode system. This common reference point resutls in a voltage between the ungrounded conductors of the two different systems.
Don
derwith,
While they are separate systems, they share a common reference point...the grounding electrode system. This common reference point resutls in a voltage between the ungrounded conductors of the two different systems.
Don
- Location
- Illinois
- Occupation
- retired electrician
Re: 120 volts 277 volts
derwith,
Because XO of both transformers are tied together. Draw two wye connected transformers and connect the center point of the two wyes, then look at the current path. It is from the ungrounded conductor of one transformer, to the grounded conductor of that transformer, to the grounded conductor of the second transformer, to the ungrounded conductor of that second transformer.
Don
derwith,
Because XO of both transformers are tied together. Draw two wye connected transformers and connect the center point of the two wyes, then look at the current path. It is from the ungrounded conductor of one transformer, to the grounded conductor of that transformer, to the grounded conductor of the second transformer, to the ungrounded conductor of that second transformer.
Don
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