LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I concur.
2pole 30a. switch for 480 v install?!
- Thread starter Copperclad
- Start date
- Status
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Wouldn't you still have 277 volts across the individual poles with 2 - 277 volt circuits from different phases - (277/480 MWBC)? The loads will have the neutral connected in this case and that should stabilize that voltage no matter what impedance differences are in the loads. There will be 480 volts potential within the switch but not across individual contacts.
Question is - is the switch rated to connect two phases to it? Are internal components insulated / separated well enough for 480 volts within the device?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
How would you get 480V to the light with a dp switch if there weren't two 277V phases?
You take one of the pairs of phases AB,BC or CA to the fixture thru the switch and the potential between these phase wires is 480V,277V is never in the mix,,,it only comes into play when only one of the phase wires is paired up with its neutral, assuming its a 3phase,4 wire system.
dick
dick
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Don?t get hung up on the values of voltage to neutral. That is not the only consideration. I agree with Chris, and his code citation is clear enough. But let me add a bit of physics to the party.
The basis of any voltage rating is the ability of the non-conductive materials to prevent leakage current from the energized portions to the surrounding world. Consider, for example, a 600 volt rated wire sitting on the bottom of a metal conduit. The voltage rating of the insulation system tells us that you can impose 600 volts on the wire, and you will not get leakage current from the energized copper wire, through the insulation system, to the conduit.
In this instance, the energized portions of the component are the switch contacts and some other stuff, and the non-conductive materials are the plastics (or whatever) that keep the contacts in their respective places. A rating of 277 volts tells me that you can impose that much voltage, and not get leakage current from one of the switch contacts, through the plastic, to the other switch contact or to the metal piece used to screw the switch into the outlet box. If you have a 2-pole switch connected to two phases of a 480/277 volt system, then there will be 480 volts trying to drive current through the switch internals from one contact point to another, and the switch?s insulation system won?t be rated to prevent leakage current. That is the reason for the requirement that the switch be rated for 480 volts.
The basis of any voltage rating is the ability of the non-conductive materials to prevent leakage current from the energized portions to the surrounding world. Consider, for example, a 600 volt rated wire sitting on the bottom of a metal conduit. The voltage rating of the insulation system tells us that you can impose 600 volts on the wire, and you will not get leakage current from the energized copper wire, through the insulation system, to the conduit.
In this instance, the energized portions of the component are the switch contacts and some other stuff, and the non-conductive materials are the plastics (or whatever) that keep the contacts in their respective places. A rating of 277 volts tells me that you can impose that much voltage, and not get leakage current from one of the switch contacts, through the plastic, to the other switch contact or to the metal piece used to screw the switch into the outlet box. If you have a 2-pole switch connected to two phases of a 480/277 volt system, then there will be 480 volts trying to drive current through the switch internals from one contact point to another, and the switch?s insulation system won?t be rated to prevent leakage current. That is the reason for the requirement that the switch be rated for 480 volts.
- Status