Disconnect Voltage Rating??

[jahilliard]

In the case of a 3 phase 480V system there is a 250V rated 400A fused disconnect installed as opposed to a 600V rated 400A disconnect. What are the realistic possibilites or dangers with this installation? I'm asking for realistic responses or possible actual issues experienced in the field under these circumstances...or possibly an explanation of what may actually happen based upon electrical theory. thanks.

 

[socalelect]

i would venture to say it has to do with the arc flash ratings of the internals, i have installed alot of them and that seems to be the only difference that i have noticed . im sure thats not the only reason thoe . i generally only work with 240 and lower voltage so i cant say for sure

 

[rcwilson]

250V vs 600V Rated Disconnect Switches

250V vs 600V Rated Disconnect Switches

Eaton's 250 V disconnects are about 55% of the height and 80% of the width of their 600V line. There's a reason for that larger dimensions.

Phase-to-phase and phase-to-ground clearances and insulation will be different. There is a good chance of a flashover across the reduced dimensions when a voltage surge occurs.

The opening between the energized fixed part of the disconenct and the switch arm will be less at 250V. It might flash over when you think the load is disconnected.

If the disconnect is opened under load, the shorter travel of the moving part may not be enough to break the arc. That will lead to a flashover and an exploding enclosure.

If the switch is a fused style, it will not accept 600V fuses. When a fault occurs, the 250 V fuses will blow up. The arc could destroy the wire, the enclosure and initiate a fire. I investigated under rated fuses causing fires that took down whole MCC's in a government building.

Bottom line- not a good idea.

 

[Jraef]

Eaton's 250 V disconnects are about 55% of the height and 80% of the width of their 600V line. There's a reason for that larger dimensions.

Phase-to-phase and phase-to-ground clearances and insulation will be different. There is a good chance of a flashover across the reduced dimensions when a voltage surge occurs.

The opening between the energized fixed part of the disconnect and the switch arm will be less at 250V. It might flash over when you think the load is disconnected.

If the disconnect is opened under load, the shorter travel of the moving part may not be enough to break the arc. That will lead to a flashover and an exploding enclosure.

If the switch is a fused style, it will not accept 600V fuses. When a fault occurs, the 250 V fuses will blow up. The arc could destroy the wire, the enclosure and initiate a fire. I investigated under rated fuses causing fires that took down whole MCC's in a government building.

Bottom line- not a good idea.

This forum needs a "Like" button feature. Well said, covered all the salient points..

I don't understand how a 250V disconnect could have been used at all, the 600V fuses will not fit (and that is on purpose just to prevent this sort of thing). So either someone gerrymandered an adapter of some sort or they used 250V rated fuses on 480V, in which case Bob's statement about the danger of a fire are very real.

 

[kwired]

Eaton's 250 V disconnects are about 55% of the height and 80% of the width of their 600V line. There's a reason for that larger dimensions.

Phase-to-phase and phase-to-ground clearances and insulation will be different. There is a good chance of a flashover across the reduced dimensions when a voltage surge occurs.

The opening between the energized fixed part of the disconenct and the switch arm will be less at 250V. It might flash over when you think the load is disconnected.

If the disconnect is opened under load, the shorter travel of the moving part may not be enough to break the arc. That will lead to a flashover and an exploding enclosure.

If the switch is a fused style, it will not accept 600V fuses. When a fault occurs, the 250 V fuses will blow up. The arc could destroy the wire, the enclosure and initiate a fire. I investigated under rated fuses causing fires that took down whole MCC's in a government building.

Bottom line- not a good idea.

I agree other than the statement that the 250 volt fuses will blow up. I would rather say they may flash across because of shorter distances just like everything else may flash across because of shorter distances. Still may result in an explosion but it is not really the fuse that exploded as much as it flashed across it. ( I think) Isn't the interrupt rating of a 400 amp 250 volt fuse similar or same to the interrupt rating of a 400 amp 600 volt fuse of same type (like RK5 for example), the main difference is the physical size just like the difference in size of fuse holder, switch parts, etc. So when that fuse blows there will be a longer gap for voltage to have to jump across if it were to flash over for the 600 volt fuse.