Class 1 Division 2 Medium Voltage Terminations

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Larry Putman

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My Company manufactures SF6 and oil insulated medium voltage switches. One of our customers has asked us to provide one of our switches in a class 1 Division 2 location. My research shows we should be able to do so except I can not find any information in regard to terminating the switch. The switch is provided with apparatus bushings that are welded in place so the switch tank (protected enclosure) is sealed. Although the cable termination is a bolted and taped connection or 600 amp deadbreak terminations. Can anyone help with locating information in regard to this matter?
 
I agree with Don's evaluation.

I do have some curiosity about the ??600 amp deadbreak terminations.? I assume they cannot be disconnected unless the switch is open.

My concern is how (or even if) the MV cables are discharged before disconnecting. Since virtually all MV cables are now required to be shielded and they can hold a capacitive charge for quite a while. I believe there may be a bit of a problem with drawing an arc if the terminations are disconnected in the classified location. Almost any arc is sufficient to be an ignition source.

Since the application is Division 2, I doubt it would be a significant problem, but I do think you should caution you user.
 
Thank you both, the cable does not have any interlock to prevent removal before opening the switch. Although to do so would require removal of a insulated cap, removal of a 5/8" threaded stud, and then pulling the elbow off the bushing. As for discharging the cable this may be done simply by taking the switch to ground position.
 
rbalex said:
I agree with Don's evaluation.

I do have some curiosity about the ??600 amp deadbreak terminations.? I assume they cannot be disconnected unless the switch is open.

My concern is how (or even if) the MV cables are discharged before disconnecting. Since virtually all MV cables are now required to be shielded and they can hold a capacitive charge for quite a while. I believe there may be a bit of a problem with drawing an arc if the terminations are disconnected in the classified location. Almost any arc is sufficient to be an ignition source.

Since the application is Division 2, I doubt it would be a significant problem, but I do think you should caution you user.
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This is where it becomes an operation issue which the Code normally does not address. It is necessary to work on energized equiepment even in classified locations. As an example it would be impractical to shut down an entire plant to change out a powered transmitter, or to fix a lighting cisuit.

The usual course in Class I Division areas is to "sniff" the area for LEL, declare it safe - e.g. non-classified - and maintain the LEL monitoring for the duration of the work.

The same course should be followed for the cited work also. In addition - since test-before-touch is the prudent measure - full protective gear, including arc-flash protection shall be worn to test the disconnect for voltage presence, as it must be assumed that it is energized before proven otherwise.
 
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