Deenergizing and replacing a transformer

[charlie b]

A small panel has two breakers that supply a transformer and a UPS. Their output goes to a ?UPS bypass switch? that is set up as ?make before break.? That switch feeds a branch circuit panel. I want to replace the transformer. I don?t think opening the transformer?s supply breaker is enough. I think the bypass switch has to be kept in the ?UPS? position, to prevent feeding UPS output voltage to the transformer?s location. But its handle is not lockable. Can this replacement be performed safely?

 

[sameguy]

If its a bypass then you have a big 3way switch ,with more poles. on/off/on or on/on like a transfer switch?
Drill a hole and add a lock?
Buy a plastic lock off?
Post a man to watch the handle.

 

[charlie b]

Here's a photo. The box is about 8x12 inches.

 

[markstg]

Tag it out, as in TO of LOTO. Maybe a person needs to be there also. yes this can be done safely. Maybe the transformer wires can be determinated at the Bypass switch (looks kinda small).

 

[growler]

Can this replacement be performed safely?

If the person doing the work is qualified they will figure out how to do it safely.

If it's me then I disconnect anything that may become energized before changes out equipment.

To physically disconnect the conductors at the source is even better than a lockout.

 

[dbuckley]

If it's me then I disconnect anything that may become energized before changes out equipment.

To physically disconnect the conductors at the source is even better than a lockout.

In theory I agree, but with this particular situation, you are on a no win situation.

To disconnect the conductors in the bypass box you would have to open the UPS bypass switch box, which has live circuits in it any time either the panel being discussed is energized, or the UPS output is present.

To disconnect them in the panel you would need the bypass switch to be in the UPS position with no possibility of it being moved.

If it were me I'd put warning notices over the switch and have a trusted colleague ensuring it isn't operated. The warning notices are in case the trusted colleague becomes incapable of guarding the switch, for example he is arrested or dies on the job.

Of course, if the UPS and its loads can be shut down, that would make the job more palatable, but then you would need a guard over the UPS too.

 

[charlie b]

Thanks for the comments. This facility has a maintenance department with "qualified persons" doing the work, and with a documented LOTO procedure. My concern is that whenever there is a need to operate the bypass switch, it is operated by the tenant, not by the maintenance group, and the tenant personnel are not "qualified persons," in the NEC sense. The job is likely to take a couple days, and the tenant won't want to shut down their equipment.

I am going to place a note on the drawing telling the EC to include the bypass switch in their LOTO process, even though it cannot be locked in the UPS position.

 

[ceb58]

A small panel has two breakers that supply a transformer and a UPS. Their output goes to a ?UPS bypass switch? that is set up as ?make before break.? That switch feeds a branch circuit panel. I want to replace the transformer. I don?t think opening the transformer?s supply breaker is enough. I think the bypass switch has to be kept in the ?UPS? position, to prevent feeding UPS output voltage to the transformer?s location. But its handle is not lockable. Can this replacement be performed safely?

Charlie are you concerned with back feeding to the panel with the two breakers? Or dose the UPS feed the transformer?

 

[winnie]

Here's a photo. The box is about 8x12 inches.

You could lock this device by locking some sort of 'custom made bubble cover' or operator shaped cutout to the box.

-Jon

 

[charlie b]

Charlie are you concerned with back feeding to the panel with the two breakers? Or does the UPS feed the transformer?

I am concerned with backfeeding from the UPS to the transformer, while the transformer is being removed and replaced, if the bypass switch was taken to its mid position (i.e., the make-before-break position).

 

[ceb58]

I am concerned with backfeeding from the UPS to the transformer, while the transformer is being removed and replaced, if the bypass switch was taken to its mid position (i.e., the make-before-break position).

The "make before break" is just that the switch will make with the bypass position before it breaks the UPS position. That way power is not interrupted. The bypass switch will bypass sending power to the UPS and directly to the UPS protected load, however there will be power coming to the UPS output terminals in the switch.
From what I see in the photo there is no disconnect on the UPS output to the switch. One section that addresses this is 645.11 which leads back to 645.10. One way to insure the output is disconnected is to remove the batteries from the UPS.

 

[qcroanoke]

The "make before break" is just that the switch will make with the bypass position before it breaks the UPS position. That way power is not interrupted. The bypass switch will bypass sending power to the UPS and directly to the UPS protected load, however there will be power coming to the UPS output terminals in the switch.
From what I see in the photo there is no disconnect on the UPS output to the switch. One section that addresses this is 645.11 which leads back to 645.10. One way to insure the output is disconnected is to remove the batteries from the UPS.

Or, if the UPS has an EPO contact, either remove the jumper, or add one till the work is done.

 

[dbuckley]

Yes, but as noted above: the owners dont want a multi-day shutdown.

I think that is reasonable. The switch can be made inoperable. It may take a shift of men with dog on guard 24x7 for a few days to ensure no-one enters the location where the switch is, but presumably that is cheaper than a shutdown.