PPE Requirements for Working on Energized 250VDC Crane Hot Rails

[Poppington93]

I have a question about NFPA requirements for working on live 250VDC crane hot rails, such as removing collector shoes for weekly maintenance without shutting down the entire bay where other cranes are in operation at.

Our DC system is ungrounded and the specific area is fed from a 1600A breaker, old ABB K 1600 to exact. I see this is within NFPA 70E for Category 2, at least for the fault current of this circuit. I want to make sure I am going in the right direction of what PPE is required for this work, or what additional info I will need to determine the best measures for having employees perform the work safer without shutting down the entire bay since we are a high operation mill.

 

[mayanees]

I think you'll need an Incident Energy (IE) calculation for that specific bus.
For the first time NFPA Link is not available or I'd list the table that's applicable for shock protection (I think it's 130.4E (B) for DC). I think they're doing maintenance on the NFPA Link forum.
The IE calc downstream of a 1600-amp breaker will likely be more than the 8 calories that Category 2 PPE is rated for, but it depends on how deep you are in the electrical system.

 

[Ragin Cajun]

DC is a different ball game. It doesn't self extinguish.
I remember my days in DC motors lab. We had fun seeing who could craw the biggest arc.

 

[petersonra]

What makes you think you can do this work energized?

Best bet is install disconnect switches for each set of crane rails.

 

[zbang]

Sounds like there are multiple cranes on a single set of rails. If you need to work on the rails themselves, just do a shutdown of those rails and ground them; it would take a very long pull to justify hot work on them.

For the shoes- If there's some sort of a retract mechanism, probably all you'd have to do is shut off the individual crane's disconnect so there's no current and pull the retract lever or use a hot-stick and gloves to lift the shoes. (Whether you can work on them in the position they retract to is a whole 'nother question, like "are the supply rails insulated or bare?" and the like.)

There are a lot "it depends" involved, of course. Do they really need weekly maintenance, anyway?

 

[Jraef]

Sounds like there are multiple cranes on a single set of rails. If you need to work on the rails themselves, just do a shutdown of those rails and ground them; it would take a very long pull to justify hot work on them.

Yep. When I did the crane systems at a Boeing facility, the rails were sectionalized so that you could disconnect individual sections specifically for this purpose, while allowing the other cranes to operate on other sections of the same building. So whenever we were needing to work on the feeds, we would move the crane to a section of the building not in use, and then LO/TO the power to that section.