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Manhole work with live circuits present
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Author:  Mike Fox [ Mon May 06, 2019 6:34 am ]
Post subject:  Manhole work with live circuits present
I have worked in manholes for decades now. My question is what are the present standard for working on a dead circuit with live circuits present in a manhole. The voltage is 5kV
Author:  Oly [ Mon May 13, 2019 12:05 pm ]
Post subject:  Re: Manhole work with live circuits present
Mike,
Some of us are not familiar with manhole work.
What is the typical work space within a manhole?
Are there exposed live bus or conductor terminations?
Have you ever witnessed corona in a manhole?
Author:  Leonard [ Mon May 13, 2019 2:41 pm ]
Post subject:  Re: Manhole work with live circuits present
Hi Mike

Greetings from North of the Border. Not that I am an expert on confined space, however from my experience a manhole (underground vault) would be considered a confined space, which presents a whole set of challenges with procedures. As Mike has asked, are there exposed terminations or connections near where the workers are present? Back 2 Summers ago I was working with a contractor up here in Toronto. They had concerns on the hazard of arc flash, perhaps more than shock. At that time there were incidents of manhole covers blowing off in the downtown Toronto area. Likely due to aging infrastructure and other issues. In assisting them with the development of entry procedures into the vsaults, the workers had with them an arc supression blanket that they would install over the conductors in the vault that in the event of a preossible flash at least the blanket would supress some of the effects of the flash. Direct contact was not a concern with these workers however they did have to consider as part of the risk assessment. If not already I would conduct a risk assessment for the task(s) being performed. Start with that.

If you require further information Mike, please do not hesitate to contact me offline - <deleted personal contact info>

Thanks
Len
Author:  haze10 [ Mon Jun 03, 2019 5:53 am ]
Post subject:  Re: Manhole work with live circuits present
I've worked a considerable amount in 5KV manholes.

1st, Manhole is a confined space, so all confine space entry requirements are in place.

2nd. Typical manholes are NOT watertight, so usually you have no live parts. My comments are limited to insulated cables passing through, or being spliced, or other deadfront type connections like 600/200A elbows.

3. A flooded manhole is your best friend. If there was not arc while cables submerged under water. Then insulation is good and indicate no live parts.


4. After pumping out the manhole dry, and following confined space entry procedure, go in with Level 4 arc flash, with tic tracer and check for any open, crack, leaking cables. Note that tic tracer does not work on 100% shielded cables. But if anything was leaking tic tracer would register. Now consider manhole free of live parts, and change into Level 2 arc flash and re-enter manhole.

5. If you are working a known dead cable, say splicing a new cable run, usually do nothing to existing cables except not permitted to handle/move energized cables.

6, If you are making a tap, into and existing cable. Attach amp probe around cable, verify amperage, institute LOTO, verify loss of amperage. Discharge cable at source or load termination using proper HV procedure. Back in the manhole, cut back small section of outer PVC jacket to reveal shield. Remove shield. Check with tic tracer. No voltage, proceed with cutting cable or stripping to conductor.
I've seen this done in both Level 2 and Level 4 suits. Depends on your comfort level. Once you have the cable apart and proved safe, change to Level 2.

I've never found any written procedures in NFPA for working in manholes and doing actual cable splicing or taps. This is just what I've seen done. This kind of work is a bit specialized.
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