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#194900 - 06/29/10 06:21 PM Manhole electrcial safety  
Cmoore  Offline
New Member
Joined: Jun 2010
Posts: 1
Mountain View, Ca
Hi all,

First time poster. I have a situation where I have contractors entering a manhole to pull cable. The manhole is equipped 7.2 kev lines, the conductors are not exposed. They plan to enter the manhole using ARC Flash PPE to lay down insultated blankets over the cables. After that they plan to work without ARC flash PPE. Does the following statement from NFPA 70E preclude the use of ARC Flash PPE Protection? Any help greatly appreciated.

(F) Confined or Enclosed Work Spaces. When an employee
works in a confined or enclosed space (such as a
manhole or vault) that contains exposed energized electrical conductors or circuit parts operating at 50 volts or more or where an electrical hazard exists, the employer shall provide, and the employee shall use, protective shields, protective barriers, or insulating materials as necessary to avoid inadvertent contact with these parts and the effects of the electrical hazards. Doors, hinged panels, and the like shall
be secured to prevent their swinging into an employee and
causing the employee to contact exposed energized electrical conductors or circuit parts rating at 50 volts or more or where an electrical hazard exists.

Arc Flash PPE Clothing, LOTO & Insulated Tools

#194916 - 06/30/10 11:51 AM Re: Manhole electrcial safety [Re: Cmoore]  
sabrown  Offline
Joined: Dec 2002
Posts: 302
Ogden, Utah, USA
Without knowing all that may be down there and what sort of protection is in place, what they plan on doing from the electrical stand point sounds very reasonable. I have seen situations below grade where when things were first installed they were properly protected but over time the protection has corroded away. It sounds like on one hand they are over killing things, but on the other they sound smart and anticipate possible problems. I think they could decide the mats are overkill once in and determinimng the site safe.

This all assumes you mean 7.2kv (7200 volts) and not 7.2 kev (7200 electron volts) which I am sure is less than the voltage that is created by air flow through my nose when I sneeze.

There are additional OSHA confined space entry requirements and permits (at least for us in the Government) dealing with oversight, rescue ect. We have training on it, but it has been some time since I took it (I am not typically involved).

Sorry that I can not give you better information. I hope that this at least gives you a place to start and those more knowledgable step in to help.

#194933 - 07/01/10 06:34 AM Re: Manhole electrcial safety [Re: sabrown]  
Tesla  Offline
Joined: Jun 2004
Posts: 1,273
Sacramento, CA
My personal experience has been that old conductors unable to dump heat suffer quite a loss of their insulation value over time.

I'd seriously recommend that utilities de-rate the ampacity of older cable before they let the smoke out.

Is there any possibility of the hot lines being de-energized long enough so that they can be hi-potted?

If not... I'd be paranoid.

Even if the hot cables are blanketed I'd want my down-hole time absolutely as low as possible. I'd be very reluctant to let the troops forgo protective gear.

The tugging schemes I've in mind do NOT require a lot of down-hole time. So I'd be very reluctant to play it slack.

My biggest worry is the nasty atmospheres found below grade. Please, ventilate generously.


#195020 - 07/06/10 01:16 PM Re: Manhole electrcial safety [Re: Tesla]  
mikesh  Offline
Joined: Jun 2006
Posts: 613
Victoria, BC, Canada
Last manhole I was in we wore low calorie, disposable suits, hardhats, and safety glasses.
No exposed live bits and no switching activities. 25 KV cables and HV transformers.

Confined space rules were higher on our list of concerns but I did not touch anything with HV under the insulation.

From an E70 perspective I am not even sure that pulling cable is an activity that requires arc flash protection but I would never wear synthetic clothing in a vault.

#195100 - 07/11/10 07:33 PM Re: Manhole electrcial safety [Re: mikesh]  
njelectricmaster  Offline
Joined: Apr 2001
Posts: 109
Lead, South Dakota
Hello from Washington,

This is just my two cents. I work with 4160v through 34.5kv in underground situations every day. because I work in the mining field I fall under the 30 cfr instead of the 29 cfr, but we do adhere to the 70E standards, so take what I have to say for what it is worth.
First thing, I would set up an emergency retrieval tripod with a winch rated for twice the wieght of the largest man. I would put a harness on anyone heading into the vault so I could pull them out in an emergency by my self.
I would set up ventilation on site and have fresh air blowing into the vault for at least 10 min before entering. I would drop a gas meter into the vault to make sure there were no deadly gases left in the vault where I was sending myself or my men.
Next I would have my men in the appropriate PPE for the voltage present, lower them in, cover the exposed lines with blast blankets, remove the flash suit, and put the retieval harness back on.
After finnishing the job required I would have them put the flash suit back on, remove the blanket, clean the vault, and hoist them back out. Then clean the site, reinstall the vault cover, and then test the new circuit.

I know my approach may be a bit lengthy and time consuming, but a life is never worth less than money.

You might want to even sit down for five min and do a pretask plan to make sure everyone is in the same frame of mind and noone has missed any of the site specific hazards.

Jon Niemeyer

Jon Niemeyer

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