Min. Approach Distances in Manholes
Min. Approach Distances in Manholes
(OP)
Can any one tell me where to find min. approach distances for A.C. voltage in manholes and vaults.
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
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Min. Approach Distances in Manholes
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RE: Min. Approach Distances in Manholes
RE: Min. Approach Distances in Manholes
RE: Min. Approach Distances in Manholes
RE: Min. Approach Distances in Manholes
RE: Min. Approach Distances in Manholes
This may put things in perspective for the safety department.
My appologies if I have misunderstood this issue.
yours
Bill
RE: Min. Approach Distances in Manholes
RE: Min. Approach Distances in Manholes
There are documented cases of insulated cables that behave as thought they had cracks or pinhole leaks in the insulation. ( I said behave because the last I read on the subject some people said they could have pinholes and others said they couldn't)
Whatever, when the insulated cables were touched or wiggled the insulation failed with great balls of fire and injured people.
Treat all high voltage insulated cables as though it were bare. Keep you hands off, do everything you need to do from outside with a hotstick. If you didn't design it to work with a hotstick do it over.
There is no reason to be in a vault with energized cables. You can't see or feel any of the "good stuff" you mentioned. You can test for it from the ends and get a little indication but that whichyou find by feeling around in the valut may be the last thing you ever find.
The "reach rule" shoud be - if you can't do it with a hot stick from up top, shut it all down and rebuild it.
RE: Min. Approach Distances in Manholes
Waross is right - tell the Safety Dept to go down there.
RE: Min. Approach Distances in Manholes
A thorough job briefing must be performed, identifying any and all hazards associated with each individual manhole.
Each crew member must know the name of the circuit being worked on, as well as the exact location of the manhole being entered.
Prior to entering the manhole, a thorough visual inspection of the cable must be performed. The employees must ensure that the conductive sheath and the ground connections are not disrupted. If any of the static wires near the elbows are broken or disconnected, they must be repaired if possible.
Arc suppressant blankets should be used where possible to prevent injuries, should an unexpected equipment failure take place.
In addition to the arc blankets, rubber protective blankets should be used, where necessary, to prevent employee contact with the energized conductors.
Dielectric boots/overshoes, rubber gloves and rubber sleeves should also be worn when working in the manholes.
Additionally, I recommend that additional layers of FR clothing or PPE be worn when entering the manholes. It is also advisable that employees wear arc rated faceshields when moving/manipulating cables in the manholes.
I have explained to my employer the problems Oyster Creek Generating Station had with the same type of cable.
The independent failure analysis and the root cause analysis prepared by AmerGen determined that the May 20, 2003, cable failure was the result of water intrusion into the Ò1CÓ cable between the insulation and the insulation shield. Apparently, underground water filtered through the conduit and cable jacket, degrading the cable insulation and causing the cable to short to ground. The cable that failed in May 2003 was manufactured by Anaconda. Prior to this event, Oyster Creek had experienced an additional ten inservice, medium voltage cable failures. Of these, six were failures of Anaconda Unishield type cables. A seventh failed cable was also Unishield type manufactured by Cablec, after their purchase of the Anaconda company. Based on a chart prepared by the licensee, the Anaconda and Cablec cable failures were either due to water intrusion or manufacturing defects that, over time, caused the cables to fail.
I have asked for FR ear plugs. I don't want to be blind and deaf.
This type of cable appears to have no fault carrying capability. And after a number of faults along with the age of the cable I believe the integrity of the cable is bad at best.
Regards Deltay
RE: Min. Approach Distances in Manholes
I don't see what it is you expect to find with a visual inspection. What ever is is' i don't think it's worth the risk.
There have been several videos of short circuits in manholes circulating on the web. I can't find any of them at the moment.
If you see the videos or have ever seen a vault after a short circuit I don't think you would go in vault wearing supermans cape.
RE: Min. Approach Distances in Manholes
I told our managers there comes a time you need an outage.There comes a time you stay out of the manholes.Just like there comes a time you would not climb a rotten pole.There comes a time you do not go in the shakey manhole.
This to has fallen on deaf ears.
RE: Min. Approach Distances in Manholes
Just draft up a memo that summarizes your understanding of what management wants you to do and ask them to sign it.
Also, you might want to take a look at the Energized Work Permit form that is required by NFPA 70E. It requires a sign-off by line management for all work on or near energized equipment.
RE: Min. Approach Distances in Manholes
Manipulation of the cables could stress the insulation or cause an elbow to disconnect. I would consider the cables to be live for such work, and use the MAD and flash hazard boundaries.
How does one repair the ground connections while the circuit is live? If the very connections that allow the equipment to be considered dead front are suspect, that the equipment fronts (and cable sheathes) must be considered live.
None of the PPE suggested will protect you from cable movement in the event of a short circuit. Note that this exposure is not only from a local event. The drunk hitting a pole a few miles away might be the initiating event for the short circuit and resultant cable movement.
RE: Min. Approach Distances in Manholes
If someone order me to go in I would tell him not just "NO" but "HELL NO". That is after I stopped laughing. If they fire you You should be able to find a greedly lawyer to go after them on a contingency basis.
RE: Min. Approach Distances in Manholes
RE: Min. Approach Distances in Manholes
RE: Min. Approach Distances in Manholes
The equipment described is shielded, except for the possibility of ground discontinuity that they are checking for.
RE: Min. Approach Distances in Manholes
1910.269(t)(7)
"Defective cables." Where a cable in a manhole has one or more abnormalities that could lead to or be an indication of an impending fault, the defective cable shall be deenergized before any employee may work in the manhole, except when service load conditions and a lack of feasible alternatives require that the cable remain energized. In that case, employees may enter the manhole provided they are protected from the possible effects of a failure by shields or other devices that are capable of containing the adverse effects of a fault in the joint.
Note: Abnormalities such as oil or compound leaking from cable or joints, broken cable sheaths or joint sleeves, hot localized surface temperatures of cables or joints, or joints that are swollen beyond normal tolerance are presumed to lead to or be an indication of an impending fault.
..1910.269(t)(8)
1910.269(t)(8)
"Sheath continuity." When work is performed on buried cable or on cable in manholes, metallic sheath continuity shall be maintained or the cable sheath shall be treated as energized.
RE: Min. Approach Distances in Manholes
I believe the age of any cable has to come into perspective. This particular cable is 33 years old and has been exposed to water intrusion since 1973. You can see the oxidation of the neutral drain wires. What I am saying is how can you see a partial discharge occurrence between the wires and the insulation shield? And if this is happening in time it will breakdown the insulation which will cause regions of stress enhancement then comes dielectric failure.
We can do a D-C Hi-Pot to check the integrity of the cable but you need an outage for that.
There are times that I am within a 1/4 inch of these circuits.
So when you read in the OSHA regs. about defective cable or abnormalities, knowledge intelligence and common sense has to prevail if we want to save lives and stop accidents..
There comes a time when a lineman will not climb a rotten pole.
We need a clear cut way to call a manhole unsafe and it needs to be deenergized.