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Min. Approach Distances in Manholes
- Thread starter deltay
- Start date
apowerengr
Electrical
Same spot as the rest - NESC section 44 or OSHA
- Thread starter
- #3
apowerengr
Electrical
"insulated" does not matter; "shielded" (or not) is the appropriate criteria for approach distances.
- Thread starter
- #5
Thank you again for your info.The system we are working on is 4kv.The type of cable is Anaconda Unishield EP 1973 . The manholes we are working in are under water most of the time so we have to be concerned with degraded cable, water intrusion ,insulation breakdown and all that good stuff. Some of the manholes are so congested you cannot fit a ladder between phases. Most of the manholes have at least 6 to 9 pistol grip type of connections on 4 way connectors. Also as far as I know this system has failed at least 3 times this year. What do you think the reach rule should be?
- Moderator
- #6
I would emphasize the importance of the safety department physically and personally checking each manhole for safety issues before work is performed. Ideally they would enter the manhole and make some trial disconnections. They seem to have assured you that it is safe.
This may put things in perspective for the safety department.
My appologies if I have misunderstood this issue.
yours
Bill
This may put things in perspective for the safety department.
My appologies if I have misunderstood this issue.
yours
Bill
If your insulation had broken down from phase to shield you would know it. I agree there is no MAD to the shielded equipment. My concern would be that conductors in such a tight space would need to be restrained extremely well to prevent movement into your worker during a fault condition.
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.
The Unishield is not a traditional shielded cable - it has drain wires embedded in the the jacket. I would want to avoid any contact with one while it was energized. (Actually, I'd want to avoid contact with any cables when they are energized.
Waross is right - tell the Safety Dept to go down there.
Waross is right - tell the Safety Dept to go down there.
- Thread starter
- #10
Thank You for your impute. We asked our safety dept. to come on site they did this is there recommendations.
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
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
Google "manhole short circuits explosions".
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.
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.
- Thread starter
- #12
I will look up manhole explosions on the net.Thanks for the idea.By the way we are being told by management that we have to go in theses 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.
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.
deltay,
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.
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.
What tasks are to be performed in the 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.
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.
Also take the memo that DCP suggested and make sure your wife and lawyer have a copy. It won't do you any good but you estate may gain from it.
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.
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.
Actually, I've had some success with the idea of asking management to sign off on a controversial safety issue. If done in a non-belligerent way, it can cause them to re-think their position. That is really the main intent of the Energized Work Permit in NFPA 70E.
apowerengr
Electrical
deltay, min approach would apply as the conductors are not shielded. Also look at NESC 323 for the requirements related to manholes and vaults including B for clear working space and C for access. If the manholes fill with water the separable connectors and 4 way modules you described are not applicable to submersible systems and the codes implie that equipment should be used within manufacturers recommendations. Min approach is 2'2" phase-to-ground and 2'3" phase-to-phase exposure. Given the unshielded nature of the system 2'3" sounds like a good starting point. Are you using 4' shotguns for elbow switching or is someone pulling elbows using gloves & sleeves?
Separable connectors built to IEEE 386 are built for this usual service condition: "c) Intermittently or continuously submerged in water at a depth not exceeding 2 m (6 ft)."
The equipment described is shielded, except for the possibility of ground discontinuity that they are checking for.
The equipment described is shielded, except for the possibility of ground discontinuity that they are checking for.
Some relevant OSHA regs:
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.
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.
- Thread starter
- #20
Thank you everyone for your support
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.
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.
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