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 Post subject: 15kV cables in a manhole
PostPosted: Tue Aug 27, 2019 8:07 am 
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Location: Rutland, VT
What electrode configuration would be for a cable running along a manhole wall?
I am thinking HOA?

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 Post subject: Re: 15kV cables in a manhole
PostPosted: Mon Sep 16, 2019 10:19 am 
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Location: New England
Can you explain your question better. You don't typically have 'electrodes' in a manhole as that term implies a conductor that is uninsulated and manholes fill with water. Cables passing through manholes are typically insulated, and installed on racks along the wall. Racks can be fiberglass, or if metal they usually use a porcelain rest under the cable.


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 Post subject: Re: 15kV cables in a manhole
PostPosted: Wed Sep 18, 2019 2:46 am 
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What if the cable is cut into while energized? What is the electrode configuration?

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 Post subject: Re: 15kV cables in a manhole
PostPosted: Wed Sep 18, 2019 9:14 am 
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Suggest spiking prior to cutting. https://www.hubbell.com/hubbellpowersystems/en/Products/Power-Utilities/Grounding-Bonding/Ground-Sets/Chisel/Ground-Set-U-R-D-/p/1647585


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 Post subject: Re: 15kV cables in a manhole
PostPosted: Wed Sep 18, 2019 9:59 am 
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It was a combination of factors/errors and the electrician stated that he had got complacent as the cable to be cut was previously de-energized and identified. Work plan changed and the electrician took it upon himself to do something.

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 Post subject: Re: 15kV cables in a manhole
PostPosted: Mon Sep 23, 2019 8:29 am 
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Location: New England
There isn't a set configuration, other than cables are normally bundled into a triangle and tie wrapped together.

If someone cuts into an energized cable inside a manhole, then they need more training.

MV and HV cables are shielded. so a tic tracer won't work on them. But, the correct method before cutting, assuming you did all the appropriate lock out and identification to best of your ability would be as follows.

1) Affix amp probe around cable, any indication of current means the cable is energized. Amp probes will still indicated current even on a shielded cable because they work off magnetism and magnetism will pass through copper shielding.

2) Strip off the outer PVC jacket layer for about a foot, while in full PPE, down to the shield. Rip off the the shield. Do this without any damage to the insulation below the shield. Now use your tic tracer, if it whines -cable is hot, do not cut. go back to your identification process. If its low tics, cable is de-energized.

don't forget to discharge the cable after lock out. Capacitance charge cable is DC and won't show on a tic-tracer.


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 Post subject: Re: 15kV cables in a manhole
PostPosted: Mon Sep 23, 2019 9:08 am 
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haze10 wrote:

1) Affix amp probe around cable, any indication of current means the cable is energized. Amp probes will still indicated current even on a shielded cable because they work off magnetism and magnetism will pass through copper shielding.


The amp probe will also pickup the current in a concentric neutral, summing it with the primary current. You'll get a zero reading on a single phase cable. Cable without current does not mean it's not energized.

haze10 wrote:

2) Strip off the outer PVC jacket layer for about a foot, while in full PPE, down to the shield. Rip off the the shield. Do this without any damage to the insulation below the shield. Now use your tic tracer, if it whines -cable is hot, do not cut. go back to your identification process. If its low tics, cable is de-energized.


Now that the shield is removed, the insulation itself is a shock hazard because the voltage gradient is gone. Center conductor and the surface of the insulation is at the same potential. There is also likely to be a difference in potential between the two shield ends. Do you have a similarly prepared energized cable to test the tracer with? I'd rather be at the end of a shotgun tool using the spiking ground linked above.


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