Unloaded Transmission Cable Shocks Worker

[stuckie27out1]

So here is the situation:

At a particular site a crew of electrical workers were putting some transmission cable in the ground. The cable was off loaded from behind a trencher machine (the cable is in a roll of around 2000 feet). Some short time less than 4 hours another crew came to put some intermediate grounds into the soil.

This is all straight forward but what happened next is hard to explain. When the worker reached in and began to cut away the insulation with a knife to get access to the concentric neutral. He was shocked with enough magnitude to have to receive a trip to the hospital. He recovered and was unharmed.

Note there was no power connected to the cable.

What could explain this strange phenomenon?

Specifics:
Cable is similar to this look at 4/0 for specifics http://www.generalcable.com/NR/rdon...-9E30-B468D4B75A85/0/p046_047_ConcenNeuUG.pdf

Weather conditions were dry and hot mid/low 90's
Worker was not wearing insulation gloves
Cable had been tested with a megger some day previous for continuity.

I have a few ideas floating around but thought I would suppress them to see what you guy thought/ or have experienced before.

 

[f95toli]

Tribolelectric charge buildup when the cable was handled?
It is a serious problem with some types of cables, it can results in voltages up a volts even if the cable is only a few feet long, so for 2000 feet cable both the charge and voltage could presumably be significant.

From the workers point of view it was probably like touching both terminals of a charged high voltage capacitor; not much current but still very painful.

 

[deakie]

Very interesting...

f95toli charge must have played a part in what was a cummulative effect...

i had immediately thought that this was problably a test cable off the line and some kind of insulation test was done...

then i read what you said...

Weather conditions were dry and hot mid/low 90's
Worker was not wearing insulation gloves
Cable had been tested with a megger some day previous for continuity.

each of those conditions are ripe for charge collection but its the megger test that did it for me...
bet that cable wasnt adequately discharged after the kit was disconnected...

what kind of currents did the megger pump down the line?
i'd expect that it would take some while to discharge after charging considering the length of the cable...

the meggers we have pumps 25 amps just for a ground test...so it would be good to know...

 

[stewartcs]

The shock was more than likely a result of the IR test performed previously. This is quite common on cables of that length if the conductors are not discharged after the test. I've had it happen to me (once) about 10 years ago. However, the shock should be minimal though.

CS

 

[dlgoff]

I was thinking that the cable could have been parallel to some overhead transmission lines and induction was charging it.