Grounding 10

[Engcan]

Hi,
I was given a report which came from recommendation from a electrical contractor, which has Professional Engg. with them about maintenance of a switchgear.

One of the recommendations was put a "Rubber-Mat" in front so that a person could stand while a person is operating a breaker.

Now here is the question:
A few months back, the local safety authority asked us to put a ground mat made of cooper cage in front of a wooden pole so that person could stand when he is operating the load break switch. It was on 15 KV. And the handle of load break switch should be connected through a 2/0 AWG wire to this mat and this mat should be grounded with a 10' road.

OK Now, I understand if there is a ground fault then the switch and person standing on mat will be at the same potential. I hope that is the reason just to have same potential.

Now in case of switchgear, if a ground fault happens, for example a breaker get shorted to ground that what will happen to person operating the breaker and standing on rubber mat. If nothing happens to him, why cannot we put a rubber mat in front of pole holding a load break switch connected to over head distribution line.

This thing is confusing me, please explain what I am missing here.
Thanks

 

[tulum]

I do not have a utility background so bare with me.

Is there a rule saying only one lineman can be in the vicinity of the equipment at one time?

If the mat was not grounded and there were two lineman then the second would not have his hand on the switch...

regards
TULUM

 

[waross]

Hello tulum
I don't know. I would not be surprised to hear that some utilities have such a rule.
Generally, the other linemen give the man opperating the switch lots of elbow room. 20 or 30 feet is not uncommon.
If a problem arose that required two men to operate the switch, the size of an Equi-Potential grid in Canada should be such that a man cannot operate the switch unless he is standing on the grid.
And probably the most dangerous place to stand would be beside the mat with your legs apart. Virtually all linemen have taken safety courses on Touch and Step Voltages and know enough to stay away from the grid or mat and away from the switch unless they are actually operating the switch.
yours

 

[stevenal]

tulum,
It might be cozy, but two on the mat would not be a problem. As I stated, adding resistance in series with the lineman can only decrease the amount of current through him. This includes the essentially infinite resistance of of an open circuit. If off the switch mat, and outside of a substation ground grid, he may want to be standing away.

Please understand that waross is not suggesting keeping the mat ungrounded. Reread his capitalized suggestion. Mat is connected to switch handle, which in turn is connected to the pole ground. Mat is at ground potential. If there is a gradient in the ground potential, handle and mat lie at the same point of the gradient.

 

[waross]

Thanks stevenal
I wish that I could have stated it so concisely.
respectfully