Requirements of a ground mat

CamEng

New Member
May 9, 2018
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#1
I have a manually operated 345 KV, 3-phase, ganged disconnect switch that isolates the Main Transformer from the Switchyard. At one point the operator would stand on a ground mat (metal grate with a bonding jumper that runs to the switch handle) while opening or closing the switch. Somewhere along the way the mat was removed and now needs replaced.

Is there an OSHA 1910.269, NESC, or IEEE standard requiring the mat?

Is there an IEEE, NESC standard that dictates the size of the mat, size of the bonding jumper and attachment hardware?
 
#2
There are two types of mats:
a) Industry tends to use a dielectric mat to provide a high resistance between the worker and ground with the intention to limit the current flow to a safe level.
b) Outdoor high voltage substations with gang operated switches, provide a conductive metal mat in order to achieve an equipotential zone. The potential difference between the workers body and the ground will always rise and fall equally providing a negligible potential differential across the workers body.

This answer focusses on the latter of the two. There are references in Subpart R t(1910.269):

1910.269(l)(5)(i)
The employer shall ensure that each employee, to the extent that other safety-related conditions at the worksite permit, works in a position from which a slip or shock will not bring the employee's body into contact with exposed, uninsulated parts energized at a potential different from the employee's.

There are several design references, however, this need not be a protracted engineering exercise. 1) Provide a conductive steel grating that is easy to move around (if portable). 2) Ensure that the square footage is large enough to prevent a worker accidentally stepping off during an catastrophic failure. Your equipotential ground mat MUST be tested together your ground testing to ensure an extremely low resistance to the ground grid.