Gradient control Mat and Snow

[TS06]

Hey,

I have had a question come to me from one of our field personnel wondering if it is safe to operate equipment which has a gradient control mat but is under a few feet of snow. My initial reaction was to say no, and to suggest shovelling out the mat prior to equipment operation. But when I sat down to think about it a little more, it just seemed like an extra layer of resistive material between the operator and the equipment, for example a thicker rubber glove. As such the parallel combination of the higher resistive operator and the near zero resistance alternate path should make the operator safer. Is this a logical thought process? Does anyone know of any standards on this issue? Thoughts?
reference to simialar thread thread238-166391
Thanks,
TS06

 

[waross]

The gradient control mat SHOULD be at the same potential as the switch handle. The snow would introduce a hazard if it formed a conductive shunt to ground around the gradient control mat. There is also the slipping hazard.
As a suggestion that may be accepted as good safety and common sense, I would suggest that the snow be cleaned from the mat so that it can be verified visually that the ground connection to the mat is in good condition.
This approach should give you the best safety. No snow hazard and confirmation that the ground connection appears to be in good condition.
respectfully

 

[tinfoil]

We now place our switch mats on-grade rather than burying them, as in the past, so that the operator may inspect the integrity of the mat and the connection(s) from the mat to the HV switch handle.

Our operating procedures require that these connections be visually inspected prior to any switching operation, or a portable may must be installed where such inspection is not possible (as many of our older installations have buried mats).

So, for us, snow must be removed from the mat to allow for inspection, or a rather large portable mat (which is in turn inspected annually for integrity) may be spread at and grounded to the switch handle, before operation of switches in the winter.