T12 fitting where retired about 8 years ago hence why you can't find any new ones.
You can't use a T12 tube in fluorescent filter.
There some led rubes that can go into a fluorescent light fitting but they need to replace the ballast with one they supply. If you can't get them for T12...
We use POI tape and the fuses/links are either locked in key safe or issued to the safety documents holder where necessary.
But that can only done where locking off is not reasonable practical.
As with all things this isn't official H&S advice and I would be speaking to your work H&S/legal...
Could be induced/circulating have seen issues with 400kv GIS stuff but not got any experience with 11kv.
As it's HV stuff it really needs looking at by someone who really know there stuff. Earthing on HV gear is real dark art.
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