I'm digging out a set of a dozen ground mounted floodlamps installed in ~ 1985.
The junctions to SWA are all made within galvanized conduit boxes, which are suspended in air inside large bucket-sized underground clay pots.
Most interestingly, the source of extremely low insulation resistance throughout the install is the potting compound. - It's a brown clay-like stuff, just like that brown Plasticine we had as kids. (Perhaps it IS Plasticine ?). I've been steadily digging it all out, and the IR has been climbing with each one I do.
It smells like clay, but is kind of oily. It's also got a very low resistance. Squidged into all the joints, with the conduit boxes filled to the lids. The overall IR is in the hundreds of ohms. I can record < 1M just with two small pointy probes barely touching the material a couple of cm apart.
I wasn't in this business in those days. Just what WAS this potting compound used then? - I guess it's absorbed water, but it seems a rum material to choose when it behaves this badly.
The junctions to SWA are all made within galvanized conduit boxes, which are suspended in air inside large bucket-sized underground clay pots.
Most interestingly, the source of extremely low insulation resistance throughout the install is the potting compound. - It's a brown clay-like stuff, just like that brown Plasticine we had as kids. (Perhaps it IS Plasticine ?). I've been steadily digging it all out, and the IR has been climbing with each one I do.
It smells like clay, but is kind of oily. It's also got a very low resistance. Squidged into all the joints, with the conduit boxes filled to the lids. The overall IR is in the hundreds of ohms. I can record < 1M just with two small pointy probes barely touching the material a couple of cm apart.
I wasn't in this business in those days. Just what WAS this potting compound used then? - I guess it's absorbed water, but it seems a rum material to choose when it behaves this badly.
known to absorb water badly?
