I assume it has something to do with grounding, but I’ve never seen this before, so I’m curious of its function and need on a particular pole.
That’s a fuse cutout. It goes inline before the transformer feeding your house. It protects the line and transformer from overloads. The lineman can also disconnect it if they need to service the transformer or electric meter.
I was standing near one while watching a building on fire when it popped. Two words: Holy Shit!
Is it “in use” as we see it here, or is this a spare?
Not in use. I’m going to guess a lineman either hung it there or dropped it nearby and forgot about it.
Edit: Example of one in use
This is what it should look like when installed:
And this is what it does when it blows, or when a lineman disconnects it:
![[SOLVED] Found on a telephone pole in GTA, Canada](https://lemmy.ca/pictrs/image/3dfa641a-585f-4d4d-a60f-063f8dccb05b.jpeg){kind=link}