Why do some above-ground HV lines have mid-span insulators?

I was looking at these overhead power lines and wondering what the insulators and bypass cables (circled in red) are for? Overhead power lines

Are those five small discs in each segment ceramic insulators? Are the bypass cables conductors?

On closer inspection it looks like they might be some sort of splice or tensioning device, which maybe isn't rated for current. But then, the bypass connectors on the right side of the splice don't exactly look like proper power conductors either....

Answers 2

  • I found a lineman who works in the city where the photo was taken and he explained the following: That's a splice that is typically done when hanging the lines when one reel of cable runs out and they have to connect it to the next one. (He also said that his union would normally cut the cable so the splice is done at the nearest pole, but in this region they contract out these installations and the contractors have "different" practices.)

    The the insulators are there because the splice has steel components that aren't rated for conduction. So they install the aluminum jumpers shown.

    HV splice with jumpers and stirrup circled

    The square piece they connect to on the right (circled above in yellow) is a copper bracket called a "stirrup." If it's ever necessary to disconnect at the splice they can use a hot stick (they call it a "shotgun") with a hook that grabs the eyebolt and can unscrew it to release the jumper cable.

  • According to a lineman friend of mine, that is a “flying 8”. He said they use them when doing restoration work. That way they can open the circuit easily in locations where they don’t already have a switch. I’m sure the lingo varies from place to place.

    He also told me that they usually go back and take those down unless it is a trouble line where they might just leave it there (preferably would have a switch instead to make it easier to operate as @DaveTweed mentions in his comment.

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