I was looking at these overhead power lines and wondering what the insulators and bypass cables (circled in red) are for?
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....
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.
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 insulators are there because the splice has steel components that aren't rated for conduction. So they install the aluminum jumpers shown.
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.
On top of what is discussed here, I asked one of my friends, and he said it is also used for controlled cable tension. It provides the same cable tension, but it's weaker than the continuous cables. It provides a safe break point if something bad happens and one of the poles falls down. If there are no weak points, it could drag the rest of the poles down.
(Image source)
But having such a connection with controlled tension provides a safe point in such events. If poles start to fall, instead of dragging the rest of the poles, the cable will separate when it reaches this connection, and the rest of the cables are safe. The next poles to this connection also usually have some cables that are used to fasten the pole to the ground to be able to compensate for the tension along the cable (weight of the cable) from the other side of the pole if this connection breaks.
These are unitaries (poly insulators) used for limiting outage impact to customers. If a line cannot be isolated with a switch or tap these can be cut in to restore up to this point or to isolate a piece of equipment or line.
