3/4 pole rotary isolator on single phase.

[oscar21]

I was reading a thread on a different forum about someone asking how to wire the above, he was going to put the incoming into the top contacts and the outgoing into the bottom contacts leaving the middle pole free. I thought well that sounds fine but it reminded me of how I've seen them wired in the past where someone has looped the neutral back through the middle pole.

If I'm wiring them on single phase I usually unscrew and disgard the neutral pole that is usually attached to the side of the switch body and just do as above, what advantage is there in loopin the neutral through the middle pole, makes no sense to me. Its not as if its an expensive component and this extends the life in some way, they are cheap as chips.

 

[Moley]

This week we came across one where the line had been connected to the top and looped back through the middle. Neutral was through the bottom contact. It caused us a bit of head scratching as the center contact had failed open circuit.

 

[Brother Blue]

There's no logic to looping it back through another pole in that scenario.
It may be a misunderstanding and just copying what you would do on a DOL starter.

If it were a DC circuit and both poles were looped back through on a four pole switch or circuit breaker it would increase the breaking capacity.

 

[Spoon]

If it were a DC circuit and both poles were looped back through on a four pole switch or circuit breaker it would increase the breaking capacity.

Correct me if I'm wrong but looping the wiring on an isolator would not increase the capacity, as its in series. If it was wired in parallel it would.

 

[Brother Blue]

Correct me if I'm wrong but looping the wiring on an isolator would not increase the capacity, as its in series. If it was wired in parallel it would.

It increases the breaking capacity not the current rating.

It is common to do put two poles in series for DC circuits as it effectively doubles the arc gap to dissipate the energy from the arc quicker.