Reversing contactor wiring.

Fimbles · Apr 18, 2021

Hello all. Hope you are well.

Can anyone please explain why there is a SINGLE black wire linking both sides of line 3 on this reversing contactor?

It runs a 400v 3 phase AC motor on a conveyor transfer unit, Left side is forward, right is reverse.

I have posted a picture of what i thought the circuit would look like, But the single black wire linking inputs has me confused.

Any ideas, Suggestions would be appreciated.

Rockingit · Apr 18, 2021

Quick guess without looking too hard is that it's because you only need to swap around two phases, so one phase is always going to be common.

ipf · Apr 18, 2021

According to your drawing, lines 1 and 3 alternate through the right hand contactor to reverse the outgoing supply.
There should be 2 other links to link 2 phases (L1 and L2)

timhoward · Apr 18, 2021

Rockingit said:
Quick guess without looking too hard is that it's because you only need to swap around two phases, so one phase is always going to be common.

Indeed. I still remember the first 3 phase factory job I did - they weren't best pleased that the milling machine was running backwards after I changed the isolator and decided to re-align/tidy red, yellow and blue.
Luckily the new 3 phase air compressor I'd installed had reverse rotation detection and refused to power up. The potential consequences of that running backwards could have been interesting!

snowhead · Apr 18, 2021

As supplied, the contactor has 3 links on the top 1,3,5 going to 1,3,5, someone has removed / lost 2 of them.
Is that the supply or motor connected on right hand bottom contactor?

[ElectriciansForums.net] Reversing contactor wiring.

ipf · Apr 18, 2021

ipf said:
According to your drawing, lines 1 and 3 alternate through the right hand contactor to reverse the outgoing supply.
There should be 2 other links to link 2 phases (L1 and L2)

Clearing up the above............There should be three links. In the photo, there seem to be two missing. Are they out of sight?

ipf · Apr 18, 2021

snowhead said:
As supplied, the contactor has 3 links on the top 1,3,5 going to 1,3,5, someone has removed / lost 2 of them.
Is that the supply or motor connected on right hand bottom contactor?

View attachment 84810

My fingers are getting slow, these days.

Fimbles · Apr 18, 2021

Thanks for all the replies gents. Previous guy who worked on it swears there were no links present.

Ill replace the magically missing links tommorow, Its the only logical answer.