Something I Just Learned about 3 Phase Wiring

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Forum topic by jsmit24 posted 07-16-2019 08:55 AM 557 views 0 times favorited 4 replies Add to Favorites Watch
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10 posts in 36 days

07-16-2019 08:55 AM

You electricians know this already… so this is for people like me who don’t know an electron from an ion.

Last night, for the first time in my new shop, I attempted to use my jointer. I was feeding a 24” long piece of white oak in, and it made a horrible noise and just battered the hell out of my board. I turned off the power and watched the blade spin down… thinking one of my cutters must have been damaged in the move to my new quarters. It was then that I noticed the darn thing was running BACKWARDS! A quick check of “3-phase motor running backwards” on bing told me that the electricians had not done their homework when installing the plug. Bottom line, you can switch one wire and reverse a 3-phase motor. Easy fix, but wow I wish I had checked that first! Who would have thunk it?


4 replies so far

View Fred Hargis's profile

Fred Hargis

5635 posts in 2941 days

#1 posted 07-16-2019 11:29 AM

In industry one of the first things we did when checking new equipment installations was to “bump” the motors. This was to insure they turned the right direction before they provided power to the equipment.

-- Our village hasn't lost it's idiot, he was elected to congress.

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439 posts in 819 days

#2 posted 07-16-2019 01:13 PM

Easily done, we used to do it all the time, when electricians were to busy elswhere, to do things like reverse fuel sawdust feeders that were starting to plug.

The rule for reversing 3 phase 3 wire connections is ” switch any two connections”.

View shipwright's profile


8336 posts in 3245 days

#3 posted 07-16-2019 03:16 PM

This is an area where Murphy rules supreme. I don’t believe I ever wired a three phase tool and got it right the first time. Always bump (and then reverse).

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese!

View BlasterStumps's profile


1361 posts in 887 days

#4 posted 07-16-2019 04:12 PM

Brings back memories of my time working as a distribution lineman for the local REA. We would on occasion rebuild a 3-phase service to an industrial user. Before we started taking things apart or switching over one service to another, we would take a reading on a phase rotation meter. Then after writing that rotation down, we could get to doing whatever job we had in the works. Once the new service was built or a cutover was ready to go, we could once again check rotation to be sure it was the same as before.

-- "I build for function first, looks second. Most times I never get around to looks." - Mike, western Colorado

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