3 Phase Motor connections

[Tommo33]

Hi All,

A 3 phase motor has been moved to a new workshop this week. Only The motor supply was disconnected from the top of isolator so the isolator and start stop station including the cable to motor were all as one when in transit so connection have not been altered. When re installing i noticed that L1 and L2 phases have been crossed over as they enter the start stop station from isolator and the motor connections are as picture. My question is have the phases been crossed over in error or for a reason??

Any help would be much appreciated.


Pictures below



//media.diynot.com/217000_216892_75198_87901460_thumb.jpg

//media.diynot.com/217000_216892_75197_99979937_thumb.jpg

 

[333rocky333]

View media item 75197 View media item 75198

 

[Jackrae]

Crossing any pair of phases on a 3-phase motor is used to set the direction of rotation.

Out of interest, do you know why the white phase is connected to the feeder cable via a connector block rather than at the motor terminal unit as the other two phases are.

 

[Tommo33]

No I'm not sure why its been connected that way instead of at the terminal. So with the phase crossed over connections it is as follows

L1 phase to W1

L2 phase to U1 ( on connector block )

L3 phase to V1

The motor is for a vacuum for a cnc machine.

 

[333rocky333]

L1 L2 L3 phase rotation is not always consistent throughout different premises, so moving from one building to another theres a 50% possibility that phase rotation could be different and could cause the motor to run in reverse,

This could be hazourdous and 3 phase supplies are really out of the depth of most Diyers

 

[ericmark]

Being as I thought clever I set up a socket for a three phase machine using my phase rotation meter.

However it would seem old socket was wrong so still went wrong way. You need to check both old and new premises to ensure correct direction on first switch on.

 

[plugwash]

They even make 16A three-phase plugs with a rotating insert so you can change the phase rotation without rewiring.

 

[ericmark]

I note all the portable refrigeration units now use inverters so it does not matter how the phases are connected.

I have come across a few critical machines which must never run in reverse but in the main it's a such it and see.

It was the case a large area of Liverpool was wrong way around where during the war emergency repairs had reversed the phases and quicker to swap in factories than redo joint. It would have caused so much disruption to swap back it was never done.

I am sure there must be other places where it is wrong way around.

The phase rotation meter comes into it's own when running generators synced together but in the main it's a case of remove drive shaft and test motor direction on the machine.

 

[Simon35]

I note all the portable refrigeration units now use inverters so it does not matter how the phases are connected.

I have come across a few critical machines which must never run in reverse but in the main it's a such it and see.

It was the case a large area of Liverpool was wrong way around where during the war emergency repairs had reversed the phases and quicker to swap in factories than redo joint. It would have caused so much disruption to swap back it was never done.

I am sure there must be other places where it is wrong way around.

The phase rotation meter comes into it's own when running generators synced together but in the main it's a case of remove drive shaft and test motor direction on the machine.

Some parts of Sheffield have incorrect phase rotation

 

[bernardgreen]

I have seen 3 phase starters with a built in phase rotation check which prevented the motor being started in reverse direction.

 

[Spark123]

Sounds like a phase failure and sequence relay.

 

[bernardgreen]

Sounds like a phase failure and sequence relay.

That's the posh name that I couldn't recall.

 

[AdrianUK]

A few years ago I installed a simulator on the island of Trinidad. When we left site on the Friday evening all was well & everything worked fine.

On Monday I arrived back at site ready to do the acceptance tests ... everything was fine until it came to sync'ing onto the mains, every time I tried it the over current protection tripped.... then it dawned on me that the synchronscope was rotating clockwise for slow & anti-clockwise for fast..... eventually the penny dropped.... the phase order had been changed over the weekend!

 

[DaftPunk]

I note all the portable refrigeration units now use inverters so it does not matter how the phases are connected.

I have come across a few critical machines which must never run in reverse but in the main it's a such it and see.

It was the case a large area of Liverpool was wrong way around where during the war emergency repairs had reversed the phases and quicker to swap in factories than redo joint. It would have caused so much disruption to swap back it was never done.

I am sure there must be other places where it is wrong way around.

The phase rotation meter comes into it's own when running generators synced together but in the main it's a case of remove drive shaft and test motor direction on the machine.

Some parts of Sheffield have incorrect phase rotation

As does the majority of Liverpool.

 

[333rocky333]

L1 phase to W1

L2 phase to U1 ( on connector block )

L3 phase to V1

Regarding the connections in the motor
If im not mistaken, wouldnt that run the same direction as if it had been connected as normal anyway
L1 to U1
L2 to V1
L3 to W1