Three phases main supply

[Boing89]

Yes you can do that at the machine.
But what’s the point in ensuring phase rotation is consistent throughout an installation?

You have an installation where phase rotation has been checked throughout.
You install a new machine, it runs backwards.
You swap the phases round in the machine, it runs forwards.

You have an installation where phase rotation has not been checked throughout.
You install a new machine, it runs backwards.
You swap the phase round in the machine, it runs forwards.

What’s the difference?

When I was in the RAF we had a hangar with 6 separate bays where we moved 3 phase machines with 125A plugs around depending on aircraft requirements. Bay 2 (I can even picture it right now) was wired the wrong way round meaning that every time a machine went in or out of there one of us had to swap the phases round. Our contractors were like you and couldn’t see the problem. Hours of work over years due to incompetence on the part of the original inspector that signed it off.

The majority do seem to like L1, L2, L3 or R, S, T.

In a factory environment where a board is only supplying 3-phase loads, each of which has three anonymous brown cables in an isolator or busbar tapoff, it's not particularly interesting to know which phase is which. You can test the sequence at the machine terminals before starting it up. But if you have a mixed load, where single-phase circuits might even dominate the total load at times and certainly overshadow the single-phase control loading of 3-phase machines, it's helpful to be able to balance them.

In the entertainment industry we use a lot of 3-phase supplies for mainly single-phase loads but with some 3-phase loads mixed in. I might plug a hoist control box into any one of a dozen 3-phase outlets in a venue. If I swap out some of the hoists, I don't want them to be overrunning their limits because they are wired the other way. At the same time, if I know there's a total of 160A to play with spread amongst three 125A circuits, I need to know that loading L1 to 100A in one DB and L2 to 100A in another DB is not going to catch me out mid-show because they are actually on the same supply phase.

I agree that it's not always essential to know which phase is which, but it's not terribly difficult to organise.

in my current role I work on wind turbine lifts which come with phase rotation relays. This prevents the lift operating in the event of incorrect phase connections.

Of course the original installer in the factory has got to connect the phase relay up the right way round in the first place. I had to go to one a couple of weeks back that rather disconcertingly for the client was trying to drive itself through the floor when they pushed the up button.

 

[LeeH]

Now how would you do that?
How would you ensure that the new machine required the same phase rotation as that in your installation?

As far as I’m concerned, the only time ensuring phase rotation is the same throughout an installation would be beneficial, is if you intend moving a machine to various locations around an installation.

Also, most 3phase machines use L1 to supply control circuitry, so swapping phases around in an installation would help balance out loads.
Instead of all the control circuits being on L1, they would be spread accross all the phases.

Machines that would come to harm or would impact safety due to the rotation will have phase rotation relays on them locking it down.

Or they should have...

 

[LeeH]

Now how would you do that?
How would you ensure that the new machine required the same phase rotation as that in your installation?

As far as I’m concerned, the only time ensuring phase rotation is the same throughout an installation would be beneficial, is if you intend moving a machine to various locations around an installation.

Also, most 3phase machines use L1 to supply control circuitry, so swapping phases around in an installation would help balance out loads.
Instead of all the control circuits being on L1, they would be spread accross all the phases.

Machines that would come to harm or would impact safety due to the rotation will have phase rotation relays on them locking it down.

Or they should have...

 

[Deleted member 26818]

My experience is varied.
Had machines that run backwards and need phases swapped.
Had replacement motors that run backwards and need phases swapped.
Had re-wound motors that run backwards and need phases swapped.
Had one machine with a number of motors, that have required some of the motors to haves phases swapped.
Had two supplies to one installation where the phases are not in sync.
In this instance, the second supply was for a smoke extract system.
Normal supply, the fans extracted. Emergency supply, the fans blew.