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.

 

[Deleted member 26818]

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.

That’s probably a scenario where checking the phase rotation would be a good idea.
How long did it take before you asked a Rock Ape to sort out the socket wiring?

 

[davesparks]

Black and grey sleeved with brown to denote line conductors

Only if they are all on the same phase, if they are on different phases they should not be sleeved.

 

[Deleted member 26818]

Only if they are all on the same phase, if they are on different phases they should not be sleeved.

If phase conductors are being used as single phase line conductors, then they should all be sleeved brown.

 

[davesparks]

If phase conductors are being used as single phase line conductors, then they should all be sleeved brown.

Yes, that's what I said, the black and grey should be sleeved brown if they are on the same phase as the brown, if they are on different phases they shoukd not be sleeved brown.

 

[Deleted member 26818]

Yes, that's what I said, the black and grey should be sleeved brown if they are on the same phase as the brown, if they are on different phases they shoukd not be sleeved brown.

You misunderstood me.
If the three phases are being used to supply single phase equipment, for instance 3 lighting circuits each on a different phase, then the conductors should be sleeved brown (or otherwise identified as being line conductors).

 

[Pete999]

That’s probably a scenario where checking the phase rotation would be a good idea.
How long did it take before you asked a Rock Ape to sort out the socket wiring?

It's Phase Sequence Lads not Rotation, from Pete999 the Pedant.

 

[davesparks]

You misunderstood me.
If the three phases are being used to supply single phase equipment, for instance 3 lighting circuits each on a different phase, then the conductors should be sleeved brown (or otherwise identified as being line conductors).

For 3 single phase circuits like that you'd use brown for each live, you wouldn't install black and grey. Or if it's in a multicore cable then you wouldnt have a black and grey as it would be at least a 7core which will have all cores the same colour.

 

[Deleted member 26818]

Why would you need 7 core?
5 core would do, share the neutral between the 3 phases.

 

[Strima]

Why would you need 7 core?
5 core would do, share the neutral between the 3 phases.

Wouldn't that depend on the neutral loading, harmonics etc?

 

[Lucien Nunes]

There is a requirement to ensure correct phase rotation throughout an Installation in Chapter 6.
I think it’s a bit pointless, as when you connect 3 phase machinery, if it runs backwards, you just swap one of the phases over.

Some machines don't like being run backwards. Best to get it right first time.

Why would you need 7 core?
5 core would do, share the neutral between the 3 phases.

Then it would be one 3-phase circuit, but you were talking about three single-phase circuits:

for instance 3 lighting circuits each on a different phase,

Each of which will have a line and a neutral.

There are two aspects to the OP. One is getting the sequence right, which three out of the six possible permutations will be. As far as machine rotation is concerned, L1, L2, L3 and L3, L1, L2 are equally good. But if you don't know which phase is which, single-phase loads can't be connected to a known phase which is sometimes desirable, e.g to even out known load imbalances.

 

[Deleted member 26818]

Some machines don't like being run backwards. Best to get it right first time.

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.

 

[Pete999]

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.

By machine I assume you mean 4 phase motors? if you have had any electrical work in your place of work, and you fear the phase sequence is not the same as it was, then I would suggest you uncouple the mechanical elements run the motor without any load to check you have the correct phase sequence for this particular motor, once you have checked and swapped phases at the motor, reconnect the mechanicals and off you go, as for taking the control from L1 surely it matters not which phase the control supply comes from.

 

[Lucien Nunes]

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

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.

 

[Pete999]

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.

Good call Lucien, I was overthinking things, of course if you have the equipment, you could, as you say check and confirm phase sequence with a meter, what was I thinking of?????? Dohhhhh