Phase Rotation/Sequence

[hightower]

So I'm using a bit of this bank holiday to do some college work. I'm at a question as follows:

Phase sequence is to be confirmed for the DBs and equipment during initial verification. State the locations at which phase sequence is to be confirmed for the circuits supplied from DB2.

I've had a look through the regs, OSG, and GN3 and can't find much on it at all. GN3 gives a little info on the process of testing but not the locations. I've looked in a few other books too and they all skip over this test.

My thoughts are the phase rotation needs to be tested at the DB, at the end of the circuit (so for example a motor it powers), and at any connections/joins in between.

Am I right in my thinking? Have I missed anything? I like to be able to write something like "reg x.x.x states" or "x.x in the OSG recommends" etc but can't find any supporting evidence.

 

[Leesparkykent]

612.12
The check on phase rotation should be made at the incoming supply and then at each position where it is necessary to assess whether there has been any alteration in the phase sequence. So in your case the origin, at the 3 phase distribution board and any other relevant 3 phase equipment in the installation/circuit.

 

[hightower]

Thanks mate, I'm looking at the green regs as I have that digitally - it just says:

For multiphase circuits, it shall be verified that the phase sequence is maintained.

I wish I had the yellow regs digitally, got to go out to the van now and get them - hadn't realised 612.12 has changed between the versions.

 

[Leesparkykent]

I'm not sure if it has mate, just a quick google as I haven't got the regs with me as I'm away couldn't you just put something along the lines of reg 612.12 says blah blah blah and to ensure this I check/confirm phase sequence at the origin, DB and any other relevant equipment installed on the circuit such as isolators, starters etc.

 

[GMES]

@hightower Just plucked this off the net not sure if it helps.

Regulation 612.12 of BS 7671 requires the checking of phase sequence in multi-phase installations, in order to ensure that the phase sequence is maintained throughout the whole of the installation.

On the City and Guilds 2394 and City and Guilds 2395 practical assessments, the phase sequence on the 3 phase installation would affect the rotation of the motor on the motor supply circuit (motor not present on the exam).

You will be required to select the appropriate Phase Sequence tester and perform a test at the Main Switch and at the motor connections.

Both tests should indicate the same phase sequence.

 

[hightower]

Thanks @GMES - So you wouldn't be required to carry out the test at any connections en route such as a starter?

 

[GMES]

Well technically I would but equally the only place I would alter the phases is at the end of the circuit, IE the Motor In the real world a lot of guys will opt for the most convenient place, Take an overhead crane in a factory that starts at the DB-Isolator-busbar -connection, most guys won't go to the trouble of going up in a lifter so will either do it at the board or isolator.

 

[davesparks]

Phase sequence and phase rotation, are the different things, or are they the same?
I'm genuinely curious about people's thoughts on this one, my tutor on the 17th ed course (the one and only mr Chris Kitcher) explained that they are as follows.

Phase rotation: either 1:2:3 or 3:2:1

Phase sequence: the phase conductors remain connected to the same phases of the incoming supply.
For example you could mix up the conductors and connect L1 from the origin to L2 terminal of a sub-DB, L2 to L3 terminal and L3 to L1 terminal. You would still have correct phase rotation (3:1:2 = 1:2:3) but the sequence is wrong.

 

[hightower]

Well it's C&G asking the question and their wording is sequence. So by your argument it seems that rotation will be correct if sequence is, but not necessarily the sequence to be correct if the rotation is. And therefore C&G have covered their bases because if the sequence is correct then the rotation will be inherently correct.

 

[davesparks]

Well it's C&G asking the question and their wording is sequence. So by your argument it seems that rotation will be correct if sequence is, but not necessarily the sequence to be correct if the rotation is. And therefore C&G have covered their bases because if the sequence is correct then the rotation will be inherently correct.

Yes from the point of view of theory and exams, though in the real world occasions do occur when the incoming supply has incorrect rotation, so maintaining the sequence as provided at the origin would maintain the incorrect rotation.