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Topic Title: Phase Rotation
Topic Summary: What is the proper test instrument and the right way to test
Created On: 13 February 2012 05:26 PM
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 13 February 2012 05:26 PM
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keithredpath

Posts: 550
Joined: 30 March 2002

I have just read an article that states phase rotation is always to be anti-clockwise and that most instruments do not tell you which phase is which.

I have assumed you check the rotation at the service head, and as long as all subsequent tests show the same direction, you dont have a problem.

Have I been wrong all this time?

-------------------------
keithredpath
 13 February 2012 05:36 PM
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OMS

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Joined: 23 March 2004

By convention, phase rotation is anticlockwise because that's how we tend to draw the vectors.

Instruments can't generally tell which phase is which as it's only doing a comparison - it is up to you to get the leads in the right order for what you are trying to achieve.

If rotation remains the same throughout the various tiers of installation, then BS7671 is satisfied - in the real world (particularly industry or process) you'll find many crosses, right back to (and in some cases including) DNO supplies.

It's only really a drama if you have more than one supply source so you want both them going teh same way for duty and standby operation - it's essential that they do for synchronised operation

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 13 February 2012 05:38 PM
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AJJewsbury

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I'm sure I read something that says York is different to the surrounding area (historically they were fed from different systems), so I'm sure it can vary. (I'll try to dig it out).

I have assumed you check the rotation at the service head, and as long as all subsequent tests show the same direction, you dont have a problem.

That was my understanding too. (Although it seems a bit daft to me that if you had two sites in different areas and moved equipment with 3-phase motors between them you couldn't adopt a single standard...)

- Andy.
 13 February 2012 05:42 PM
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spinlondon

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Probably the most useless test ever.
 13 February 2012 05:57 PM
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UKPN

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--"probably the most useless test ever"

but important enough to be in the supply regs.

Regards.
 13 February 2012 06:26 PM
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OMS

Posts: 22864
Joined: 23 March 2004

Originally posted by: UKPN

--"probably the most useless test ever"

but important enough to be in the supply regs.

Regards.


What supply regs

What ESQCR actually says is:

(7) The number and rotation of phases in any supply shall not be varied by the distributor except with the agreement of the consumer or, in the absence of such agreement, the consent of the Secretary of State who may impose such conditions, if any, as she thinks appropriate

So you network guys can deliver them in any order, but you musn't swap them about without whispering in someones ear

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 13 February 2012 06:56 PM
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UKPN

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Joined: 17 January 2012

--as everyone knows, at the meter position, the cables, regardless of
the rotation at the service, (which depends how the incoming cables
fall), have to be marked L1,L2,L3,N. by law.
When a new service is installed, the meter operator will do a phase/polarity check at all three positions, the service, the meter and the
DB.
The DNO/Supplier/Meter operator has no control what happens afterwards on consumers installations.

So far from being useless this test is very important, which is why the
"wiring regs" now include it in the 17th edition.

Regards.
 13 February 2012 07:05 PM
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Jaymack

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Originally posted by: spinlondon
Probably the most useless test ever.

It is for a single phase site! A glib statement though.

Phase rotation requires to be maintained throughout, particularly so on large industrial sites with hundreds of motors, many transformers and lots of switchgear. All drawings for single line distribution and motor controls that I was involved in, had the phase rotation vector placed in the top right hand side of drawings, as a matter of routine.

Electric motors have a particular direction of rotation, when connected to the phase sequence of a 3 phase supply, as required to the manufacturing standards. Any spares in stores, should be checked for the correct rotation after being rewound; or even when new! Motor connections should never be changed to give the correct direction!

Regards
 13 February 2012 07:25 PM
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OMS

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--as everyone knows, at the meter position, the cables, regardless of the rotation at the service, (which depends how the incoming cables
fall), have to be marked L1,L2,L3,N. by law


Indeed, what it doesn't require is that building A has the same phase rotation as building B if fed from the same distributor cable, just that the cut out's will be marked L1, L2 and L3 regardless - by your own admission, and from my experience, jointers often roll the phases over to suit how the cable arrives at the cut out crutch.

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 13 February 2012 07:51 PM
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slittle

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Can also depend if it's OH or UG feed in my experience as with CT supplies the cutout is sometimes mounted above the chamber on a OH supply.

Either way as long as it's marked correctly it doesn't really matter.

My rotation meter will soon complain if it's wrong.

Stu
 13 February 2012 08:19 PM
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ArthurHall

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The DNO cutout can have either phase rotation as long as its marked. Meters though are usualy only certified for a particular rotation so the meter installer should cross the input tails as required and the output of the meter should be standard.
 13 February 2012 08:39 PM
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John Peckham

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I I&Ted a new installation on a London Underground Station a couple of weeks ago. The installation was a new DB feeding an equipment room. Undergound stations have 2 LV supplies. One from the DNO and one from the London Undergrounds own network know as the LUL supply. This new DB was fed from a new change over panel which in turn is fed from the DNO intake room and another supply from the LUL intake room. When trying to select the LUL supply on the changeover panel the contactor would not come in. The reason I discovered was the phase reversal relay was holding out the contactor. Further investigation proved the LUL supply was reverse rotation to the DNO supply. A phase rotation meter was used to prove that.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 13 February 2012 11:27 PM
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alancapon

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Originally posted by: keithredpath
I have just read an article that states phase rotation is always to be anti-clockwise and that most instruments do not tell you which phase is which. . .

Using the UK / European system it is impossible to identify a specific phase as L1, unless you have a definite known L1 to compare it against. Once L1 has been identified, a meter can decide which is L2 and L3, due to the rotation. The American system is slightly different, and it is possible to locate L2 with a voltmeter, then use a phase rotation tester to locate L2 and L3.

In terms of test equipment, I use a non-contact phase rotation tester made by Martindale - the Martindale PSI-4000.

Regards,

Alan.
 13 February 2012 11:30 PM
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spinlondon

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I've seen a system where two supplies from the same DNO substation have different sequences.
I happened to be working on the BMS near to where a smoke extract system was being commisoned, and could hear the motors attempting to reverse whenever the supplies were changed over under load.
I pointed out to the guys commisioning the system what was occuring and was informed that phase rotation had been confirmed on both supplies.
Not only was the breaker tripping whenever they changed over, but they also managed to burn out the main switch due to a loose neutral connection.
Eventually they swopped over two of the conductors on one of the supplies and it worked fine.
I've also noted that in many cases motors themselves will have different sequences. Change one motor on a machine and the new or re-wound motor will operate in reverse.
Confirmation of phase sequence is only of any real use, where a machine is likely to be connected at different points in an installation.
 13 February 2012 11:39 PM
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spinlondon

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That's because often the Americans use a high leg delta or center tapped delta system, where voltage between one phase and neutral will be 208V, and between either of the other phases and neutral 120V.
The 208V phase is determined to be L1.
 14 February 2012 06:28 AM
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Jaymack

Posts: 5571
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Originally posted by: spinlondon
I happened to be working on the BMS near to where a smoke extract system was being commisoned, and could hear the motors attempting to reverse whenever the supplies were changed over under load.

The motors would quickly trip out though! Interestingly enough, before solid state controls, Brook Igranic (BHI), in the 40's onwards, had a system of 3 phase automatic plug braking for overhauling loads on gantry cranes, this was known as OPOTOR, (Opposite Torque). In my 'Appy days and later as a shift electrician, I found this on motors with wound rotors, used for lowering crane masts on gantry cranes, to position steel billets in bloom mills. During fettling, setting the relays operated by feedback sensing from a shaft mounted generator, sorted the men from the boys! (Reversed plugging and regenerative braking is also used to quickly arrest machine tools etc.)

I've also noted that in many cases motors themselves will have different sequences. Change one motor on a machine and the new or re-wound motor will operate in reverse.

That is why written procedures, training and discipline are required by responsible management. I have only had one new motor in my career, that operated in reverse to the standard; this G.E.C. motor was later found to have been damaged in transit and rewound, (not by G.E.C.!) As a factory engineer for many years, both home and away, I had a policy of testing all spares including motors; by replacement in some cases, for electronic spares such as VSD's. Incidently, spare motors should have the shafts turned to a formalised procedure, to avoid bearing brinelling and grease hardening, not many people know that.

Some driven equipment can be damaged by reversed rotation, even for a jog start, these should have a direction indicator. Some cooling fans on motors are designed for operation in one direction only, to increase the efficiency; reverse these and you lose the cooling effect and reduce the kW rating. (Unidirectional motors).

New or replacement motors, should always be run uncoupled from the driven equipment for a period; and for various reasons.

Confirmation of phase sequence is only of any real use, where a machine is likely to be connected at different points in an installation.

Not so, this is not practical. The commissioning period is the time to confirm for correct phase sequence, especially so for equipment that could be connected in parallel. I had 1 project where the contractor managed to cross the main connections from 3 transformers to an MCC suite of 3 panels, fortunately this was detected by phasing out to the commissioning procedures, before any likelihood of damage was caused. If any distribution equipment etc., is in conflict with the site standard, this should be clearly labelled.

Motor application for a particular duty requires experience and knowledge of the different types available ....... and the different types of bearings for different drive methods, (belts etc.)

So endeth the lesson, let us now prey. (sic)

Regards
 14 February 2012 06:01 PM
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perspicacious

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"So endeth the lesson, let us now prey. (sic)"

What if I don't want to be a PV installer?

Regards

BOD
 14 February 2012 09:22 PM
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dg66

Posts: 1712
Joined: 11 January 2008

The regs dont mention phase rotation,its phase sequence that must be maintained,phase sequence and phase rotation are two different things.

-------------------------
Regards

Dave(not Cockburn)
 14 February 2012 10:05 PM
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alancapon

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Phase Rotation is the property that is measured by a test instrument to determine Phase Sequence.

Regards,

Alan.
 15 February 2012 09:05 PM
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dg66

Posts: 1712
Joined: 11 January 2008

Phase rotation could be be the same throughout an installation,but the phase sequence could be different

-------------------------
Regards

Dave(not Cockburn)
IET » Wiring and the regulations » Phase Rotation

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