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#150905 - 01/07/06 11:06 PM Phase sequence

Registered: 12/08/05
Posts: 862
Loc: Titirangi, Akld, New Zealand
What's the situation in other countries?

Here in NZ especially in the W.E.P.B. area it's a 50% correct or reversed saga.

I maintain the phase sequence or rotation has to be correct ( clockwise ) at the LT side of a distribution transformer and at the customer premises. Certainly for new jobs!! Some powerboards were "exempt" from the regs. and didn't always bother to check. When wrong excuses, It's too hard, or we do it later, ran out of time.

For the sake of a couple of extra minutes at the job. at least its done correctly.

The generators we connect up in case of cable faults and other unplanned outages are all Red,Yellow,Blue, clockwise.
At night faults.
There is always the uncertain part. Was this transformer wired up correctly or not?

We try to confirm it where there is a 3 Ø customer nearby, but this is not always possible in suburbia. There could be a 3Ø sewer pump or 3Ø garage workshop with a lathe etc.

Also it makes a shambles of the colour coding of the cables sometimes.
The product of rotation, excitation and flux produces electricty.

Arc Flash PPE Clothing, LOTO & Insulated Tools
#150906 - 01/08/06 02:06 AM Re: Phase sequence
iwire Offline

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
First there is no NEC standard for color coding phase A may be Red in one building and blue in another.

For that matter phase A will likely be Brown and Black in the buildings I work in.

Brown for 480 volt systems and Black for 208 systems, again those colors are not standard they are more of a habit in this area.

The NEC requires this.

408.3(E) Phase Arrangement. The phase arrangement on 3-phase buses shall be A, B, C from front to back, top to bottom, or left to right, as viewed from the front of the switchboard or panelboard. The B phase shall be that phase having the higher voltage to ground on 3-phase, 4-wire, delta-connected systems. Other busbar arrangements shall be permitted for additions to existing installations and shall be marked.

But, when I connect to the power company (or they connect to me) I do not know which conductor is truly A.

Some have said any connection that results in clockwise rotation is correct and that may be so but I have never seen that written in a code or standard.

So once we land the conductors at the service disconnect we do not change from that point on except as needed at motor terminals.

Bob Badger
Construction & Maintenance Electrician

#150907 - 01/08/06 05:24 AM Re: Phase sequence
Ron Offline

Registered: 03/13/02
Posts: 577
Loc: White Plains, NY
I don't know of any requirement in the USA that maintains that phase angle advances positively from A to B, B to C or C to A.
I agree that it would be nice, although once it is established for the building, it's done and can be documented that way. That's why motorized equipment is generally "bumped" before real startup occurs.
Temporary generators during an outage surely can be a problem terminating.

#150908 - 01/08/06 08:11 AM Re: Phase sequence
Roger Offline

Registered: 05/18/02
Posts: 1779
Loc: N.C.
In buildings where a temporary generator may be (is suspected to be) used, I like to mark the rotation in the gear with the rotation meters lead sequence verses phase.

Actually it would be a good idea in any building.

Example: Rotation is Clockwise with meter leads connected - Red=A White=B Blue=C or
Red=L1 White=L2 Blue=L3

BTW, I remember a discussion a few years back about the letters RST as used on rotation meters, but I don't remember if anyone ever explained their orientation or meaning.



#150909 - 01/08/06 10:01 AM Re: Phase sequence
gfretwell Offline


Registered: 07/20/04
Posts: 9025
Loc: Estero,Fl,usa
IBM always had this fight. We actually made it worse when we spec'ed "clockwise at the face of the plug" We meant the "plug", electricians assumed receptacle. The reality was it ended up a 50/50 chance anyway. Everyone had their own way of fixing the pronlem form calling the el;ectrician back to swapping the wires somewhere in the equipment. We were not even consistant where we swapped the wires in our equipment. You could find older boxes that had phases swapping two or three times before it got to the load.
Finally we decided it was going to be clocwise at the face of the receptacle, all the time and we were going to fix our stuff. At the same time engineers put phase detectors and a quick plug swap method of swapping phases in machines that showed reversed phases.
Since we stopped using big motors on stuff I doubt they even care about phase rotation in newer stuff. A "mainframe" these days is a rack full of PC boards and a Disk Array (RAMAC) is a rack full of 3.5" drives.
They don't leak oil on the floor anymore.
Greg Fretwell

#150910 - 01/08/06 10:36 AM Re: Phase sequence

Registered: 12/08/05
Posts: 862
Loc: Titirangi, Akld, New Zealand
[quote]Actually it would be a good idea in any building.

Example: Rotation is Clockwise with meter leads connected - Red=A White=B Blue=C or
Red=L1 White=L2 Blue=L3

Thets the way I like to see it done too.
It's true to refer it to the actual phase markings at the TX or dist. board.

I usually do mark the LT supply after we had a cable fault and supply has been on a temp. generator and reentated afterwards back on normal supply.
The product of rotation, excitation and flux produces electricty.

#150911 - 01/11/06 02:45 PM Re: Phase sequence
Radar Offline

Registered: 04/30/04
Posts: 349
Loc: Los Angeles, CA
A twist on this thread. I remember a job in an older part of Los Angeles some years ago, we had replace the service and most of the wiring (the building was basically gutted and rebuilt as I remember). The utility service was a 240V 3Ø 4W high-leg system (LA-DWP). I believe the NEC requires the high leg phase to be landed on phase B - with no regard for phase rotation.

Form what we understand, this particular utility normally brings power into a 3Ø customer service with the high leg on phase C. So, in order to comply with NEC, the switchgear manufacturer has to include a transition piece which switches phases B & C, thereby reversing the phase rotation.

This all came to light, of course, because the switchgear was made and delivered without the transition, but that's another story.

There are 10 types of people. Those who know binary, and those who don't.


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