# How to identify phases



## WronGun (Oct 18, 2013)

On a 3-phase system how would you identify a,b,c phase? 

I got a call from a client of mine whose office building lost power from a transformer that blew up. 

Poco did there replacement but they want an electrician to verify phases at main switch gear before they turn on. 

They don’t want roof top units spinning backwards. 

Wouldn’t this require both of us working together and doing a continuity test? 

It seems they don’t know how they re-terminated there phases 


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## 3DDesign (Oct 25, 2014)

Fluke 9040 is one meter.


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## Bird dog (Oct 27, 2015)

First off, I would think their specs would tell them the proper phase rotation to wire it. I would not assume the service was wired ABC. Secondly, if any of the HVAC equipment has scroll compressors, you may want someone else HVAC co. or maintenance verify rotation before *they* turn the power back on to the unit.


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## WronGun (Oct 18, 2013)

At this point I’m just going to show up. It’s seemed to work for so far. 

I may turn around if they can steer me in the right direction 


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## mitch65 (Mar 26, 2015)

Unless they are asking you to identify that the secondaries off of their transformer are phased the same at both ends... Like Bird dog said, they should have a spec for the primaries. Then find a 3 phase fan, or something else where rotation is known but isn't critical, to start first, if it spins the right direction you are good to go.


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## eddy current (Feb 28, 2009)

That is how I had to do it ^ once on a late night blow up.

Only turned on a small pump load, checked it's rotation and then turned on everything else.


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## WronGun (Oct 18, 2013)

Well

there are 8 rooftop units I will just turn the disconnect off on all of them and once power is back I will turn 1 on and see how it spins. 


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## paulengr (Oct 8, 2017)

mitch65 said:


> Unless they are asking you to identify that the secondaries off of their transformer are phased the same at both ends... Like Bird dog said, they should have a spec for the primaries. Then find a 3 phase fan, or something else where rotation is known but isn't critical, to start first, if it spins the right direction you are good to go.



That’s how we do it. You also need to look for good access. Often guards get in the way. Pumps are often marked with an arrow or just plain blatantly obvious if you know how a pump is supposed to work.

There are phase meters. So you open all the breakers to loads that might automatically start the.n try one that’s easy to tell. If you have to the Amprobe PRM-6 is really good. It can read live lines and also residual magnetism in a motor. So you hook it up to the motor side of a starter and get a direction. Then hook it up to the line side and turn the power on. If it’s right you’re done. Otherwise pick the easiest place to switch. It can be on the utility side or the customer side. Then check again just to be sure. The PRN-6 works as long as the motor has run at least once in its life. It’s nice on critical loads where you are wiring up a motor for the first time. Amprobe is owned by Fluke but most of their stuff is either better than Fluke, cheaper than Fluke, or both.

There are 6 combinations of 3 leads. Half of them are ABC, half ACB. There is no marking or spec typically for utilities. Just like everybody else they try to get it right but especially if you have to fix some terminations it gets lost in the shuffle. Most industrial customers put it in the spec to verify every time.



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## WronGun (Oct 18, 2013)

I don’t get it though, they installed all the old wires on there new xformer. Everything still has phase tape on it. 

Wouldn’t you Put it back the same way and call it a day ? 

Dont these guys understand phase rotation ? 

They need to pay me emergency rate to do what I’m doing ? Doesn’t make sense? 

I’ve been sitting here for 2 hrs waiting for them to show up, but they keep stalling the owners... I’m starting to think having the owners try to get an electrician after hours is their way of pushing the time slot back.... 

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## Bird dog (Oct 27, 2015)

WronGun said:


> I don’t get it though, they installed all the old wires on there new xformer. Everything still has phase tape on it.
> 
> Wouldn’t you Put it back the same way and call it a day ?
> 
> ...


CYA for them & you do the same. :smile:


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## paulengr (Oct 8, 2017)

It’s all CYA. Getting it wrong can be an expensive mistake. One case became a $250k gear box repair.


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## paulengr (Oct 8, 2017)

Put another way...they’re linemen, not mechanics.


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## MechanicalDVR (Dec 29, 2007)

WronGun said:


> Well
> 
> there are 8 rooftop units I will just turn the disconnect off on all of them and once power is back I will turn 1 on and see how it spins.
> 
> ...


Don't do that!

If that is your plan disconnect the compressors and just run the fans to check.

You really should have a phase rotation meter.

A Fluke T+ Pro has rotation capability on it.


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## paulengr (Oct 8, 2017)

They’re company linemen. It’s a monopoly. The company makes money based on a percentage. The more they run up the bill, the more the shareholders make. You’re on utility time. I once took 12 hours at a Dominion plant to change a thermocouple in 10 minutes. Hanging out in the truck is “working” at utilities. That’s why they have spacious and comfortable cabs.

Second they’re linemen, not mechanics or electricians.


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## Cow (Jan 16, 2008)

MechanicalDVR said:


> Don't do that!
> 
> If that is your plan disconnect the compressors and just run the fans to check.
> 
> ...


I have a similar thought. 

I would look for any sort of 3 phase motor load near the panel you can verify rotation on. If it's right, then everything else would be too.

If no other motor load is closer, then I'd go up to the roof and manually push one of the fan contactors in to verify rotation. Some may not be comfortable with this method though...I am.


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## Southeast Power (Jan 18, 2009)

i was just on a project with a planned outage.
The 600 amp CT meter on the transformer pad had a clockwise arrow and ABC in the middle of it.
We were getting ready to put the facility on a new generator during a planned outage to change the service. 
We checked the rotation as part of a procedure we wrote for the and yup, CCW ABC. 
The line crew showed up and I asked them to check rotation. They opened the door of the transformer and it was terminated Blue Black Red. CCW.
We kept everything the same and swapped the line side of the generator breaker.

Moral of the story, don't trust POCO markings.

Back to the OP. The best phase rotation meter isn't going to tell you what the building was before power was cut.
You need to just do it the old fashioned way like mentioned and bump on something like a small motor. A MOTOR THAT ISNT ON A VFD. :wink:


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## eddy current (Feb 28, 2009)

WronGun said:


> They need to pay me emergency rate to do what I’m doing ? Doesn’t make sense?
> 
> I’ve been sitting here for 2 hrs waiting for them to show up


Calls like that is when it’s better to be the employee, rather than the employer.


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## WronGun (Oct 18, 2013)

Just thinking .....but If rotation was backwards wouldn’t it effect the interior vents air flow ?


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## MadDawg (Jun 12, 2012)

If there are any VFD's in the plant, the display should show phase reversal, if it is set up in the parameters.

Safest was is as mentioned many times, any 3 phase motor/fan/water pump,etc,,, is best.


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## paulengr (Oct 8, 2017)

WronGun said:


> Just thinking .....but If rotation was backwards wouldn’t it effect the interior vents air flow ?
> 
> 
> Sent from my iPhone using Tapatalk


Yes and no. A backwards fan still moves air but poorly.

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## paulengr (Oct 8, 2017)

MadDawg said:


> If there are any VFD's in the plant, the display should show phase reversal, if it is set up in the parameters.
> 
> Safest was is as mentioned many times, any 3 phase motor/fan/water pump,etc,,, is best.


I don't rely on this because not setting it up means you just get nothing...looks OK. Plus a VFD itself doesn't care. It's going to convert everything to DC and then back to AC in whichever direction you want, except cycloconverters that are extremely rare. A lot of larger industrial (but not commercial) grade compressors have a separate phase protection relay because of the cost of repairing the screw after it backs up and wipes out the bearings (50% of the compressor price tag).

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## glen1971 (Oct 10, 2012)

As said before, a phase rotation meter is good, but it won't tell you what it was... ABC is a good rule of thumb, but not every service is initially set-up that way.. 
Also as some have said, find a fan or pump that has a vendor marked rotation on it and do your rotation check there. If it's a pump, be careful because some don't like to go backwards.. Once one is verified right, the rest will be good.


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## matt1124 (Aug 23, 2011)

Find a scroll compressor and press in the contactor. You’ll know right away, won’t hurt it a bit. 

You need to be careful on a/c fans. Many units have 3 phase compressors and single phase fans.


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## Ultrafault (Dec 16, 2012)

in soviet russ.... I mean st. louis the poco supplies cba through out the entire grid. for the longest time I just thought you always read rotation oppisite the shaft end. little did I know the services are set up for reverse rotation right off the bat. 

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## wildleg (Apr 12, 2009)

as per the other thread about leaving things nice for the other guys, this is why some guys permanently mark rotation on the service or MDP.


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## MechanicalDVR (Dec 29, 2007)

Cow said:


> I have a similar thought.
> 
> I would look for any sort of 3 phase motor load near the panel you can verify rotation on. If it's right, then everything else would be too.
> 
> If no other motor load is closer, then *I'd go up to the roof and manually push one of the fan contactors in to verify rotation.* Some may not be comfortable with this method though...I am.


I'd do that too if I didn't have a rotation meter with me to check the main, but even a T+ Pro has ability to check rotation.

But if the power has been off a while chances are high the controls are looking for the a/c to run and powering the unit without disabling the compressors could be a problem.


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## macmikeman (Jan 23, 2007)

Silly macmikeman been known to bring his own motor along for the commissioning of jobs, I get mine running the right direction first, the actual fans, compressors, ice cream makers, etc are gonna swing the same way .


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## MechanicalDVR (Dec 29, 2007)

WronGun said:


> Just thinking .....but If rotation was backwards wouldn’t it effect the interior vents air flow ?


If the fan motors are three phase.


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## MechanicalDVR (Dec 29, 2007)

macmikeman said:


> Silly macmikeman been known to bring his own motor along for the commissioning of jobs, I get mine running the right direction first, the actual fans, compressors, ice cream makers, etc are gonna swing the same way .


That's a pretty heavy phase tester to stick in your pocket!


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## WronGun (Oct 18, 2013)

I ended up buying a brand new fluke 9040 for $100..... definitely the tool for checking rotation 


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## MechanicalDVR (Dec 29, 2007)

WronGun said:


> I ended up buying a brand new fluke 9040 for $100..... definitely the tool for checking rotation


Always good to have.


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## brian john (Mar 11, 2007)

1. Every commercial electrician should own a phase rotation meter.
2. All utilities I have worked with use clockwise rotation though sometimes they do F' up.
3. If there is a generator on site you can verify phasing across the ATS Generator source and utility with two multi-meters. ASSUMING the electricians installed the generator with matched phasing to the utility.
4. Let them hook it up check a small 3-phase motor and if it is wrong have the utility fix their screw up.


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## MDShunk (Jan 7, 2007)

I've been using the Knopp phase rotation "meter" my entire career. It's essentially a palm-of-the-hand sized 3 phase motor and... it works on VFD outputs at pretty much any Hz level.


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## MTW (Aug 28, 2013)

T+ Pro.


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## bostonPedro (Nov 14, 2017)

http://en-us.fluke.com/products/ele...-9040-phase-rotation-indicator.html#resources


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## MDShunk (Jan 7, 2007)

MTW said:


> T+ Pro.


Fee Fi Fo


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## MTW (Aug 28, 2013)

MDShunk said:


> Fee Fi Fo


:confused1:


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## bostonPedro (Nov 14, 2017)

MDShunk said:


> I've been using the Knopp phase rotation "meter" my entire career. It's essentially a palm-of-the-hand sized 3 phase motor and... it works on VFD outputs at pretty much any Hz level.



I have used this meter also and once people get by the looks of it they realize its a good tool. This particular meter in fact saved my ass on one job where the outside hook up was CBA and had been for years.


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## Wirenuting (Sep 12, 2010)

The four rooftop AC’s I landed yesterday were an example of checking rotation before removing the old ones. 
All 4 old units were taped B/O/Y and were left hand rotation. 
When we landed the new units I gave them right hand. My helper started to retape the phases for what it really was. I told him to leave our end colored as it was because we were not going into the distribution panel to retape the other end. We weren’t scheduled for an outage. 

We powered up with control off and I bumped a fan... winner winner chicken dinner.


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