# Three Phase refresher



## HARRY304E (Sep 15, 2010)

:blink::laughing:

Okay my job tomorrow Is put back up a 3phase strait 208 volt No Grounded conductor service drop.

At my customers site a Fed ex Truck pulled up on the side walk where there are usually cars parked and ripped the pipe off the building.:laughing:

The meter socket looks good no damage same with the panel.

What I don't know is what was the Phase rotation before this happened. 

The load is only two roof top A/C units.

What I'm thinking about is,It is common that phase A is Black B is red and C is blue, There is no guarantee that even if I mark them at the weather head that way that I will get A,B,&C in the right order.

So I'm over-thinking this,But I want to cover all the bases before I power up.

It has been more than ten years since I've have been involved with a situation like this and I had better make sure I know My chit..:laughing:

What say you?


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## TGGT (Oct 28, 2012)

Make sure the discos are off before you bug up, then when you're done, go back up to the disco, bump (turn on and off quick) to check rotation of the fan, and if they're running backwards, take any 2 legs in the disconnect and swap them. Bump again to make sure.


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## 480sparky (Sep 20, 2007)

Or get a phase rotation meter.


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## HARRY304E (Sep 15, 2010)

TGGT said:


> Make sure the discos are off before you bug up, then when you're done, go back up to the disco, bump (turn on and off quick) to check rotation of the fan, and if they're running backwards, take any 2 legs in the disconnect and swap them. Bump again to make sure.


Yup It looks like I've got to include that in the price.


Good man..


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## erics37 (May 7, 2009)

208 3-phase no grounded conductor? :001_huh: You sure?

Anyway you can get a phase rotation meter and stick it on there, but that'd only do you good if you knew rotation prior to the accident. If the only 3-phase loads are the rooftop units then it shouldn't be a big deal. I've seen some of those that take 3-phase and then only have single-phase fan motors anyway, in which case rotation would be irrelevant. If it does has a 3-phase fan motor then just bump the power and see which way it turns.

There's a more proper procedure for testing motor rotation but I'll be damned if bumping an AHU isn't good enough for me.


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## HARRY304E (Sep 15, 2010)

480sparky said:


> Or get a phase rotation meter.


I've got one ,the problem is the phase rotaion is unknown before this happened.


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## djmessina (Apr 29, 2012)

*Yup*



TGGT said:


> Make sure the discos are off before you bug up, then when you're done, go back up to the disco, bump (turn on and off quick) to check rotation of the fan, and if they're running backwards, take any 2 legs in the disconnect and swap them. Bump again to make sure.


Nerve wracking as hell but that's how I do it. Nothing like sweating burning out a compressor in a 15 ton rooftop unit. I even called an hvac buddy and he states "if it makes an awful grinding noise shut it off and switch the rotation" me:"isn't there a better way?"

Good luck and if you would rather not do it call an hvac guy to do it so its on him. FedEx is probably paying the bill anyway.


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## sbrn33 (Mar 15, 2007)

Most of the time the fans on 3 phase A/C's are single phase.


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## HARRY304E (Sep 15, 2010)

erics37 said:


> 208 3-phase no grounded conductor? :001_huh: You sure?
> 
> Anyway you can get a phase rotation meter and stick it on there, but that'd only do you good if you knew rotation prior to the accident. If the only 3-phase loads are the rooftop units then it shouldn't be a big deal. I've seen some of those that take 3-phase and then only have single-phase fan motors anyway, in which case rotation would be irrelevant. If it does has a 3-phase fan motor then just bump the power and see which way it turns.
> 
> There's a more proper procedure for testing motor rotation but I'll be damned if bumping an AHU isn't good enough for me.


Not sure of the exact voltage but It's not 480 Volts .



> If the only 3-phase loads are the rooftop units then it shouldn't be a big deal. I've seen some of those that take 3-phase and then only have single-phase fan motors anyway, in which case rotation would be irrelevant. If it does has a 3-phase fan motor then just bump the power and see which way it turns.


Okay good that's what I'm looking for..:thumbsup:


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## 480sparky (Sep 20, 2007)

HARRY304E said:


> I've got one ,the problem is the phase rotaion is unknown before this happened.


The right meter will give you the rotation of both the incoming line and the motor. You check both before terminating the conductors at the motor.


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## glen1971 (Oct 10, 2012)

You are correct in assuming that there is no guarantee in rotation.. There has been more than one piece of equipment damaged by the wrong rotation...

Some larger HVAC units have a phase reversal relay inside them to prevent the equipment from going the wrong way.. You can check them and see if there is an indication for reversal (flashing light, or contacts holding you out)... If there is nothing oyu might want to recommend installing one.. I've had alot of success with Omron's K8ABPM2 (480 vac)...

If there is no monitor in place, check the fans for rotation arrows, air flow direction etc.. Can you isolate the compressor(s)? If you can then unhook them and note where they went (T1/T2/T3) and try for a bump with only the fan in the circuit... If the rotation is correct, then isolate the power and reconnect the compressor as was previously connected.. If the rotation is wrong, then isolate the power to the unit and isolate the power at the main. Swap 2 of your phases and try again.. If the fans are correct, then isolate the unit and reconenct the compressor...


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## HARRY304E (Sep 15, 2010)

djmessina said:


> Nerve wracking as hell but that's how I do it. Nothing like sweating burning out a compressor in a 15 ton rooftop unit. I even called an hvac buddy and he states "if it makes an awful grinding noise shut it off and switch the rotation" me:"isn't there a better way?"
> 
> Good luck and if you would rather not do it call an hvac guy to do it so its on him. FedEx is probably paying the bill anyway.


Ahhh The POCO will be paying the bill because the drop was under 15 feet,.

But this a great Idea as well because the building owner's Brother In law Is An HVAC Guy so know I can get him there to make sure nothing got toasted When the accident Happened.


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## micromind (Aug 11, 2007)

djmessina said:


> Nerve wracking as hell but that's how I do it. Nothing like sweating burning out a compressor in a 15 ton rooftop unit. I even called an hvac buddy and he states "if it makes an awful grinding noise shut it off and switch the rotation" me:"isn't there a better way?"
> 
> Good luck and if you would rather not do it call an hvac guy to do it so its on him. FedEx is probably paying the bill anyway.


As noted, a lot of A/C units have single phase fan motors. 

If the compressor is indeed 3ø, it'll make a horrible racket if it's reversed only if it's a scroll type. The reciprocating type usually doesn't care which way it turns. If it does, there'll be a phase failure relay that won't let it start if reversed.


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## ponyboy (Nov 18, 2012)

I've hooked up some massive RTUS and MAUS And all I do is wire it up, turn breaker on, leave disco off, tell tinner its ready to go. If a phase is backwards they'll either tell me about it or swap it themselves


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## HARRY304E (Sep 15, 2010)

Thanks guys,,,This Is what the forum is for.....:thumbup::thumbup::thumbup:


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## Spark Master (Jul 3, 2012)

Any rooftop over 6 tons will have 3 phase blower motors. If air is blowing out the return duct, with dust, you know you have it backwards.


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## BBQ (Nov 16, 2010)

erics37 said:


> 208 3-phase no grounded conductor? :001_huh: You sure?
> 
> Anyway you can get a phase rotation meter and stick it on there, but that'd only do you good if you knew rotation prior to the accident. If the only 3-phase loads are the rooftop units then it shouldn't be a big deal. I've seen some of those that take 3-phase and then only have single-phase fan motors anyway, in which case rotation would be irrelevant. If it does has a 3-phase fan motor then just bump the power and see which way it turns.
> 
> There's a more proper procedure for testing motor rotation but I'll be damned if bumping an AHU isn't good enough for me.


It is bad to reverse the rotation on refrigeration compressors once they have been running in a direction for years already.


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## leland (Dec 28, 2007)

480sparky said:


> The right meter will give you the rotation of both the incoming line and the motor. You check both before terminating the conductors at the motor.


 Got a link?

Ckt must be energized for my meter to operate.


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## BBQ (Nov 16, 2010)

leland said:


> Got a link?
> 
> Ckt must be energized for my meter to operate.


It uses residual magnetism to determine motor rotation.


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## leland (Dec 28, 2007)

http://www.knoppinc.com/Specifications/Leaflet No 427 K-3 Instructions Rev E.pdf

I have an old Knopp K-3, given to me by a retiring line supervisor for BECO, along with a nice 1200A amp probe, back in the 90's.:thumbsup:
Nice unit, has come in handy many times.


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## Ultrafault (Dec 16, 2012)

If you can afford to replace these compressors DO NOT change the phases at the disconects they may be synchronised. Have an hvac come to turn them on. I would not be responsible for these if I was no positive I knew how they operated.


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## Deepwater Horizon (Jan 29, 2013)

Wait...doesn't the NEC require a grounded conductor be run to the service disconnect and main bonding jumper even if it's not required by the load served? Where is your fault clearing path without the grounded conductor?


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## BBQ (Nov 16, 2010)

Deepwater Horizon said:


> Wait...doesn't the NEC require a grounded conductor be run to the service disconnect and main bonding jumper even if it's not required by the load served? Where is your fault clearing path without the grounded conductor?


I imagine this is what you are thinking of.




> *250.24 Grounding Service-Supplied Alternating-Current
> Systems.
> 
> (C) Grounded Conductor Brought to Service Equipment.*
> ...


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## hardworkingstiff (Jan 22, 2007)

Deepwater Horizon said:


> Wait...doesn't the NEC require a grounded conductor be run to the service disconnect and main bonding jumper even if it's not required by the load served? Where is your fault clearing path without the grounded conductor?


I was wondering the same thing.


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## Deepwater Horizon (Jan 29, 2013)

It looks like Harry has to bring this up to code then.


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## hardworkingstiff (Jan 22, 2007)

Deepwater Horizon said:


> It looks like Harry has to bring this up to code then.


Well, he was going to do it on 1/22, so maybe Harry will let us know what happened.


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## BBQ (Nov 16, 2010)

What if it was really a 230 delta service?


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## Deepwater Horizon (Jan 29, 2013)

BBQ said:


> What if it was really a 230 delta service?


Well then, no grounded conductor required. :blink:

Maybe Harry had his beer goggles on when he made his OP? :drink:


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## BBQ (Nov 16, 2010)

Deepwater Horizon said:


> Well then, no grounded conductor required. :blink:
> 
> Maybe Harry had his beer goggles on when he made his OP? :drink:


Unless I missed it Harry never made 100% clear what he had.

It could be grounded delta for all we know.


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## Deepwater Horizon (Jan 29, 2013)

BBQ said:


> Unless I missed it Harry never made 100% clear what he had.
> 
> It could be grounded delta for all we know.


Grounded delta, open delta, zig zag, 4 wire....:laughing:


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## hardworkingstiff (Jan 22, 2007)

BBQ said:


> Unless I missed it Harry never made 100% clear what he had.


Other than he said "straight 208", so that would make me think Wye.

But you are correct, he never really made it 100% clear.

HARRY! Come back!


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## BBQ (Nov 16, 2010)

I would think wye expect for the missing conductor and he also said this..



HARRY304E said:


> Not sure of the exact voltage but It's not 480 Volts .


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## HARRY304E (Sep 15, 2010)

Yup the voltage was high at 249 volts,They sent 4 bucket trucks and 8 men plus one traffic cop on a side street to string 30' of #1- 3wire triplex.:laughing::laughing::no:


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## aftershockews (Dec 22, 2012)

ponyboy said:


> I've hooked up some massive RTUS and MAUS And all I do is wire it up, turn breaker on, leave disco off, tell tinner its ready to go. If a phase is backwards they'll either tell me about it or swap it themselves


Same here. Even on resi, I leave water heaters, furnace units and AC compressors disco'd and let the trade that installed the unit be the one to turn on the juice.


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## Deepwater Horizon (Jan 29, 2013)

HARRY304E said:


> Yup the voltage was high at 249 volts,They sent 4 bucket trucks and 8 men plus one traffic cop on a side street to string 30' of #1- 3wire triplex.:laughing::laughing::no:


So what was the actual system you were dealing with? :001_huh:


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## HARRY304E (Sep 15, 2010)

Deepwater Horizon said:


> So what was the actual system you were dealing with? :001_huh:


Three phase delta.


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## Deepwater Horizon (Jan 29, 2013)

HARRY304E said:


> Three phase delta.


Corner grounded?


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## HARRY304E (Sep 15, 2010)

Deepwater Horizon said:


> Corner grounded?


I do not know ,just 3 hots.


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## hardworkingstiff (Jan 22, 2007)

HARRY304E said:


> I do not know ,just 3 hots.


Something is strange.


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## Big John (May 23, 2010)

I sorta wanna try and figure out what the hell y'all are talking about... but I sorta don't....


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## HARRY304E (Sep 15, 2010)

hardworkingstiff said:


> Something is strange.


It is just three hots coming in ,No grounded conductor,However who ever did the service drove 2 ground rods but I think that is wrong,I'd have to read the code .


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## Deepwater Horizon (Jan 29, 2013)

HARRY304E said:


> It is just three hots coming in ,No grounded conductor,However who ever did the service drove 2 ground rods but I think that is wrong,I'd have to read the code .


Only 3 ungrounded conductors clearly makes it a delta system. The question remains is if it's ungrounded or not.


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## HARRY304E (Sep 15, 2010)

Deepwater Horizon said:


> Only 3 ungrounded conductors clearly makes it a delta system. The question remains is if it's ungrounded or not.


I really don't know ,I could not get a clear answer from the POCO guys.


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## hardworkingstiff (Jan 22, 2007)

HARRY304E said:


> It is just three hots coming in ,No grounded conductor,However who ever did the service drove 2 ground rods but I think that is wrong,I'd have to read the code .


What did he connect the ground rods to? Just a ground bar and nothing from the service entrance conductors? 

Was there a ground fault detection system?


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## hardworkingstiff (Jan 22, 2007)

Deepwater Horizon said:


> Only 3 ungrounded conductors clearly makes it a delta system. The question remains is if it's ungrounded or not.


I was speaking to a state code official who was telling me they were having an argument with a local PoCo that provided 3 hots to a service w/out a grounded conductor, the problem is the transformer they tapped was a Wye. So while almost always your statement is correct, I've heard of an instance where it would not be accurate.


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## Deepwater Horizon (Jan 29, 2013)

hardworkingstiff said:


> I was speaking to a state code official who was telling me they were having an argument with a local PoCo that provided 3 hots to a service w/out a grounded conductor, the problem is the transformer they tapped was a Wye. So while almost always your statement is correct, I've heard of an instance where it would not be accurate.


That's weird. :blink: In any case, that would not be NEC compliant, but you know that already.


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## JohnR (Apr 12, 2010)

erics37 said:


> There's a more proper procedure for testing motor rotation but I'll be damned if bumping an AHU isn't good enough for me.


 Not picking on you, but I have run into a freezer unit for a walgreens cooler that if it was bumped backwards would blow the compressor. 
For RTU's and AHU's I do the same thing in a pinch.


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## varmit (Apr 19, 2009)

You can buy motor rotation indicating meters. You connect these to an UNPOWERED motor and turn the motor in the desired direction by hand. If this meter indicates that A-B-C gives the correct rotation, then connect your other (powered) phase rotation tester to the incoming power and determine the phases. Then terminate the incoming lines to give the correct phase arrangement for the equipment. 

If the motor is accessible, I usually do this so I don't need to swap rotation later.


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## frenchelectrican (Mar 15, 2007)

HARRY304E said:


> I really don't know ,I could not get a clear answer from the POCO guys.


 
Harry .,

There is the other way you can tell if the delta is grounded is look at the POCO cans if overhead and useally centre can will have one conductor grounded but if not grounded at all then you have floating sonvagunner.

With grounded delta you should read apx 240 volts L-L or 240 L-G on two phase and 0 V at one L-G termation which it is grounded by purpose at transfomer location.

Now with ungrounded it will float about 240 volts but L-G will not be consist reading it will bounce allover the place ( avce voltmeter )

Merci,
Marc


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## erics37 (May 7, 2009)

BBQ said:


> It is bad to reverse the rotation on refrigeration compressors once they have been running in a direction for years already.





JohnR said:


> Not picking on you, but I have run into a freezer unit for a walgreens cooler that if it was bumped backwards would blow the compressor.
> For RTU's and AHU's I do the same thing in a pinch.


I see y'alls points! Thanks. I guess most of the AHUs I've worked on only do heating anyway. I don't do much new construction either but most of the new units I've seen come with phase reversal monitors that won't let me start it up if it's backwards :thumbup:


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