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Three Phase Compressor Set


Martin

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Hi folks

 

Got a contract this week to install a supply for a three phase compressor, nothing unusual or difficult. The comp set has input terminals marked U,V,W which to my mind required L1,L2,L3 respectively but when it was switched on the motor rotated in the wrong direction. Swapping L2 and L3 made it go the right way, so customer was happy, however this has me a bit perplexed. The site supply has clockwise phase rotation and I assume the compressor requires anticlockwise phase rotation, is this likely the case or am I being rather dense here?

 

Regards

Martin

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ProDave

Perhaps the supply into the building is wrong, who knows. But you got it going the right way so I would not waste any more thought on the matter.

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apprentice87

Hi there,

 

All depends on which direction the makers intended the thing to run!! HOWEVER, i would not try "experimenting" with motor direction again, because it is only a matter of time before you find something that will be damaged by running backwards. You need a phase rotation tester, one that identifies the motor terminals too, so that you KNOW what will happen before you power things up...

 

I have one of these and would not be without it....

 

http://uk.rs-online.com/web/p/phase-rotation-testers/5131834/

 

john...

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Evans Electric

How does the meter know which way a machine needs to turn  though Apprentii ?

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ProDave

And don't think of "correcting" it by swapping the rotation at the board. Who knows how many other machines would then go the wrong way.

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apprentice87

Hello!! Right.. What you do is this...

 

Test the incoming supply to the machine with the meter, you want clockwise phase rotation, so connect the leads marked "U" "V" "W" and "L1" "L2" "L3" from the meter to the brown, black and grey [or RYB] and press the button, the "clockwise" light should come on.

 

Next, with the motor disconnected, connect the leads from the meter to the motor. Turn the motor by hand, IN THE DIRECTION YOU WANT IT TO GO about 3rpm is fast enough! Swap the meter leads around on the motor until the "clockwise" light comes on, and then label the terminals "L1" "L2" "L3". Connect these to the incoming "L1" "L2" "L3" and the motor will go the way you want first time!!!

 

Which way the motor turns????

 

You could either rotate the machine by hand and see what the motor does, OR if the motor runs [before you take it to bits and re-wire it] but you cannot see the output shaft, simply rest the meter on the motor casing. [no leads] and it will tell you which way the motor is running!!

 

john..

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kerching

I WANT one

I do not NEED one

I have not NEEDED one in 40+ years

But I WANT one

I did once see a star delta setup,that when it switched from start to run it instantly "tried" to reverse!

Do not know how he did it, but I believe that he didn't really want to be doing that!

Just saying

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Sidewinder

Oh, I have one, and yes they are useful!

IMHO...

 

If anyone needs one, I'd try Megger Mark @ isswww.co.uk, via the forum PM system, I'm sure you'll get a good deal.

 

Some of the kit I've worked on is rotation sensitive, and you can't even "flick" the power on to check direction as it would cause mechanical damage, and to uncouple the load is a LOT of work, think hours possibly days, that's when they start to pay for themselves.

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Andy™

I WANT one

I do not NEED one

I have not NEEDED one in 40+ years

But I WANT one

Just saying

 

good to know its not just me

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Evans Electric

I'd like one too but won't be buying one  now .

I 've always told the customer / setter/ commisioner /etc  that it may go backwards and let them do the necessary .  Other than a simple machine , say a grinder or pedestal drill  I never try anything ........buggered a machine up years ago by switching on & pressing start .

 

I wired a spiral binder in last week ...went off to find the guy to try it ....couldn't find him, went for a Gypoe,s ...got back , he'd appeared , switched on and had it running  ...lucky it went the right way , it still had factory settings so it was OK  .    Theres a small conveyor belt attached to them  , we usually try that without the main drive  , if its right the rest is right .    

 

Some of the old roller doors were'nt fully interlocked , so we always wound them by hand to a foot off the bottom limit ....never tried them fully open as the up limit would be inoperative . 

Different now , you can't send them down & walk away for one .

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I WANT one

I do not NEED one

I have not NEEDED one in 40+ years

But I WANT one

I did once see a star delta setup,that when it switched from start to run it instantly "tried" to reverse!

Do not know how he did it, but I believe that he didn't really want to be doing that!

Just saying

I have seen that trick as well Star one way and delta the other, the overload and fuses did not like it

must get one Monday!

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Nothing to worry about as others have said.  When ever we connected up a motor a rotation check was always carried out and to us it was always 50 50 as to it being correct.  A rotation check was always carried out, just the quickest on off you could get on the supply to say which way the motor would go.  The exception to this would be any very sensitive piece of kit to wrong rotation where other safeguards would have to be put in place such as de-coupling the motor.

 

As a side piece of info and as a general rule only so not guaranteed:

For a brand new motor connecting it up L1L2L3 to UVW the motor will go counter clockwise when looking from motor cooling fan.

Handy when connecting up banks of new motors on a new contract.

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kerching

When i used to install car lofts I always wound them up a bit before applying power.

Having seen one unscrew itself from the floor when the motor direction was wrong and it was looking for the TOP limit on its way DOWN

Better to be safe than overly confident

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ProDave

When i used to install car lofts I always wound them up a bit before applying power.

Having seen one unscrew itself from the floor when the motor direction was wrong and it was looking for the TOP limit on its way DOWN

Better to be safe than overly confident

Poke the limit switch with a stick LONG before it gets there to make sure the right limit switch is operating.  It's not like a car lift moves very fast.

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Thanks for the thoughts. I have a Megger phase rotation meter but for obscure reasons, old age probably, I didn't associate the reading with the likely direction of the motor. I'll know better next time. BTW is there a defined standard in the UK for the supply of three phases, ie will RYB or BnBkG always produce clockwise rotation assuming phases haven't been swapped somewhere between sub station and DB.

 

Regards

Martin

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Read my post #12

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  • 3 weeks later...

I got caught out using a phase rotation meter. Easy job fit a socket made sure rotation was correct. However rest of factory was wrong. In the main only need for meter is when connecting two generators together I no longer carry it. Not been used for years.

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just got a Fluke 9062, never knew they a meter like this ,will ave me a lot of hart ache   

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steptoe

I got caught out using a phase rotation meter. Easy job fit a socket made sure rotation was correct. However rest of factory was wrong. In the main only need for meter is when connecting two generators together I no longer carry it. Not been used for years.

How was the rest of the factory wrong,?

Did you change the rotation?

Fitting a socket,  or anything for that matter, you only change the rotation at point of connection, NOT at source.   :shakehead 

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kerching

Back in the day here was a local Gas Board monkey we called Terry Feckwit

He fitted a new 3ph motor on a heat exchanger at my biggest clients...we were not allowed to do it as it was part of their quote

Motor ran wrong way

He pratted about changing the rotation at the local DB incomer!

Prannock!

This board supplied conveyor belts, catering equipment, dishwasher nd the goods lift!

He was a liability. He had seen me pushing contactors in...tried it himself with a star delta WHILST it was running!!....no idea why....he put the ensuing BANG FLASH PHURTTTTT BOOM down to a faulty coil?!?!

Created loads of work for us"..nice!

They slotted him in the end

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