# 3 phase Motor Question



## McClary’s Electrical (Feb 21, 2009)

gord said:


> A few questions on motor connections.
> 1.When would you connect a motor in Wye,the current draw would be lower(correct ?) do you loose HP connected this way?
> 
> 2.How do you size the overloads for a motor?
> ...


 
1) Correct and yes you lose HP

2) Depends on the service factor of the motor. Generally 115 to 125 % of the FLC


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## micromind (Aug 11, 2007)

1) If the motor is designed for wye start and delta run, it'll produce about 1/3 of its rated HP in wye. It'll also draw about 1/3 of the starting amps that it would in delta. 

2) Overloads for a motor are sized according to the starter manufacturers specifications. You'll need the full-load current, the service factor, and if the motor and starter are operated in the same ambient temperature. 

Generally speaking, a properly sized overload will trip within a minute or two at 115% of FLA. A standard overload will trip within 20 seconds at 6 X FLA, this is called 'class 20.' There are also class 10 and 30. 

A class 10 is used on 'high strung' motors. Like submersible pumps and hermetically sealed refrigeration compressors. These motors cannot take much abuse, so the overload needs to trip sooner than normal.

Class 20 is used for about 90% of motors. 

Class 30 would be used for a motor that is connected to a high inertia machine. Most NEMA frame motors can handle a class 30 overload, and design D ones certainly can. I'd be a bit leery to use one on an IEC motor though.


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## Jlarson (Jun 28, 2009)

micromind said:


> ...and if the motor and starter are operated in the same ambient temperature...


That's kinda an important one lots of people seem to overlook. The temp outside where the pump is and the temp in the air conditioned panel might be just a wee bit different :laughing:


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## gord (Sep 7, 2009)

Thanks for the replies.

So why would you choose to to run a motor connected in Wye when you are going to loose HP?
Is there a calculation of how much HP you loose or rule of thumb?

Gord


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## Paulusgnome (Mar 28, 2009)

gord said:


> Thanks for the replies.
> 
> So why would you choose to to run a motor connected in Wye when you are going to loose HP?
> Is there a calculation of how much HP you loose or rule of thumb?
> ...


You wouldn't usually run the motor in the wye/star configuration at all. 

What you might do is to start the motor in wye/star, and switch into delta once the motor has reached 80% of full speed, using a star-delta starter. This method is fast going out of favour now, with soft-starter prices approaching the prices of star-delta starters and offering much gentler treatment of motor, load and supply that an SD starter ever did. 

There are nevertheless still cheapass people about who insist on saving the last cent by using an SD starter despite the disadvantages.


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## McClary’s Electrical (Feb 21, 2009)

gord said:


> Thanks for the replies.
> 
> So why would you choose to to run a motor connected in Wye when you are going to loose HP?
> Is there a calculation of how much HP you loose or rule of thumb?
> ...


 

The post above mine sums it up, but I just wanna add that around here, the power company doesn't really want you to start anything bigger than 100 HP accross the line. At a minimum you would use a Wye/Delta starter setup. Ideally a softstart or VFD is the way to go.


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## John Valdes (May 17, 2007)

If the motor is a dual voltage motor and you only have 6 leads, the wye would be for high voltage and the delta would be for the low voltage.

Example. Motor, 3 PH, 50/60 Hz. 460-380/240-220 volts on nameplate.

For the 460-380 you would connect the motor in a wye. If the voltage is 240 or 220 you would wire it in a delta.


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## starter (Oct 24, 2010)

John Valdes i had a similer experience,it was wired for the wye which is high voltage and our plant we run on low voltage. We could not figure out why the motor were running hot and tripping the overload until i goggle that particular motor and saw where wye for high voltage delta for low voltage.


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## Introyble (Jul 10, 2010)

micromind said:


> 1) If the motor is designed for wye start and delta run, it'll produce about 1/3 of its rated HP in wye. It'll also draw about 1/3 of the starting amps that it would in delta.
> 
> 2) Overloads for a motor are sized according to the starter manufacturers specifications. You'll need the full-load current, the service factor, and if the motor and starter are operated in the same ambient temperature.
> 
> ...


I had to thank this response since I couldn't argue. 

I've had the absolute worst time with augar applications. For some reason I can't remove the human idiot element from anything with a fkn screw.


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## micromind (Aug 11, 2007)

Introyble said:


> I had to thank this response since I couldn't argue.
> 
> I've had the absolute worst time with augar applications. For some reason I can't remove the human idiot element from anything with a fkn screw.


I had the same problem on a slat conveyer at a hot plant. 

they sorta forgot to dump a bunch of diesel down the conveyer one day, and the hot tar cooled, freezing the slats solidly in place. 

After about 15 tries of having the starter go from wye to delta with the rotor locked, they finally burnt the motor up.


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## Introyble (Jul 10, 2010)

micromind said:


> I had the same problem on a slat conveyer at a hot plant.
> 
> they sorta forgot to dump a bunch of diesel down the conveyer one day, and the hot tar cooled, freezing the slats solidly in place.
> 
> After about 15 tries of having the starter go from wye to delta with the rotor locked, they finally burnt the motor up.


I say anything moved with a screw shouldn't be moved or moved in another way.

I swear to you I have had an impossible time with them. They lock constantly. Reversing, no good. Programmable no good, heaters no good. Some person on a production quota always seems to burn up the motor or starter(s) no matter what I do. Honestly, I am lost what to do in this situation.


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## Rock Crusher (May 6, 2013)

I don't know if it will help or if you have already tried it. But the place I used to work was the same way. Once I started showing them my research and the calculations I did, the numbers did the talking. The numbers I showed also included the money saved using the normal cost of motors and other equipment from the supply house and a call to the power company for the KWh cost for us.
Basically I did my research to prove my point, since just telling them wasn't working.:thumbsup:

I said used to work because I got an offer at another company was WAY! too sweet to pass up.
Good luck


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