Farm Three Phase

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Ohfarmer42

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Ohio
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Farmer
We are upgrading are farm grain bin site to three phase power. Our local electric coop is giving us the choice of 480/277 or 480/240. The 480/240 has the high leg or “wild leg” as they call it. We will still have a separate single phase service so powering single phase loads off the upgraded service is not necessary. My question is which would be better for powering multiple motors over 10hp up to 40hp got the grain bins.
 
Welcome to the forum. We're not permitted to help DIYs, but your question is not that.

The main difference is wye vs delta. I would recommend the former, the 480Y/277.

The motors won't care, but the high-leg system creates a higher voltage to earth.
 
The OP is not doing DIY work and is here seeking professional opinions on what system would best suit his needs. The mod's have discussed this and we're allowing the thread to remain open.
 
Thanks for the recommendations. I am not doing the work and have an electrician coming but he’s busy doing other work right now. I’m just trying to get the incoming power figured out. My electrician said either would work but got confusing on the pluses and minuses of each. This is a big investment for our farm and I want to make sure I get it right.
 
480/277V wye.

The two systems are equivalent for basic 'across the line' motors.

The balanced 480/277 wye system is better for any variable speed controlled motors, and more and more motors are being controlled in this fashion.

Jon
 
The only advantage I can think of for the high leg system is if you have any 240 volt single phase motors or loads. That said, you will have limited capacity to a degree for the line to neutral 240 volt loads.

The 480/240 system won't allow the use of slash rated circuit breakers, which will increase the cost some and may lead to longer lead times when you need one. For example the common Siemens 480 volt breaker is a BQD and is slash rated. You'd have to move up to an NGB on the high leg system which is a 600 volt breaker. For fused safety switches there would be no difference in equipment.
 
The other available voltage is 120/208 but my electrician and the equipment dealer like the 480 as there is some long runs like the 40hp leg motor 100’ in the air. I am concerned about the dangers of 480 with the possibility of an arc flash.
I do have some single phase motors at the bin site already and thought the 240/480 high leg would be a good choice as we could use some single phase out of it but am concerned about having to make sure the wild leg is never wired in the single phase circuit and the possibility of uneven phase loading with the single phase motor running with the three phase. We currently have a single phase service we are keeping so I think it would be best to keep the single phase motors on that and replace with three phase as they go bad.
I think the 277/480 wye service sounds best as we will probably have to incorporate some vfd’s to control the speed of some augers and may have to put a soft start in on some of the bigger motors.
Thanks again for all the reply’s.
 
Do they let you keep your 240/120 POT ? Around here, very rare, but I have seen 2 pad mounts set side by side. Only on a retrofit upgrade, not an original installation.
 
Yep. We have a single phase pad mount supplying a 400 amp to our grain bins and shop and a 200 amp to the house which also feeds some buildings. They said we could keep that as is if we wanted. The new 3 phase service and new pad mount transformer will just supply the grain bin system.
 
OT:. Make sure the weakest link is at the beginning and not the end. More than once I've come across grain systems that had hi capacity dryers or mills with augers either feeding or removing product that were not sized correctly. That is a millwright design issue. Not the electricians.
 
All other things being equal, the higher the voltage, the lower the current, the lower the voltage drop, and the lower the wire size and cost.
 
If the only loads being served are 3 phase loads, I would opt for the 480/240 wild leg system because I can probably use single phase distribution equipment and not 3 phase distribution equipment that would be required for the 480Y/277 system.
 
Ohfarmer42 said:
The other available voltage is 120/208 but my electrician and the equipment dealer like the 480 as there is some long runs like the 40hp leg motor 100’ in the air. I am concerned about the dangers of 480 with the possibility of an arc flash.
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There is a lot of talk and fear about arc flash but really it is rare and is almost always related to people not dealing with electricity in a safe way.

Ohfarmer42 said:
I do have some single phase motors at the bin site already and thought the 240/480 high leg would be a good choice as we could use some single phase out of it but am concerned about having to make sure the wild leg is never wired in the single phase circuit and the possibility of uneven phase loading with the single phase motor running with the three phase. We currently have a single phase service we are keeping so I think it would be best to keep the single phase motors on that and replace with three phase as they go bad.
I think the 277/480 wye service sounds best as we will probably have to incorporate some vfd’s to control the speed of some augers and may have to put a soft start in on some of the bigger motors.
Thanks again for all the reply’s.
Click to expand...
It seems to me that if you plan to have any VFDs, you are better served with a wye system.
 
don_resqcapt19 said:
If the only loads being served are 3 phase loads, I would opt for the 480/240 wild leg system because I can probably use single phase distribution equipment and not 3 phase distribution equipment that would be required for the 480Y/277 system.
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How's that?

With a 480V corner grounded delta, you only have 2 ungrounded conductors and could conceivably use panels with just 2 buses. But both 480/240V delta and 480Y/277 have 3 ungrounded conductors required to get 480V delta 3-wire to supply the motors.

Cheers, Wayne
 
I'm kind of late to the party, but I can't see any advantages (but lots of disadvantages) of the high-leg system, especially if there's already a 240/120 single phase system for things that want real 240.

Chalk up another one for 480/277.
 
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