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Step Down Transformer to Reduce Conductor Size Over Long Run

Step Down Transformer to Reduce Conductor Size Over Long Run

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  #1  
Old 12-10-13, 12:58 PM
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Step Down Transformer to Reduce Conductor Size Over Long Run

Need to supply two 230V motors and one 115V motor with an outdoor circuit that is over 600' long. The 230V motors are rated 4 amps each. The 115V motor is rated 5 amps. I would like to install a 15 or 20 amp convenience outlet in the area as well.

To supply the 230V motors I only need a red and black conductor of relatively modest size (e.g., #6). I would need to add a neutral (white) conductor, and increase the conductor sizing significantly, to supply 15 or 20 amps at 115V. I do not want to try to swap the 115V motor for a 230V motor, or drop the convenience outlet.

What would be the disadvantages, if any, to my using a 230V-115V step down transformer at the end of a 230V circuit to supply the 115V motor and convenience outlet? A good quality transformer of appropriate size is still considerably less expensive than the added cost of sizing the circuit to deliver 15 or 20 amps of 115V over that long of a distance.

I can live with a decrease in reliability (i.e., the transformer may fail over some period of time) because a temporary disruption in the 115V supply won't cause any real hardship. Is more power used with a transformer as compared to a full 115V circuit, such that the incremental additional cost of electricity over time is a factor that needs to be considered? Any other potential disadvantages with using a transformer to downsize conductors over such a long run?
 
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  #2  
Old 12-10-13, 01:03 PM
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Given the cost of cable you might look on places like Ebay for a step-up transformer to output 480 from the panel and a 480/240 transformer with a center tapped secondary for use at the other end.
 
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Old 12-10-13, 01:33 PM
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The only downside I can think of is that no device is 100% efficient. That said, the loss to inefficiency through the transformer shouldn't be much.

I like Ray's suggestion of step-up/step-down xfmrs,
 
  #4  
Old 12-10-13, 04:46 PM
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Long Run

I like rays idea. At 480 volts you could run 600ft using #8-cu with just under a 10-volt drop using a 5KVA trans. With #6-cu you would have a VD around 6-volts. You would not need to install a neutral. Your neutral would be established at the transformer and you would need a small panel for distribution. GE makes a QMS encapsulated transformer that works well (keeps kids and critters out) unlike some open transformers with a rain shield.
 
  #5  
Old 12-18-13, 03:56 PM
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Thanks for the helpful comments. I'm a little confused about Ray's suggestion.

If I install a step up transformer at the panel, I still have to install a step down transformer (230V/115V) at the end of the circuit, don't I? That means two transformers instead of the one I orginally was considering.

My 230V load requirements are modest (under 10 amps), so even though its a 600' run, does it really make that much sense to purchase and install a 5KW step up transformer and separate distribution panel rather than just purchase conductors that will handle a 10 amp 230V circuit of that length? The cost differential between conductors in the #4 - #8 range isn't prohibitive, as compared to say #6 v. 0/1. I probably have to go from #6 to 0/1, if I size the conductors for a 20 amp 115V circuit just so I can supply a convenience outlet for occasional use. That's why it occurred to me to explore the step down transformer at the end of a 10 amp 230V circuit.

Finally, just so I understand, no one can think of a good reason not to go with a step down transformer at the end of a 10 amp 230V circuit that is 600' long so that I can avoid installing conductors large enough to supply the convenience outlet with 20 amps of 115V power? From the comments, I get the sense that it's a good idea all around.
 
  #6  
Old 12-18-13, 10:40 PM
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Step Down transformer to reduce conductor size

I don't see any problem with what you want to do. If you use a 2kva trans you will get around 16.6 amps at 120V. If you use a 3kva trans you can get 25 amps at 120V or around 12.5 amps on each leg so you could have two receptacles. The GE QB transformers are encapsulated and weatherproof. You could run (2)#4 CU (1)#6 ground and VD would be about 2%. You can go 125% on the transformer primary so a 20 amp breaker. The secondary is a separately derived system and single-phase transformers (other than 2-wire which this is not) require the secondary conductors to have overcurrent protection. The secondary would require a #8 GEC to a grounding electrode. The overcurrent protection would depend on how you connect the secondary (120V only or 120/240).
 
  #7  
Old 12-22-13, 09:10 AM
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Just what I was looking for bahtah. Thanks so much.
 
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