350 foot run to AC

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electricblue

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I gotta run a 60a circuit to a ac compressor about 350'. I'm worried about voltage drop that far. I'm planning on running #1. A buck boost would save me if something goes wrong. Right?
 
In general buck boost is not a good idea for solving voltage drop. When there is no load or light load voltage will be high.

You said you were planning to run #1 - I assume to compensate for VD. If you do that what is your reasoning for the buck boost?

You also said 60 amp circuit - but I am assuming by that you mean the unit requires a 60 amp breaker. Remember that breaker is sized to allow starting without nuisance tripping, actual current the unit draws (which is what you should do voltage drop calculations with) is probably around half that figure. I did not do any calculations but off top of my head I'd bet you can get by with smaller conductor and still have reasonable voltage drop results - if I am right on actual load being nearly half the 60 amps.
 
I'm just worried about spending all that money and something not working right. I've had issues with 208 volt pool heaters. If they drop 1 or 2 volt you got problems and voids warranty.
 
electricblue said:
I'm just worried about spending all that money and something not working right. I've had issues with 208 volt pool heaters. If they drop 1 or 2 volt you got problems and voids warranty.
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Yeah there is more to it than that.

This table shows what voltages equipment is expected to operate with.

ANSIC841.jpg


As you can see equipment designed for 208 volt supply should work with voltages from 181 through 220.
 
electricblue said:
I'm just worried about spending all that money and something not working right. I've had issues with 208 volt pool heaters. If they drop 1 or 2 volt you got problems and voids warranty.
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If your equipment can't handle less then 2% drop, there is a problem even if you severely oversize conductors for voltage drop reasons. Oversized conductors only eliminate voltage drop due to resistance in the the segment of the circuit that is oversized. Transformers will pass on any change in delivered voltage as well.

It is still hard to guarantee there will not be voltage drop from either the presence of other loads on same service or from other utility issues, nearby customer loads causing voltage changes, etc. If you have super sensitive equipment that don't like such fluctuations you need a UPS or other conditioned power supply.

I don't know a lot about pool heaters. If a resistance electric heater voltage drop just means less heat from that heater. Now controls for the heater whether electric heat or other heat source could have some voltage sensitivity issues, but hopefully any well designed equipment can take a 2% variance with little problems.
 
kwired said:
If your equipment can't handle less then 2% drop, there is a problem even if you severely oversize conductors for voltage drop reasons. Oversized conductors only eliminate voltage drop due to resistance in the the segment of the circuit that is oversized. Transformers will pass on any change in delivered voltage as well.

It is still hard to guarantee there will not be voltage drop from either the presence of other loads on same service or from other utility issues, nearby customer loads causing voltage changes, etc. If you have super sensitive equipment that don't like such fluctuations you need a UPS or other conditioned power supply.

I don't know a lot about pool heaters. If a resistance electric heater voltage drop just means less heat from that heater. Now controls for the heater whether electric heat or other heat source could have some voltage sensitivity issues, but hopefully any well designed equipment can take a 2% variance with little problems.
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The pool heaters are no different than an ac CU but nobody uses 200volt motors.
 
electricblue said:
The pool heaters are no different than an ac CU but nobody uses 200volt motors.
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So I take it they are heat pump style pool heaters that you are talking about. Might be most common type you see, but though I am never around pools, I'm sure there are other heater types.

The compressor motor itself can probably take a pretty wide voltage range without causing it much harm (doesn't mean warranties won't be picky about actual voltage) Actual performance issues from voltage drop are more likely to come up involving the controls more so then the motor itself.
 
electricblue said:
I agree. I've suggested 200 volt motors for pool equipment but they say they are hard to come by and expensive. Look at the specs. There are all 230-208.



http://www.aquacal.com/aquacal-tropical-economic-pool-heat-pump
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If the motor is actually dual voltage rated as 230/208 (230/200?), then it should be good for 208 -10%. This is very different from trying to run a single voltage listed 230V motor from a 208 supply, hoping that the 208 service will be in the high half of the allowed range.
 
electricblue said:
We've got off subject but that's fine. I'm not sure if a compressor is like a wound motor as far as voltage goes.
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Did you mean to say wound rotor motor?

AFAIK all common hermetic compressors have induction designed rotors and are not that much different with general electrical characteristics then any other general purpose induction type motor driving similar torque characteristic loads.
 
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