long wire run ,wire gauge

Old 10-22-04, 10:58 PM
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long wire run ,wire gauge

I want to run a 350 foot outdoor wire from my garage wall plug to a outside water well to supply heat for the winter. My plug is on a 20 amp breaker. I want to run a 750 watt space heater on this line or a 125 watt heat lamp if the space heater is too large. How do I figure what gauge of wire I need to safely do this?
Old 10-23-04, 06:38 AM
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There are numerous voltage drop calculators on the web. Use Google and you can find any number of them.

However, let me comment on your idea. Starting from the existing receptacle is not necessarily a good idea. Do you know what else is on this circuit? What is the distance from the panel to this receptacle? It may not be a straight shot if there are other receptacles in between. Plus there is the smaller wire (probably 12 guage) that your long run will traverse before it gets to your larger wire.

You would be better off determining how long the run will be from the panel, and then installing a new circuit.
Old 10-23-04, 09:32 AM
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The 125-watt heat lamp will only add one amp to the load, and voltage drop won't be an issue. 350 feet of 12-gauge will only drop about 1 volt, not enough to worry about.

The 750-watt space heater will add 6 amps of load, so Bob's concerns about overloading the circuit are more significant. So make sure the circuit can handle the extra load. If so, you could still use 12-gauge wire. The voltage drop will be about 7 volts, but the heater won't care. It will just produce a bit less heat.

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