Voltage Drop

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dnbob

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Rochester, MN
I need to control a 3 amp load from about 1000' away. If I run #8's from the controller to the load, would pigtailing 12" of #12 or #10 to the #8's at the controller make the #8's ineffective for voltage drop? I need to get the #8's onto a selector switch, but will not accept wire that large.

Bob
 
Re: Voltage Drop

Bob, your pigtail only needs to be sized to match the overcurrent protection of the circuit.

:)

Dave
 
Re: Voltage Drop

#12 is fine Bob. The resistance in the 1 ft. of #12 is practically non existent in terms of voltage drop.

Dave
 
Re: Voltage Drop

If what you have is a switch loop 1000 feet long that controls a contactor coil then the contactor will never deenergize if your control voltage is 120 volts AC. The capacitance between the wires will tend to bypass your switch.

If the switch directly controls a load and the load is inductive, you could actually have a voltage RISE because of the wire capacitance.

Also, the capacitance of alledgedly waterproof wire goes up when wet. If the conduit is flooded the water acts as a giant capacitor plate that is in intimate conyact with the insulation. I have seen this phenomenon disable a variable frequency drive and the circuit was THWN wire in PVC conduit in the ceiling of a food plant. Turns out that the 3rd shift sanitation people will fill up light fixtures and conduits with the pressure washers just for fun.
 
Re: Voltage Drop

mc5w, that's interesting information. I've never run a switch loop that far. Would using 208 or 240v rated coil prevent this?(capacitance issue) If so, would it require switching both phases or just one?
 
Re: Voltage Drop

dnbob, Is it 1000 feet one way? If it is you have to firgure the voltage drop going to and the return of the grounded conductor. So 1000 x 2= 2000'. If you already had it at 500 x 2 then forget what I just said.
Jim
 
Re: Voltage Drop

dnbob - also what do you mean by the term "controller"?

Do you mean the NEC definition of the Article 430 term?
What is your load? Is this something as simple as a 1-way switch supplying a load or a recept. ?

I know what mc5w is getting at if it is an extremely long motor control circuit.
 
Re: Voltage Drop

Bob, I would suggest at least No. 6 Copper for the 1000ft distance with 3 amp load. The VD will be about 3 volts or 2.5 percent.
 
Re: Voltage Drop

We are running power to 4 trafic signals on a dirt racetrack, 1 for each corner. the farthest one is 1000' from the control, which is a selector switch and pilot light for each color. each light will have either 1 - 60 watt or 1 - 100 watt lamp, so the load is minimal.

I should clarify, that only 1 lamp is 1000' away, the other 2 on that conduit run are at 200' and 600'. The 4th light is on a separate run.

thanks for the reply's!

Bob

[ April 22, 2005, 06:58 AM: Message edited by: dnbob ]
 
Re: Voltage Drop

Use 120V LED lamps. They are readily available in 8" and 12" for standard traffic signal displays, cost about $100 each, last a really long time, about 100,000 hours, 20 watts draw. You could operate the lamps at 12VDC and a battery/solar power with a 24 vdc control circuit. DC is best for long control circuits. Old municipal fire alarms would run for miles and miles on 19 gage copper, at 120 VDC.
 
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