....programmable light switch/timer (Retitled)

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Old 09-14-05, 01:28 AM
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....programmable light switch/timer (Retitled)

I bought a programmable light switch/timer, that uses a solar calendar to turn the lights on and off at sunset and sunrise, for my outside lights. It has an LCD digital readout for programming. Looks simple enough to connect...one black wire, one blue wire and one white wire.

Problem is, and I didn't think to check this before I bought the switch, the switch wiring is a switch loop to the lights, which means there is no white, or neutral wire at the switch box to power the switch.

Am I screwed, or is there another way around this dilema?

Thanks...Randy

BTW, I noticed on this switch, and I've seen it on other timer switches, the white wire is a smaller gauge than the other wires. Why is this?
 
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Old 09-14-05, 04:38 AM
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You cannot use this switch. Take it back and buy another. They make them in varieties that do not need a neutral. Some have a battery, others only work with certain bulbs, and run small amount of current though the circuit to power the electronics.

The white wire on this switch is smaller because they only need a small amount of current to power the electronics, and code and the UL allows the wire to be smaller in this case.
 
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Old 09-14-05, 03:21 PM
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Well, that's what I thought you, or someone, would say, so how about this?

Luckily, this circuit is contained in conduit, and I just happened to have a spool of #12 white wire(THHN) left over from a previous job, so can I just pull in a new white wire from the light where the power is to the switch?

Thanks.
 
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Old 09-14-05, 03:42 PM
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The answer is yes, you can add a new neutral wire to the conduit, assuming that the conduit is not full, which it most likely isn't, since this is a switch loop. You may have to use the existing wires as a pull wire for a string, and then use the string to pull the entire group of wires.
 
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Old 09-15-05, 12:27 AM
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Got it...not as bad as I thought it was going to be.

I was able to push a fish tape through and then pull the wire back from the power source. Installed the switch and it's working great.

Thanks for the help, racraft.

Randy

BTW...what is full for 1/2" EMT?
 
  #6  
Old 09-15-05, 09:18 AM
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Originally Posted by rcash54
BTW...what is full for 1/2" EMT?
For conduits more than 24" long: (9) #12 THHN/THWN or (12) #14 THHN/THWN

De-rating rules may make that many wires impractical however.
 
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Old 09-15-05, 09:34 AM
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Originally Posted by ibpooks
For conduits more than 24" long: (9) #12 THHN/THWN or (12) #14 THHN/THWN

De-rating rules may make that many wires impractical however.
ibpooks (here I am again, and this time thread hi-jacking). Is there a chart available that shows how many cables of each size can fit into the different conduits? (I'm talking physically fit, not taking into account derating... which we're talking to death in another thread)
 
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Old 09-15-05, 09:56 AM
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What you are looking for is called "conduit fill", and unfortunately it is just as complicated as de-rating in terms of special cases and rules. It boils down to the sum of the cross-sectional areas of the wires inside a conduit cannot be more than 40% the total cross-sectional area of the inner diameter of the conduit for a conduit with 3 or more conductors.

The factors involved here are the inner diameter of the conduit (which varies by type; rigid, PVC, EMT, etc), the gauge of the wire, and the type of wire insulation. There are many NEC tables that provide all of this information for a calculation by hand, but many people use computer software to calculate conduit fill for them. Google for the term and you will find some online calculators.

Not to over do it here, but there are rules similar to conduit fill for junction boxes also called "box fill". Even if your conduits are large enough to hold dozens of wires, you may be required to use massive junction boxes on either end to terminate the wires.
 
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Old 09-15-05, 05:31 PM
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For conduits more than 24" long: (9) #12 THHN/THWN or (12) #14 THHN/THWN
Thanks, ibpooks.
 
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