Posted: 1/17/2005 5:38:42 AM EDT
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I just installed a ceiling fan where there was no fixture or wiring. I went up to the attic, pulled up the floor, moved the insulation, and installed a box on a brace between the joists and carfully cut a hole for the box. All that went perfectly. In order to wire it, I tapped into the line (at a pre-existing box) that supplied the attic light and the attic vent fan (small one). When I purchased the wire, I got 12/2 (if I remember correctly), which ended up being a much thicker guage than the existing house wiring. The run was about 35 feet. My question is, is there a problem with supplying thicker guage wire from thin (typical) guage wire. Keep in mind that the fan has no light, and draws .9 amps at max. Given the load, and the fact that it's the only item on the wire, I don't think there will ever be a problem, but I thought I'd verify. |
As long as the thinnest wire in the path is rated for the current, it wont pose any problems. |
It is if you have a thinner wire in the link. If you use 14 gauge from the breaker box to your attic, then 10 gauge from your attic to the fan you've created a *potential* problem is you try to drive a load rated for 10 gauge wire, as you'll overload the 14 gauge at the beginning of the path. |
That's what I thought, but the problem never shows when driving a ceiling fan. |
 The problem most likely wouldnt show unless you overloaded the wire and started afire!! So lets hope the problem DOESNT show itself!! Just check to make sure your wiring is rated for the load (Or loads) you have on it. Naturally, use the ratings for the thinnest wire in the path and use a load that assumes everything is on that is tied into the wire. If the load is at or below the rating your fine. If its at or above I'd step VERY carefully cause your on thin ice. Remember, the thing with wire is you might save 10 or 20 bucks upfront but it just isnt worth it if you burn down your 200,000 or 300,000 dollar house!! |
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There is no way that using a wire gauge rated for a higher load will cause any problems in a properly wired circuit. If the supply wiring to your splice were say 14 gauge wire, then according to the NEC the breaker or fuse that supplies the feed would have to be rated 15amps. Therefore if you loaded your circuit with a maximum that the 12/2 could carry, 20 amps, it would blow the breaker, protecting the 14 gauge wire. If your breaker is a 20amp, and you think that the wire is 14 gauge, you would probably be best served replacing the breaker to match the weakest link, ie the 14 gauge wire. If you are in doubt about the total load, you could purchase a cheap clamp on ammeter and measure the load on that circuit. HTH -Space |
Damn, beat me too it. +1 |
Any time the load exceeds or even approaches the 14g capacity, shouldn't the breaker trip anyway? From what I can see, the problem would be someone later coming along later seeing the 10g wire, but not seeing (or realizing the significance of) that it's supplied by say 14g, then adding a heavy load. Actually I guess that's what you were saying. An example might be if you (or a later occupant) remodeled to make it into a bedroom and added, say, some space heaters, extra lighting, A/C, outlets, etc. that exceeded the capacity of the 14g or the breaker for that circuit. Then either the breaker would be tripping, or the 14g would be getting hot. Would it make sense to tag both ends of the 10g saying is fed with the smaller wire and that the total load should not exceed that capability? Using a wire smaller than the existing wire would be dangerous (and, I'd bet, a code violation) because then the breaker could supply more amps than that section of wire could handle. If there was a short at the load or somewhere in the small section, then the smaller wire would be getting real hot and you'd have a fire problem. I've come to think about these things, because the neighbor is an electrician and when his washing machine starts a cycle, his lights dim noticeably for a second. |
