Belts, suspenders & wiring

[daavidfost]

I've done a fair amount of DIY wiring over the years, and with a new (to us) 1870's farmhouse and barn, I'm looking at doing more. I'd like to pose a broad question about wiring - I'm a very belt-and-suspenders type and I've always erred on the side of making wiring a larger size than needed, especially when the electrical load is close to the wires capacity.

Am I doing something wrong? If I run a #10 wire instead of a #12, giving me the option to upgrade the circuit at a later time, is it the same as someone who thinks that if their car takes five quarts of oil, then putting in ten must be better?

Thanks for any insight into this.

David

[mdshunk]

Running larger gauge sizes than necessary in a dwelling is largely unnecessary and wasteful in my opinion. To begin with, if you run 10 for 12, you'd have a harder time terminating it under device screws intended for 12 or 14. It would be right difficult to dress larger wires back into the boxes at finish time. In reality, under what circumstances would you really need to change a 20amp circuit in a dwelling to serve 30 amp loads? None in my opinion.

There is only one reason to upsize conductors in a residential setting that I can think of, and that is to eliminate voltage drop. This wouldn't be an issue in the house itself, but may be an issue for feeders to outbuildings. Feeders and branches to outbuildings would benefit from having the conductors upsized if they are some distance away from the service panel. Use the Voltage Drop Calculator on this site to find out for sure.

In fairness though, some contractors never run anything smaller that 12. Namely, they do not run #14. They run 12 for 15 and 20 amp circuits. That may be the only upsize exception that I can think of.

[daavidfost]

Thanks for the quick repy.

What's the reason that many contractors don't use 14? Is it something other than the wire's capacity?

I probably shouldn't have used a 10 for a 12 as a specific, but your answer was informative. As you suggested, running wire to an outbuilding would be better example: the wiring for our barn-garage that might be turned into an apartment should have the ability to be upgraded from 100 to 200 amp service since we think that needing it would be likely.

Thanks again!

[mdshunk]

Myself, I run #14 for 15 amp circuits, but I can't blame guy for running all #12. Personal preference I guess. Price is nearly the same. If a circuit is ever upsized in a dwelling, changing a 15 amp circuit to a 20 amp circuit (if all #12 was run) may be desirable in rare circumstances. For instance, if your entry light fixture has two 60 watt lamps, and the wife sees a neat fixture that looks like it belongs in the Waldorf that take 9 zillion lamps, you may be glad you had 12 run. Guys just have "minimums" that they work with, and for some it is to run all #12. On the same note, some guys will not run 1/2" conduit on an EMT job. The absolute minimum is 3/4". I'd be interested myself in learning why some people don't run #14 in a dwelling. There are valid reasons not to run #14 on commercial work (more fixtures per circuit, voltage drop because of distance), but I can't reconcile that to residential.

[Wgoodrich]

Remember the NEC is a minimum standard.

Often times an electrician will get frowned on doubting his or her knowledge when a home owner has a large home and they plug an iron in the receptacle in the bedroom and the bedroom or bathroom light dims due to voltage drop experience.

Not a hazard but longer runs designed for general use will if 14 awg wire will often dim lights with larger loads not normally use in those lighter wired rooms such as vacuums or irons heavy loads. This often will cause dimming making the home owner think the electrician short sheeted them on wiring.

Not dangerous but an invite to lose the next job if homeowner is not made to understand production low cost housing design.

I agree, 10 awg is over wiring trying to do better but inviting worse. Most devices are not designed to take connetions of 10 awg wire. Kind of like putting a diesel semi engind in a volkwagon. Not compatible and if not done right can invite bad connections causing damage or fire invites. Too much of a good thing can become a bad thing.

Just my opinion

Wg