In article ,
Jeffrey J. Kosowsky wrote:
We are about to install several new circuits as we upgrade the
electrical systems in this very old house.
- For "normal" rooms (i.e. not kitchen, bathroom, garage, workshop, or
outdoors), should one go with standard 15A circuits or should one put
in 20A "just in case"?
- Even if you just put in 15A breakers and receptacles now, does it pay
to pull through #12 wire just in case you ever later want to
upgrade?
- How big is the difference in price for wiring (per foot) and for
circuit breakers?

Cost difference: Minimal. It's only the wire, and that is a small
fraction of total cost.

Someone who has a little spare time should go through the calculation
of the resistive loss of 14-gauge versus 12-gauge wire (which is
quadratic in current, so mostly matters for heavily loaded circuits).
I vaguely remember calculating that before we built the house, and
concluding that assuming constant energy usage (motors with constant
load or constant brightness demand from illumination), it would save
about 3% of the electricity to use 12-gauge wire, if a circuit is
highly loaded (something like 80% of breaker rating).

I would always go with 12-gauge wiring for receptacle circuits.
Otherwise, you'll more easily get into a situation where a breaker
trips because you plugged in a space heater, or are using a blow dryer
for some craft project while the toaster is going, or something like
that. Also reduces annoying flickering of lights when big appliances
turn off and on.

On the other hand, I would usually go with 14-gauge wiring for
lighting circuits, just because the stuff is easier to work with
(easier to make up boxes, easier to wire neatly, and don't have to use
such large boxes).

Matter-of-fact, I would always wire receptacle circuits on a separate
breaker from lighting circuits. Like that you can work on one of them
and use the other one to have lights. Say your kid breaks the
receptacle in his room on a winter evening, and you have to fix it
before bedtime (because the baby monitor has to be plugged into it).
Or you are working on installing a new light fixture on a dark
afternoon. This is easy to do if each room can be illuminated from
two different circuits (with a portable plug-in worklight for the
second case), without having to resort to extension cords.

So this is exactly what we did when we built the house: All receptacle
circuits are 12-gauge with 20A breakers. The lighting circuits are
mostly 14-gauge with 15A breakers. In some cases, I actually used
12-gauge wire for parts of lighting circuits with "big" lights (like
the 200W exterior floodlights), just to make sure resistive losses are
minimal.

Along the same lines: When wiring a shop area, go one size larger on
the wires (even if that means having to wire the tablesaw outlet with
8 gauge wire, which is really nasty to work with). If you ever
upgrade your tools (buy a larger welder, or a 5HP tablesaw) you'll be
glad you did. And, whenever stringing wire for a pure 220V outlet
(for example for a dryer or a motor), use 4-wire cable (which is
confusingly called something like 10-3) and run a neutral wire. If
you ever have to change the circuit for something entirely different,
you'll be glad you don't have to replace the wire in the wall. For
example, we changed a laundry room into an office area, and turned the
220V 30A dryer outlet there into a dedicated computer circuit, reusing
the existing 10-3 wire for a single 20A circuit (removed the dryer
outlet, put a regular 120V outlet in, removed the 30A two-pole
breaker, and used just the black and white wires with a regular 20A
breaker).

Some other posters suggested using spec-grade receptacles. Excellent
idea. I don't know what the difference between spec-grade and
commercial grade is (or if there is any), but I find working with
reasonable quality hardware (like good commercial receptacles) much
more pleasant.

In a related post, (Don Klipstein) wrote:
I strongly recommend to not cheap out. I believe that current
code for new construction permits 15A capability as opposed to 20A
only for lines dedicated to specific loads. As in no outlets, or
one outlet (which should be for a specific load that does not draw
more than 15A) plus no other loads. I could be off a little, but I
believe 15A is a "cheap out" permitted in a few specific instances.

I completely agree on the sentiment. But to my knowledge, the
national code (NEC) does still allow 15A circuits for all manners of
uses. Matter-of-fact, I know of nothing in the code that would
prevent someone from running very odd things (like 6A or 10A circuits
for lighting), as long as the load calculation for these circuits are
OK. Regular 120V 15A outlets (the usual ones) can only be put on 15A
and 20A circuits, and kitchens and bathrooms require a certain number
of dedicated 20A circuits. But, as far as I know, it is still legal
to use 15A circuits for lighting (which I think is a good idea), and
for receptacles (which I happen to think is a bad idea).

Has that changed recently?

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