Wire sizing in residential

[Sterling]

The most common one I see in older residential work is 14 AWG wire on 20A breakers, almost universally on circuits that were originally 15A and had the breaker swapped without running new wire...that's the obvious one.
The less obvious one is voltage drop on long runs. A 12 AWG circuit to a garage that's 80 feet from the panel is technically code-compliant but in practice you'll see enough voltage drop at load to cause problems with motors and sensitive electronics. Running 10 AWG on longer garage and outbuilding circuits costs a bit more upfront and saves headaches. Anyone else find themselves upsizing wire more often than the minimum on longer runs?

 

[Alan]

Once you factor in voltage drop and real loads, upsizing wire often ends up being cheaper than troubleshooting later.

 

[PGB1]

Sterling mentioned long runs. That is something people neglect. In normal houses, I don't know how much it is a problem. McMansion maybe?
Heavy loads, of course.

A goof people often make is de-rating from the wrong starting point. (Such as de-rating #14 starting at 15, not 20 amps.

An often missed upsize is the grounded circuit conductor. With so many non-linear loads, consideration to that neutral is quite important.(Again, maybe not so much in houses.)

Constantly I upsize for distance vs. load in industrial when prudent. Distribution projects, too.
Convincing the money people to allow an upsize to raceway and conductor (or bus bar, transformer, or...) is usually not too difficult when you ask them to compare the cost of the up-size versus the cost of 2,500+ people on one, single assembly line stopped from working while the house electricians find and repair the cause. One plant I do work at costs 1.75 million dollars per 10 minute stop work. (Stops are always done in 10 minute segments. A union thing.)

Sporting events are another. We always over-sized temporary wiring for broadcast trucks, demark, and related for the professional football, basketball and auto racing venues we managed. Broadcast drop outs cost a fortune per second in lost ad revenue.


Paul

 

[Alan]

Sterling mentioned long runs. That is something people neglect. In normal houses, I don't know how much it is a problem. McMansion maybe?
Heavy loads, of course.

A goof people often make is de-rating from the wrong starting point. (Such as de-rating #14 starting at 15, not 20 amps.

An often missed upsize is the grounded circuit conductor. With so many non-linear loads, consideration to that neutral is quite important.(Again, maybe not so much in houses.)

Constantly I upsize for distance vs. load in industrial when prudent. Distribution projects, too.
Convincing the money people to allow an upsize to raceway and conductor (or bus bar, transformer, or...) is usually not too difficult when you ask them to compare the cost of the up-size versus the cost of 2,500+ people on one, single assembly line stopped from working while the house electricians find and repair the cause. One plant I do work at costs 1.75 million dollars per 10 minute stop work. (Stops are always done in 10 minute segments. A union thing.)

Sporting events are another. We always over-sized temporary wiring for broadcast trucks, demark, and related for the professional football, basketball and auto racing venues we managed. Broadcast drop outs cost a fortune per second in lost ad revenue.


Paul

Exactly, people focus on material cost without thinking about failure cost. In industrial settings, a little extra copper upfront can prevent extremely expensive downtime later.