Electrical Problem

[Julie Moriarty]

As I mentioned, I'm not an electrician (except in Mexico) but my understanding is the wire gauge needed for any circuit depends on two things - the maximum sustained amperage and the length of the wire. Not accounting for both can be a mistake. For example, a wire correctly sized for a short run may not be enough for a very long run. Do the calculations. For these reasons and more I ran 8 and 6 gauge from 50amp breakers to several places in my shop.

You are right, John. It's called voltage drop - the longer the wire run from the panel, the more resistance the wire creates. Excessive resistance can cause dangerous heat build up. In the trade we typically begin to look at the need to calculate voltage drop when pulling wire if the run exceeds ~100'.

But when looking at loading breakers, the rule of thumb we used (I worked in the Chicago area) was not to exceed 80% of the breaker's designated ampacity. In other words, add up the amperage of all of the loads on a given circuit and make sure it doesn't exceed 80% of the breaker rating. eg: 20A breaker = 16A maximum load.

Another thing a lot of people don't understand is breakers, or fuses, are there to protect the wire connected to them, not the load. The breaker is designed to trip before the wire heats up and fries, sometimes resulting in a fire.

[John K Jordan]

...
But when looking at loading breakers, the rule of thumb we used (I worked in the Chicago area) was not to exceed 80% of the breaker's designated ampacity. In other words, add up the amperage of all of the loads on a given circuit and make sure it doesn't exceed 80% of the breaker rating. eg: 20A breaker = 16A maximum load.
...

I like the 80% rule. I never used a percentage but "instinctively" sized circuits to leave plenty of head room. Especially for motors and welders (and underground "drops") I like to err on the side of the next larger wire gauge when potentially getting close to the breaker/panel capacity. I figured it was better for the breaker to pop long before the wires got hot. (This reduces the calculated voltage drop at potential full load as well.) Bigger copper is more expensive but not that much compared to the other costs. My longest underground run here at the farm was 650' to a breaker panel on a pole, 80 amp breaker, wire sized for 100 amps. For now it only pulls a few amps but I have plans for a farm equipment building there.

For wiring I didn't do myself (such as moving into a house) I also like to check the screw and wire nut fasteners in boxes and the panel. I sometimes found things too loose to suit me.

Once when a big heat pump failed I found one of the three breakers in the outside subpanel burned where it connected to the panel. It looked like it had started corroding long before. When replacing the panel and breakers I applied silicon dielectric grease to the contacts (hot bus bars?) to the humidity . I now do this in all panels and all connections exposed to humidity.

Imagining being an electrician in a large metro area makes my head ache.

JKJ

[Julie Moriarty]

My longest underground run here at the farm was 650' to a breaker panel on a pole, 80 amp breaker, wire sized for 100 amps. For now it only pulls a few amps but I have plans for a farm equipment building there.

Allowable ampacity increases for a given size conductor when running through free air, like hanging it on a pole, as opposed to installing it in conduit. #3, which is the go to conductor for 100 amp loads, is rated at anywhere from 120A to 165A in free air, depending on insulation. For bare copper wire, that number jumps to 195A.

As far as working in a large metro area, it's probably not a lot different than working solely in small rural areas. There are still those who know just enough about electrical installations to be dangerous. One of the things I enjoyed most was trying to figure out what one of them did in the past in order to fix a problem that surfaced much later.

[John K Jordan]

...One of the things I enjoyed most was trying to figure out what one of them did in the past in order to fix a problem that surfaced much later.

That can make a great puzzle! I found and fixed four wiring errors at this timberframe house we moved into in '04. Then later I met a neighbor who said he wired the house. I understood the reason then.

The first challenge was a malfunctioning 4-way light circuit with one switch jammed into a 4-gang box along with three other multi-way switches. I'm pretty sure the max number of conductors was exceeded in that box. After testing continuity between all conductors on all switches on the problem circuit (and testing the switches, too) the fix was simply swapping two wires on one switch. The fun was in figuring out which two!

In tearing out cabinets I found connections in walls without boxes and romex run in insane places. One had a trim nail through the hot conductor! The protective insulation was a coat of paint over the nail.

The real mess was in the crawl space which required major rewiring when we moved a wall. About 24" of headroom and spiders everywhere with a nearly undecipherable web of romex cables any self-respecting spider would be ashamed of. The electrician must have been drunk when he put lights and receptacles on random circuits, one connected in a loop. After many tests and diagrams I was satisfied with new runs and four junction boxes. I like to put to/from labels on every cable and box in case I (or the next guy) needs to change anything. And tack up a wiring diagram in a plastic bag!

JKJ