Had some wiring repaired at my house this week, that is the thing that got me thinking about this
It made me wonder if two wires running 110 volts each and physically in contact, could generate enough of a magnetic field to interfere with each other somehow, thus generating enough heat to melt the insulation covering them. Maybe if they were just a tiny bit out if phase with each other?
Not an issue or there would be a lot of problems.
Also the wires basically can’t be out of phase under almost any circumstance. But even if they were, that wouldn’t generate heat.
There is an induction factor, but a 110v house line isn’t going to be enough to notice.
All that said, if 2 lines are running next to each other and both are over the rated load but not exceeding the breaker’s rating they would each get warm or hot. With two hot wires so close, the chance of fire goes up considerably.
This is a real issue with 14 gauge wire connected to a 20amp breaker. Or back in the fuse days, the wrong fuse being used. I saw a lighting circuit with a 30a fuse once, very dangerous.
Copper is not that susceptible to induction heating.
As noted by What_Exit, current-carrying wires that are in close proximity can overheat. For this reason the NEC places limits on how many current-carrying wires can share the same conduit.
There’s another problem with current-carrying wires that run parallel to each other: an excessive force is generated on each wire if the current is high enough. I don’t think it’s an issue for home wiring, but it can be a problem in a short-circuit situation in an industrial setting.
what if its aluminum wire?
Yes, my house was built in that time when aluminum wire was thought to be a Good Idea for some reason
Induction won’t be the problem.
Not matching breakers/fuses to wires is the concern along with deteriorating insulation and poor connections. Aluminum isn’t great, but if it isn’t moving, it should hold up for a very long time.
Aluminum is a perfectly cromulent conductor; the problems with aluminum house wiring mostly have to do with connecting aluminum conductors to copper wires or fixtures. The two have different current ratings and different rates of expansion, which can lead to overloads and loose connections over time. Induction won’t get it particularly hot. If you’ve got melty wires, the most plausible explanation is too much load on the circuit, or loose connections causing arc faults. Both are serious fire hazards, so it’s good that you’ve corrected it.
Indeed. I have an aluminum wire running from a subpanel to my oven. Some years back I had a new oven “professionally” installed. A couple years later the breaker for the oven started to randomly trip. I pulled out the oven and discovered that the so-called professional installer had connected the aluminum wire to the oven’s copper wiring with ordinary wirenuts. Over time the differential expansion of the aluminum and copper had loosened the wirenet causing arcing, which actually MELTED the plastic cap of the wirenut. I shudder to think of what could have happened if this had started a fire in the wall behind the oven.
Cost was the reason. Copper was expensive. Aluminum was much less expensive.
Several decades ago I lived in a neighborhood that had three homes burn down in one year due to aluminum wire and loose connections.
If you have aluminum wiring, be a little paranoid about loose connections.
If the house was built between (roughly) 1965 and 1975 then it probably has AA-1350 aluminum wire. An yea… that stuff is problematic.
AA-8000 aluminum alloy wiring was introduced (I think) in the late 1970s, and is still in use today. Its creep rate and CTE closely match that of copper.
When you buy a switch or receptacle you will usually see “AL-CU” or “CU-AL” stamped on it. This means you can use it with either copper wiring or AA-8000 aluminum alloy wiring. It does not mean you can use it with AA-1350 aluminum wiring.
There is one potential issue, you can get a voltage induced into an adjacent wire but only matters if the second wire is disconnected - it can charge up and give a little bit of a nip - it acts like the second plate of a capacitor - not sure it would be much of an issue on 110v.
This can also give false readings if you use a digital multimeter, when you are trying to chase down a fault and you disconnect the suspect wire at both ends it can look as if the disconnected wire is live. It tends not to happen on conventional moving iron multimeters
There’s such a thing as “ghost voltages” when using a digital multimeter (DMM) to troubleshoot wiring. When you deenergize a circuit and expect to read 0 VAC, the DMM will show 30 VAC or whatever. It usually occurs due to capacitive coupling between an energized circuit and the deenergized circuit you’re working on, and this capacitive impedance forms a voltage divider with the high input impedance of the DMM. To prevent this from occurring you can place a 1 kΩ to 5 kΩ resistor in parallel with the DMM, or use a DM with a “LoZ” feature.
Yes, I got startled with a bit of a zap from a wire that was disconnected on both ends. Only possible theory was it induced from live wires that it was running nearby.
this, nearly word for word, is what my electrical problem was
As I understand, the main problem with aluminum as others mention is connections. Aluminum was used for wiring when copper prices spiked; it is softer and has a different heat expansion rate than copper, so over time “firm” connections became less and less so. The sockets and other electrical connect points didn’t use aluminum. An outlet or other connection, that screw down point when loose gets hot, so it’s a vicious cycle - heat expands aluminum more than screw down, deforming it, it cools, connection is even looser, more heat next time - until something gets so hot it melts or starts a fire. The same problem could exist with copper, but because it was not likely to deform as easily over time, less of a problem. (I did however own a house built in 1962- and by mid-90’s, the main breaker kept popping progressively easier until it became a weekly occurrence. I had an electrician look at it, and found the main wire from the pole was so loose by then he could pull it out by hand. Tighten it up, never ad a problem since. )
Remember when you could get small transistor radios with AM? The advice at the time was to tune to a non-station spot, then wave the radio near the outlet box (or other wire connection). If you heard louder static, then there was likely a loose connection in that electrical box. With aluminum wire, it was a very good idea to open the box and re-tighten the screws on the wires to fix the connection. (Of course, the same applies with copper-copper connects, but significantly less likely). The problem was so widespread that eventually the government discouraged the use of aluminum wire in Canada.
I remember some advice once about not coiling an extension cord due to it possible creating stronger induction…
Code dislikes running too many wires together due to the risk of worn insulation creating unexpected high voltage shorts. Particularly, don’t run low-power or signal cable (i.e. phone, ethernet) along with power cable in the same tray or conduit unless it’s all armoured.
You are certainly talking about a pair of insulated wires.
As for the aluminum/copper thing, a master electrician explained the rule about when to use copper and when to use aluminum. He said, “The rule is use copper”. Certainly some valid reasons to use aluminum but I think he meant stick to that rule if you aren’t an electrician.
I’ve had that happen. I was tearing my hair out trying to figure out why I was reading something like 40 volts on a line that should have been either 0 or 120 or 240. I finally realized that it was just being induced by something nearby. While a DMM will sense the voltage, there’s virtually no amperage behind it. Some people, especially working in these situations, will put a light bulb on the two wires and then check it for voltage. If it goes to zero, it was a ghost voltage.
Another option is to use a solenoid voltage tester (like this). In addition to putting a small load on the line, it also gives you audible and haptic feedback as you hear and feel the solenoid moving.
A house I lived in many years ago had aluminum wiring. Never had any major problems but I did notice that the bathroom outlet got quite warm when I was using the hair dryer. It’s typical of issues with aluminum wiring, generally related to termination points on sockets and switches or connections to copper wiring. Apparently you’re never supposed to use the quick-push connections with aluminum, always the screw connections, and even those can develop problems as you suggest.
That would only happen at very high current draws - but even then the main problem is heat generation - PVC is a very good thermal insulator and a coiled cable - especially if it is on one of those portable cable reels - will build up significant heat.
If you are only drawing a couple of amps - which is to say it is using less than 200 Watts then you’ll be ok, but when you move up to using welders, electric heaters, kettles, electric irons or maybe a number of appliances on the same extension then you are running a risk - the heat builds up, the insulation resistant falls, the cable resistance rises and you start to get thermal runaway.