My 93-year-old aunt’s dryer went out today. The problem was a blown fuse (it’s an old house that still uses Edison-base fuses). When I looked in the fuse boxes, I saw that most of the fuses are 30 amp. A couple are 20 amp.
I doubt that the house has 30-amp wiring. It was built in 1951, so it seems more likely that it has 15-amp wiring, or maybe 20 amp.
The dryer is electric and is plugged into a 240 volt outlet. That circuit has a 30 amp fuse on it. I believe most 240 volt circuits are rated for 30 amps, even in an older home. But almost all the fuses are 30 amp, including the ones for 120 volt circuits.
I didn’t see anything in the fuse boxes that said what fuses to use. I’m concerned about the safety of my aunt’s home. She’s not likely to overload her circuits with a lot of electrical equipment, but it’s still possible that some combination of loads could draw, say, 25 amps on a single circuit. That could overheat the wiring and cause a fire.
I tried explaining this to my aunt, but I don’t think she understood what I was telling her.
Is there any way for me to tell what size fuse to use for each circuit?
The thickness of the wiring is what determines the current it can handle. A 15 amp circuit uses #14 AWG copper. A 20 amp circuit uses #12. An easier way to tell is by looking at the sockets in the wall. The normal plug on a 15 amp circuit has two parallel blades. A 20 amp plug will have one blade turned so that they are perpendicular. The plug in the wall has one hole that is tee shaped so that either the normal plug or the special 20 amp plug would fit.
The function of circuit protection, whether it be circuit breakers or fuses, is to protect the permanent wiring in home (most of which is inside the walls) from overheating. As mentioned by @Ancient_Nerd, 14 AWG wiring is protected by a 15 A fuse or circuit breaker, and 12 AWG wiring is protected by a 20 A fuse or circuit breaker. This is true for “typical” wiring; if the home is really old, it might have K&T wiring, and the code might be different for that.
To determine the wiring gauge of a branch circuit, I find it easiest to simply look inside the main panel. If you’re uncomfortable with doing this - which would be completely understandable - you can take Ancient_Nerd’s suggestion and look inside receptacles. A person who is familiar w/ wiring can tell what gauge it is by simply looking at it. If you’re unsure, you can temporarily disconnect the wire (from the fuse box or receptacle) and “measure” the diameter of the copper using some wire strippers. Disconnect power before doing this, of course.
Of course if you try evaluating it at the outlet end, that also means constructing an accurate map of which fuse goes with which outlet(s).
Fussing with old wiring in old boxes and old outlets is a recipe for breaking things, or more accurately, things breaking, as soon as you touch them. There can be a real cascade there which leads to breaking more stuff with each thing you fix. Beware a sticky swamp of trouble if you put a screwdriver to anything.
This in not a reliable way of determining ampacity, especially in a 75 year old house. A 20A circuit can legally use 15A outlets. Code only requires a 20A outlet (tee-shaped slot) if it is the only outlet on a circuit. Besides, a house of that era likely has ungrounded non-polarized outlets unless it has been updates - and the continued existence of a fuse box indicates that little to no upgrading has been done.
You are correct, a 30A breaker/fuse on a circuit serving 15A/20A outlets (regular wall outlets) is against code even if the wiring is the necessary size.
In my experience, older houses often have fewer circuits with higher capacity (20A vs 15A). Modern houses tend to have lots of 15A circuits, where older houses will have a couple of 20A circuits that run all the outlets and lights in several rooms.
That said, the dryer circuit is going to be on it’s own fuse, unless it was wired really incorrectly.
If the wiring is in such a state as to result in a cascade like you describe, it’s already broken, and you need a professional electrician in there right now.
No, @Chefguy is correct: fuses and circuit breakers can and will fail simply due to time in service. In a fuse, for example, the element will expand and contract a little bit every time a load is turned on and off, respectively. And the bigger the load, the more it expands. This will fatigue the element, and it will eventually break, even though there was never an over-current situation. (Thankfully, though, the failure is fail-safe.)
After identifying any high amp circuits like the water heater I think the simple solution is to just replace all the other fuses with 20 amp time delay fuses, for example Bussmann BP/TL-20 20 Amp Time Delay, Loaded Link Edison Base Plug Fuse, 125 volts. I see them on Amazon at 9 for $24. And buy a few extra as spares. You may have to reset some clocks after they have been disconnected.
One concern I would have about her having an electrical fire is if she likes to use the common 1500 watt portable electric heaters. You need to check out the circuits she might be using and make sure that is properly fused.
The dryer circuit should actually have two 30 Amp fuses. Might as well replace both. If the wires are visible, they will be thicker than most of the other ones. The cable will probably have four conductors. Two hot. One neutral and a ground.
If she has an electric water heater, that will also be two 30 Amp fuses.
It does. Only one of them blew, and I replaced it with another 30 amp fuse.
There’s another panel with a combination of 20 amp and 30 amp fuses. That panel must be for the 120 volt circuits. I’m inclined to replace all the 30 amp fuses in that panel with 20 amp fuses and see how it goes. Even if the house has 15 amp wiring, it will be safer than what’s there now.
There are circuit breakers that can be screwed into an Edison socket. I might replace the fuses with those. That would be the end of replacing anything for a long while.
You might want to look a little more thoroughly for what looks like a second fuse box. A house I once owned, built in the mid 1950’s had that. Where the wires first came into the house, there was a box with four 30A fuses. Wires from that went to the second fuse box on the opposite corner of the garage. My electrician friend called one of them a load center. That second box had 15A fuses for the individual circuits in the house. A dryer outlet, that I never used, was wired to the first box.
I would change nothing until I had a complete understanding of all the wiring. Each fuse box AKA load center, each outlet or built-in lighting fixture, etc.
Armed with a complete and accurate map of the terrain, then, and only then, can you smartly start improving things.
And document what you learned and did. A problem with doing arbitrary hunch-based work is that leaves a record, in the form of the current configuration, that future you or somebody else will be relying on as a kind of base case. If it was done in the blind, you’re building a trap for them. Just as whoever (presumably) dropped 30A fuses into her low amperage draws 20 years ago did to you.
Don’t rush this. Carefully examine the innards of each fuse box and document the AWG of the wiring for each circuit. And then install a new, appropriately-rated fuse for each circuit. If you’re the least bit uncomfortable with doing this - which would be completely understandable - hire an electrician. Or at the very least, have a friend help you who is well-versed in electrical matters like this.
