Our 1939 house has knob and tube wiring. It has 4 15-amp fuses and 2 20-amp fuses added on later for dishwasher and refrigerator. Lately, fuse #3 (one of the 15-amp fuses) has been blowing when we run the vacuum. After the fuse blows, we leave off any lights and the computer and anything else not necessary and finish vacuuming, but yesterday, the vacuum blew the fuse again twice with nothing else running and we finally gave up. Today, the fuse blew when we were just sitting watching TV. The things powered on that fuse are a large desktop computer, 2 TVs (27" CRTs), 2 Tivos, a couple of 100-watt incandescent lamps, and some 23-watt fluorescent lights. The outlets that that fuse controls run along 3 outer walls and ceilings and a basement rumpus room.
How do we troubleshoot what’s going on? Are our wires ready to burn up? If we have to get in an electrician, I’d like to be able to narrow down where to focus on.
A typical vacuum draws 12A, which doesn’t leave much for everything else. Add up the amperage load on that circuit, and see how much you are drawing. There’s not too much else that can cause a fuse to blow - it could be getting too hot due to a bad fuseholder, but that would be pretty unusual.
You are seeing an increasing load on that circuit. Since you aren’t putting the load on (still only one vacuum cleaner at a time), something else is. In all likelyhood this is a bad thing. Heat is likely. If at all possible, get that wiring checked by an electrician as soon as you can. In fact, I wouldn’t replace the blown fuse. Doing without vacuuming is a whole lot better than doing without a house. As for home troubleshooting, you are dealing with really old wires. Unless you have experience with such, I don’t think you are likely to detect all the problems on your own.
Knob and Tube was (dangerously) obsolete by the 1950s or 60s. You really need to rewire the whole house. My father did in the 60s to 70s. I had to help.
empty the vacuum bag to help it run cooler. make sure to have the plug prongs shiny and bent slightly to fit tight.
use screw in circuit breakers to substitute for fuses, you will save a bucket of money.
replace receptacles with new good conducting ones, old ones might have some corrosion or looseness which increases current draw. this has to be done carefully because the old wiring in the box is fragile, often fragile enough that rewiring is the only alternative after the insulation falls off the wires in the receptacle box.
in the fuse box you would want to carefully clean the wires and contacts. with the main fuses pulled and the box deenergized (except the incoming wire, lugs and fuse contacts which are still energized and a fatal hazard) you would carefully disconnect and clean wire ends and screw areas and fuse sockets to be shiny metal. this has to be done with care and skill as to not create a hazard and maybe destroy fragile wiring. if you weren’t as skilled as an electrician then i would get one to do this.
i’ve worked on old wiring and it takes a huge amount of skill, patience and time to not make a situation worse.
ultimately the safest and most useful solution is to get totally rewired.
Me too. Knob and tube gives me the heebie jeebies. Technically it should be ok as long as it is properly maintained, but as johnpost said, it takes a lot of skill and effort to properly maintain it. In wiring that old you often see connection problems due to corrosion, and you also often run into cases where it wasn’t properly handled (like someone fills their walls with insulation and doesn’t realize that you can’t do that to knob and tube wiring). Another common problem is people shoving 15 amp fuses onto 12 amp wiring, which is just a major accident waiting to happen.
If it were my house, I’d have all of the old wiring ripped out and I’d put in a modern breaker panel. It will cost a bunch of money, but you’ll be a lot less likely to burn your house down.
I’ve seen some areas or insurance companies that don’t allow these. YMMV.
if you rewire the house an electrician can often safely abandon the old wiring in place, where it isn’t in the open. this can result in less repair of interior walls and ceilings. anything in the open is best removed and can be done quickly.
Like so many others said, get it rewired soon. I am surprised at how cheap it really is to have a new load center installed and wiring. A good electrician can work fast and make it right. This is a capital improvement to your home that you can enjoy now and improves the value. The old wiring would severely detract from the value if you ever sold. Insurance might even be a problem with your current setup. Why not enjoy the upgrade now? You will ultimately need to do this upgrade anyway.
PS. I have seen older vacuums that only drew 3-4amps as opposed to the higher amp draw of newer ones. The Salvation Army might have one.
I have been doing electrical work for years. Both commercially and for myself.
the fact that the fuses are blowing with normal load points to something** incredibly** wrong.
You need to troubleshoot this immediately, we are talking major fire hazard.
If it was me I would get a cheap clamp on ampmeter and check the current on that wire where it goes into the box. Start unplugging things and watch the current draw, if it doesn’t go to zero with everything unplugged, take the fuse out and leave it out until you find the load/short and fix it.
Start with an amp prob. If you lhave not used on before it will be cheaper to call an electriction. Less that a trip to hospital or having the fire department come to your house.
We are using the screw-in pop-out fuse/breakers. We’ve known for a long time that we need to upgrade, but hoped to avoid it longer after having major plumbing disasters last year. Oh, well, at least it’s almost tax refund time, and we’ll be also be able to get a better price on our homeowner’s insurance, as only one company in the whole world seems to offer insurance on fuse wiring. Sigh.