Getting a shorted circuit to work again
June 22, 2012 12:05 PM   Subscribe

One of our electrical circuits has stopped working (shorted?) after turning the AC on too high. I've taken a look in the circuit box, but it's not the type of switches I'm used to. Can you help me figure out how to get the circuit working again? Photo of circuit box. Photo of accompanying diagram.
posted by ocherdraco to Home & Garden (25 answers total)
Those are fuses. There is no "switch" (you really mean "circuit breaker"), instead when you overload a circuit a piece of metal inside that glass piece melts and the circuit breaks that way.

You need to replace the one of those fuses that has the metal strap you can see through the little glass window missing or melted. I can't tell from the photo which one that is. When you do change the fuse you'll unscrew it and screw in the replacement. Treat it like a light bulb with a live socket: Don't get your fingers anywhere near the socket.

And be absolutely sure that you replace it with one that has the same current rating. Match the "15" or "20" that's on the one you pull out.
posted by straw at 12:09 PM on June 22, 2012

Response by poster: I should add that I don't know which is the circuit in question — the box is utterly baffling to me.
posted by ocherdraco at 12:09 PM on June 22, 2012

You have old fashioned fuses in your breaker box. You should be able to see which fuse is blown through the little glass window on each fuse. It should have little burnt markings on the inside, or a small wire that's broken. The fuses will unscrew like a light bulb. Figure out which is blown, go to your local hardware store and ask for whatever amp fuse that was blown (show them the picture if you want), the go home, unscrew the old fuse and screw in the new one.
posted by slogger at 12:10 PM on June 22, 2012

Hello Fuse Box!

You'l need to take the fuse out and probably replace it. Take the one that blew (it will resemble a blown light-bulb) to the hardware store and the guy will give you a replacement. Cheap as dirt.

You might want to buy some others as long as you're there. In case they blow again (and they will)

Having fuses on hand was very normal back in the day.

If you own the house, you might want to look into upgrading to a 200 amp circuit box.

Thanks for the laugh.
posted by Ruthless Bunny at 12:10 PM on June 22, 2012

I would go a step further, and shut down power to the box entirely before swapping the fuse (there should be a lever on the side of the box). Also, do NOT use a penny or other coin to bypass the fuse - incredibly dangerous, even if you've seen it done on TV.
posted by Slap*Happy at 12:13 PM on June 22, 2012 [1 favorite]

Response by poster: Ah, beautiful! So, we have a fuse box. I knew my terminology was all wrong, but I didn't know the right words, so I couldn't use them.

This is a rental apartment, so no upgrades possible, I'm afraid.

Is there a way to figure out which outlets and fixtures are on a particular fuse?
posted by ocherdraco at 12:13 PM on June 22, 2012

Also, look on top of the outside of the box. That's where we always stored our extra fuses.
posted by The 10th Regiment of Foot at 12:15 PM on June 22, 2012 [1 favorite]

Is there a way to figure out which outlets and fixtures are on a particular fuse?

Unscrew the fuse and see what works and what doesn't!
posted by The 10th Regiment of Foot at 12:16 PM on June 22, 2012

Response by poster: Slap*Happy, I can't find a lever. There just seems to be the fuses themselves.
posted by ocherdraco at 12:16 PM on June 22, 2012

Response by poster: Also, this box is fully inside the wall.

To change a fuse, do I just pull the dead one out?
posted by ocherdraco at 12:21 PM on June 22, 2012

They screw out. Lean a knuckle on it and twist.
posted by Ruthless Bunny at 12:23 PM on June 22, 2012

You'll unscrew it, just like a light bulb.
posted by straw at 12:24 PM on June 22, 2012

Exactly the same as a light bulb in fact.
posted by The 10th Regiment of Foot at 12:26 PM on June 22, 2012

Slap*Happy, I can't find a lever. There just seems to be the fuses themselves.

Time to call the landlord - it's either fed off of another circuit box, or there's a "trick" to opening the main (turning off the power to the box). He'll know the "trick" or tell you where to turn off the power.
posted by Slap*Happy at 12:27 PM on June 22, 2012

Note that if you do go through the trouble of unscrewing each fuse and seeing which outlets in your apartment suddenly deactivate, the bottom of the diagram you posted is meant for writing that information into each of the spaces (so you or future tenants never have to do it again).
posted by nobody at 12:40 PM on June 22, 2012 [1 favorite]

In terms of the shut off, yeah, if you can find it it's worth turning off but you can very easily replace a fuse without shutting off the power to the box. Electricity is not going to jump out and bite you. Don't stick anything in there (obvs), and don't be soaking wet and you will be fine. This was how everybody did it for years and years.

When you look in the glass window at the back of each fuse you'll see a little metal (copper?) ribbon. One of them is burned - there are probably scorch marks in the window and the coppe rmight be completely disintegrated. Looking at your picture I am leaning towards bottom left but it's awfully hard to tell from the photo.

For ten or fifteen bucks you can buy several fuses of each type and be ready for next time. Good luck! You can do this!
posted by dirtdirt at 12:44 PM on June 22, 2012

Fuse box blues! When you go to the hardware store to get the fuse you need, you might make a list of the other types of fuses in your box and get a spare or two. All of those little numbers and letters matter and they also come in two types of base--the part that screws in--so you have to get exactly the right one for each socket. Until I had a breaker box installed, I seemed to blow a fuse only when the hardware store was closed.

Trial and error with finding which things work on which circuits. Another thing that might help is not to have two heavy energy using appliances on the same circuit. To this day I can't use the microwave and the toaster at the same time in my very old house.

It might not be unreasonable to ask your landlord to have a dedicated line installed for the air conditioner.
posted by Anitanola at 12:49 PM on June 22, 2012

On the off chance that all of the fuses you've found are intact, you will have to go hunting. It's not unheard of for old buildings to have more than one fuse/breaker box, sometimes installed near each other, other times not. Sometimes there will be another box in a totally irrational location, for instance in a neighbor's apartment. Just a heads-up.

But yeah, what everyone else has said: look in the window of each fuse and see which one has a missing or damaged little metal bit. That's your blown fuse. Carefully unscrew it (turn it counterclockwise) take it to the local hardware store, and ask somebody to sell you three more of exactly that specification of fuse. Screw one of the new fuses back in, keep the other two as spares, and you're in business.
posted by Scientist at 12:57 PM on June 22, 2012

Oh, there's also circuit breaker fuses you can get, that you only have to replace once (here's an example of one from Home Depot).

Certainly much, MUCH more expensive than the one-use kind but if you think you're likely to keep popping fuses then it's certainly less aggravating in the long run. Once installed, they act more like the circuit breakers you're used to. If the circuit overloads, that little pin in the middle pops like turkey thermometer. Just fix what caused the overload and then push it back in and you're good to go. Might be worth considering if you think the AC is likely to repeat it's performance.
posted by Freon at 1:16 PM on June 22, 2012 [2 favorites]

Slap*Happy, I can't find a lever. There just seems to be the fuses themselves.

In an apartment of a vintage that'll have that panel you probably don't have a main disconnect. Heck you might have to turn off part or all of the building in order to cut power to your panel, especially if electricity is included in your rent.

Assuming your A/C is a plug in window unit you should probably have a time delay fuse on that circuit. A time delay fuse has a bit of a margin to prevent the fuse from blowing from the start up current of the motor while still protecting the building wiring with the correct rating.

Ideally when changing fuses you should have everything on the circuit off when you screw the new one in (or the old one out if it's OK). This will minimize arcing that can occur on a live circuit. Something to keep in mind if you decide to map out what fuse is for what device.
posted by Mitheral at 2:43 PM on June 22, 2012

Under no circumstances should you place a penny at the base of one of these ancient fuses no matter what anyone in the trailer park tells you. Go to your local independent hardware store and buy double the number of all the fuses similar to the ones in the box, and then replace all of them at once keeping the spares as backup.

Seriously, the penny thing works right up till it burns the whole place down.
posted by vozworth at 6:01 PM on June 22, 2012

You might also try cleaning or changing the filter in your air conditioner - mine only blows the circuit breaker when it's working harder than it should be, and I know it's past due for maintenance time. Check your make and model online for a manual on where it is and how to clean/change it.
posted by halfbuckaroo at 7:32 PM on June 22, 2012

If it's a rented apartment, just get maintenance to come fix it.
posted by DMan at 8:54 AM on June 23, 2012

Like everyone else on Earth with a lease, I'm responsible for "every repair under $50," so hold your breath and wait for maintenance to show up. Really.
posted by halfbuckaroo at 4:07 PM on June 23, 2012

Response by poster: Okay! So, further update: after inspecting the fuses pretty thoroughly, none of them were actually blown. Before calling the landlord, I thought I'd check the situation at the outlet again just to make sure I hadn't missed anything obvious. Sure enough, the AC's plug is the kind that can switch itself off (in case of power surges, I presume?) and all I had to do was hit the reset button.

(And the fact that the alarm clock plugged into a socket on the same circuit had turned itself off was just a coincidence—its plug had just gotten tugged out of the socket.)

So, no fuse replacement needed this time, but at least now I know I have a fusebox, and I'll have some extra fuses on hand.
posted by ocherdraco at 9:07 AM on June 25, 2012 [2 favorites]

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