Light Bulbs & Fuses

[jeff48356]

In the house I grew up in as a child, there were screw-in fuses instead of breakers. I've always wondered what would happen if you put a light bulb in a fuse socket, or a fuse in a light socket. Can anyone answer this? I've never tried it! :grin:

 

[iwire]

Its a nice way to trouble shoot a short.

The lamp ends up in series with the circuit instead of parallel

 

[infinity]

A fuse in place of a lamp will likely cause the fuse (or another OCPD in the circuit) to blow or open. The lamp in place of a fuse will be in series with any load on the circuit and will be dim based on the voltage drop across it. A circuit with no load will cause the lamp to be dark.

 

[micromind]

I carry a basic light socket wired to alligator clips and a 200 watt lamp. When I am troubleshooting an electronic circuit, such as a PLC, that blows fuses, I'll connect the lamp across the fuse holder. The impedance of the circuit under test is considerably more than a 200 watt lamp, so if there's still a fault, the lamp will light. When I've solved the problem, the lamp stays off or glows very dim. It saves alot of fuses.

If you put a screw-in fuse in a lampholder and turn on the switch, you'll find out which will blow first, the fuse, or the circuits' protective device. It'll almost always be the fuse.

If you put a lamp in a fuseholder, and nothing in the circuit is on, nothing will happen. If you turn on something with more impedance than the lamp (a radio, for example), the lamp might glow dimly, or not at all, and the load will work ok. If you turn on something with less impedance than the lamp (a toaster, for example) the lamp will burn bright, and the load won't work.

It's a matter of dividing voltage across multiple resistors, (the lamp and the load) but remember, the resistance of an incandescent lamp is much lower when the filament is cold, and rises rapidly as it heats up.

 

[brian john]

I carry a basic light socket wired to alligator clips and a 200 watt lamp.

Done the same for years, plus a handy trouble light in a fix.

Its a nice way to trouble shoot a short.

and used the same set up on CB protected branch circuits

 

[wbalsam1]

A circuit with no load will cause the lamp to be dark.

This much I understand...:grin: :grin:

 

[zbang]

In the Things That I Don't Want To See department- someone had taken one of those two-lightbulb-sin-one-socket things, screwed it into the fuse block, put a small bulb in one side and a 20(!!) amp fuse in the other. Said that was so they can see when the fuse blows, read about in PopSci or something like that. That was one of the best arguments I've ever seen for Type-S conversions. Sorry, no photo .

 

[electricalperson]

when i went through the electrical program at my highschool we had light bulbs wired in series going to each of the boards we used to practice on. instead of an arc when something shorted the lamp would turn on. the light came on also when we used a drill when we wired the house we had inside

 

[frenchelectrican]

That is one of the basic common troubleshooting tool you will have to use that it work on both breaker or fused circuits.

That part will really save alot of aggraviations to find a short sometime it can be hidden so the lightbulb do crank engough voltage and limited the current so i can pinpoint where is the short is.

Merci, Marc

[ this should be a common item you should keep in the service truck or tool box it is a timesaver item ]

 

[LarryFine]

when i went through the electrical program at my highschool we had light bulbs wired in series going to each of the boards we used to practice on. instead of an arc when something shorted the lamp would turn on.

Years ago, I read an article about an electric train power supply that used a paralleled pair (for less resistance) of 12v bulbs as a track-current limiter. The cool filaments provided almost no voltage drop, but a track short would illuminate the bulbs and limit the 'fault' current.

 

[RayS]

Years ago, I read an article about an electric train power supply that used a paralleled pair (for less resistance) of 12v bulbs as a track-current limiter. The cool filaments provided almost no voltage drop, but a track short would illuminate the bulbs and limit the 'fault' current.

I've also seen small, "automotive dome light" bulbs used inside Bose 802 speaker cabinets for the same reason- lo resistance till excessive current flows, and self resetting once the power drops. I never did like those speakers, but I thought it was a novel protection idea if you can ignore the sound issues like power compression...

 

[zbang]

but I thought it was a novel protection idea if you can ignore the sound issues like power compression...

A couple of years ago, a friend of mine presented a paper to the Audio Engineering Society (#5881?) about using tungsten-filament lamps as speaker protection. After measuring the characteristics of a bunch of different lamps and doing some listening tests, the conclusion was that they hurt the sound and don't actually protect the speaker.

 

[RayS]

A couple of years ago, a friend of mine presented a paper to the Audio Engineering Society (#5881?) about using tungsten-filament lamps as speaker protection. After measuring the characteristics of a bunch of different lamps and doing some listening tests, the conclusion was that they hurt the sound and don't actually protect the speaker.

Interesting. I'd like to see that. It seems like it would work for protection, but I didn't like the sound...