Interesting fuse/breaker behavior

JHZR2

JHZR2

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I bought an additional 2000sf garage/loft last summer, and have been slowly working on it. Back in WWII and prior it was a location where the local butter and milk distributor kept his trucks and a small amount of cold storage. It had power, but the whole thing was still glass fuses. Most of the distribution in there was 240 for the truck refrigeration units and the one in the building I guess.

I had a modern entry installed, with 100A service. The wiring that went through one of the fuse boxes, a lot of conduit, and on to various lights and a few receptacles all seemed fine, so I installed a CAFCI 15A breaker on the new main service, which fed the legacy switch/fuse box that the lighting and few original 110 receptacles were on. It is wired so everything in there is fed by the one 15A CAFCI.

This was it before I rewired the incoming power “line” with modern conductors. After the fuse/switch still are the legacy “load” outgoing conduit/conductors.

A0E50C26-793E-4849-A471-A70169477A1F.jpeg


Upstairs has some 8” fluorescent bulbs for lighting the large space (~1000SF). I think one of the ballasts burned or shorted out. I need to open it up. While the CAFCI caught it and opened up, after I reset it, I noticed that the fuse had opened up.

I replaced the fuse with another to help with my investigation, and eventually it opened too. Interestingly, the CAFCI didn’t detect any overcurrent or arc event and never tripped. But the 30A (yes, 30A was in there) fuse opened.

I’m planning to keep this fuse box, and just replace the light or ballast (or wiring if need be). I’d rather not mess with this old wire and conduit already in place as it is only for a few legacy lights, and I’m installing new receptacles where I want/need them. 15A is a lot of breaker for the rest of the load to be on the legacy circuit.

Given that the fuse opened before the CAFCI in some cases, should I replace the fuses? Should I put in 15A fuses? I’m not sure the rating much matters because the main protection is the CAFCI breaker. Or should I put a penny under the fuse and continue on? Obviously if I removed this switch, I’d just have the same legacy wiring coupled to a length of modern wire in a junction box. I prefer to not mess with the legacy wiring at all, but because of that and the fact that the fuses are like $10 for two, what’s my best bet? If I wired it out of the circuit, the rest of the circuit would look like the penny under the fuse :)

Since the fuse did act faster and provide value, I’m also inclined to keep it there. Double protection. But it was a 30A fuse with 14ga wire. So would you replace with a 15A fuse instead?

Thanks!
 
Fuses do respond quicker than a breaker.

Breakers have a trip curve where they may take several minutes to trip due to a "slight" overload. And the time to trip goes down as the amount of overload goes up.

Does that mean you should keep the fuse in the circuit? I wouldn't.
 
brianl703 said:
Fuses do respond quicker than a breaker.

Breakers have a trip curve where they may take several minutes to trip due to a "slight" overload. And the time to trip goes down as the amount of overload goes up.

Does that mean you should keep the fuse in the circuit? I wouldn't.
Click to expand...
I would have thought that the I2t or trip curve, and sensitivity of a CAFCI would be faster than a 2x rated fuse.

Why not keep the fuse in the circuit? Nothing is mission critical, it’s only feeding maybe half the connected loads if one blows, and obviously it helps prevent excessive conditions on the old wiring.

If a bona fide arc or fault, or sustained overcurrent, the 15A breaker would still interrupt.
 
" But it was a 30A fuse with 14ga wire. So would you replace with a 15A fuse instead?"

Size the fuse to protect the wire.
 
JHZR2 said:
Why not keep the fuse in the circuit? Nothing is mission critical, it’s only feeding maybe half the connected loads if one blows, and obviously it helps prevent excessive conditions on the old wiring.
Click to expand...

Because it's old crap that's another failure point. Rip it out and get rid of it.
 
KJSmith said:
" But it was a 30A fuse with 14ga wire. So would you replace with a 15A fuse instead?"

Size the fuse to protect the wire.
Click to expand...
The CAFCI breaker in the panel is sized to the conductors. The fuse/switch is acting more like a junction box.

brianl703 said:
Because it's old crap that's another failure point. Rip it out and get rid of it.
Click to expand...
It’s not mission critical, and I always worry that more messing with old wires and insulation is just asking for more problems.
 
Fuse probably blew first because it was closer to the short, broke the circuit before it made it back to the breaker.
 
JHZR2 said:
It’s not mission critical, and I always worry that more messing with old wires and insulation is just asking for more problems.
Click to expand...

I had a fuse panel in a rental property. One of the fuses would blow for no reason. Found that the fuseholder itself was bad, making a bad connection, and no replacement was available since fuses are obsolete.

I can't say that didn't result in my general impression that old fuse panels are nothing but trouble and should be removed!
 
dishdude said:
Fuse probably blew first because it was closer to the short, broke the circuit before it made it back to the breaker.
Click to expand...
That fuse panel is closer by about 12” of wire. The short is 30 feet away, fwiw…
 
JHZR2 said:
I would have thought that the I2t or trip curve, and sensitivity of a CAFCI would be faster than a 2x rated fuse.

Why not keep the fuse in the circuit? Nothing is mission critical, it’s only feeding maybe half the connected loads if one blows, and obviously it helps prevent excessive conditions on the old wiring.

If a bona fide arc or fault, or sustained overcurrent, the 15A breaker would still interrupt.
Click to expand...
Not necessarily. As you can see by the example breaker curve below it takes a lot of current for the time delay to flatten to an instantaneous response. Even with a time delay fuse, the fuse curve is much sharper. Coordinating fuses and breakers can be a real bear. Sometimes you get stick in the middle where it is race to see who trips first. That’s likely where you’re at. I’d go 15 if you’re going to keep the fuse panel. With the smaller fuse you’ll probably eliminate the trip race.

 
JHZR2 said:
I bought an additional 2000sf garage/loft last summer, and have been slowly working on it. Back in WWII and prior it was a location where the local butter and milk distributor kept his trucks and a small amount of cold storage. It had power, but the whole thing was still glass fuses. Most of the distribution in there was 240 for the truck refrigeration units and the one in the building I guess.

I had a modern entry installed, with 100A service. The wiring that went through one of the fuse boxes, a lot of conduit, and on to various lights and a few receptacles all seemed fine, so I installed a CAFCI 15A breaker on the new main service, which fed the legacy switch/fuse box that the lighting and few original 110 receptacles were on. It is wired so everything in there is fed by the one 15A CAFCI.

This was it before I rewired the incoming power “line” with modern conductors. After the fuse/switch still are the legacy “load” outgoing conduit/conductors.

View attachment 103362

Upstairs has some 8” fluorescent bulbs for lighting the large space (~1000SF). I think one of the ballasts burned or shorted out. I need to open it up. While the CAFCI caught it and opened up, after I reset it, I noticed that the fuse had opened up.

I replaced the fuse with another to help with my investigation, and eventually it opened too. Interestingly, the CAFCI didn’t detect any overcurrent or arc event and never tripped. But the 30A (yes, 30A was in there) fuse opened.

I’m planning to keep this fuse box, and just replace the light or ballast (or wiring if need be). I’d rather not mess with this old wire and conduit already in place as it is only for a few legacy lights, and I’m installing new receptacles where I want/need them. 15A is a lot of breaker for the rest of the load to be on the legacy circuit.

Given that the fuse opened before the CAFCI in some cases, should I replace the fuses? Should I put in 15A fuses? I’m not sure the rating much matters because the main protection is the CAFCI breaker. Or should I put a penny under the fuse and continue on? Obviously if I removed this switch, I’d just have the same legacy wiring coupled to a length of modern wire in a junction box. I prefer to not mess with the legacy wiring at all, but because of that and the fact that the fuses are like $10 for two, what’s my best bet? If I wired it out of the circuit, the rest of the circuit would look like the penny under the fuse :)

Since the fuse did act faster and provide value, I’m also inclined to keep it there. Double protection. But it was a 30A fuse with 14ga wire. So would you replace with a 15A fuse instead?

Thanks!
Click to expand...
whats the supply voltage in the above pictured disconnect? 120 or 240v? if it's 240 where are you pulling a neutral for lighting and 120 receptacles? Looks like old 2 wire cloth cable bringing service to the disconnect. Is the white a fused neutral or being used for the 2nd hot leg?
 
you'll most likely find out there is a neutral/ground issue.. either neutrals being shared or neutral touching ground.
 
Is it a ton of work to eliminate that old fuse/disconnect box?

I don't see how doing so could cause more issues other than taking some time and effort.

Like said above, it's only going to eliminate potential problem spots likes loose/dirty/corroded connections, scuffed wires or insulation.

Seeing that cloth insulated wire takes me back to most of my (personal) home reno work. LOL. Nothing wrong with the wire itself. Just everything else with it. Can't imagine how many feet of that stuff I've pulled out and redone.
 
The old cloth stuff is dangerous. I’ve worked with and around it for years always better to pull new cable whenever possible. Whenever stuck with using it for existing work I would cut it back splice in a junction box and run 18-24” of new cable to lighting fixtures or ceiling fans. Good chance 99% of the time the conductor insulation is compromised and new didn’t have the temperature ratings that newer cable and wire have.
 
Schandyman said:
The old cloth stuff is dangerous.
Click to expand...

Have you ever seen the cloth-jacketed romex with the undersized ground wire? 14AWG hot and neutral, 16AWG bare ground. This stuff was used in the 60s and before.

The ground wire WILL burn open before the breaker trips if some moron puts a 30-amp breaker in place of a 15-amp because the space heaters they're using to keep the house warm keep tripping the 15....

(The 16AWG bare ground was pressing against the 14AWG hot in the load center, and I suspect that the 14AWG got hot enough for the insulation to soften so the 16AWG pushed through to it and promptly burned open between that and the ground bar. This also left the 16AWG ground wire leaving the load center electrically live).
 
brianl703 said:
Have you ever seen the cloth-jacketed romex with the undersized ground wire? 14AWG hot and neutral, 16AWG bare ground. This stuff was used in the 60s and before.

The ground wire WILL burn open before the breaker trips if some moron puts a 30-amp breaker in place of a 15-amp because the space heaters they're using to keep the house warm keep tripping the 15....

(The 16AWG bare ground was pressing against the 14AWG hot in the load center, and I suspect that the 14AWG got hot enough for the insulation to soften so the 16AWG pushed through to it and promptly burned open between that and the ground bar. This also left the 16AWG ground wire leaving the load center electrically live).
Click to expand...
How bout that thin tin filler in the old bx cable I've seen that used as a ground and at sometime the bx lost its bond at the load center or wall box... no good
 
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