Broken/defective fuse panel

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LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Hello, gang. I went to a weird troubleshoot yesterday. They have an outdoor fuse box with the typical two pull-outs at the top with four plug fuses below. The far left plug fuse pops instantly when replaced.

What's weird is that, with the fuse out, I read (with a solenoid tester) 120 between the fuse's screw-shell and the load terminal directly below it. Those two points should be solidly interconnected. Any ideas?
 
Weird

Weird

I can't remember on those old panels if the line goes to the tip or the shell of the screw-in fuse holder but it seems since the fuse would be in series with the load, you could read 120V from the line side of the fuse holder (shell or tip) and the load terminal if a load wire is still connected.
 
grant said:
I can't remember on those old panels if the line goes to the tip or the shell of the screw-in fuse holder but it seems since the fuse would be in series with the load, you could read 120V from the line side of the fuse holder (shell or tip) and the load terminal if a load wire is still connected.
Click to expand...


Take a look at 240-50-E
The screw shell shall be connected to the to the load side of the circuit.
 
The screw shell is on the load side of the fuse. If there is a direct short somewhere to ground on the load side of the fuse that blows, then there will be 120V between the shell and the load terminal below it. I believe the two fuses on the left are fed from the same side of the line. I think I wrote this like I meant to.:wink:
 
John,
If there is a direct short somewhere to ground on the load side of the fuse that blows, then there will be 120V between the shell and the load terminal below it.
Click to expand...
There should always be zero volts between those two points as they are physically connected.
Don
 
The screw shell can get torn, or worn, loose from the load side bar that extends to the branch circuit terminal screw.

I haven't seen it often, but I have seen it. My recollection is that it stands a good chance of being a "damage beyond repair". Taking the fuse center button screw and mica washers out of the bottom of the screw shell (if possible) will reveal more information.

The 120 Volts between the terminal and the shell is interesting, and a second thing, I suspect. If there is also 120 volts between the terminal and the neutral, the circuit is being backfed from another circuit.
 
LarryFine said:
Hello, gang. I went to a weird troubleshoot yesterday. They have an outdoor fuse box with the typical two pull-outs at the top with four plug fuses below. The far left plug fuse pops instantly when replaced.

What's weird is that, with the fuse out, I read (with a solenoid tester) 120 between the fuse's screw-shell and the load terminal directly below it. Those two points should be solidly interconnected. Any ideas?
Click to expand...

Man there can be several things wrong with itespecially if it is outdoors..I agree with Al on this..either it is shot due to natural or un natural causes or it is being back feed..can you get us a pic of the panel..
 
don_resqcapt19 said:
John,

There should always be zero volts between those two points as they are physically connected.
Don
Click to expand...
OK, he was talking about the load terminal of the fuse he was testing. I thought he was thinking of the load terminal of the next fuse down.
 
Larry.,,

I dont know if this will work but screw in the light bulb yeah the lightbulb something like 75 or 100 watter and screw it in and it that really light up bright then you got a short there but if dim or dark then you should be ok but stay bright what you do real quick is unhook the conductor below of that affected fuse and see if still getting 120 v comming out if so then unscrew it and the load termal should read 0 volts but if still reading 120v then the insulating washer or mica washer is cracked or damaged and can bypass it.

this kind of damge can happend if someone really overtoqure it and it can pull the shell up someway and bypass the whole thing.

Merci, Marc
 
al hildenbrand said:
If there is also 120 volts between the terminal and the neutral, the circuit is being backfed from another circuit.
Click to expand...
that was my thought too.i would remove the wire from the load screw.then check the screw and the wire.that at least would tell if its backfeed
 
grant said:
I can't remember on those old panels if the line goes to the tip or the shell of the screw-in fuse holder . . .
Click to expand...
It's always line to tip.

electricman2 said:
The screw shell is on the load side of the fuse. If there is a direct short somewhere to ground on the load side of the fuse that blows, then there will be 120V between the shell and the load terminal below it. I believe the two fuses on the left are fed from the same side of the line.
Click to expand...
Yes, the shell is on the load side, and (should be) solidly connected to the load terminal. I should be reading nothing between them, but 120v between either one and the line side, i.e., the tip.

I'm only looking at a single terminal, so the same-or-opposite-phase issue is not relevant.

don_resqcapt19 said:
There should always be zero volts between those two points as they are physically connected.
Click to expand...
Yeah. :)

al hildenbrand said:
The screw shell can get torn, or worn, loose from the load side bar that extends to the branch circuit terminal screw.
Click to expand...
I'm leaning that way myself. Unfortunately, there are non-removable tamper-proof adapters in there.
If there is also 120 volts between the terminal and the neutral, the circuit is being backfed from another circuit.
Click to expand...
I will be going back, probably tomorrow, and will check. It may be more complicated than this, however; this circuit is presently out of order, which is what led to me being called. A back-feed should be poroviding power.

This is probably not the original service, but in spite of that, there are two separage 2-fuse switches alongside. I have a feeling I'm going to find something weird that should have malfunctioned a long time ago. :rolleyes:

In the it's-always-something category: I am giving a service-change proposal, but they will be adding onto the house this spring, the panel is on the rear of the house, and it would be best to do the service at the same time.

cschmid said:
..can you get us a pic of the panel..
Click to expand...
If I think I need more input tomorrow, I will, if I remember . . .

"Try to remember . . . the kind of September . . . "

frenchelectrican said:
Larry.,,

I dont know if this will work but screw in the light bulb
Click to expand...
Marc, I've been doing that for years, even with a rubber pigtail lampholder in breaker panels. (And I always connect the line to the center contact. :) ) I'm old-school, too. Well, compared to the majority here, I think.
 
zdog said:
that was my thought too.i would remove the wire from the load screw.then check the screw and the wire.that at least would tell if its backfeed
Click to expand...
"Captain Kirk! I shall consider it!" ~ Spock with a beard in Mirror, Mirror

STMirrorMirror.jpg
 
Someone may have used two screw-in fuses to power a 240V load (waterheater?).
You may be reading the return voltage from the other leg.

I would trace the wiring in the panel and make sure that it's not half of a 240V circuit.
 
Update: Nothing to report. I wasn't able to get back there today. Tune in again tomorrow.

"Same bat-time, same bat-channel!"
 
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