Can someone idiot-check my fuse box diagnosis?

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drummer4468

Pre-takeoff checklist
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drummer4468
So I'm trying to figure out some problems with a very old fuse box in my garage.

The first indication of an issue was that a GFCI outlet didn't work at all. Not sure if that's related yet, but possibly.

Opened the 4-circuit fuse box and read the voltage in all sockets, three read around 120V between terminals and about 240V between the two hot posts as expected, but the top left one is reading about 68V post-to-collar. (Forgive my terminology if not proper, "post" refers to the vertical center contact bar, and "collar" refers to the contact the fuse screws into).

Readings were taken with no loads on this circuit except for a few LED shop lights, and everything works fine except that outlet.

I have not opened up the box itself to expose the wiring yet (almost afraid to, with how the rest of this house is wired), that can wait till daylight so I can have power off and not hold a flashlight. Anything in particular I should look for? I'd say it's gotta be corrosion or short-to-ground, but I would imagine a short or mis-wiring bad enough to drop the voltage by half on one phase would trip the breaker, no?

fusebox.jpg
 
Just put a penny in there and call it good. :D

Also, replace it. Easy job and no worries about fuse replacement,
 
drummer4468 said:
So I'm trying to figure out some problems with a very old fuse box in my garage.

The first indication of an issue was that a GFCI outlet didn't work at all. Not sure if that's related yet, but possibly.

Opened the 4-circuit fuse box and read the voltage in all sockets, three read around 120V between terminals and about 240V between the two hot posts as expected, but the top left one is reading about 68V post-to-collar. (Forgive my terminology if not proper, "post" refers to the vertical center contact bar, and "collar" refers to the contact the fuse screws into).

Readings were taken with no loads on this circuit except for a few LED shop lights, and everything works fine except that outlet.

I have not opened up the box itself to expose the wiring yet (almost afraid to, with how the rest of this house is wired), that can wait till daylight so I can have power off and not hold a flashlight. Anything in particular I should look for? I'd say it's gotta be corrosion or short-to-ground, but I would imagine a short or mis-wiring bad enough to drop the voltage by half on one phase would trip the breaker, no?

View attachment 115083
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Not sure I'm misreading your post, but I think you're not measuring correctly.
 
EdFred said:
Just put a penny in there and call it good. :D

Also, replace it. Easy job and no worries about fuse replacement,
Click to expand...

Agreed, replacement is the best route, and what I should have done ages ago when I bought the house. But now in the process of selling said house, and trying to simply fix what's wrong if I can.
 
MauleSkinner said:
Why would it read 68v?
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That's what I'm trying to figure out! It's making me scratch a hole in my head. A short doesn't make sense as it should be blowing the breaker or already on fire if it's dropping the voltage THAT much.

asicer said:
Not sure I'm misreading your post, but I think you're not measuring correctly.
Click to expand...

I may not be...hence the idiot check. It's been a long time since I've worked with AC fuse boxes as opposed to breakers. But even if I'm not measuring correctly, but measured them all the same and I still can't explain why one socket out of the four has a different reading.
 
Come to think of it, I AM measuring incorrectly. But it still doesn't explain the one outlier reading
 
Measure the voltage from the center terminal to the ground, perhaps the bolts that hold the face plate on.

You will almost certainly find the voltage is fine. You were measuring leakage to ground, and a voltage as high as you measured is good.

For the GFCI outlet, in daylight, uncover it, and verify that the white is on silver, black is on brass/yellow metal, and green on green. Then remove the fuse box cover and verify that all the whites are securely connected, and the bare/green are secure. If those checks are good, replace the GFCI.
Voltmeter check dead before removing the GFCI.
 
geezer said:
Measure the voltage from the center terminal to the ground, perhaps the bolts that hold the face plate on.

You will almost certainly find the voltage is fine. You were measuring leakage to ground, and a voltage as high as you measured is good.

For the GFCI outlet, in daylight, uncover it, and verify that the white is on silver, black is on brass/yellow metal, and green on green. Then remove the fuse box cover and verify that all the whites are securely connected, and the bare/green are secure. If those checks are good, replace the GFCI.
Voltmeter check dead before removing the GFCI.
Click to expand...

Yup, that makes a ton of sense. I realized as i was typing the above reply that I wasn't getting a true phase-to-neutral reading using just the socket. I'll pop the cover off tomorrow just to take a peek, and check on that GFCI outlet. Thanks for the (in)sanity check!
 
No clue what the problem is, but I'll toss out a possibility. An open neutral on a 240/120 branch circuit can lead to weird voltages between power and neutral, and situations that are potentially dangerous. I've worked in buildings that had old wiring where the neutrals were not done consistently or correctly. In a sub panel, neutral and ground are not supposed to be connected together. That's been true since at least the 1980's. But at some point before that, from what I've seen it was a bit wild west. I've seen 3 15A circuits being fed by one 14 gauge neutral, for example, and that's not a good thing.

Bottom line and less rambling - make sure you have good neutral wiring all the way back to the main box. For GFI's, you're going to need the neutrals to be paired with the hots or they won't work right. That should always be the case for safety, too...and in my opinion more important to get that right than grounding, in terms of fire safety vs shock.
 
drummer4468 said:
Come to think of it, I AM measuring incorrectly. But it still doesn't explain the one outlier reading
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So if I'm still not misreading your post, the results will vary depending on the load if you use that method of measuring. It could be that the outlier had nothing plugged in while the others did.
 
drummer4468 said:
Agreed, replacement is the best route, and what I should have done ages ago when I bought the house. But now in the process of selling said house, and trying to simply fix what's wrong if I can.
Click to expand...

If you're selling, that seems like more reason to change the box out for breakers. Home inspectors have a way of scaring the hell out of people over things like this. It's cheaper to deal with it now, rather than negotiating a padded list repair demands from a buyer.

Just my $.02, which ain't worth what it used to be with inflation and all...
 
What is the problem with the GFCI outlet? No power or it won't test (trip when you push the test button)? And if the latter, did it work before?

If no power, the outlet may have failed. They do fail at times.

If it won't trip with the test button, that is typically an issue with the ground. If it never worked, due to the old wiring, there may not be a ground. Or it may have become disconnected.

Or, the GFCI may have failed. I would check the ground, then replace the GFCI (they are cheap).
 
Charlie Golf said:
If you're selling, that seems like more reason to change the box out for breakers. Home inspectors have a way of scaring the hell out of people over things like this. It's cheaper to deal with it now, rather than negotiating a padded list repair demands from a buyer.
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Agreed. Around here, if your house that was built 20 years before gfci's were even invented doesn't have them on all your exterior outlets, an inspector will write a full paragraph on how you'll die and the place will burn down the first time you plug in a weedwhacker. Imagine if they saw fuses.

It's a four circuit panel. A box and 4 breakers would be under $100. Easy DIY in a couple of hours.
 
All good points. I'll look into just replacing the box with a breaker subpanel if I have time. Honestly didn't realize how cheap they were, I figured it was a few-hundred-dollar job so I applied the "ain't broke, don't fix it" principle. Long story short, I bought this house as a fixer-upper amidst one of the most half-assed "renovations" I've ever seen. So I've had to pick and choose my battles with it as life gave me less time/resources to devote to upgrades and whatnot.

As for the GFCI outlet, it's an outdoor outlet that I never really used for years, then I realized that it didn't work anyway. I think the issue was that it wouldn't reset IIRC, so it's possibly miswired or has a bad ground.
 
Let'sgoflying! said:
what would a DC voltmeter read, if 120v was applied across the leads?
Just wondering.
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A digital DC meter measuring AC voltage will either display the average of the sine wave (around zero), or fluctuate wildly depending on its sampling rate or mathematics capabilities, due to measuring changing points on the 60Hz sine wave. An analog needle will basically vibrate at the line frequency, averaging about zero. Yes, I made sure my DMM was set to measure AC lol
 
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