Fused service panel/fuse box

I’ve looked and I’m not finding a great answer… How does one inspect a fused box? I get there are many, many similarities between a fuse box and breaker panel; wire gauge, load size, neutrals, grounds where they exist, etc… What I don’t have a warm fuzzy on is knowing what to look for specifically with a fuse box. I haven’t run into a fuse box and would like to not see one for the first time while I’m trying to figure it out. I recognize recommending an upgrade to a more modern system to embrace grounds, newer wiring, etc… I could very well be overthinking this - I’ve been accused of that before… It’s the absence of having hands on a fuse block that concerns me. Thoughts on the inspection part?

As you’ve mentioned to start with if they’re plug fuses then the equipment is old. Old equipment means that over time more people have had a chance to get in there and do non-code compliant work. The biggest issue is that larger than permitted fuses often get installed. You would need to check each branch circuit conductor size against the fuse size. Other defects like those that would exist with circuit breaker panels would also need to be checked.


That’s for sure… When I find fused load centers, almost all of the fuses have been replaced with 30 amp sizes, no matter the circuit.

Along with metallic “non-fuse” inserts, that bypass the safety features of a the fuse itself.


If I can, without shutting off something critical, I pull the fuses just to check if someone put a copper penny behind it. I have found a penny quite a few times.


What are you going to do with all that money, Joe? :laughing:


Basically a fuse is supposed to perform the same function as a breaker, to protect the wires from an overcurrent condition. Fuses are actually, IMO, better overcurrent protection than breakers, but that’s a discusion for another thread.

The reason, at least as I know it, why circuit breakers were invented, was because fuses are too easily by-passed with pennies or in some panels simply installing a larger fuse. Not that someone can’t install a larger breaker, but they need to remove the dead front to do that, and most people have enough sense not to go there.

I make the statement that the equipment is outdated by todays standards and that replacement should be considered, I also look for the usual issues, double taps are the most common issue, aside from the age of the panel itself, that I find.


First, if it’s been there 100 years you have an existence proof. If it’s live it’s clearly been functioning for a long long time. You may have nothing to do other note the age and move on. Your #1 question as an inspector can and should be “is it functioning as needed”. Just check for discoloration wear heat damage, just as you would with a breaker panel.

Second, you definitely compare the fusing rating to the wire size. And mention that a common problem is the wrong fuse being inserted. Bone up on Type-S rejection bases, or even carry them with you.

Third, you recognize that fuses are inherently more reliable than breakers. They can’t stick, jam or break. They don’t wear out.

Fourth, you look for unauthorized additions or changes over the years.

Fifth: like the asbestos? Yep, that white paper is asbestos.

Sixth: don’t panic. Take a high resolution picture and post it here for more advice.

Essentially every defect you can find with fuses, you can find with a breaker based panel. The most common issue I find is the fuses wrong size, followed by screws that are no longer tight.


This helps. Being a bit, well “me”, I think it would be great if some of this was covered in our basic training - the required 90 hours. That said, it feels a bit odd to say “I need to be told something obvious” to folks who see this as an obvious thing. But… to an overthinker, nothing is obvious! Thank you, everyone.


You make an excellent point and you should consider bringing it to the attention of the education department.

That said, there are sooooo many variations in homes. It is impossible to include it all. Another thing to consider, the existence of fused boxes is diminishing rapidly so they are really the exception and not the rule in most areas. Though I have no data to support this, only my experience.

We used to call those “Lincoln” fuses! :rofl:

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The first thing to write is a need to be evaluated by an electrician. while your in the panel look for burn marks, overcrowding, multi wire taps and of course aluminum wire.

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Changing to a breaker panel will not change the wiring method or adding grounds to ungrounded circuits. It would also do nothing for overloaded or inadequate circuitry. System grounding would be upgraded for things like lightning and surges. It would be easier to add afci protection.

Hi, Tom.

First thing I think of is, updating OCP Over Current Protection.

Before dead front is dismounted, I look at the collar or Amperage for over fusing.
Secondly, burnt fuses.
When I opened fronts I checked to see if the front was energized, deadfront fasteners, circuit terminations and AWG, cable material.
Then, the box for open knockouts, missing bushing,
Lastly, bonding.