# How to tell what fuses to use? **URL:** \ **Category:** Factual Questions\ **Created:** [September 10, 2025, 6:03am UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905 "2025-09-10T06:03:59Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [September 11, 2025, 12:24pm UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/21 "2025-09-11T12:24:36Z")
As a long-time DIYer, one of my rules of thumb is/was to _never_ work on electrics alone. Have somebody able-bodied there, even an unskilled somebody, to rescue you if you get zapped. And make sure they know what to do if you do get connected to live current and can’t release yourself. Or do release but are unconscious / unresponsive. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [September 11, 2025, 3:03pm UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/22 "2025-09-11T15:03:21Z")
> [@Chefguy](#): > > As a former electrician, I’m just offering a possible reason for the failure. No need to be a dick about it. I agreed that fuses can fail without reason and used a snarky analogy. The sound of zebra hoofbeats is more gentle, I guess? I do not agree that it is useful to OP, struggling to even identify the fuse, to suggest as equally likely what must be among the rarest modes of failure. Further, to do so seemingly in contradiction of my advice to identify a busted fuse for the glaring red flag warning that _you know it to be_ gets my pushback every time. Fictitious reader: > Dryer’s out again, eh, Grandma? 'Lectrician here said you prolly just got dried, worn out fuses. Put in a new one and see if the clothes dry. No, they didn’t say not to oil the socket, I think a little would be ok. I’ll check it out in a couple weeks when I visit for your 94th birthday. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [September 11, 2025, 3:23pm UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/23 "2025-09-11T15:23:18Z")
> [@LSLGuy](#): > > As a long-time DIYer, one of my rules of thumb is/was to _never_ work on electrics alone. It depends on your skill level and risk threshold. For me, I have worked on 120 V/240 V countless times alone, and I simply make sure I de-energize the system beforehand if it’s convenient to do so. For the rare instances when it’s very inconvenient to do so, I am _very, very_ careful. Worse case is that I get zapped with 120 VAC. That hasn’t happened to me in decades, thankfully, but it used to be more commonplace when I was younger and less experienced. Even though the odds of it being lethal are very low, I am much more careful now. But that’s me… I would never advise anyone else to do this. ---
**Author:** ![GargoyleWB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gargoylewb/32/199_2.png) [@GargoyleWB](https://boards.straightdope.com/u/GargoyleWB)\ **Post date:** [September 11, 2025, 9:20pm UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/24 "2025-09-11T21:20:16Z")
Agreed, my old 1930s house had exactly the same arrangement, with a little secondary fuse box tucked in the wall joists. ---
**Author:** ![TokyoBayer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tokyobayer/32/13989_2.png) [@TokyoBayer](https://boards.straightdope.com/u/TokyoBayer)\ **Post date:** [September 12, 2025, 1:07am UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/25 "2025-09-12T01:07:57Z")
> [@Crafter\_Man](#): > > Worse case is that I get zapped with 120 VAC. That hasn’t happened to me in decades, thankfully, but it used to be more commonplace when I was younger and less experienced. That happened to me a couple of times as well, until I got really serious about de-energizing the circuits before I started working on them. I did do something really stupid as a teenager. My dad hired a handyman to do some things to the electrical work on the house, and the guy wound up causing a huge spark where the main lines came to the house, and a small fire which quickly went out on its own. The power lines fell down a ways until they were about seven feet above the ground. They had gotten quite hot and, being 17, I wanted to see how hot they were so I just touched them. Fortunately, they were no longer live, but it could have been not so good. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [September 12, 2025, 1:35am UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/26 "2025-09-12T01:35:29Z")
After seeing the big wires going into their house, most people assume the shock hazard from them must be much worse than the shock hazard at a 120 VAC receptacle. Or they assume the shock hazard in a circuit breaker panel must be much worse than a 120 VAC receptacle. But they’re all pretty much the same: any conductor is, at most, 120 VAC relative to earth, anywhere in or around the house. Assuming you are grounded, the shock you would receive touching one of the big wires going to your house would be no better or worse than the shock you receive from touching the hot wire at a receptacle. Having said that, it’s possible to receive a 240 VAC shock, but those are really rare: you would have to be isolated from ground, touch one conductor, and then touch the conductor of the other phase. ---
**Author:** ![Jeff\_Lichtman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jeff_lichtman/32/1531_2.png) [@Jeff\_Lichtman](https://boards.straightdope.com/u/Jeff_Lichtman)\ **Post date:** [September 12, 2025, 4:24am UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/27 "2025-09-12T04:24:42Z")
Here’s a picture of all the fuse boxes at my aunt’s house, with annotations. [![](https://i.imgur.com/PCHWvnI.jpeg) ](https://i.imgur.com/PCHWvnI.jpeg) ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [September 12, 2025, 7:38am UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/28 "2025-09-12T07:38:51Z")
Wow. If it were me, I’d tear down that wall and rip all of that out. And install a modern circuit breaker panel. ---
**Author:** ![Lancia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lancia/32/17174_2.png) [@Lancia](https://boards.straightdope.com/u/Lancia)\ **Post date:** [September 12, 2025, 3:33pm UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/29 "2025-09-12T15:33:01Z")
> [@Crafter\_Man](#): > > If it were me, I’d tear down that wall and rip all of that out. And install a modern circuit breaker panel. QFT. The phrase “throwing good money after bad” applies here, I think. Get a couple of quotes from reputable electricians for replacing that mess with a proper modern breaker panel and upgrading the service to 200A, have the work done, and then don’t worry about it ever again. Not only will it make it safer/easier for your aunt use, it’ll make it safer/easier for the next person who owns the house as well. Edit: just FYI my knowledge of home electrical systems is minimal, so bear with me, but… am I understanding this setup correctly and that is a 60A service? Each of those 60A fuses protects one leg of the 240v system? If so, then upgrading all those disparate fuse boxes to a single breaker panel and upgrading to a 200A service would be extra prudent. I’m having a hard time believing a modern home can function on 60A service, even if most appliances are gas. Beyond the safety and convenience issues, it would future-proof the home for the next owners/tenants. ---
**Author:** ![DavidNRockies](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidnrockies/32/6279_2.png) [@DavidNRockies](https://boards.straightdope.com/u/DavidNRockies)\ **Post date:** [September 12, 2025, 3:53pm UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/30 "2025-09-12T15:53:37Z")
Got a **[clamp-on ammeter](https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-measure-current-with-clamp-accessory)**? Feel like checking the actual current draw of the dryer? That might be the actual source of the problem. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [September 12, 2025, 6:10pm UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/31 "2025-09-12T18:10:52Z")
> [@Lancia](#): > > I’m having a hard time believing a modern home can function on 60A service, even if most appliances are gas. My 1920ish gas-fired single family home in Chicago has a pair of 1950-60s era fuse boxes very much like OP’s gray ones at lower right. A small one is in the attic near the service entrance and the bigger in the basement. I’m 80% certain none of the fuses are greater than 40A and I’ve always assumed it was 60 amp service, typical for the date of the install. I have (up to) two window air conditioners (not central) and the occasional blender or power tool draw might dim the lights a little but I doubt I get close to half of my capacity. A radiator circulator runs in the winter, maybe a few hundred watts. An EV charger would need an upgrade, I’m sure, but I don’t feel like I sacrificing anything in the meantime. I’m not saying it’s the safest firetrap on the block but I’m also not wishing for more. ---
**Author:** ![Ancient\_Nerd](https://avatars.discourse-cdn.com/v4/letter/a/ed655f/32.png) [@Ancient\_Nerd](https://boards.straightdope.com/u/Ancient_Nerd)\ **Post date:** [September 13, 2025, 7:53am UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/32 "2025-09-13T07:53:35Z")
It’s hard to be sure from the picture but that does not look like #8 wire from those 40A fuses in the box on the left. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [September 13, 2025, 10:36am UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/33 "2025-09-13T10:36:29Z")
Good catch! It doesn’t even look as stout as the wires leaving the 30A fuses at lower right. Which fuses are the ones the OP is concerned about being excess ampacity. It’s clear to me the OP has a latently dangerous situation there. A pro needs to evaluate all this ASAP. Ideally replace the whole assembly, but at a minimum understand the situation and come up with a list of urgent problems to address. It _may_ be that just installing properly sized fuses for the wiring they protect is sufficient to forestall the fire risk and will still provide enough juice for an elder’s modest needs. Mom probably isn’t running her Cuisinart, her microwave, her instant pot, and her hairdryer all at once. Probably. If proper fuses keep blowing under reasonable use case loads, then (at bare minimum) it’s time to upgrade the wiring downstream of those fuses to support the demand she really has. I say “reasonable” because at a prior residence I had 15A service to one set of kitchen outlets. Which gang of outlets had a toaster, a microwave, and a coffee maker all plugged into them. Using any two of them was fine, but if the coffeemaker was actively boiling water & you activated the other two, decent odds the breaker would open. Of course when making breakfast in a hurry at 4am trying to dash off to work, multi-tasking all those appliances was only natural. Oops. Turns out that was an unreasonable expectation, but one I learned to work around. ---
**Author:** ![Ancient\_Nerd](https://avatars.discourse-cdn.com/v4/letter/a/ed655f/32.png) [@Ancient\_Nerd](https://boards.straightdope.com/u/Ancient_Nerd)\ **Post date:** [September 13, 2025, 6:21pm UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/34 "2025-09-13T18:21:30Z")
Should we even get started on the wire colors? Hot lead: Black because it can fry you to a crisp Green lead: Ground connected to the earth, new since 1951 White Lead: Neutral. ---
**Author:** ![Elmer\_J.Fudd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmer_j.fudd/32/1211_2.png) [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)\ **Post date:** [September 13, 2025, 7:56pm UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/35 "2025-09-13T19:56:04Z")
> [@Ancient\_Nerd](#): > > Hot lead: Black because it can fry you to a crisp > > Green lead: Ground connected to the earth, new since 1951 > > White Lead: Neutral. Never assume that’s always correct. [![](https://i.etsystatic.com/32047215/r/il/b960b8/5388775258/il_794xN.5388775258_16nl.jpg) ](https://i.etsystatic.com/32047215/r/il/b960b8/5388775258/il_794xN.5388775258_16nl.jpg) ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [September 13, 2025, 8:25pm UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/36 "2025-09-13T20:25:55Z")
Of course not. It’s sort of “trust (a little) but verify.” But @Ancient_Nerd’s point is that in the pic we see clear evidence of stuff mis-wired versus the standard. Which is yet another thing about this house that _ought_ to be corrected ASAP. Before somebody trusts who didn’t verify. ---
**Author:** ![Marvin\_the\_Martian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/marvin_the_martian/32/2898_2.png) [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)\ **Post date:** [September 13, 2025, 10:40pm UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/37 "2025-09-13T22:40:48Z")
Where are you seeing an insulation color issue? I don’t see one but not sure I am looking in the right place. I do think I see aluminum wire in the box with the two 40A fuses. ---
**Author:** ![Ancient\_Nerd](https://avatars.discourse-cdn.com/v4/letter/a/ed655f/32.png) [@Ancient\_Nerd](https://boards.straightdope.com/u/Ancient_Nerd)\ **Post date:** [September 13, 2025, 11:55pm UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/38 "2025-09-13T23:55:02Z")
> [@Marvin\_the\_Martian](#): > > I do think I see aluminum wire in the box with the two 40A fuses. Okay after looking a little closer You are correct. Last night, I did not pick out the black wire going from the left fuse into the flexible conduit. It looked like all it had was two thin white wires. ---
**Author:** ![FinsToTheLeft](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/finstotheleft/32/2930_2.png) [@FinsToTheLeft](https://boards.straightdope.com/u/FinsToTheLeft)\ **Post date:** [September 14, 2025, 1:49am UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/39 "2025-09-14T01:49:47Z")
> [@Marvin\_the\_Martian](#): > > I do think I see aluminum wire in the box with the two 40A fuses. AL on larger gauge wires is not an issue and it is still in use today. The issue was with 15A and 20A branch circuits which typically had connections at every switch and receptacle on the circuit rather that higher amperage circuits which were straight runs from the breaker panel to the appliance. ---
**Author:** ![Marvin\_the\_Martian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/marvin_the_martian/32/2898_2.png) [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)\ **Post date:** [September 14, 2025, 2:52am UTC](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905/40 "2025-09-14T02:52:54Z")
> [@FinsToTheLeft](#): > > AL on larger gauge wires is not an issue and it is still in use today. For stranded wire larger than 8 AWG. What I see looks solid and smaller. [Previous page](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905.md?page=1) [Next page](https://boards.straightdope.com/t/how-to-tell-what-fuses-to-use/1022905.md?page=3)