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CAn I use a 20amp fuse in a fuse box that says 30amp?

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Deal Addict
Oct 17, 2010
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CAn I use a 20amp fuse in a fuse box that says 30amp?

i was planning on changing all 4 fuses in this box . there not broken but i figured with age they would blow.

this one fuse i wanted to change from a 30amp to replace with a 20amp. reason being the wiring in the room that is connected to that fuse is old so if something were to ever happen, i didnt want the wiring to get to hot. so i assume i could use a lower fuse so that if something were to short or whatever, the use would blow before a fire.

would that be acceptable thing to do? (asside from rewiring the whole room)
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Oct 15, 2007
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thatsnazzyiphoneguy wrote: i was planning on changing all 4 fuses in this box . there not broken but i figured with age they would blow.

this one fuse i wanted to change from a 30amp to replace with a 20amp. reason being the wiring in the room that is connected to that fuse is old so if something were to ever happen, i didnt want the wiring to get to hot. so i assume i could use a lower fuse so that if something were to short or whatever, the use would blow before a fire.

would that be acceptable thing to do? (asside from rewiring the whole room)
Fuse required is to protect the wiring and is based on the wiring it’s serving. Lowering a fuse amperage won’t protect you any more than with the proper amperage used.
Using a higher amp fuse for What the wire is rated for is where you get into trouble.

14 gauge (most common). Would be used with a 15amp fuse
12 gauge would be used with a 20amp


A 30 amp fuse is used with 10 gauge copper or 8 gauge aluminum, If you lower the amperage then you may possible blow the fuse depending on what the circuit is serving.
To complicate matters a previous owner could have used larger fuses where they shouldn’t have been used.

What loses power when you unscrew the 30 amp fuses?


Also there no need to replace the fuse due to age, either they work or they won’t. Replacing with a new fuse just cause will accomplish nothing
Everything has been said before, but since nobody listens we have to keep going back and beginning all over again. - Andre Gide
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Feb 11, 2007
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Red_Army wrote: Fuse required is to protect the wiring and is based on the wiring it’s serving. Lowering a fuse amperage won’t protect you any more than with the proper amperage used.
Using a higher amp fuse for What the wire is rated for is where you get into trouble.

14 gauge (most common). Would be used with a 15amp fuse
12 gauge would be used with a 20amp


A 30 amp fuse is used with 10 gauge copper or 8 gauge aluminum, If you lower the amperage then you may possible blow the fuse depending on what the circuit is serving.
To complicate matters a previous owner could have used larger fuses where they shouldn’t have been used.

What loses power when you unscrew the 30 amp fuses?


Also there no need to replace the fuse due to age, either they work or they won’t. Replacing with a new fuse just cause will accomplish nothing
+1, they don't really age. They blow when they're overloaded.
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Oct 14, 2010
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thatsnazzyiphoneguy wrote: CAn I use a 20amp fuse in a fuse box that says 30amp?
this one fuse i wanted to change from a 30amp to replace with a 20amp. reason being the wiring in the room that is connected to that fuse is old so if something were to ever happen,
Where does it say that a 30 Amp fuse should be in that position? Are you just assuming this should be a 30 Amp fuse because that is what you found there.

In fuse boxes of that era, most fuses were rated at 15 Amps. The exception would be for the stove, which were normally paper cartridge fuses. Is this the main panel for the house, or is it an auxiliary panel which was added to supply a dryer (for example).

What does this fuse feed?. If it is just lighting, it should probably only be a 15 Amp fuse, To be certain, read the wire's gauge number that is connected to this fuse. If the wire reads 10 gauge, then you can leave the fuse in.
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Oct 17, 2010
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Red_Army wrote:
Fuse required is to protect the wiring and is based on the wiring it’s serving. Lowering a fuse amperage won’t protect you any more than with the proper amperage used.
Using a higher amp fuse for What the wire is rated for is where you get into trouble.

14 gauge (most common). Would be used with a 15amp fuse
12 gauge would be used with a 20amp


A 30 amp fuse is used with 10 gauge copper or 8 gauge aluminum, If you lower the amperage then you may possible blow the fuse depending on what the circuit is serving.
To complicate matters a previous owner could have used larger fuses where they shouldn’t have been used.

What loses power when you unscrew the 30 amp fuses?


Also there no need to replace the fuse due to age, either they work or they won’t. Replacing with a new fuse just cause will accomplish nothing
engineered wrote: +1, they don't really age. They blow when they're overloaded.
Rick007 wrote: Where does it say that a 30 Amp fuse should be in that position? Are you just assuming this should be a 30 Amp fuse because that is what you found there.

In fuse boxes of that era, most fuses were rated at 15 Amps. The exception would be for the stove, which were normally paper cartridge fuses. Is this the main panel for the house, or is it an auxiliary panel which was added to supply a dryer (for example).

What does this fuse feed?. If it is just lighting, it should probably only be a 15 Amp fuse, To be certain, read the wire's gauge number that is connected to this fuse. If the wire reads 10 gauge, then you can leave the fuse in.
Thank you gentlemen for the detailed responses. i guess i should be more detailed in what the fuse box supplies.

first off, i recall the fuses being replaced maybe 10 years ago by someone who bought them at the dollar store. so i figured, they dont got much life for "cheap" fuses if there is such thing hence whhy i wanted to replace them with name brand ones from home depot or canadian tire.

i attached a pic again, its engraved in the black plastic background saying 30amps. so i assume that would mean it takes 30amps? and another pic that shows the wires coming out of it.

its not a house, a old downtown sstyle building. one fuse feeds the apartment above, which i believe is just normal 2 prong outlets and lights.

another fuse feeds a commercial kitchen for the exhuast hood, microwave, and lighting and coolers on main store level floor.

the other 2 i think was an outdoor sign no longer in use and lighting. i will have to chck the box again as it is written on a chart next to it.
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Oct 15, 2007
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Rick007 wrote: Where does it say that a 30 Amp fuse should be in that position? Are you just assuming this should be a 30 Amp fuse because that is what you found there.

In fuse boxes of that era, most fuses were rated at 15 Amps. The exception would be for the stove, which were normally paper cartridge fuses. Is this the main panel for the house, or is it an auxiliary panel which was added to supply a dryer (for example).

What does this fuse feed?. If it is just lighting, it should probably only be a 15 Amp fuse, To be certain, read the wire's gauge number that is connected to this fuse. If the wire reads 10 gauge, then you can leave the fuse in.
I wouldn’t speculate too much, it’s a commercial application, and it does say 30 amp on the BUS
Everything has been said before, but since nobody listens we have to keep going back and beginning all over again. - Andre Gide
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thatsnazzyiphoneguy wrote: i attached a pic again, its engraved in the black plastic background saying 30amps. so i assume that would mean it takes 30amps? and another pic that shows the wires coming out of it.

its not a house, a old downtown sstyle building. one fuse feeds the apartment above, which i believe is just normal 2 prong outlets and lights.

another fuse feeds a commercial kitchen for the exhuast hood, microwave, and lighting and coolers on main store level floor.
Red_Army wrote: I wouldn’t speculate too much, it’s a commercial application, and it does say 30 amp on the BUS

This fuse panel was not manufactured specifically for this building. The 30 Amp label is a maximum that can be supplied without overheating the panel itself. This is similar to car tires not being built for a single vehicle. They may have a 50 PSI rating on the sidewall which is the absolute maximum pressure that can be put into the tire before they can explode. The car manufacturer will normally recommend 30-32 PSI for a soft comfortable ride with the best handling.

The actual value of the fuses needs to be determined by the size of the wire which is connected to the panel.

Since this is armored cable, we cant read the gauge on the outer jacket. The panel cover should be removed to properly observe the wire size. Since this building is semi commercial, the wire may well be 10 gauge, but better safe than sorry. Don't decide by the panels maximum rating.
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Rick007 wrote: This fuse panel was not manufactured specifically for this building. The 30 Amp label is a maximum that can be supplied without overheating the panel itself. This is similar to car tires not being built for a single vehicle. They may have a 50 PSI rating on the sidewall which is the absolute maximum pressure that can be put into the tire before they can explode. The car manufacturer will normally recommend 30-32 PSI for a soft comfortable ride with the best handling.

The actual value of the fuses needs to be determined by the size of the wire which is connected to the panel.

Since this is armored cable, we cant read the gauge on the outer jacket. The panel cover should be removed to properly observe the wire size. Since this building is semi commercial, the wire may well be 10 gauge, but better safe than sorry. Don't decide by the panels maximum rating.
Thank you and I agree. As I’ve already posted this information I was just stating that we shouldn’t be speculating too much as many variables can come into play by doing ao
Everything has been said before, but since nobody listens we have to keep going back and beginning all over again. - Andre Gide
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Oct 17, 2010
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Red_Army wrote:
Fuse required is to protect the wiring and is based on the wiring it’s serving. Lowering a fuse amperage won’t protect you any more than with the proper amperage used.
Using a higher amp fuse for What the wire is rated for is where you get into trouble.

14 gauge (most common). Would be used with a 15amp fuse
12 gauge would be used with a 20amp


A 30 amp fuse is used with 10 gauge copper or 8 gauge aluminum, If you lower the amperage then you may possible blow the fuse depending on what the circuit is serving.
To complicate matters a previous owner could have used larger fuses where they shouldn’t have been used.

What loses power when you unscrew the 30 amp fuses?


Also there no need to replace the fuse due to age, either they work or they won’t. Replacing with a new fuse just cause will accomplish nothing
engineered wrote: +1, they don't really age. They blow when they're overloaded.
Rick007 wrote:
Where does it say that a 30 Amp fuse should be in that position? Are you just assuming this should be a 30 Amp fuse because that is what you found there.

In fuse boxes of that era, most fuses were rated at 15 Amps. The exception would be for the stove, which were normally paper cartridge fuses. Is this the main panel for the house, or is it an auxiliary panel which was added to supply a dryer (for example).

What does this fuse feed?. If it is just lighting, it should probably only be a 15 Amp fuse, To be certain, read the wire's gauge number that is connected to this fuse. If the wire reads 10 gauge, then you can leave the fuse in.
Rick007 wrote: This fuse panel was not manufactured specifically for this building. The 30 Amp label is a maximum that can be supplied without overheating the panel itself. This is similar to car tires not being built for a single vehicle. They may have a 50 PSI rating on the sidewall which is the absolute maximum pressure that can be put into the tire before they can explode. The car manufacturer will normally recommend 30-32 PSI for a soft comfortable ride with the best handling.

The actual value of the fuses needs to be determined by the size of the wire which is connected to the panel.

Since this is armored cable, we cant read the gauge on the outer jacket. The panel cover should be removed to properly observe the wire size. Since this building is semi commercial, the wire may well be 10 gauge, but better safe than sorry. Don't decide by the panels maximum rating.
i went ahead and removed the panel. im guessing i may need to resort to getting an electrician to confirm what kind of proper amps needed for the fuses but since its an easything to replace, im hoping i can find it here ;)

i attached the pictures of what the wires look like inside the fuse box:

would you guys say some of the fuses should not be a 30?

thank you all again for your detailed advice and input
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thatsnazzyiphoneguy wrote: someboooooodyyyy
I can confirm you need to hire a LEC ... nothing more.
I'd rather be outdoors camping, kayaking, and mountain biking ...
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Apr 8, 2010
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toronto
here's the thing... no offense to you but it seems like you're not to confident as to what you're doing hence asking for some guidance here.

do yourself a favour and hire an electrician. someone with the very limited details might give you the correct answer making assumptions. here's the thing.. that person isn't there nor has the full picture and thus there might be a chance you burn down your building.
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Feb 9, 2006
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thatsnazzyiphoneguy wrote: someboooooodyyyy
You have two choices:

Call an Electrician and fix all the deficiencies and violations in the panel and verify the wire type

or

Turn a blind eye to it because it works

Because ain't no one here gonna be able to tell you what's going on in that rat's nest.
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thatsnazzyiphoneguy wrote: someboooooodyyyy
If you’re in the GTA and need a referral for a LEC, PM me
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thatsnazzyiphoneguy wrote: someboooooodyyyy
You determine the maximum size of the fuse by determining the size of the wire connected to it ( example #12, #14, etc as suggested in post #2). The problem is that we cannot tell the size of the wires in your panel by just looking at them, It looks like a black and red plastic covered wire in the bottom right corner may be #10, but I'm sure that the majority are not #10 which is the only wire large enough to carry 30 amps.

Your panel is a mess, That red and black wire may be the supply lines, and not connected to a fuse at all. I also can't even be certain if you have more than one circuit connected to any one fuse. It contains old cloth covered wire as well as some plastic covered wire from later in the 20th century. Because it is as old as it is, it is even more important that you do not use fuses rated larger than safely allowed. Using the 30 amp fuses you currently have is plain dangerous.

Is this the only electric panel in your building?. It looks like a sub-panel because it does not contain a main shutoff switch.

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