When is an Amp not an Amp?

[WizeOne]

Went out today to buy some fuses for the outside Christmas lights. The old fuse cap said 125 volt-7 amps.

The vendor only had 240 volt-7 amp fuses. They looked the same, the fuse wires appeared the same, so I bought them. The guy at the store said that the voltage thing was controversial but many considered there to be no difference between voltage rated fuses of a given amp rating.

That seems logical to me. Seems like an amp should be an amp regardless of the voltage or even AC vs DC.

What say you all?

 

[Barnacle_Bill]

Re: When is an Amp not an Amp?

You can safely use a fuse rated higher in voltage but not lower.

 

[bandit86]

Re: When is an Amp not an Amp?

exactly

 

[WizeOne]

Re: When is an Amp not an Amp?

It seems to be unanimous then! Thanks

 

[rwise]

Re: When is an Amp not an Amp?

Yep!

 

[Dunaruna]

Re: When is an Amp not an Amp?

I thought your standard house voltage was 110, how come the vendor had 240 in stock?

We (downunder) have 240v as standard.

 

[WizeOne]

Re: When is an Amp not an Amp?

I thought your standard house voltage was 110, how come the vendor had 240 in stock?

We (downunder) have 240v as standard.

True, 'tis 110 v. I don't even think the store had a bin for the 110v x 7a fuses. Go figure?

 

[Tail_Gunner]

Re: When is an Amp not an Amp?

True, 'tis 110 v. I don't even think the store had a bin for the 110v x 7a fuses. Go figure?

When the amp is not in phase bro.........

 

[WizeOne]

Re: When is an Amp not an Amp?

When the amp is not in phase bro.........

Wha? You lookin' for lumps of coal in your stocking??

 

[BoatBuoy]

Re: When is an Amp not an Amp?

I thought your standard house voltage was 110, how come the vendor had 240 in stock?

We (downunder) have 240v as standard.

Most homes here have 2 voltages. The 240v. is normally for those devices that use electricity(as opposed to natural gas) for water heater, range, clothes dryer, or home heating/cooling.

The 120v. is for everything else (lighting, small appliances, etc.).

 

[Dunaruna]

Re: When is an Amp not an Amp?

O/K, thanks.

 

[ebry710]

Re: When is an Amp not an Amp?

Most homes here have 2 voltages. The 240v. is normally for those devices that use electricity(as opposed to natural gas) for water heater, range, clothes dryer, or home heating/cooling.

The 120v. is for everything else (lighting, small appliances, etc.).

It is true that a house has 220/240v, but that is because it has two 110/120 volt legs coming into it. Since they are from a different sources they are additive. Only at the point of the appliance is there truly 220/240. Lines going to the appliance are 110/120.

So the question stands.....why a 240 fuse at a hardware store?

 

[haskindm]

Re: When is an Amp not an Amp?

Because the fuses (like most everything else) are not made in this country. Most of the world uses 240-volt for household wiring and since the 240-volt fuses are fine for 120-volt uses, that is how they are labeled. If they were labeled 120-volt they would not be usable where the supply voltage is higher.

 

[Chris1956]

Re: When is an Amp not an Amp?

The small glass fuses we used in cars in the 70s and earlier are 240Volts with amperages from .25 - 40A or so. It therefore does not surprize me that the Christmas lights were 240V, since they were likely glass fuses similat to the automotive "LittleFuse".

 

[fdmsiv]

Re: When is an Amp not an Amp?

Most of those little Buss fuses are usually 250V, don't think I have ever seen one less than 250V

 

[180shabah]

Re: When is an Amp not an Amp?

Those fuses are not just for 240v, they are for anything up to 240v.

 

[MrBigStuff]

Re: When is an Amp not an Amp?

The guy at the store said that the voltage thing was controversial but many considered there to be no difference between voltage rated fuses of a given amp rating.

Now you know to never rely on that guy's advice because he's dead wrong. The voltage rating IS important because the fuse is designed to work at or below that voltage rating. The issue is when the fuse is subjected to an overload condition and what happens inside the fuse. If the circuit voltage exceeds the fuse rating, it may not work properly and could result in the fuse exploding or a circuit fire when it does not open up as designed. This is especially true when the fuse design uses a filler material.

That seems logical to me. Seems like an amp should be an amp regardless of the voltage or even AC vs DC.

Again, this is incorrect for all fuse types. The ceramic bodied fuses are rated the same for AC or DC operation but most glass fuses are derated for use in DC circuits. It has to do with the time constant of the applied power to the load.

The reason you do not see many 125V glass bodied fuses is that it does not typically cost more to fabricate one that will withstand 240V and the manufacturer then only has to make and stock one part to fit both uses. The latter benefit is realized all the way down the chain to the consumer.

 

[WizeOne]

Re: When is an Amp not an Amp?

Now you know to never rely on that guy's advice because he's dead wrong. The voltage rating IS important because the fuse is designed to work at or below that voltage rating. The issue is when the fuse is subjected to an overload condition and what happens inside the fuse. If the circuit voltage exceeds the fuse rating, it may not work properly and could result in the fuse exploding or a circuit fire when it does not open up as designed. This is especially true when the fuse design uses a filler material.




Again, this is incorrect for all fuse types. The ceramic bodied fuses are rated the same for AC or DC operation but most glass fuses are derated for use in DC circuits. It has to do with the time constant of the applied power to the load.

The reason you do not see many 125V glass bodied fuses is that it does not typically cost more to fabricate one that will withstand 240V and the manufacturer then only has to make and stock one part to fit both uses. The latter benefit is realized all the way down the chain to the consumer.

Got it, thanks! I will sleep with confidence that my 240v glass fuses, in a 120v string of lights will not burn my house down.