Question about 5x20 mm fuses.

[Eug]

My PB-13 Ultra subwoofer amp died, so I got a replacement. The replacement is a different amp which uses different fuses, so I wanted to get some details on getting extra fuses.

The spec on the amp for the fuse is T4AL250V. However, the spec on the actual fuses included is T4AH250V.

Let me know if this is correct:

T4AL250V is Slow-blow 4 amp glass at 250 Volts.
T4AH250V is Slow-blow 4 amp ceramic at 250 Volts.

Although the amp came with ceramic fuses, am I OK to replace with glass, given that the amp itself has the T4AL250V spec stamped right on it?

What about the maximum wattage with 120V AC? Is it 4A x 250V = 1000W max? Or is it 4A x 120V = ~500W max? I'm assuming the former, since it's supposed to be a 1000 Watt amp.

BTW, my previous amp was a BASH 750W, but it used T6.3AL250V, which is 1575W.

 

[William Gaatjes]

I never really thought about it, i think that choosing glass or ceramic is a factor if the fuse can explode or not with serious overload situations (short circuit) . On the other hand, the characteristic of the fuse wire may also be dependent on the glass or ceramic and filled with sand or not.
I do not think that for a music system it is really an issue. I would use either.

edit:
The voltage is okay. It is specified for 250V so 120V is fine.
A fuse does not carry wattage, An ideal fuse (0 resistance) has 0 watts. For it is in series with the appliance and you would not want to loose voltage over it.

 

[William Gaatjes]

See a fuse like a switch. When it is closed, your appliance gets power. When there is an overcurrent condition, the switch opens to interrupt the flow of current to your appliance and therefore stop the use of power.

 

[SparkyJJO]

Either is OK. Ceramic tends to be considered better than glass, but if it calls for glass as the spec then get glass as spares if you like.

 

[Eug]

Either is OK. Ceramic tends to be considered better than glass, but if it calls for glass as the spec then get glass as spares if you like.

OK thanks. Is my interpretation of the labeling correct?

I'd get the ceramic just because the sub came with them but I'm having a very hard time finding them locally in ceramic. So I'll have to do glass unless I got them from eBay or something, and I'm a little bit wary of doing that.

 

[nickbits]

Did you blow the spare that comes with it too? I'm not sure which one in the tray is the spare but just swap them if you haven't tried that already.

 

[nickbits]

Also when I talked to customer service they didn't say one way or another glass vs ceramic, only "slow blow 250v 6.3 amp"

 

[LTC8K6]

What can happen with plain glass fuses during a large overload is vaporization of the fuse link. This can coat the glass and make it conductive, defeating the purpose of the fuse and allowing current to keep flowing.

 

[Red Squirrel]

I'd try to match as close as I can, but probably not a huge deal. A site like Digikey may have them.

 

[William Gaatjes]

What can happen with plain glass fuses during a large overload is vaporization of the fuse link. This can coat the glass and make it conductive, defeating the purpose of the fuse and allowing current to keep flowing.

Yeah, that could be right. This can be caused by arcing at higher voltages like 230V or 120V. When you interrupt a large current flow, the current will try to remain flowing causing an arc after the fuse wire has melted. In a sand filled fuse (and i think the ceramic ones are the ones with sand filled but i have also seen glass fuses with sand filled), the sand dampens the arc.

It is something like this but on a very very much smaller scale :
First few seconds.

https://www.youtube.com/watch?v=yX5TIDLvMyw

 

[William Gaatjes]

This is interesting to watch :

https://www.youtube.com/watch?v=8xONZcBJh5A

It explains the difference between voltages and currents.
And the possible danger.

 

[Eug]

This is interesting to watch :

https://www.youtube.com/watch?v=8xONZcBJh5A

It explains the difference between voltages and currents.
And the possible danger.

Thanks, but you didn't answer my question. Does the fuse blow at 4A x 120V = ~500 Watts, or does it blow at 1000 Watts since it's rated for 4A x 250V?

The fuse is a 250V fuse, but my AC line is 120V.

In other words, does using this fuse on a 120V line effectively make it an 8A fuse? Or is it still a 4A fuse? Cuz if 4A, then it would blow at ~500 Watts on a 120V line. If it's blowing at ~500 Watts, then I don't understand the amp's 1000 Watt rating.

BTW, the previous amp was rated for 750 Watts, but came with a 6.3A fuse. It should be noted that 6.3A x 120 V is about 750 Watts.

 

[NutBucket]

It blows based on current.

Either one will be fine. The only reason the fuse should blow is if there is a problem with the amp.

 

[LTC8K6]

Fuses blow at their current rating, as far as I know.

Fuses designed to break high currents are usually filled with some inert powder like sand.

*****

Can the fuse voltage exceed the application voltage?

Yes - Fuses are designed for use in circuits at any voltage as long as they don't exceed the fuse's maximum voltage rating. (Exception - medium-voltage fuses from 2,400 to 38,000 volts may only be used at the voltages designated on the fuse's label) The voltage rating of a fuse is a safety rating that should never be exceeded.


How should I select the proper fuse amperage when I know the circuit amperage?

Always follow NEC guidelines for applying low-voltage fuses. Generally, the MINIMUM fuse size should be based on 125% of the circuits full load current. Time-delay fuses should be used for inductive loads and fast-acting fuses used to protect non-inductive loads.

What is the difference between interrupting rating and the fuse's ampere rating?

The interrupting rating is the maximum amount of energy the device can safely withstand. The fuse's ampere rating is the amount of current that the fuse will allow through before beginning to operate. Both ratings are determined through testing.


Why is the interrupting rating important?

The interrupting rating is important because it is a safety rating. If a device with a low interrupting rating is used in circuit that has a higher available fault current (the amount of energy that is potentially available if a fault were to occur), the device could potentially fail (rupture or explode) as it attempts to clear the fault, causing a safety hazard.

http://www.littelfuse.com/technical-resources/frequently-asked-questions.aspx

 

[LTC8K6]

Just for fun, here's a demo of a power line lighting arrestor with exploding disconnector:

https://www.youtube.com/watch?v=M1NM6rlSwqA

 

[Eug]

Fuses blow at their current rating, as far as I know.

Fuses designed to break high currents are usually filled with some inert powder like sand.

*****

Can the fuse voltage exceed the application voltage?

Yes - Fuses are designed for use in circuits at any voltage as long as they don't exceed the fuse's maximum voltage rating. (Exception - medium-voltage fuses from 2,400 to 38,000 volts may only be used at the voltages designated on the fuse's label) The voltage rating of a fuse is a safety rating that should never be exceeded.


How should I select the proper fuse amperage when I know the circuit amperage?

Always follow NEC guidelines for applying low-voltage fuses. Generally, the MINIMUM fuse size should be based on 125% of the circuits full load current. Time-delay fuses should be used for inductive loads and fast-acting fuses used to protect non-inductive loads.

What is the difference between interrupting rating and the fuse's ampere rating?

The interrupting rating is the maximum amount of energy the device can safely withstand. The fuse's ampere rating is the amount of current that the fuse will allow through before beginning to operate. Both ratings are determined through testing.


Why is the interrupting rating important?

The interrupting rating is important because it is a safety rating. If a device with a low interrupting rating is used in circuit that has a higher available fault current (the amount of energy that is potentially available if a fault were to occur), the device could potentially fail (rupture or explode) as it attempts to clear the fault, causing a safety hazard.

http://www.littelfuse.com/technical-resources/frequently-asked-questions.aspx

OK, I think I understand things now. My SVS PB-13 Ultra's old BASH amp (which became defective after 7 years) was rated at 750 Watts, and had a 6.3A fuse rating, which is 750 Watts.

My new replacement Sledge amp is rated at 1000 Watts, but has only a 4A fuse rating, which is less than 500 Watts.

However, the fuses (for both amps) are slow blow / time delay, so they can handle way more than the fuse rating for very brief moments. I'm assuming the circuit is designed to handle very short bursts of power over 500 Watts, but if it's more than a few moments, then it will blow the fuse. Interestingly, the specs say that the 1000 Watt rating is continuous, with peak dynamic power up to 3600 Watts. I don't see how that is possible with a 120V AC supply, but I always view these specs with a healthy dose of salt.

According to Littel Fuse, a time delay / slow blow fuse of this type can run at 150% (720 Watts) for up to 60 minutes, and 210% (1000 Watts) for 2 minutes.

As mentioned, the amp itself has the glass AL spec'd fuse stamped on it, but the SVS website advertises they come with ceramic fuses. So it sounds like glass fuses are fine, but I will note that for my BASH, when the glass fuse blew, it sent shards of glass everywhere inside the casing around the fuse. So, I just ordered some Little Fuse ceramic fuses off eBay.

BTW, the new amp did come with two fuses, which was nice, since I blew the fuse in the first week. It's been working fine since though so far, after I configured it properly, which included turning the gain way down (configuerd by Audyssey).

 

[William Gaatjes]

As mentioned, fuses blow at the reated current. However, fuses have an I - T curve that explains when the fuse will go for agiven current. Just follow the current. As i wrote, fuses do not carry wattage. The voltage mentioned is about the voltage that the fuse is designed for to handle. There is no voltage times current eguals powe for a fuse. A 1A fuse rated at 250V will also blow when you let more then 1A flow at 12V. The power from your amplifier reads like pmpo power and such. Fake numbers that never apply.