Hi everybody, a question came up in our forum that maybe you guys know the answer. Why are automotive fuses rated at 32 volts?

See: https://www.ford-trucks.com/forums/s...hreadid=100604

Thanks!

Barry

 

That's a good question. I am wondering if just has to do with an agreement for more interchangeable parts.

As said, they are safe for all voltages below 32v. As a company, would you want to invest in lines for 6v, 12v, 24v, etc?

Just a thought, from the business side of my brain.

That's just a thought, but agreements for interchangeable parts is like a world peace agreement, really hard to believe.

 

fuses have two ratings, amperage and voltage. The voltage rating is the rating of the insulating materiel used on the fuse. If you exceed that voltage you can get a shock through the insulation.

 

Glass fuses are not insulated, are they? That's what they are talking about here.

I've never even seen a fuse rated below 32v.

 

I always wondered too, since amperage is amperage, no matter what voltage. Some years ago I found out some things.

AC or DC makes a big difference in the fuse design.

A DC fuse will be designed a little different to make sure when the fuse blows, current will not jump the gap. They say once DC current arcs, it has more of a tendency to keep the arc going, rather than AC which stops more readily. As an example, when a stick welder is set to DC current, it is much easier to strike an arc, and keep it going, than when the welder is set to AC.

So the DC fuse will sometimes have a sandy looking stuff inside, to help break the arc that occurs when the fuse blows. And I always assume a lower voltage fuse will usually be rated for DC. 24vdc is another common control voltage used in factories and such, which use alot of fused circuits.

There is alot more going on than I know about fuse design, but that's one little tid-bit I picked up along the way somewhere.

 

Glass is an excellent insulator. Look up on the power line poles.

 

I was thinking of the ends. Okay, maybe the thinest structurally sound glass has a rating of 32v?

Thanks for the insight, wasn't think of the glass acting as an insulator.

Food for thought.

Thanks, mantta

 

While I have never seen a good explanation, the voltage rating has to due with arcing when the fuse blows, I think.

 

VOLTAGE RATING
The voltage rating of a fuse is NOT an indication of the voltage the fuse is designed to withstand while carrying current. The voltage rating indicates the ability of the fuse to quickly extinguish the arc after the fuse element melts and the maximum voltage the open fuse will block. In other words, once the
fuse has opened, any voltage less than the voltage rating of the fuse will not be able to "jump" the gap of the fuse. Because of the way the voltage rating is used, it is a maximum rms voltage value. You must always select a fuse with a voltage rating equal to or higher than the voltage in the circuit you wish to protect.

Going by that I would have to guess that since most trucks are 12VDC than a 32V fuse is more than sufficient..

 

Well said. Exactly what I was trying to say but could not muster up the words!
Larry, Retired ENCS(SS), USN

 

Thank you all for the information. It's been interesting, but:

We still haven't answered BBB's question.

Why 32v in a 12v application?

I know that 12v wouldn't work because it's actually around 14v when running.

I guess the only people that might know would be the automotive design engineers that do the electrical circuits.