@VOLVO-V70 I’m all ears… can you tell me what to search for? E46 fuse set doesn’t turn up much.
1 Like
I can’t remember the last time I changed a fuse. Many cars have spare fuses in slots that are not active, so just check that.
I had cut the thermostat wire at the air conditioning compressor while whacking weeds. Had to call the hvac guy. After splicing the wire went to the furnace and replaced a blown fuse. Looked just like any other flat fuse. Nothing special.
The fuses can be purchased at an auto parts store, he is asking what the voltage ratings mean.
The parts department at the Lexus dealer I worked for would sometimes tell me “We don’t have that fuse, I will order one”. I brought an assortment of fuses from home so I could repair cars in a timely manner.
I am surprised someone didn’t ask how many miles are on the car? More questions than answers. Nobody needs to know the specific BMW model, the vehicle operates at 14.5 volts, 32-volt fuses are sufficient for common passenger cars.
Very nicely stated.
2 Likes
I was asking why he needed to order online. The last time I change a fuse was on my lawn mower. 20Amp, I never looked at the brand or voltage, just grabbed it off the rack at an auto parts store. Then found the short causing the fuse to blow
1 Like
It seems simple but the choice of fuse in the design is a rather complex analysis taking into account all the factors; type of power, wiring, interconnections, load dependencies and so on. There are many fuses available to satisfy the myriad of different scenarios. Fortunately, for something like an automotive fuse, the replacement choice is rather forgiving.
I’ve worked on fuzing (sic) for missiles. It’s like the exact opposite of a fuse. It is designed to produce and sustain a plasma arc upon activation. These are used on our arsenal of submarine launched Trident II D5 nuclear missiles. There, it is bad if it does not sustain the arc when activated. It would be really, really bad if it activated prematurely 
Light fuze and get away…
2 Likes
The voltage rating in a fuse has to do with how much voltage can it handle without arcing through the shell to an external conductor or ground. It’s a rating of the fuses insulation where the current (amps) rating is how much current will it conduct from one terminal to the other.
Generally the insulation value is around 2.5 times the circuit voltage. Some commercial diesel vehicles use a 24V starting voltage so fuses for these circuits would have to be rated at 80 volts. Your house wiring is 240 volts split into two 120 volt circuits 180 degrees apart so your house wiring is rated at 600 volts. Some commercial building have 480 volt circuits that use 1200 Volt rated wiring.
I don’t believe there are any consumer vehicles, even diesel powered, use a 24 volt starting system.
1 Like
Yeah I never noticed any different fuses for my diesel. I do have a couple spare 220v fuses for my air conditioner but they are the cigar shaped ones. Still not needed in 20 years.
That’s not entirely true. It is more fundamentally related to the ability to self-extinguish the plasma arc inside the fuse housing. If the conductors are too close together for that to happen or the debris from the melted fuse reduces the creepage and clearance to a point the voltage sustains the arc, the fuse fails to provide circuit/load protection. Of course the fuse also has to provide sufficient dielectric withstand to not arc to other adjacent elements but that is more of a circuit design responsibility (e.g. circuit board creepage and clearance based on voltage).
1 Like
No 600 Volts in the standard to cover all the Voltages from 120 up to 600 that are used in residential and commercial buildings. 240 in residential and 480 in commercial is common. I assume they mean 600 Volts AC since the National Electric Code is dumbed down for non engineer types who wouldn’t know that AC has peaks that are higher than 600 while DC is just 600.
Fuses are designed to “blow away” the molten metal or to melt something to isolate the conductors to prevent bridging. That is not really part of the voltage rating. In distribution transformers, large current limiting fuses are filled with sand that will melt around fusible conductors to prevent bridging.
But resistance to bridging (isolation) is an important part of fuse design.
Fuses are designed to “blow away” the molten metal or to melt something to isolate the conductors to prevent bridging. That is not really part of the voltage rating. In distribution transformers, large current limiting fuses are filled with sand that will melt around fusible conductors to prevent bridging.
But resistance to bridging (isolation) is an important part of fuse design.
The NEC would not allow you run 600 Volts on a 600 Volt rated wire. The rating has to be substantially above the nominal applied voltage. Generally the rating has to 1.5x the nominal applied voltage at a minimum.
1 Like
The part of my brain that processes ‘regular’ math was burned out during gestation, so I never was able to understand electrical math, or grasp Ohm’s Law.
So how 120v and 180° become 600 is hopelessly beyond my ability to grasp…!
(If it was, I’d have made a load of money by now as an electrician or elect. engineer)
Being a business type and not an engineer type there are many things I don’t understand and don’t want to understand. I’ve done substantial wiring, plumbing, carpentry, etc. you don’t have to understand, just find the correct procedures and copy them.
2 Likes
Of course they are, that is most definitely part of the design for voltage rating. It’s called creepage distance and would be no different than if you had solder blobs across the circuit board or cartridge fuse body, reducing the dielectric withstand distance between the fuse ends/conductors. Because they cannot guarantee the distribution of molten particles inside the envelope, the distance between conductors and fuse envelope material are all part of the voltage holdoff design in the event of a current overload to ensure the arc extinguishes.
Some years back, we used 2 foot sections of thin walled copper pipes for our high current inverter designs used in plasma treating systems as a last line of defense. They tended to “fail” spectacularly. As with anything, the terms high voltage and high current are relative…
A 120 Volt AC sine wave circuit peaks at 169.7 Volts DC. The root mean square average is 120 volts and is equivalent to 120 volts DC for resistive loads. So a 600 Volt AC circuit would have 849 Volt peaks.
1 Like
So if I set my multimeter to 500V DC, and stuck the probes in a household receptacle, I’d get a reading of approx. 169-170V?
Never knew.
I was in ‘special’ schools from grades 1-12, so there was no actual knowledge imparted, or gained, to obtain my HS diploma.
Thanks dude.
No, most DVMs will show the RMS value of the AC voltage. If you want to see real-time peak to peak values, you need a true RMS meter than can also display peak or an oscilloscope…
Thanks Twin:
See, this is the basic stuff I wish they taugh me back in high school, even though I was sent to effed-up school because of my home situation.
Instead, they taught us Shakespeare, which had no practical life use.
Many classes you take have no immediate practical life use but will benefit you greatly. While Shakespeare may not seem like it’ll help you, it’s far more long term benefits than taking a cooking class.
1 Like