Lox voltage fuses and ratings, determining low voltage oversurrent protection.

ACDCBag420

Member
Location
Rutlant Vermont
Occupation
Solar
Hey everyone thanks in advance for all the feed back this site is usually one of the best places to ask questions like this. I'm having problems finding better information about sizing overcurrent protection for low voltage systems. My problem is that I need to protect a battery monitor with a nominal voltage of 48 volts dc. The manual calls for using an inline fuse with an overcurrent protection of five amps or less. After looking at what is readily available I picked up an automobile fuse and inline fuse holder. My problem is I got home to find out that the fuse is rated for 32 volts. Im seeing online that a low voltage DC system is anything under 150 volts. Is it going to be safe to use a 32 volt 5 amp automobile fuse to protect my battery monitor with a nominal voltage of 48 volts DC. About to order an inline fuse holder rated for 600 Volts with a ferraze fuse that can take one amp, but still wanted to post in here to see if anyone could answer my question. Thanks for the feedback.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Automotive fuses are designed with a shorter element for less voltage drop as compared to a higher-voltage fuse designed to open with a larger gap to avoid arcing.

Between you and me, I would use that fuse, but to be absolutely compliant, it should e the next-higher rating, like 150v.
 

WasGSOHM

Senior Member
Location
Montgomery County MD
Occupation
EE
See Mr. Fine's answer.

As near as I can tell, fuses are rated for voltages because a fuse that melts too quickly causing a very short duration arc will cause a high voltage spike in a circuit that contains a coil.
So a 32v fuse should not be used with line voltage circuitry.

The formula is
induced voltage in a DC circuit = circuit inductance x the change in current divided by time.

If 8 A goes to zero in a millisecond in a circuit with 0.1 henry inductance you will get an 800 V spike for 1 millisecond.

Circuit distributed capacitance reduces this and is hard to figure so I think fuse voltage ratings were determined by experiment and experience.

If a component fails after 7 years, was this because a wrong fuse voltage was used? Too high an ambient temperature? The fuse took too long to clear the overcurrent?
Good luck trying to prove this.

If you have a schematic, post it. Some circuits are hardier than others.
 
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