Determing what size fuse to use

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Forum Name: General Discussion
Forum Discription: General Mobile Electronics Questions and Answers
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=60565
Printed Date: May 15, 2025 at 11:58 AM

Topic: Determing what size fuse to use

Posted By: Emperor62
Subject: Determing what size fuse to use
Date Posted: August 02, 2005 at 7:53 PM

Anyone have a formula or technique for determining what size fuse to use ina connection? For example 2 relays to have a constant ground for a 5 wire pwr window setup using three wire switchs? Maybe bad example, heres another. Determing fuse rating for a fan relay. Appreciate it/

Replies:

Posted By: geepherder
Date Posted: August 02, 2005 at 8:36 PM

I was always told to fuse at 125% max safe current draw.

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My ex once told me I have a perfect face for radio.

Posted By: Mad Scientists
Date Posted: August 03, 2005 at 5:25 PM

You're supposed to fuse to protect the wiring, but you could always measure current draw and fuse slightly higher.. to use your example of fan relay, if you measure draw at 13 amps, fuse for > 13 amps.. say 15a or 20a fuse. Make sure the wires will not smoke before the fuse blows.

Jim

Posted By: stevdart
Date Posted: August 05, 2005 at 8:32 PM

Emperor, first you have to determine what wire size to use for the amperage draw. In those two examples you listed the power windows will draw a lot of amps but the fan will draw very little. Once you have the wire gauge, choose the fuse according to that.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Posted By: Randy Ewalt
Date Posted: August 12, 2005 at 4:40 AM

take the total amperage of the circuit and multiply it by .75 and that will give you your fuse size.I do this stuff for a living.You also have to take into consideration the current draw when the fan first starts running.

Posted By: geepherder
Date Posted: August 13, 2005 at 5:48 PM

I think you mean 1.25. That's what you learn in a military electronics classes. It wouldn't make sense to fuse a circuit below it's total amperage.

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My ex once told me I have a perfect face for radio.

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