Determing what size fuse to use

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Emperor62

Member - Posts: 2

Joined: May 11, 2005

Posted: August 02, 2005 at 7:53 PM / IP Logged

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/

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geepherder

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Posted: August 02, 2005 at 8:36 PM / IP Logged

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

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

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Mad Scientists

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Joined: February 07, 2004

Location: United States

Posted: August 03, 2005 at 5:25 PM / IP Logged

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

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stevdart

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Posted: August 05, 2005 at 8:32 PM / IP Logged

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.

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

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Randy Ewalt

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Joined: July 08, 2005

Location: United States

Posted: August 12, 2005 at 4:40 AM / IP Logged

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.

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geepherder

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Posted: August 13, 2005 at 5:48 PM / IP Logged

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.

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

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Determing what size fuse to use

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