Fusing for my amps

Tim · Post by **Tim** » Sun Aug 23, 2009 4:28 am

Just a quick question, I am gonna order the rest of my electricals today and I need to know how to figure what size fuses to get.

My dist. block for my amps takes the anl fuses two of them, one for each amp.

My sub amp has two 50's in it.

My mid amp has two 25's in it.

Will it be as simple as 1 100 amp for my sub amp
and 1 50 amp for my mid amp??

I also need to know what size to get to go from the battery.

I know there is a formula for all this, but I cant remember what it is.

Just needin a little help.

Thanks,

Tim

Ryan from Ohio · Post by **Ryan from Ohio** » Sun Aug 23, 2009 6:49 am

Same size or close to on the high end if there is no exact fuse for the distro block.

The front fuse should be the sum of the amp fuses plus some extra. Since your at 150 I would go for a 200 amp fuse.

Tim · Post by **Tim** » Sun Aug 23, 2009 10:58 am

alrighty then thanks Ryan. I really sorta thought I was on the right track but I just wanted to make sure and ask somebody.

thanks again,

Tim

falkenbd · Post by **falkenbd** » Mon Aug 24, 2009 6:54 am

Your amps have their own fuses...

SO, you aren't really fusing to protect the amps, you are fusing to protect the car (from wire shorting)...

Therefore you need to fuse for the wire size that is being used....

You CAN go smaller on fuses, as it won't hurt if you won't use the full capacity of the wire (and you shouldn't)

SO, the fuse NEAR THE BATTERY, needs to be no bigger than the current that the wire is rated to carry....

If you step the wire size down in the trunk, you need to fuse each new smaller wire (FUSED DISTRO BLOCK)

BUT, if you use a small enough fuse up front, you don't need fuses in the back....

Lets say you have a 4 awg wire from battery to trunk, if you split that into 2 8 awg wires, and put a 50 amp fuse up front, you would still be safe because the 8 awg wire shorting would still trip the fuse up front.

Your questions would pretty easily be answered if you had gone here http://bcae1.com/wire.htm

Here is a chart of max fuse rating for wire size (From bcae1.com)
00 awg 400 amps
0 awg 325 amps
1 awg 250 amps
2 awg 200 amps
4 awg 125 amps
6 awg 80 amps
8 awg 50 amps
10 awg 30 amps
12 awg 20 amps
14 awg 15 amps
16 awg 7.5 amps

Bwcad1 · Post by **Bwcad1** » Mon Aug 24, 2009 6:59 am

Ryan from Ohio wrote:Same size or close to on the high end if there is no exact fuse for the distro block.
The front fuse should be the sum of the amp fuses plus some extra. Since your at 150 I would go for a 200 amp fuse.

and that would cause fires on 8ga and some 4ga wires.

Falken is correct the fuse goes with the wire not the amps. Your wire's capacity should already be bigger than what your amp should draw meaning your fuse should be based on the size of the wire not the size of the amp. On my 1/0 i use 250amp fuse (based on length) and on my 4 Gage usually 80-100 again based on length.

Ryan from Ohio · Post by **Ryan from Ohio** » Mon Aug 24, 2009 11:00 am

Bwcad1 wrote:and that would cause fires on 8ga and some 4ga wires.

Yes fusing that high on those sizes may be an issue.

He is asking about fuses sizes. Not what wire to use...

You can fuse for the wires ratings or fuse as needed. Makes no difference. If his amps total 150 he can fuse 200 at the battery without issue. If its 1/0 he could fuse higher without issue- but theres no need.

I prefer to fuse as I stated simply because I dont want to have 300 amps to pop my 1/0 when 200 is mroe than enough as is...

matter of preference here Tim. The only "wrong" was is to under fuse or over fuse the wire.

Bwcad1 · Post by **Bwcad1** » Mon Aug 24, 2009 11:01 am

Ryan from Ohio wrote: I dont want to have 300 amps to pop my 1/0 when 200 is mroe than enough as is...

What? Please explain to me how 200 amps blowing a fuse would be any diffrent than 300amps? I prefer to run fuses based on gage because a smaller fuse will cause voltage drop so fuse at the wire's rating and you wont have to worry about it.

Ryan from Ohio · Post by **Ryan from Ohio** » Mon Aug 24, 2009 11:31 am

Ummm

It blows at 200 amps instead of 300? Which is less than 300.

I dont have voltage issues/drops. Only time thats been an issue is when alts die or are about to.

falkenbd · Post by **falkenbd** » Mon Aug 24, 2009 11:42 am

Ryan from Ohio wrote:Yes fusing that high on those sizes may be an issue.
He is asking about fuses sizes. Not what wire to use...
You can fuse for the wires ratings or fuse as needed. Makes no difference. If his amps total 150 he can fuse 200 at the battery without issue. If its 1/0 he could fuse higher without issue- but theres no need.
I prefer to fuse as I stated simply because I dont want to have 300 amps to pop my 1/0 when 200 is mroe than enough as is...
matter of preference here Tim. The only "wrong" was is to under fuse or over fuse the wire.

He did actually ask what wire to use in the first post...

Fuse for the wire, or smaller, period. If you NEED a bigger fuse than recommended for the wire, you have other problems.

TIM:

This is a GREAT TOOL for figuring out what wire and stuff to use:

http://bcae1.com/images/swfs/systemdesignassistant.swf

Everyone needs to read bcae1.com over and over again, if you are or are hoping to make money on car audio, you should know this stuff like the back of your hand...

Ryan from Ohio · Post by **Ryan from Ohio** » Mon Aug 24, 2009 11:56 am

falkenbd wrote:He did actually ask what wire to use in the first post...

All I seention of is what fuses from the rear block and the front inline off battery.

unless you mean another post.