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hi youtubers jeff cote here with ask pys

so we've got a question here from a

fellow boater and he asks

jeff where does the idea that the

alternate refuse should be at least

1.25 times the alternator output

good question i've seen this before

right

and this is important when you're fusing

a wire especially

a charger an alternator for instance or

solar

you want to make sure that you never

have nuisance tripping

so if your alternator for example is

outputting 100 amps right it's a 100 amp

alternator

are you going to put 100 amp fuse on

there because remember 100 amp fuse

means they can tolerate 100 amps but you

normally don't want to ever

size a fuse for maximum rated amperage

and expect it to run there it's like for

example our cars might be able to rev up

to 6000 rpm

but we're not redlining our cars same

thing with for example shore power

a shore power breaker might be 30 amps

but you should not be running your shore

power at maximum

amperage at 30 amps all the time it

allows you to go to 30 but you know if

you're

close to always being at the max you

might get nuisance tripping

and if you have nuisance tripping on

your alternator you're not just

blowing the fuse you're blowing up the

alternator

so when i'm sizing a wire that is

connected to an alternator i'm fusing

that alternator what do i want to do

i want to make sure that that alternator

will never ever

accidentally trip that fuse because if

it does

i don't only learn the fuse but i'm also

losing the alternator

so what we do is we do a ratio of 1.25

so if i've got a 100 amp alternator i'm

going to

make sure that the wire can handle 125

amps

no problem and i'm also going to put a

fuse that is

rated for 125 amps therefore i am

preparing or preventing the alternator

from ever blowing up that fuse

i am now also running an alternator

less than the maximum amperage that the

fuse and the wire can handle

so well beyond or within the

capabilities of that wire and that fuse

and then i never get nuisance tripping

so that is the logic behind

fusing an alternator but same thing for

battery charger and

solar you always want to give yourself a

little bit wiggle room so that you don't

have nuisance tripping

thank you for watching this pys video if

you've got further questions

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you

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