help with fuse size

[Redrig]

Hello all,

I am in the process of doing a total re-wire of my 1977 OMC, it is an 18 footer and the wiring right now is a mess, the fuse block is only 4 fuses with many assecories attached to those 4, plus the wiring is a total rats nest. Many of my switched accessories are spliced together, it just needs to be overhauled.

I have bought all new gauges, switches and a new 14 gang fuse block with ground bar for it. (here from Iboats)

the gauges and switches are pretty stratight forward but I have a question on what fuse to run for each of my accessories or a rough guestimate, like I said right now there are several spliced into the old style glass bullet style fuses.

the following are my accessories and keep in mind this is a 1977.

OMC electric tilt motor (currently not fused just ran direct)
Blower
Bilge
Wipers
Horn
instrument lights
bow\stern lights
fish finder
cd player
cigarette lighter

Any help on approxiamtely what fuse for each of these would be great.

Thank you.

 

[boat1010]

Re: help with fuse size

I'm not real sure about all the things you have listed but was thinking that if you look in the owners manual for you car it would give you some ideas for what they use on the car. I.E. windshield wiper, blower.... well now that I start listing, the car has just about all the things listed. Hope that helps a little..

 

[Silvertip]

Re: help with fuse size

Hello all,

I am in the process of doing a total re-wire of my 1977 OMC, it is an 18 footer and the wiring right now is a mess, the fuse block is only 4 fuses with many assecories attached to those 4, plus the wiring is a total rats nest. Many of my switched accessories are spliced together, it just needs to be overhauled.

I have bought all new gauges, switches and a new 14 gang fuse block with ground bar for it. (here from Iboats)

the gauges and switches are pretty stratight forward but I have a question on what fuse to run for each of my accessories or a rough guestimate, like I said right now there are several spliced into the old style glass bullet style fuses.

the following are my accessories and keep in mind this is a 1977.

OMC electric tilt motor (currently not fused just ran direct)
Blower
Bilge
Wipers
Horn
instrument lights
bow\stern lights
fish finder
cd player
cigarette lighter

Any help on approxiamtely what fuse for each of these would be great.

Thank you.

Owners manuals for each of the items will list MAX current draw. Fuse about 10% above that but NEVER higher than the ampacity of the wire feeding the accessory. But here are some estimates.

Blower, bilge, wipers and horn are very likely in the 10A range.
Instrument and NAV lights will be fine with 5A fuse.
Fish finder will be fine with a 3 amp.
CD player probably needs a 5 amp if it has any output power to speak of.
The Accessory receptacle is a question mark since what you plug into it determines how much protection you need. The general practice would be to fuse it for the ampacity of the wire you wired it with. Remember, the fuse doesn't protect what's plugged into it -- it protects the wiring going to the receptacle. If a problem exists in whatever you plug into the receptacle it will be toast anyway.

 

[Redrig]

Re: help with fuse size

I'm not real sure about all the things you have listed but was thinking that if you look in the owners manual for you car it would give you some ideas for what they use on the car. I.E. windshield wiper, blower.... well now that I start listing, the car has just about all the things listed. Hope that helps a little..

Good idea, I will do that.

maybe I will just run a 25 for the bilge and blower.

what do you think about for the OMC tilt motor ? right now it is just ran directly and not fused. should I fuse it? or just keep it as is?

I would imagine that motor has a decent amount of amp draw.

 

[boat1010]

Re: help with fuse size

It should have a fuse. You are just asking for trouble to have anything electrical that isn't fused. I would think a 15 or 20 amp would be big enough.

 

[NYBo]

Re: help with fuse size

The tilt motor should be drawing power from the engine's wiring harness, which will be protected by a fuse or circuit breaker.

 

[ac0j]

Re: help with fuse size

Most late model stereos have a fuse either in the back of the radio or in the wireing at the radio, most are 10 amps.
The fuses in the fuse block are there to prevent wire damage or fire in the event something shorts out. A blower or bilge pump will only draw the current it needs to operate, NO MATTER what size fuse you put on it. If it gets shorted or locked up, it will draw an infinite amount of current. SO fuse size is not that important, as long as it is big enough to allow the item in question to run normally, and not so big that the wireing fuses before the fuse. You could put 30 amp fuses in everything, If it blows the 30 amp its a bad circuit or part anyway, and the fuse will blow and protect the wire as it should.
Fuses blow because of a problem, they DO NOT prevent problems.

 

[Silvertip]

Re: help with fuse size

maybe I will just run a 25 for the bilge and blower.

If you mean use a 25 amp to protect BOTH the bilge pump and blower, that is a big mistake. The blower and bilge draw very different amounts of current. Therefore the wiring on the bilge pump would burn up before the fuse blows. Think about what you are doing here. A 25 amp fuse would need about 12 gauge wire.. The bilge pump probably has 16 gauge wire which is much smaller and cannot handle 25 amps if a short should occur. Wire and fuse sizes must be considered carefully. You can use fuses smaller than the rating of the smallest wire in the circuit, but definitely not larger.

 

[ve3rpm]

Re: help with fuse size

Actually a 25 amp fuse is in the 10 gauge range. 12 gauge is 20 amps max with an allowable constant current draw of no more than 16 amperes. Also, don't forget to size your ground wire accordingly... I've seen people forget the other half of the equation.

 

[NYBo]

Re: help with fuse size

Actually a 25 amp fuse is in the 10 gauge range. 12 gauge is 20 amps max with an allowable constant current draw of no more than 16 amperes. Also, don't forget to size your ground wire accordingly... I've seen people forget the other half of the equation.

Those sound like the wiring specs for 120 VAC.

 

[zopperman]

Re: help with fuse size

Posting mainly to subscribe.. doing a very similar project. Good luck bud

 

[Grandad]

Re: help with fuse size

Redrig, you've got a good start by purchasing a fuseblock with an adequate number of fuses. Do yourself a big favor and put each component on its own fuse. Putting the bilge pump and blower on the same fuse means that when one of these blows the fuse, you lose both of these critically important items. Also, it makes it more difficult to troubleshoot why a fuse blew. One more thing; as you've already recognized, grouping 2 devices often requires increasing the size of the fuse. As the fuse size increases, you lose the protective benefit of the fuse. By the way, my bilge pump, an Attwood V1250 that can pump 1,000 GPH at a 3' head draws only 2.6 amps and is marked maximum fuse size 4 amps. My blower draws 3 amps and is also marked maximum 4 amp fuse. - Grandad