What fuse to wire in-line

[4x15mph]

I am installing an 2nd auto bilge and want to wire this directly to the battery like others have done. I know I need to put a fuse in-line. I don't know anything about electrical

Pump is 12V, 3 amps and will use 18 gauge wire for connections.
1) how do I know what size fuse to use? I ordered a marine, 10 amp... is that too high or low?
2) where can I get 18 gauge wire that can be used in this marine application? Can I use any kind as long as i use marine connectors?

Thank you

 

[mb300sd]

10 amps should be fine to protect 18 gauge. You should be able to find tinned marine grade on ebay, but I've never had issues using standard automotive TXL, soldered with marine heat shrink on both ends.

 

[subysti]

As far as the fuse goes you answered your own question. The pump,is 3 amps. 18 gauge wire is a max of 4.8 amps so I wouldn't go over a 4 amp fuse otherwise the wire would just melt and could cause a fire.

 

[Bill D]

I used this wire for my second bilge install. Just make sure you buy good quality tinned wire for marine applications. 18AWG is rated for a max of 20 amps, so your 10 amp fuse will be fine. You don't need special connectors, just make sure they are crimped properly and use heat shrink to prevent corrosion. Selecting wire gauge in a 12V system is really about limiting voltage drops over a length of a run. When there is too high a voltage drop, you will increase current draw and create heat.

http://www.amazon.com/Duplex-Tinned-Marine-Wire-Black/dp/B00MI59JD4?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o04_s00

If you want to double check the current ratings, there is a good chart here.

http://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity

 

[subysti]

Not sure where west marine gets their info from but I do this for a living, 18awg at 20amp draw will melt if its anything over 6" but even then I wouldn't trust it. The pump is 3 amps so just use a 4 or 5 amp fuse. 20 amps you're looking at 10 or 12 awg. Look at your circuit breakers at home.

 

[Bill D]

For future readers, there is a really good wire selection chart at the link below.

http://assets.bluesea.com/files/resources/newsletter/images/DC_wire_selection_chartlg.jpg

 

[2nazt]

I have my second pump waiting to install and it says the fuse to wire inline right on top and on manufacturing company website also. It is rule 27s 1100gph and calls for a 5amp

 

[4x15mph]

Lots of great info; my pump came and the instructions have a chart that shows 2.5A for the current of this pump. The manual also says to use a fuse as specified in the chart. It sounds like the fuse needs to be chosen to guard against the amperage rate at which the wire used will actually melt and the amperage of the electronic/device is part of that equation that factors into what wire is used (18 AWG in this case). I think I get it and I am glad I asked since having the 10amp fuse would not have done much given that my wire would have melted before then. Good to know

@subysti , I think you answered this and recommend no more than 4 amp. I will shoot for 3-4 amp.

Thanks everyone for the help

 

[4x15mph]

And then there are AGC fuse types versus MDL... Unless someone tells me not to use AGC (fast acting), I will go with AGC.

 

[2nazt]

@4x15mph how did it turn out? I'm trying to decide how to wire mine. Just run a secondary switch behind helm until I order a new switch panel. I do not have a battery switch yet so direct to battery is not an option. I also need to stop and get the wire tomorrow to finalize it.

 

[4x15mph]

Turned out great. You can wire it directly to the battery even without a switch if you buy a pump that has an automatic float switch. It will only cycle on power if/when the water triggers the switch which should not happen often/ever if you aren't on the water.

I wired in a fuse between the battery and the new pump right at the battery so that it is easy to change.

 

[2nazt]

Awesome thanks! I bought an automatic like the stock but 1100gph.

 

[4x15mph]

That's a big pump so make sure you check out the recommended fuse as well as the hose diameter that goes along with that pump. The hose for mine was 3/4" and I would expect your pump to use the next step up, 1 1/8" diameter. You will like having this extra backup or redundancy

 

[2nazt]

It is 1 1/8" hose and pump calls for an inline 5amp fuse. We mainly do ICW and the ocean so it's great peace of mind for sure.