Wire guage size for Perko Switch

Tug · Posted: Tue Mar 30, 2010 12:36 pm Post subject: Wire guage size for Perko Switch

I have search everywhere but can not find any definative answer to this question. I know that wire gauge is linked to amps and lenght of the wire needed. I am installing a Perko Battery Switch...my batteries are less than 3 feet apart...the Perko switch will be no more than 6-8 feet away..i called a boat dealer and he said 10-12 gauge is good....than i called a mechanic and he said 3-4 gauge is all i need . Any one remember what size gauge wire they used when they installed their Perko Battery Switch...Thanks Tug

Captains Cat · Posted: Tue Mar 30, 2010 1:07 pm Post subject:

Are you talking about wires from the batteries TO the switch? If so, they need to be as big as the cables that are in your car that run from the batteries to the starter, etc. Those cables have to carry the starting current to your engines. They need to be as big as the cables that run from the switch TO your engine to start it.

If you are talking about the wires from the switch up to your accessories, I'd use at least #10, unless it's a longer run than 8-10 feet, then you should go down to #8 or so.

BTW, the bigger the guage on the wire, the smaller it is...

Charlie

cemiii · Posted: Tue Mar 30, 2010 1:26 pm Post subject:

I can't say this is definitive, but my boat banks are all connected with 2 gauge, tinned, 105 degree insulation marine wire. My deisel truck is all wired 2 ga. between the batteries.

2 gauge is the standard for short runs to carry loads up to 210 amps outside an engine compartment. Lugs should also be tinned and crimped. This takes a pretty heavy duty crimper.

Beside ampacity, voltage drop is another major concern with smaller gauge wiring. You may be able to get by with smaller gauge, but you will limit your future capacities (bigger alternator/ inverter, etc). Generally you want large enough wiring that you do not lose more than 3% of your voltage over the run. At 100 amps, you would lose about 3% over a 10' span (20' both ways) on 2 ga. I don't think I'd go less than that. I'm sure others will have input.

My wiring from the back of the boat to the panel is 8 gauge and protected by an 80A breaker near the battery.

Here is a good online source, I have had good service from, with reasonable prices. They will custom build your wires for a nominal fee if you provide the dimensions and they have professional hydraulic crimpers.

http://shop.genuinedealz.com/Marine%20Electrical%20Supply/

There are technical calculators there as well.

thataway · Posted: Tue Mar 30, 2010 8:24 pm Post subject:

I agree if you are going to be running the engine start through this switch, then you need at least as big as the engine start cables, or bigger. I prefer 1/0 or 00 for short runs like this. The run of 6 feet is really not just six feet, but also you have to add in the run to the engine and the ground back from the engine--which may be as much as 20 feet (round trip)--as noted above.

One of the issues you get into here, is fusing. ABYC suggests that any wire from the battery needs to be fused within 7" of the battery, with the exception of the engine start cable. For this reason the battery switch is kept as close to the batteries as possible.

I also agree with running #8 to the consol, if you have added any but miminal electronics, but puting a circuit breaker right after the switch.

tsturm

Tug · Posted: Wed Mar 31, 2010 6:30 pm Post subject:

I was just talking about the wires' that run from the battery(s) to the switch...i will put the Perko Switch as close to the batteries as possibe.

Tried that Marine Tex Tuesday...filled 4 screw holes from an old transducer that i removed. Temp..was only about 60 F and i used a heat lamp overnite. Seems to be in the process of setting ok.....doing some other screw holes tonite. Suppose to be around 21 C tomorrow ..plan on using that : Cetrol Marine Natural Teak : on my bulkhead...did the sanding and tapping today.
Thanks Tug