Shutoff switch wire size and distance

[jrob4267]

Hello, newbie here with a general beginners knowledge and vocab concerning electrical systems and dc in general. I’m currently working on a ground up, custom build with no electric when purchased, at its framed out stage.

This is what it looks like now after many hours!

My main question is concerning gauge of wire from a 100ah battery to the shut off switch and how far away it can be.

I have a few options on where to place the shutoff switch. (I know, poor planning, but this where I’m at!)

My first choice (most aesthetically pleasing and convenient) would be approx 10’ from battery to switch and 10’ back to battery compartment.

Second choice (convenient but not pleasing): approximately 3’ to and from

Last choice (read, don’t want to do this one if at all possible - not convienent at all, looks great cause you can’t see it!). At battery, less than a foot each way.

A couple questions:

Does distance matter, within reason, as long as wire is sized properly?

For each choice, what is the correct wire size?

Thanks in advance,
Jim

 

[GTS225-TNT]

Here's the perspective of a retired electrician. That master switch, (as applied to a drag race car), is to kill all power in the event of a crash. From an electrician's point of view, a master switch does the same thing, BUT.......just having a switch offers no protection in the event of a damaged wire grounding out and causing overcurrent and potential fire.
T'were me, I'd find a way to mount that master as close as possible, (right next to), your battery. Barring that, mount a replaceable fuse holder right at the battery positive, and size it according to your full potential load. This way, should that primary power wire get damaged, either out to the switch, or back from it, the fuse will blow and protect your investment.
You can always troubleshoot the problem later, as you'll still have your camper (relatively) intact, rather than a pile of charred wood and melted foam.

Roger

 

[GTS225-TNT]

Sorry.....didn't address the distance question. In the lengths of a camper, distance isn't going to matter much at all, unless you're REALLY trying to engineer things right to the ragged edge, like sizing the wire for 1 amp draw and nothing more. Even then, wire isn't engineered that way. Ampacity tables can be found on-line for wiring under different environments.

You'll have to clarify what you mean in your last question of "for each choice, what is the correct wire size?".

Roger

 

[jrob4267]

There will be a battery post mounted fuse. Thanks for your response.

 

[Grummy-TNT]

How far away the switch is is not critical, however, the location of the switch so it can be handy in an emergency is probably more important. As long as you properly fuse the wire as close to the battery as possible, the switch can be just about anywhere because you are using it as an On-Off tool. If the wire is routed poorly and shorts out, it doesn't matter where a switch is put because the fuse is supposed to shut things down when things go bad.

Distance certainly matters for amp draw however. You first must know what your potential amp draw is going to be in order to know what size wire you need. There will be a big difference in both safety and cost to run 10' out and 10' back between drawing say, 20A or say 150A. Note that if you see any wire that seems tons less money than another, it could be copper coated aluminum which I would avoid at all costs. You want pure copper.

So, back to amp draw and wire size. As an example, for a 20' run capable of handling 20A, you should use at least 8G. To go that distance where an Inverter may draw 150A, you need 2/0 G and 20' of that will run you at least $100 for copper. Too, understand that if you need to draw inverter level draws, you have to also check that your battery is made to deliver that draw as many 100Ah lithium batteries for example will shut down if you try to draw more than it is rated for.

So, you MUST know how much current will be on those wires before you can choose a size. If you search on line for DC wire ampacity charts, you can find many... here is one:https://www.qualitypowerauto.com/Wi...V2bvJdnnBMl70UFMbUoVPTBPjyz1jO30B3oybJfH_Iny9

 

[Rich796]

Low volt DC wire gage, amp ratings. Vary much more, than they do for residential 120/240v AC. For run lengths.

A 10 foot wire run in low volt DC. Could easily require a step up, of a gage or two. To meet the required amp rating, and situational use.

100 amp 3 feet or less you are probably good at 4awg. 10ft + 2awg. This is assuming a free air install, and the actual need to pull a 100amp draw continuously/frequently. ( Which would be highly unlikely, if you are only running a single 100amp battery )

If you do not need to pull that many amps frequently or ever. You can down grade your wire selection. To what your actual needs/usage is.

You can put the disconnecting switch where ever you want. ( it should be conveniently located. Incase of an emergency. As stated above ) It's sole purpose is to disconnect the main feed power. From all distribution/fuse panels/devices/outlets/equipment, in the trailer.

The battery terminal, Inline replaceable fuse. Is the down stream circuit protection. For the disconnecting switch wiring.

If your only draw is some lights/usb chargers and a fan. You may only need to size your disconnecting switch/wiring. For 20 or 30 amps. Or 12/10/8 gage depending on actual amp draw and wire run lengths.

( there is no reason to run 100amp rated wiring. In this situation. It would be completely over kill. And, needlessly expensive. )

If you are going to be running heavier loads an A/C and high wattage inverters. You'll need to size/connect them appropriately.

 

[Wolfgang92025]

Found this on the Net....

 

[Rich796]

Is that a DC low voltage, automotive/RV rated chart ?

The two smaller charts here, at the bottom. Give rated amps per gage, per run length. Based on 3 & 10% voltage drop.