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Wire gauge

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PrivatelyJeff

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I am installing an auxiliary fuse box in my car to run my radios and I was wondering what guage wire to run from the battery. I will be running 2 scanners, plus provisioning out for a CB radio and a ham rig for later (25 amps total). The fuse box will also be connected to a relay that is controlled by a low voltage disconnect switch to prevent drain.

Also, on a parallel circuit I will have a 400 watt inverter (I mainly use it for its USB ports). What guage should I use for that? It would also be wired similarly. The battery is on the drivers side and the equipment will be in the center console area and this is a vert small car.

I’ve looked around online but everyone says different things so I’m lost.
 
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SteveC0625

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Figure up the amp load on each circuit then use any one of dozens of wire gauge charts that are easily found on the net to figure the minimum wire size needed. It's good practice to go a size or two larger than you think you need.

 

SteveC0625

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I’ve looked up several but they all give different advice.:(
Take it from an experienced installer and upfitter: you can not go wrong by using the largest recommended size. If you use wire that is too small, it's a guaranteed recipe for all kinds of troubles, not the least of which is fire.
 

PrivatelyJeff

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Take it from an experienced installer and upfitter: you can not go wrong by using the largest recommended size. If you use wire that is too small, it's a guaranteed recipe for all kinds of troubles, not the least of which is fire.
But that’s the problem. Some say go with 8 gauge, which would be fine except I can’t find connectors for the relays. Would 10 gauge work? I can find plenty of stuff for that.
 

KC4RAF

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Do as Steve posted, figure the amperage of all the devices you plan to install, add those figures, look on the chart he added in his post. Best bet is to ALWAYS go higher so you can add something later on.
Example:
CB=5 amps
scanner=.25 amps
Ham transceiver=25 amps
total=30.25 amps.
wire size=~12 gauge (10 foot run at 36 amps = 12 gauge
Yeah, 10 gauge will work.
And as far as connectors go, you just have to search. There's several online stores that have what you need.
(fwiw; I would go at least 1 trade size larger than that chart shows.)
 

PrivatelyJeff

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Do as Steve posted, figure the amperage of all the devices you plan to install, add those figures, look on the chart he added in his post. Best bet is to ALWAYS go higher so you can add something later on.
Example:
CB=5 amps
scanner=.25 amps
Ham transceiver=25 amps
total=30.25 amps.
wire size=~12 gauge (10 foot run at 36 amps = 12 gauge
Yeah, 10 gauge will work.
And as far as connectors go, you just have to search. There's several online stores that have what you need.
(fwiw; I would go at least 1 trade size larger than that chart shows.)
Thanks. I can find stuff for 10 gauge and smaller easily but 8 gauge and larger is impossible. I couldn’t easily find 8 gauge spade connectors for the relays anywhere. I’m still trying to find 10 gauge relay harnesses to make wiring easier.
 

mmckenna

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Thanks. I can find stuff for 10 gauge and smaller easily but 8 gauge and larger is impossible. I couldn’t easily find 8 gauge spade connectors for the relays anywhere. I’m still trying to find 10 gauge relay harnesses to make wiring easier.
Looks like you are going to do a proper job of this, so here's some info I can add to what's above.

There are purpose built devices that will handle low voltage disconnect, high voltage disconnect as well as timer controlled ignition sense. Lind, Charge Guard and a few others are the ones that come to mind.
While they'll cost you more than just a relay, they provide some nice features and make the whole install a bit easier, as they are designed to run 30 amps (or more depending on the model). They have appropriately sized connection points. These are the sorts of things you'd commonly find controlling power for emergency vehicles. They are often worth it since they put many features in one box and make it a lot easier to wire up.

Shop around on E-bay, and you can find new or like new ones for $20 or so. Last one I bought looked brand new, in the original box and was $20 bucks.

https://lindelectronics.com/products/shutdown-timers/
Havis Products | CG-X Chargeguard-Select

Lind Electronics Shut Down Timer Model SDT1230-014 LR | eBay
Havis CG-X ChargeGuard Select Control Module | eBay

etc. There's a lot on E-bay, or you can pick up a new one if you shop around.

As for the wire size, there's a couple things to look at:
1. current draw.
2. allowable voltage drop
3. conductor "loop" length

Using this formula, it'll tell you what size conductor you need. There are some online calculators that will do it for you:
DC Cable Sizing Tool - Wire Size Calculator - MM2 & AWG - solar-wind.co.uk (be aware, length is in meters. Also, use the "loop length" for the conductor length, that's the length of the + feed AND the length of the return/negative lead combined.

There are other out there.
I've got the formula at work, not here at home, so I can get that for you if you want it.

As for the conductors themselves, make sure you get the wire that is rated for automotive use. The correct cable will have an SAE-J number on it, like: SAEJ1128. The jacket is rated for the heat, gas, oil, etc. that it will be exposed to under the hood on it's way to the battery. In addition to the insulation, it'll have a fine stranded wire inside that works well in environments that will be exposed to vibration.

As for finding the crimp connectors, they are out there. When you go above 10 gauge (numerically lower numbers) you won't be able to crimp with your hardware store crimpers. Running a smaller cable might be fine for what you are doing, but don't do it simply to save money on crimp connectors.

Using the right install parts will prevent a lot of headaches later. Vibration, improperly crimped connectors, corrosion, etc. are all things that can make you go crazy down the road.


Most of all, use the right type of wire for this. The THHN type stuff you'll find at the local hardware store isn't the right wire. While the TH series wire will often have some oil resistance, they use larger/stiffer strands that can risk breaking with vibration.
 

PrivatelyJeff

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Thanks. This is the wire I’m looking to use.

InstallGear 10 Gauge 25ft Black and 25ft Red Power/Ground Wire True Spec and Soft Touch Cable https://www.amazon.com/dp/B01NBE1YQ4/ref=cm_sw_r_cp_tai_a6zZzbZBZWD6W

I was just looking at using a simple LVD and relays because I don’t need timed power control, but I’ll look into them. It’s just in case something gets left on (not likely), I can still start my car or use a small booster if need be. I also have an ammeter wired up already so I can see what’s up if something goes wrong.

As for wire, I’m thinking 10 gauge is fine. Each run will be about 6 feet. My car is a 2011 Ford Fiesta, so it’s not very big. The wire will come off the battery, straight to a fuse, then relay, then cab of car, where it will hit a fuse block with built in ground block (or the inverter for that line), where each device will pull off its power and also ground.

The inverter will ground back the battery and the fuse block will ground to the nearest grounded bolt I can find.

I’m going to wrap all wires in shrink tubing and cover it in wire loom as well, from battery to their terminal point.
 

mmckenna

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That's copper clad aluminum wire.

It won't have the same current capacity as a copper only conductor of the same size. Also, aluminum doesn't take kindly to frequent flexing.
It'll work, but I might say upsize it. I'd also suggest getting the copper only wire. Again, it'll cost a bit more, but it'll be a better install.

Back in the 70's, they used aluminum wiring in some residential construction. That didn't always work out well. I'd be hesitant to use it in a car. I know stereo guys use it, but I'd shy away from it myself.

The short wire run will help you. Less resistance in the sorter path. That will work in your favor.

Heat shrink would be overkill for covering the entire length of wire.
I'd use it over the crimp connectors, get the "marine" grade if you can. Marine grade heat shrink has an adhesive liner that melts when you heat it up. It does a great job of sealing the connections from corrosion and helping prevent flexing. For the rest of the cable run, the split loom is sufficient.
 

mmckenna

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Thanks for the heads up

So like this then?
Grand General 55261 Red 10-Gauge Primary Wire https://www.amazon.com/dp/B00INVF40E/ref=cm_sw_r_cp_tai_WZBZzbMJG3SJW
I'm a bit skeptical of that.
Yes, it would work. If you read the reviews, there's a few suggestions that it's not truly 10ga wire. It is also not showing the SAE-J rating. Other might say I'm taking it a bit too far with the SAE rated wire. I know what I'd use at work.

Probably, work just fine. But, for a little bit more, this has the right ratings:
https://www.amazon.com/JEGS-Perform...TF8&qid=1506661637&sr=1-23&keywords=10ga+wire

I know heat shrinking the whole thing is a bit much, I tend to like to over do things as a precaution and to also help wire management as there may be other wires running in the loom run.
Well, my feeling is that heat shrink is expensive. If you get the right cable, you don't need it. Figuring out the difference in cost would tell you.

You'd probably be better off purchasing the correctly rated cable and putting it in split loom and securing it all well along it's path. That will prevent damage.

Instead of purchasing all that heat shrink, get the marine grade stuff I mentioned above for your connectors.
 

mmckenna

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Would this work (with the proper protections)?
https://www.ebay.com/i/172871115118
Looks like it would, but hard to tell if it's any good.

You'd still need to enclose it inside something for protection.
By the time you do that, you might be able to get a charge-guard unit for the same price.



Low voltage disconnects are nice. They'll do what you want. Basically protect your battery if you leave the radios on.
Personally, I've found the timers to be a good option. They'll provide the LVD, plus they will automatically connect and disconnect power based on the ignition. With the timer, you can set it to leave power applied to the radios for a set period of time. Nice if you want to sit in your car and listen to the radios.
 

PrivatelyJeff

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I’ll buy that wire then. :) I’ll definitely use marine grade on the connectors but I’ll still probably still use standard on the rest of the run as I already have a small spool of it from a previous project. Plus it allows me for better management of wire inside a loom run, as the run may have other wires running parallel to it.

As for those LVDs, I found them on amazon and they have fairly good reviews on them. I know I’ll need some boxes for them, but that’s ok. I would use those more expensive ones if this was for a critical system, but they would triple the cost of this project so far as I would need two of them for each circuit.

I don’t want timers as I don’t want these devices to lose power unless the battery gets critical. I turn them off when I get out anyway. The disconnects are to purely prevent accidental discharge of the battery. The car also has its own LVD built in to prevent other stuff inside from draining the battery.
 
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