FAQ:12v Wire sizes and Fuses Made Easy

[bdosborn]

Sick of the arguments so I deleted this.

[madjack]

...another good one Bruce...well done .....................................................

[bledsoe3]

Bruce, your recent posts on electrical items will make thing much less confusing for future builders. I wish you would have done this BEFORE I did mine. Is it easier now that certain members are not here to argue?

[bdosborn]

Is it easier now that certain members are not here to argue?

Jim,
I just didn't bother before.
Bruce

[Miriam C.]

Clear as rain water. Thank you Bruce! Anyone wanna make a sticky

[sdtripper2]

Aunti M:

Anyone wanna make a sticky

We are on top of this subject and have put this at the top sticky of the Electrical Secrets section.
Electrical Considerations when building a trailer START HERE

Go to the section 2) Discussion of trailer wiring inside and the use of a power panel and or using a a GFCI circuit:

Look for
Question:
Internal power panels, wire gauge questions & ground fault circuit (GFCI)?
And there below the question you will find>

BRUCE(bdosoborn) Discusses wire gauge and fuse sizes


Aunti M:
We will pick out such threads in the future with great data and keep adding that information to some of these
docs uP in the sticky sections under one title so all data will be in one place for easy finding.

Also go here for more ongoing Sticky inputs:
T&TTT Forum Suggests 5 Trailers for New builds HERE~
Hurricane Hinge, Hatch, Struts, Seals, Doors START HERE

[HotWheelsFiero]

Great write-up, thanks.

Instead of me wondering what will work and what won’t… could I just select the best wire no matter what I am running and just install it throughout the TD? Just in case an appliance/light gets “upgraded”? So, in that case could I wire the whole thing with 8g? Would the cost of doing such be cost prohibitive? Just wondering.

Thanks,
Bruce

[Nitetimes]

8ga??? You could certainly use that if some of your upgrades include installing a welder, plasma cutter a 30,000 BTU AC/Heat unit maybe a full size electric range.

And expensive doesn't even begin to cover that right now, you're looking at nearly a buck a foot for single wire stranded 8ga.
And the amount of work you would have to do would be the other thing that would keep me from doing something like that.

If you wire the whole thing with 12ga you will be more than prepared for anything you put in it. Except the supply from the battery to the fuse panel, you can use your 8ga for that.

[madjack]

Bruce, ol' buddy...running 8ga to everything would be akin to whacking an ant with a 16# sledge...it'll work but is extreme overkill...we use 14ga, which will carry 15a to everything but the battery to fuse block...we used 10 ga for that...this is all 12v stuff...we ran 14ga for the 120v stuff except for the power in line which is 12 ga...
madjack

[asianflava]

8ga from the battery to the fuse block would be fine. But the whole thing? You'd have to make a massive hole just for your cable runs.

[bdosborn]

Great write-up, thanks.

Instead of me wondering what will work and what won’t… could I just select the best wire no matter what I am running and just install it throughout the TD? Just in case an appliance/light gets “upgraded”? So, in that case could I wire the whole thing with 8g? Would the cost of doing such be cost prohibitive? Just wondering.

Thanks,
Bruce

See the "Don't know, don't care" section. That's about as generic as it gets.
Bruce

[bdosborn]

Bump.

[madjack]

Bruce, ol' buddy, I gave ya a sticky so ya wouldn't have to bump this excellent thread anymore...keeps the dents in check...doanchano
madjack

[Joe G]

Great thread!

I made a few wire gauge charts to use at work, and thought I'd post them for the benefit of everyone here as well.
I wire 8-10 old cars per year complete from scratch, and created these charts as a quick reference for choosing proper wire sizes.

Revised 5/7/08:
The main objective of this post was to illustrate how the length of a wire effects it's amp carrying capacity.

It has been brought to my attention that tiny RV's have more stringent electrical efficiency requirements than automobiles do, so it is a good idea to use heavier wire in your trailer than what you might find in your car.
Below is a revised wire chart that reflects the recommendations of professional TD&TTT builders:



(end of revision)


The following charts show the minimum wire gauge sizes required to meet two different maximum voltage drop requirements at 12 volts.

The first is for 10% voltage drop - the industry accepted standard for modern cars. I consider this the bare minimum for safety.

10 Percent Voltage Drop Chart

Personally, I prefer a larger safety margin, so I use the 5% standard shown in the second chart. My mentor in auto wiring thinks this is excessive, but I like to think of it as cheap insurance. In rare cases I even use a 2% standard for some electronic devices, but that's just total overkill for most applications.

5 Percent Voltage Drop Chart

Planning out your electrical system and making sure it's components are rated for the demands placed on them will help ensure that the electrical system will provide you with years of safe and trouble free service.

Anyway, I hope someone out there finds this useful.



Joe G

[brian_bp]

...I made a few wire gauge charts to use at work, and thought I'd post them for the benefit of everyone here as well.
I wire 8-10 old cars per year complete from scratch, and created these charts as a quick reference for choosing proper wire sizes...

Nice charts!

...The charts show the minimum wire gauge sizes required to meet two different maximum voltage drop requirements at 12 volts.

The first is for 10% voltage drop - the industry accepted standard for modern cars...


Personally, I prefer a larger safety margin, so I use the 5% standard shown in the second chart. My mentor in auto wiring thinks this is excessive, but I like to think of it as cheap insurance.

This nicely illustrates the voltage drop problem. While it was pointed out earlier that cars often use quite small wire compared to what some of us might choose, in that application they care very little about voltage drop, because electrical efficiency isn't very important.

In a car, the battery is used for very short-term energy storage (as the regulator cycles the alternator output on and off, and demand surges and wanes), and longer-term to store just enough to crank the engine (about one amp-hour for an easy start). The alternator is there as endless supply of more electrical energy.

In a battery-operated installation such as an RV, if you 10% voltage drop in the wire, then 10% of your battery energy is being wasted in heat in the wire. Larger gauge wire to stretch battery endurance - within reason - can be a good tradeoff.

10% of 12V is 1.2 volts... which is significant. In a trailer, the 5% guideline seems much more appropriate to me.


Also remember, these charts address only voltage loss, not the temperature which results for the heat generated by losing that voltage to resistance. Hot wire buried in a wall seems like a bad thing to me.