Safe to mix wire gauges?

[Dirt Ferguson]

I am wiring up a license plate frame with a led light on the top of it. The factory wires that come off the light are 22 Ga.

Is it safe to use 20 Ga wire to extend the wiring to tap into the main license plate light wiring?

 

[george_tlc]

Nothing wrong with extending with larger diameter wire.

The real issue is that the wiring in the vehicle you are tapping into has a fuse to protect that wire in case of a short. 22 ga would be smaller than any of the stock lighting wiring and so could fuse if there is a downstream short (e.g. in your LED light) if the stock fuse allows excessive current to flow beyond the 22 ga capability. This is obviously a worst case situation, but it doesn't hurt to plan for the worst case...

Just make sure that your 22 and 20g wiring is run where it can't cause a fire in case of a short.

cheers,
george.

 

[Dirt Ferguson]

Thanks @george_tlc the wiring will be run from my rear bumper to the underside of the cargo area, so should be safe enough,

 

[Dirt Ferguson]

Follow up question: I think the amazon listing was wrong about the gauge of the wire.

I found some 22 ga wire and it is much thinner than the pigtail on the light. Is there a way to find out the true gauge of the wire by measuring the OD with a digital caliper? Is wire OD standardized for gauge?

 

[e9999]

I doubt that it is accurate enough to estimate the wire gauge by OD since the insulation can be just about anything. I do measure the gauge of most of the wires I cut and put connectors on, and I've seen thickish wires with 18 ga and less, which is not much by power wiring standards, and smaller ODs with bigger gauge.
However, if you measure the ID that can give a much better idea, although you still have to differentiate based on the number of strands. There are tables online.
22 ga is really very thin. I picture that as electronic circuit wiring, not really something to use for license plate light, even LED.

 

[LandLocked93]

+1 ^^

Follow up question: I think the amazon listing was wrong about the gauge of the wire.

I found some 22 ga wire and it is much thinner than the pigtail on the light. Is there a way to find out the true gauge of the wire by measuring the OD with a digital caliper? Is wire OD standardized for gauge?

My experience with Amazon non-US made wiring on Amazon has been the opposite - usually smaller gauge than what they state. lol Many a 4ga copper crimp has fit on Amazon 2ga wire. Tho granted it too was an Amazon copper crimp.

Anyhoo, if the pigtail is larger than known-22ga, how does it compare in size to the factory harness wire you want tap into? If same size or larger you should be good.

As @george_tlc says, it's going the other way - smaller gauge on the end of larger wire - that things get dicey.

 

[Dirt Ferguson]

I ended up buying some 14ga wire from my local auto parts store. I know the guy who owns the shop, talked things over with him and tapped into the license plate light wiring underneath the cargo area.

 

[Julian73]

Word of warning. Wire gauge is based on cross sectional area of the wire itself (very hard to measure multi strand wire). The OD of insulation has nothing to do with the gauge. fancy (and more expensive) insulations are thinner. aircraft grade Mil-spec M22759/x ("Tefzel") (uses a teflon type insulation capable of supporting 150 deg C; TXL GXL, SXL insulation's are gradually thicker t=thin, S = standard) and are rated for 125 C; marine grade wires such as TEW .. are typically 105C while standard wires are thick pic rated for 80C. Cheaper insulation material is not as good an electrical insulator so must be thicker, and also is not as heat resistant (this is internal resistive heat in the wire) and thus a lower temp rating (cheaper) can not carry as much current for a given gauge. I try to use Tefzel in smaller gauges (12, 14, 18), along with TXL and GXL mid sized wires (8, 10, 12) except on very heavy gauge where I go Marine; amazon 80C wire just doesn't cut it. I just can't spend thousands on too much Tefzel, its only draw back is that its very stiff (due to the insulation type and requires a large bend radius. I use the xXL garden when I need flexibility.

 

[Dirt Ferguson]

@Julian73 thanks for the heads up. What is a safe, cost effective, wire brand to go with for automotive wiring? Sounds like Tefzel is top shelf. Thanks.

Electrical work is new for me and I understand the importance of doing things the right way so as to avoid catastrophe down the line.

 

[jht3]

bumping this back up

why doesn't toyota specify the wire gauge in the EWD? i'm used to BMW which does, in mm. eyeballing the wire outside diameter doesn't work, as already stated, but can't get a solid idea of the sizes common to toyota. anyone know?

i have a bunch of wiring projects in the queue so need to stock up on various wire gauges. in my stash is various stuff i've accumulated over the years; mostly general purpose wire in 10, 18, and 20 from the usual scumbags. lots of it unmarked so a guess. but was thinking about starting all over with white GXL in 12, 16, and 20 for lights, 12v or 5v plugs, and signal wires. with 4 or 6 welding wire for big things like an aux fuse box.

what wire does everyone keep on hand?

 

[Julian73]

It really doesn't mater what Toyota is using in their wire sizes as unless one is replacing a section for repair it is what is needed for the fuse rating, length and usage. Equally important is what temperature rating is the cable for. As to sizing your own accessory installations I would highly recommend that you do actual voltage drop calculations; these are based on wire resistance, length of run from battery to load and return back to battery, continuous and peak average of the load and how much drop that load can accept. Some minor things can take a 10% drop, others can not exceed 3% and critical electronic systems met need to be within 1.5%


All said and done I try to use 125 C and 150C rated insulations .. ie GXL, TXL, SXL and MilSpec Tefel for wires smaller than 8 gauge. I have an assortment of 8, 10, 12, 14, 18,and 20 AWG .. for 2/0/, 1/0 I order precut specifically for application and unfortunately these are typically lower grade battery cables; i do avoid welding cable as its not a durable insulation; however I do look for marine ratings and teh standards are higher. Also for the 2, 4, 6 AWG I stick with Ancor marine wiring 105 C.

 

[jht3]

It really doesn't mater what Toyota is using in their wire sizes as unless one is replacing a section for repair it is what is needed for the fuse rating, length and usage. Equally important is what temperature rating is the cable for. As to sizing your own accessory installations I would highly recommend that you do actual voltage drop calculations; these are based on wire resistance, length of run from battery to load and return back to battery, continuous and peak average of the load and how much drop that load can accept. Some minor things can take a 10% drop, others can not exceed 3% and critical electronic systems met need to be within 1.5%

yea, i know it doesn't matter but i've never seen a list of the common sizes they used and was curious. In my BMW diagram for the E30 generation, it calls out 4 mm2 (10 AWG) for the hot side of the ignition switch, 2.5 mm2 (12 AWG) for the output to fuse box/starter/cig lighter, 1 mm2 (16 AWG) for headlights, and .75 (18) or .50 (20) for all the low draw stuff in the cabin. So I have a pretty good idea what a major OEM did.

i have done voltage drop calculations and that's where I came up with the 12, 16, and 20 for running LED driving lights, USB ports and powerpole plugs in the cab, and relay coil triggers. 4 to the back quarter panel for the aux fuse box. and for all the devices i plan on installing i'm well within a 2% drop and could most likely be just fine with 14 and 18 feeding things at a 5% drop. no plans for anything large like an inverter or compressor, but maybe a goal zero type aux battery down the road.

part of my rationale for the sizes i picked was the terminal end compatibility. 12, 16, and 20 were roughly at the largest size supported by the terminal types i've been looking at. Either basic insulated/noninsulated terminals or Metri-pack or Deutsch DT/DTP. I'm leaning towards Metri-pack for waterproof light connections mostly for the cost in housings as well as crimping tools. Inside the cabin I've always been fine with Molex as I could pick them up easily at RadioShack (R.I.P.). Nothing i'm wiring is mission critical or going to the moon. In various pro level BMW race cars my friend's shop builds they use Deutsch, but for that use case it makes sense.

mostly trying to avoid having $$$ tied up in wire gauges and connector sizes i don't really need. hoping to learn from others that have BTDT, and shooting for a quality level somewhere between lamp cord and wire nuts and mil-spec Tefzel and Deutsch

i do avoid welding cable as its not a durable insulation; however I do look for marine ratings and teh standards are higher. Also for the 2, 4, 6 AWG I stick with Ancor marine wiring 105 C.

thanks for the feedback on the welding cable jacket. i was more focused on the quality and flexibility of the copper strands than the insulation. i'll switch to looking for flexible marine rated cable.

 

[ntsqd]

My experience with welding cable is contrary to Julian73's, but I use only Carol brand cable. Carol cable is my go-to for large cables on a vehicle and has been for over 20 years. Have never had a problem or even a potential problem. The insulation on quality welding cable is designed for abrasive environments. Think about where a welding cable is normally used and how it is used. It does tend to have thicker insulation due to the application. I can live with that. This stuff:

https://na.prysmiangroup.com/sites/na.prysmiangroup.com/files/media/documents/Carolprene%20105%CB%9AC%20Welding%20Cable%20MSHA%20Approved.pdf

Note that it is rated 105°C. I use a Greenlee hex die crimper and adhesive lined heat-shrink to make my own winch and starting cables.

I have used Ancor's paired 6 gauge cable to connect our camper's battery to the truck's charging system. It is not as flexible as the welding cable, but it is still good stuff. I used it specifically because of the outer "Romex" sheath's extra protection and ease of installation.