Wiring up some lights...

Ok, can anybody tell me a good set of guidlines to use when wiring up accessories. I am getting ready to run a couple of 130W lights and I was going to use 8-guage because that is what I have at the house. How do you determine what guage wire to use? Thanks.

There's tables to determine the correct gauge given load and length of wire, plus external factors (heat, etc) out there. Don't have one off hand..

But, make SURE you use a relay and a fuse.

Here you go http://www.the12volt.com/info/recwirsz.asp

Thanks! Ok, these charts seem to contradict themselves. Say I am running (1) 100w light. The "recommended cable size" chart says for 100w, use 10-guage. Ok, then the "current draw by power" chart says 100w pulls 16 amps. Well if I'm only pulling 16 amps, according the third chart "power & ground cable specs", I will be fine with 14-guage because it's capacity is 25 amps.

See what I'm saying? So would you use 10- or 14-guage?

I have 4 130w lamps on my rig and used all 10ga for the wirring.. I also rewired my head lamps to 10ga since converting to H4 lamps...

Unfortunately, that chart seems to be more directed towards stereo amps. You would be safe to go with the 14, but it is safer to go bigger. The top chart also factors in distance. The longer the run, the larger guage wire is needed to maintain the current flow without any loss.

The equation for calculating current requirement is as follows:

Amps = Watts / Volts

For your 100w light, it would be Amps = 100 / 12 = 8.333333333. Round that up to 10 amps to match available fuse ratings.

Amplifiers are not 100% efficient, which is why the chart shows 100 watts needing 16 amps. They are using a 50% efficiency rating which is pretty low for amps these days.

Use at least 10-gauge. The 14-gauge will work, but you'll get voltage drop through the wire which will make your lights a bit dimmer. Many people install a relay kit to brighten their headlights as the factory often uses 14 or 16 guage and you get a volt or two of drop through the wiring.

I recommend using a relay. Running a lot of current through the dash or switch isn't very wise. Especially if you get a short in your lights and the wire overheats and burns. It helps prevent any fires.

Hooking up relays are really easy. Also, the switch only has the current running through it needed to activate the relay. That can be as little as 2 amps.

For the wires to the lights, use 10 gauge. It can handle a higher load and if you do run into a probem (water in the lights, crushed wire, etc.) it won't burn as fast. Just make sure the fuse you use is no more than 25% over what the lights will pull.

Use separate wires, fuses and relays for each light set.

My light sets are Hellas and they came with relays. I just bought some lighted switches for the dashboard. A different color for the front/bottom, top, and rear.

1) USE A RELAY. This allows you greater flexibility in switch selection, and it's safer (because the lead carrying the high current can be shorter.)

2) Watts = Volts x amps. Take the nominal wattage rating of the bulbs, divide by 12 (nominal system voltage,) and you have current. Add up the total wattage on that set of lamps (2x100W = 200W. 200W/12V = 16-2/3 - use a 20A fuse and rate the circuit for 20A total.) The typical DIN/ISO "Bosch-style" relay is rated for 30A max through the terminals.

3) Using the maths above, determine the current supply required. I've got to expand my ampacity chart (current capacity by wire gage) on my site, since it's mainly focussed on the larger gages - but there are several others out there. Select the wire gage that will carry your fused current safely, and use one size larger.

4) You can safely use 16AWG or 18AWG for the switch-to-relay leads, since that's down around 1/10A (you can use much smaller wire, but it gets fiddly to handle.)

Thanks 5-90. This is good because I am now understand the why/what/how's of this stuff so I can figure this stuff out on my own in the future. A few questions....

1) Understand about the relay but how does it give you greater switch selection?

2) So, I will have 2 130w lights on one switch, which means that they are pulling 21.6 amps so use a 30 amp relay, right?

3) Use 8-guage to carry 21.6 amps.

4) Why can I use a smaller guage for the switch-to-relay lead? How is it only 1/10? I think I was misunderstanding what the wiring schematic should look like. So, the relay will have 3 wire coming to it right? 1 from the lights, 1 from the switch, and 1 to the power? If that is correct, I understand why you can use the smaller guage from switch-to-relay. Isn't there only 1 lead going from switch-to-relay?

One more...would you use an inline fuse? Does the fuse go in between the power source and the relay? I was thinking about building a power distribution center with fuses so whenever I want to add a new accessory, I can just plug in the appropriate fuse size and run the wire to the block and have it nice and clean.

This is fun! I am learning!

BruceB83 said:

Thanks 5-90. This is good because I am now understand the why/what/how's of this stuff so I can figure this stuff out on my own in the future. A few questions....

1) Understand about the relay but how does it give you greater switch selection?

2) So, I will have 2 130w lights on one switch, which means that they are pulling 21.6 amps so use a 30 amp relay, right?

3) Use 8-guage to carry 21.6 amps.

4) Why can I use a smaller guage for the switch-to-relay lead? How is it only 1/10? I think I was misunderstanding what the wiring schematic should look like. So, the relay will have 3 wire coming to it right? 1 from the lights, 1 from the switch, and 1 to the power? If that is correct, I understand why you can use the smaller guage from switch-to-relay. Isn't there only 1 lead going from switch-to-relay?

This is fun! I am learning!

Click to expand...

1) You have more latitude in selecting a switch to trip a relay, simply because of the lower current requirement. If you were picking a switch to turn the lamps on and off directly, you'd need a switch good for 20A or so. The spec for a DIN/ISO relay is about 1/10A for "trip" - so that's all you need the switch to handle. Suddenly, appropriate switches are much more "available" - and you can use nearly anything you like (provided it can handle 1/10A or more...)

2) Relays are 30A - unless they state otherwise on the datasheet (I think a mini-DIN relay is only good for 15-20A, for instance. And, there are DIN "power relays" - good for up around 70A.) For 21.6A, use a 25A fuse, and wire for 25A.

3) Sounds about right - but I'd have to check my notes. As I'd said, I have to expand the chart on my site - I've mainly done it for "distribution" at this point. It's in the Tech Archive, under "Electrical Specifications" if you want to see it (link to my site in sig.)

4) You can use a smaller wire between the switch and relay because there's less current involved.

To use an analogy - compare the flow of electricity to the flow of water. "Voltage" becomes "pressure," and "current" becomes "flow rate." If you want to flow more water in a given instant, you need a bigger pipe/hose. If you don't need so much flow, you can use a smaller hose. "Voltage" rating of a wire is governed by insulation quality - not wire gage. You can shove 10kV thorugh a 24AWG wire - if the insulation is up to it, and the current doesn't exceed the ampacity of the conductor. You can shove 10,000psi through a rubber hose - if the hose is up to it (these ratings are common in industrial hydraulics.) But, you can only move so much fluid per unit time through a 1/4"ID hose. If you need more fluid, you need a bigger hose.

More current? Large wire. Less current? Small wire. Unless you're an electrical engineer, it's the same thing. (I know there are EEs who will accuse me of oversimplification, but I'm not trying to teach to their level...)

I don't have a wiring diagram handy, but go to the "instructions" section of my site, and download the wiring diagrams for the solenoids I offer. A solenoid can be thought of as a high-current relay (I carry them for 85A or 200A continuous current flow...) and it works on the same principle. Once you see those diagrams, you'll have a better idea (and we can look at the same picture so my explanations will work better.) I've been thinking about doing a "relay explanation" - just haven't gotten to it yet...

So, does it make a little more sense now?:rtm: :read:

Makes sense. So let me make sure I understand this. Voltage should be considered when choosing the type of wire to use. Current is considered when selecting the size of wire to use. I guess this is where something like 10-guage "speaker" wire and 10-guage "automotive" wire differ, right? They are the same size "pipe" but the "walls" are thinner on the speaker wire. I can't open up your solenoid diagram right now b/c adobe is acting up...I'll check it out later.

You can try this site for relay wiring.

http://ovo.ca/wiring/wiring.html

BruceB83 said:

Makes sense. So let me make sure I understand this. Voltage should be considered when choosing the type of wire to use. Current is considered when selecting the size of wire to use. I guess this is where something like 10-guage "speaker" wire and 10-guage "automotive" wire differ, right? They are the same size "pipe" but the "walls" are thinner on the speaker wire. I can't open up your solenoid diagram right now b/c adobe is acting up...I'll check it out later.

Click to expand...

Correct. Speaker wire works at relatively low voltage (3-5V,) it does not need as much insulation (Hell, I've not even seen 10AWG speaker wire lately!)

Another factor in insulation quality is operating environment - for instance, SOOW is water-resistant, handles well in the cold, and that sort of thing - while SJOOW wire adds oil- and grease-resistance. Both are usually rated at 600V for insulation breakdown (at voltages higher than 600V, you start running the risk of arcing from the inner condctors - through the insulation!)

There are two qualities you want in automotive wire, for everything except spark plug wires ("secondary ignition")

1) Voltage. Automotive systems are rated at 12VDC nominal (~14VDC operating,) while heavy truck Diesel electrics are rated at 24VDC nominal (~28VDC in operation.) Since most automotive wire uses 300V insulation, this isn't a problem.

2) Petroleum/solvent resistance. Engine fuels (and, to a lesser extent, detergents used in lubricants) are organic solvents - which means they can dissolve organic compounds, like rubber & Neoprene. Either of these can be reformulated to increase resistance to various organic solvents - which is why some wiring is rated as "oil-resistant." You want this - especially underhood! Sometimes, other compounds are used for insulation jackets - while Neoprene is common, I've also seen Viton, PTFE, and various cross-linked polymers as well. For instance, I think Painless Performance uses cross-linked polyethylene as a standard insulation on all their wire - it's overkill, but that's why I like Painless (cross-linking a polymer makes it more stable and more resistant to solvents.)

The voltage and environmental ratings are required by Code to be printed/stamped on the outside jacket of the wire or cable, and it's usually quite simple to look up the standard codes (like SOOW or SJOOW, or THN/THHN, as used on industrial wiring.) These codes can tell you what sort of metal is used for the conductor (typically copper or aluminum,) whether it's solid or stranded, what the insulation ratings are, whether it's rated for "burial" use or not (important with household wiring, for instance...) and the like.

I'll probably be adding a "How it works" page for relays sometime fairly soon, but I've got to get a few other things out of the way first...

Cool, your help has been GREATLY appreciated. Thanks for walking me through this and teaching me what I need to begin to know.

BruceB83 said:

Cool, your help has been GREATLY appreciated. Thanks for walking me through this and teaching me what I need to begin to know.

Click to expand...

No worries. It's what I do...

BruceB83 said:

Cool, your help has been GREATLY appreciated. Thanks for walking me through this and teaching me what I need to begin to know.

Click to expand...

Did you get the diagram I sent you? I will post it on here also for anyone else who's interested.