It depends on the actual length of the wire run to the junction box. Here is a link to a calculator that will tell you what you need to know.

https://www.wirebarn.com/Wire-Calculator-_ep_41.html

I usually change the percentage of voltage drop to 1% from the 2% it defaults to, but that will cause it to recommend a larger wire size. There is nothing wrong with using a bigger wire, except for cost.

I have seen several charts online that recommend wire sizes for given loads, but they are just "rules of thumb" since they fail to take the length of the wire into account. Wire resistance increases with length.

Be sure to add a fuse, circuit breaker or fuse link to your main line as close to the battery as possible to prevent a fire in the case of a short.

Unless the fans will be individually grounded, a common ground cable for both fans may need to be oversized, also.

 

Great calculator. Thanks for posting it.



6 ga for up to 12' and 4 ga for up to 18'.
For individual, 10 ga up to 10'

 

The only wire you need for electric fans is some baling wire to hang them from a rafter in the garage, then install a properly-engineered crank-driven fan with viscous-drive clutch. Just my opinion. Carry on.

 

I appreciate nice mechanical fans also. I need to use electric on my current build for space and aesthetics. Hopefully, no issues.

 

Because of the initial current draw save your self any problems by getting a kit like this that includes a relay. https://www.ebay.com/itm/185-165-Th...XGV/UcSjYRTwQ2HPyqC3i1AE=&checksum=2645348203058a108d1f63634b01aac4e8319ad6055b You should give this article a good look. https://watsons-streetworks.com/a-current-topic/

 

I have relays already. What was asking about is for the line I’m running to the junction box. The power to the relays will then attach to the junction. I used the calculator previously supplied and I’ll be running an 8 ga wire.

Techinspector, curious about why the dislike for electric fans. I prefer factory appearance myself but when I go to SEMA every year the top line custom $500,000+ cars shown there all have electric fans. What are these builders getting wrong that you would set them straight on? Surely if mechanical factory style fans were just plain better more guys would use them, no?

 

Electric fans are OK, I got used to the idea of electric controlled fan clutches if heavy trucks. Almost all would have a manual override switch, some had tell tale light so you would know if it turns on automatically.
At first they were on/off, but the became soft start so it was smoother engage.


Space is the biggest consideration favoring electric. You do what you gotta do.

 

On a street driven application, I gotta agree with techinspector. Belt driven fans are a better choice...Now, for a custom street rod, clearance issues, and other applications, nothing wrong at all with an electric. There are some out there now that pull as much or more air as a belt driven fan...pretty much all new cars run them these days as well. Trucks still run a belt driven unit. Reason is because it limits failure of the fan. A clutch fan failure default is locked up so it will still cool the engine.....

Big advantage to the electric fan is you only run it if needed, and if you wire it up yourself, you can connect it so that you can turn it off as needed too, or connect it through a temp sensor to control it. Basically gives you lots of options that you don't get with a mechanical fan....

As to the wiring, I have yet to see any fan installation where anything larger than 14ga. wire is needed or has been used...but as it's already been mentioned, going larger will not hurt anything.....

 

As to the wiring, I have yet to see any fan installation where anything larger than 14ga. wire is needed or has been used...

Well, here's one. I'm running a Cooling Components fan that pulls over 60 amps on start up and runs at almost 50. The popular Thunderbird,Taurus, and Lincoln Mark 8 fans are similar, as are some Volvo fans. I know the Volvo fans run a 70 amp relay. It takes a lot of power to move a lot of air. The Cooling Components fan directions state that it will fry a typical 30 amp relay. The leads on the motor are 10 gauge.

I totally agree with your statement in a lot of situations. Most of the fans on the market run puny little motors that take very little power, but not all.

 

That’s my point. All these crazy custom applications, regardless of clearance issues, (many of these builds relocate the engine posterior my so if anything there is more room up front) and essentially all new cars, run electric fans. If mechanical were better that would not be the case. I understand that you might say mechanical is more reliable but I’ve also thrown my fan belt and overheated my car so nothing is 100 reliable. This sounds more to me like the arguments that were common 10 years ago about carb vs EFI. Except for a few die-hard old timers that argument has been settled. I run both mechanical and electric and it depends really on the application and what your trying to achieve, i.e. original appearance or custom.

As fir the gauge of wire, again this is for the main power to the junction box to power both fans so it has to be 8 ga. You are correct that the power to the individual fans is 12 or 14ga I believe.

 

I run fan and headlight relays directly off the inner fender mounted battery using 10gauge to each relay. I take the 4 to 6 10 gauge wires. Put them into a single 2/0 copper terminal, crimp it then seal it. That lug is connected to the battery.

The lug connected to the 2/0 lug is a 0000-0004 lug which goes down to the starter then up to a firewall mounted distribution stud.

The alternatior(s) 4 to 0000 wire goes to that distribution stud as does the sense wire with diode.

Your main veins of your power system should be overbuilt. The things that turn on your relays you should use calculations for. Generally though I just use 12 or 14 for the rest.

For areas like the trunk area I run a minimum or 2 gauge back which feeds things like taillight, fuelpump, and other relays. I use a distribution stud here also.

I run the ground wires along the main power wires to both my positive AND negative distribution studs mounted at the firewall and trunk areas. This also makes it simple for a 2nd(or more) batteries to reside in a vented box in the trunk.

Doing so eliminates several rust related issues.


You want your electrical system to last 30-40 years. If your going to spend the money to make it reliable then exceed what the calculations call for.


Typically I run the rear power off the starter stud and off the ground stud near the starter at the rear belhousing. It runs inside the frame making its way up into the trunk in a clean manner. If there is concern of exhaust heat these wires are ran inside heater hose.
DO NOT run wires under the carpet where they may rub against steel.

With fans make sure your not exceeding the amps of the controller. If a controller is only rated for 25amps your going to have a issue running 2 fans.
It is best to have that controller power 2 30/40 amp relays keeping the controller happy.
You can power 3 or even 4 fans off of one controller this way. But you need to take into account that load is hitting all at once so a time delayed relays or a second controller should be used.

I have been using time delayed relays for years. They do cost in the $15-20 range. But If you want to turn on say 3 items you can set the first with a normal relay, the second with a 5 second delay and a 3rd with a 10 second delay giving your alternator time to maintain full voltage.
You can do the same thing with multiple controllers by setting diffrent temps of say 195, 200, 205F. But your running the relays off those controllers anyway and the use of timed relays leads to less wiring clutter.

Engine setback gets a thumbs up in my book. Just make sure you think about maintenance by making the engine/transmission mounts easily removable. Exhaust comes into play making sure you dont wrap headers around a steering shaft. Front clip comes into play making sure it can be pulled easily then installed maintaining alignment by using studs/ body panel adhesive washers in place of bolts. Thing will drop in the same place time after time.

If engine setback is not a option consider throwing out the A/C condenser to allow you to tilt or recess the entire radiator.

If you can think of it someone has done it. Hundreds of years of engineering are at your fingertips if your willing to search for it.

 

I had no room for a decent mech fan. Believe me, I have been driving this car for almost 25 years and have tried many engine driven fans. Clutch, no clutch, flex and fixed blade. With and without a shroud. Shroud created high speed air flow issues and wasn't big enough due to radiator size to fit doors to open at road speed.

The big Ford electrics wouldn't fit, but the Cooling Components unit would just slide in behind a decent size radiator. After fighting overheating issues all these years (including ruining a really nice 383 stroker), the problem was finally solved. And yes, the 98 amp alternator I had wasn't up to the task of driving the CC fan. I switched it out for a 150 amp part and now everything is fine. I'm also using the Cooling Components 2-speed solid state fan control. This replaced the single speed control I was using that drove the fan in high speed only with a 70 amp relay.

Sorry to the OP for the hijack.

 

electric fan wiring

I kept mine simple with a 30 amp fuse from junction, 10 gauge wire into and out of relay to both fans. 12 gauge circuit to activate relay. Has worked fine without any issues.

 

fans

I would no smaller than 10 gauge, I used 80/60 amp relay on start up some fans can exceed 30 amps and run at 15/8 amps. It's good to amp draw start up, and when they running. You won't to make sure you very good ground wiring.

 

fans

here's few more pics, the 1st 1 fan start up

 

I have a 16" Spal fan as a back-up to my mechanical flex fan. I bought it with the installation kit, really little other items were needed outside of some lugs. Can you find an installation kit for your fans? It saves a lot of figuring/chasing more stuff.

 

I'm running a Cooling Components single speed smaller fan. I have it wired into a 70 amp relay and ran 10 gauge wire (12 would have been fine). I control it using the Holley Sniper.

I have the opposite problem from most folks, I have a hard time keeping mine up to temp. I also have the fan running when the AC compressor is on.

 

Wire gauge size is important, I would go no smaller than 10ga.
I would also pay close attention to termination. Wire terminals that push on are noted for their failure, as are crimp on terminals. Fan motors, beside their high current draw, set up a kind of induction in the wiring. This is produced by the contacting of the brushes during the rotation. Unlike the load produced by a lamp which is purely a resistive load, a motor's load varies with speed, and the frequency of the make/break of the brushes. This creates an inductance in that circuit, which works on all terminal and conductors. Any terminal that is not a 100% connection will be heated causing eventual failure.
I solder and heatshrink all wire to terminal connections and avoid using push on terminals.

 

different wire guages

Here's my question. I am currently running dual fans through a single relay ( 1 puller and 1 pusher that is on with A/C on). I have had this setup for years but I know I am running undersized wiring (14 Ga. I think). I am in the process of fixing this.

Most sites I have researched recommend minimum 10 Ga. wire to the load however, both pigtails that came with the fans (I think the puller is Spahl and I don't remember what the pusher is but they are both about 15" fans on a '62 Vette) are either 12 Ga or maybe even 14 Ga.
So what good does it do to to run 10 Ga. from the power source if you are choking it at the load?

For the record, I plan to split the system and run a relay for each fan with a temp and a manual switch for the puller.

 

Here's my question. I am currently running dual fans through a single relay ( 1 puller and 1 pusher that is on with A/C on). I have had this setup for years but I know I am running undersized wiring (14 Ga. I think). I am in the process of fixing this.

Most sites I have researched recommend minimum 10 Ga. wire to the load however, both pigtails that came with the fans (I think the puller is Spahl and I don't remember what the pusher is but they are both about 15" fans on a '62 Vette) are either 12 Ga or maybe even 14 Ga.
So what good does it do to to run 10 Ga. from the power source if you are choking it at the load?

For the record, I plan to split the system and run a relay for each fan with a temp and a manual switch for the puller.

I'm not an electrical engineer but my understanding of it is that it's not about performance but about safety. The wire off the fans may be 12 or 14ga but presumably the manufacturer believed that was sufficient to power the fans individually. The supply to your relay needs to be at least 10ga (mine needed to be 8ga to the junction box I was using to power the fans) because your running power for both the fans through the single power wire and relay. It will need to handle twice the current of the separate fan wires. In addition, most people put the relays in close proximity to what they're controlling, so the power wire to the relay is typically longer in length, which also requires a larger wire.The wire to each individual fan from the relay need only be as large as the pigtail wire from the manufacture, again as long as the relays are reasonably close to the fans. If at some point you elect to use two relays, one for each fan, then you could reduce the gauge of the wire you run to the relays, but not to the fans. I recommend you use the tool that was posted in this thread about how to calculate wire gauge requirements to be sure you are using the correct gauge.

 

10-12 gauge. Forgot who posted it but Wirebarn has good product and the calculator comes in handy. If you have , or in the need for a high amp sealed relay look up TE connectivity. They make a 70 amp and 150 amp relay. Really heavy duty and sealed on the trigger ends on the 150 amp model. Pretty much will handle about anything out there in terms of fans.