This is from an article in JP mag.
"I've heard things like the Taurus fan pulls 80 amps on a standing start into the "High" speed. I'm not sure if these guys are even measuring it. That amperage happens for milliseconds, and not only is it hard to measure, but most decent relays and connectors can handle a surge like that. Most regular fans that you can get from the aftermarket suggest a normal 30-amp Bosch relay. That includes 16-inch fans that pull upwards of 2500cfm.
Amperage Draw (amps) Ford Taurus Fan Low Ford Taurus Fan High SPAL VA18- AP71/LL-59A
Cold standing start 6.15 9.95 10.15
Warm standing start 3.14 10.7 11.43
Moving start 2.72 7.42 7.78
Continuous draw cold 1.8 4.29 5.11
Continuous draw warm 4.54 6.55 7.21
Since I had my Auto Meter DM-40 multimeter handy and access to both a Ford Taurus fan and a 3430cfm SPAL fan, I decided to take some measurements. In theory, starting the fan from stop should take more juice than if it is spinning-and a warm fan should take more to start than a cold fan. The SPAL constantly drew more than the Taurus fan on "High," but it is suggested to wire it up with a regular Bosch relay."