Not enough information.
First, you need to know if there are any other outlets on this circuit. Usually a circuit breaker or fuse will provide power for 4 to 8 outlets. Second, you need to know what the current rating is for this circuit (if it is a breaker, there is a number on the toggle indicating the current rating, if it is a fuse, it will be written on it where you can easily see its rating). In the USA it is usually 15 or 20amps depending on how old your house is.
I would guess that it is a 20amp circuit because it is in the garage. But check your fuse box or circuit breaker panel to be sure.
Here's a math example assuming it is a 20amp circuit and also assuming it is the only outlet on the circuit:
Voltage x Amps(current)= Watts
120V x 20amps = 2400Watts
If it is a 15amp circuit:
120V x 15amps = 1800Watts
Most importantly, SAFETY FIRST.
Once you've done your research and figured that your circuit can handle the load, there is still one more possible snag - the circuit can still be overloaded if the 4x extension cord you are using is pretty long (50ft+). The longer the cord, the more voltage drop your circuit will have and to compensate you will draw more current from the circuit. One easy indicator of this obviously is you will trip the breaker or burn out the fuse but also the cord will feel warm to the touch.
My experience is that you will be fine as long as you don't exceed the max Watts for the circuit. Just be careful and feel the cord as you use it to see if it is getting hot.
David M., May 2009
