What unit of measure is used to describe the amount of work a surge suppressor can do before it stops protecting from electrical surge?

Answer 1

There are 3 items that can be used for surge suppression measurements. Most of the plug in strips use Joules as a measure but this can be very misleading. Joules is a measure of energy. Energy is current (amps) times voltage (volts) times time (seconds) or E=I*V*t.

Voltage during a surge is critical in determining if downstream equipment is protected. So low voltage rating are important. Current during a surge is important as this is a measure of how many amps are flowing diverting the surge from the downstream loads. So high surge current rating are important. Time is not generally critical, but is determined by the characteristics of the surge. For standard surge testing, the time is identical for the same waveshape.

So Joules appears useful at first glance because it incorporates voltage and current in one measure. However, one can increase the joule rating by increasing the voltage (bad) while decreasing the current (also bad). Joules can also be manipulated by using waveforms that are not standardly used in the industry.

So rather than use Joules, it is much better to look at the voltage during a surge and the maximum surge current a product uses and ensure the testing is with a recognized standard surge waveform.

Answer 2

That number varies with each type protector.

Protectors for one type of surge and that work by absorbing energy are rated in joules. These are typically hundreds or a few thousand joules.

Protectors for all types of surges and that work by connecting energy harmlessly to earth are rated in amps. This second type protector is for all types of surges including lightning. Lightning typically can be 20,000 amps. So a minimal 'whole house' protector is 50,000 amps.

Obviously that first type protector fails on other and destructive type surges. Since hundreds of joules cannot absorb surges that may be hundreds of thousands of joules (ie due to linemen errors or lightning). Amps is the useful measurement for more robust protectors that address all types of surges.

Answer 3

Joule (pronounced "jewel")

Answer 4

Joule