how do i figure out how many Joules i should be looking for?
Destructive surges are hundreds of thousands of joules. That energy dissipates harmlessly. Or dissipates destructively inside the house.
One way to promote ineffective protectors is to grossly undersize it. A surge too tiny to overwhelm protection inside all appliances, instead, destroys a grossly undersized (ie hundreds of joules) protector. Then a majority will claim to that protector "sacrificed itself to save my computer". The word scam is appropriate.
Do not worry about joules. Worry about what effective protectors do. Dr Kenneth Schneider
describes what every protector must do in: Section 6.4: When Should You Worry About Lightning?
> Conceptually, lightning protection devices are switches to ground. Once a threatening surge is
> detected, a lightning protection device grounds the incoming signal connection point of the
> equipment being protected. Thus, redirecting the threatening surge on a path-of-least
> resistance (impedance) to ground where it is absorbed.
> Any lightning protection device must be composed of two "subsystems," a switch which is
> essentially some type of switching circuitry and a good ground connection-to allow dissipation
> of the surge energy.
If a protector does not have the always required short (ie 'less than 10 foot') connection to earth, then even its joules numbers will be tiny to promote sales. Protection is always about where hundreds of thousands of joules dissipate - harmlessly. Since lightning is typically 20,000 amps, then a properly earthed 'whole house' protector starts at 50,000 amps. Because only ineffective protectors fail. Effective protectors earth the entire surge - and remain functional.
Do not worry about joules. Effective protectors do not protect by absorbing energy. In fact, better protectors are larger to absorb *less* energy. Effective protection is always about less energy inside the protector; more energy harmlessly outside a building in earth. Worry about what absorbs that energy. Only earth ground does the protection. Worry about what *diverts* surges harmlessly to earth. A low impedance (ie 'less than 10 foot') connection to single point earth ground. Install one 'whole house' protector so that everything ... including the dishwasher, bathroom GFCIs, furnace, and plug-in protectors ... are protected.
What most needs protection from a surge? Smoke detectors. Just another reason why informed consumers earth one 'whole house' protector rated at least 50,000 amps.
BTW, battery backup devices have how many joules? Virtually zero. But just enough above zero so that advertising and urban myths can call it 100% protection. How many recommend that UPS for surge protection when its numbers say near zero protection? Most people are that easily manipulated by advertising.
