Electrical surges addendum

In my last post I talked about electrical surges, how devices like vacuums generate them and how good-quality surge protectors guard against them. I can already see it, someone who it read is thinking "are you saying that a vacuum on the same circuit as a TV or computer without a surge protector would mean instant damage to the TV/computer?" Surely you can't be making that claim, because I've done just that before and the TV/computer still works, so your claims are false. Well, I don't claim this scenario will always result in damage to the TV/computer, but if you repeat this scenario eventually it will fail. Let me explain why this is.

The electricity coming into your house is AC (alternating current). The problem is very few devices use AC, most require DC (direct current). Therefore, every TV, computer, radio, etc. has an AC to DC power supply. Inside that power supply is the same protection circuitry located in a surge protector. That's why the device does not fail after one power spike.

"If the TV/computer protects itself against surges, why bother with a surge protector?" I'm glad you asked. The first reason is what I said in the last post - the circuity can only protect against X number of surges, after that it's useless. So if you don't use a surge protector eventually the TV will break and you'll have to replace or repair it, but if you use a surge protector you can replace the surge protector for much cheaper. The second reason is because the TV/computer probably contains a low-level of protection, i.e. it only protects against a low number of joules of energy. A good-quality surge protector will protect against more joules.

Also, if the TV/computer is on or off during the surge makes little difference. The device is probably more susceptible to surges when powered on, but may still be overloaded when turned off. The only way to truly protect it is by disconnecting it from the socket.

One final thing I'll mention is polarized AC plugs. You've probably noticed some AC plugs are polarized (one connector is larger than the other). If AC flows in both directions why is the plug polarized? The answer has to do with the protection circuitry. Manufactures put the protection circuitry on the "hot" wire and leave the "neutral" wire unprotected. Thus the polarized plug ensures the protection circuity is properly protecting the device. Manufactures could protect both the hot and neutral (and indeed some do), but this costs more money. If you've ever "forced" a polarized plug to fit the wrong way, the device was no longer protected. Also, if you have a wiring fault in your home, the device is unprotected as surges could come up the neutral wire. Both of these are still more reasons to use a good-quality surge protector. A good surge protector protects hot, neutral, and ground.