Surge protectors are an inexpensive way to protect your setup against power spike damage. There are some insights for you to learn more about surge protectors.
1. Lightning strike is a typical cause but not the only
Power spikes are fast, short duration electrical transients in voltage (voltage spikes), current (current spikes), or transferred energy (energy spikes) in an electrical circuit. Spikes are typically caused by
- Lightning strikes
- Power outages
- Tripped circuit breakers
- Short circuits
- Power transitions in other large equipment on the same power line
- Malfunctions caused by the power company
- Electromagnetic pulses (EMP) with electromagnetic energy distributed typically up to the 100 kHz and 1 MHz frequency range.
- Inductive spikes
Lightning that hits a power line can give 10k or more volts. A motor when switched off can generate a spike of 1,000 or more volts. There are many factors to cause a power spike, but your devices are not in danger all the time.
2. Surge protection system
The most effective place for surge suppression equipment is at the building’s electrical entrance panel. According to IEEE recommend, we should provide surge protection in three levels. First, power distribution cabinet, prevent high energy spike crush into the building grid. Second, distribution board, reduce the rest energy after first filter and reduce the internal spikes caused by device switch on/off. Last, the device adapter like phone charger or PSU, provide complete protection for electronic equipment.
All the three levels protection was provided already when you are use electronics in residential. That’s why your computer not damaged although you never used a surge suppressor for it.
3. About joule rating
The Joule rating number defines how much energy a MOV-based surge protector can theoretically absorb in a single event, without failure. Generally, the more joules the better, as this means the device can handle one large surge, or multiple smaller surges, before your device is in danger. But you may still find how much rating do you need, according to ANSI/IEEE C62.41 and UL 1449 (3rd). The energy of a power spike with 6,000 volts and 3,000 amps can be 90 joules. For the power spike caused by lightning hits, this number can be 1000 joules (20kV, 10kA). Considering the MOV matching so derating by 20% or more is usually required. So, the answer of how much joules can be enough is, you need at least 110 joules or 1200 joules, depends on prevents lightning or not.
Another thing you should to know is surge protectors doesn’t last forever. The joule rating will change every time it takes effect. There is no way for us to know how much protection it has left. If you've had your current surge protector for more than a few years, it's probably worth replacing. But you can use it for fans, lights, or toaster still.