Joule ratings of surge suppressors

June 11, 2011 at 20:41:01
Specs: Macintosh
I have read the older thread, and there was plenty of inaccurate info - so I felt the need to correct. "electricity" does not flow, LOL, current does. Voltage is the resulting pressure. This said, here are my 2 cents:

Most voltage surges occur when high-power equipment, such as any motors (vacuums, garage door), heating elements (electric ovens, large printers), heavy battery chargers, etc'. are turned ON/OFF. Some do by nature, such as your iron or hot-plate. a seized motor is the worst case, since it draws max power when the shaft is locked, plus the added surge. (TIP: start your vacuum when it's off the carpet)

A dedicated circuit for your office is a great idea, unless you want to dedicate a circuit for your vacuum cleaner in every room...

A surge suppressor (suppressor, not eliminator) does just that, it suppresses sudden changes in voltage (so does your PC power-supply, to an extant). without getting too technical, the surge is best described in term of the energy it delivers, and hence the joules rating.

A lightning hit is an extreme case, and I wouldn't expect a $30 suppressor to prevent the damage.

and now to the discussion: what kind of joules rating should your suppressor have?

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June 11, 2011 at 20:58:27
here's a good thread:

the last one slid into a lightning strike discussion, although many interesting facts are introduced..

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June 11, 2011 at 21:33:39
Well, thanks for setting us all straight on that. Might have been a good idea to link to the pevious post that prompted your response here so we too could laugh at it.

One thing though, 'electricity' doesn't have a strict definition as do current, voltage, power and energy so it's really not a misuse of the word to say it 'flows'.

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June 12, 2011 at 00:23:12
It depends on how large a surge you expect. All bets are off with a lightning strike,

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June 12, 2011 at 08:47:24
> It depends on how large a surge you expect. All bets are off with a lightning strike,

Protection is installed for direct lightning strikes and all lesser transients. An earthed 'whole house' protector makes all types of surges irrelevant. For example, a lightning strike is typically 20,000 amps. So a minimally sized 'whole house' protector starts at 50,000 amps. Direct lightning strikes are earthed without protector damage.

Surges are current sources. That means voltage increases as necessary to blow through anything that might stop it. If the connection to earth is very conductive (short), then the same 20,000 amps flows to earth with near zero voltage.

Concept for all surges was demonstrated by Franklin. A destructive surge seeks earth ground. So it strikes an electrical conductor - a wooden church steeple. But wood is not very conductive. 20,000 amps through wood creates high voltage. 20,000 amps times high voltage is high energy. Church steeple damaged.

Franklin connected a lightning rod to earth. 20,000 amps via a conductive earth wire is near zero voltage. 20,000 amps times near zero voltage is near zero energy. No damage.

Voltage is only a symptom of something that foolishly tried to stop a surge. Critical to protection, always, is a short (low impedance) connection to earth.

A less than $50 protector is effective even for direct lightning strikes. A $30 power strip that would somehow stop a surge would only cause a voltage increase. Can even make damage easier. In every case, it is about how current flows. A low impedance connection means a short ('less than 10 foot') connection.

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