Re: are surge protectors rated in Joules or Amps?
- From: bud-- <remove.budnews@xxxxxxx>
- Date: Thu, 03 Jul 2008 11:24:06 -0500
w_tom wrote:
On Jun 30, 11:39 pm, "JohnO" <johno@!NOOSPAM!heathkit.com> wrote:..w-tom vs the world!
Hardly. w_tom verses the sales promoter who will not admit he
promotes these protectors.
Poor w_ thinks that anyone who opposes his outlandish ideas (which are not in this post) is a sales promoter. Totally false.
The best information on surges and surge protection I have seen is at:
<http://www.mikeholt.com/files/PDF/LightningGuide_FINALpublishedversion_May051.pdf>
- "How to protect your house and its contents from lightning: IEEE guide for surge protection of equipment connected to AC power and communication circuits" published by the IEEE in 2005 (the IEEE is the dominant organization of electrical and electronic engineers in the US).
And also:
<http://www.nist.gov/public_affairs/practiceguides/surgesfnl.pdf>
- "NIST recommended practice guide: Surges Happen!: how to protect the appliances in your home" published by the US National Institute of Standards and Technology in 2001
The IEEE guide is aimed at those with some technical background. The NIST guide is aimed at the unwashed masses.
..
UL approval..
requires total number of joules to be listed.
Nope. UL does require the current and clamp voltage to be listed and defines how to measure them.
The IEEE guide cautions against comparing Joule ratings because there is no standard for measurement. So some manufacturers play games to inflate their Joule ratings. Because of that some other manufacturers have stopped supplying Joule ratings - including SquareD.
It is too bad, because Joule rating, like w_ says, is an indicator of suppressor life. But current ratings go up with Joule ratings.
Service panel and plug–in suppressors do not protect by absorbing surge energy, but absorb energy in the process of protecting. Joule ratings are for the energy that is absorbed by the MOV. This is not the energy in the surge.
As Rahul said Joules are the product of clamp voltage, current through the protective device, and surge duration. (But the voltage and current change during the event.) The "8/20uS" figure indicates the measurement was made with a pulse of 8 microseconds rise time and 20 microseconds duration. This is one of the standard test pulses and is similar to a surge produced by lightning. It is fairly reliable to compare Joule ratings if the test method (8/20) is stated.
The common practice, as Paul said, is to add the Joule ratings of protective devices in the suppressor but this should also be indicated by the manufacturer (and often isn‘t). Protective devices for power wires are almost always MOVs.
Stated Joule ratings are for a single event - one surge that puts the MOV at its defined end of life (but still functional). If the energy hits are much smaller, the cumulative energy rating is much higher. For example a MOV might have a (single event) rating of 1,000J. If the individual hits are 14J the cumulative energy rating might be 13,000J. High ratings give a much longer life than you might expect.
Francois Martzloff was the NIST guru on surges and wrote the NIST guide. He has written "In fact, the major cause of [surge suppressor] failures is a temporary overvoltage, rather than an unusually large surge." Temporary overvoltage is long duration - seconds to hours?days.
..
285 joules is high enough to claim surge protection but so close to..
zero as to be almost no surge protection.
I would rather see higher ratings. But 285J is not as "close to zero" as w_ believes.
Martzloff wrote a technical paper (available on the internet) which looked at a MOV at the end of a branch circuit, with no service panel surge suppressor, with surges on incoming power lines of 2,000 to 10,000A and with branch circuits of 30 feet and longer. The probability of a surge over 10,000A is near zero. The maximum energy dissipated in the MOV was 35 Joules. In 13 of 15 cases it was 1 Joule or less.
I recently bought a plug-in suppressor that had ratings of 30,000A and 590J per MOV for each of the 3 MOVs. The 30,000A rating is not real in that it is not possible to get 30,000A on a branch circuit (short of lightning hitting the house). But 30,000A goes with the high Joule ratings.
--------------
According to NIST guide, US insurance information indicates equipment most frequently damaged by lightning is
computers with a modem connection
TVs, VCRs and similar equipment (presumably with cable TV connections).
All can be damaged by high voltages between power and signal wires.
Note that all interconnected equipment needs to be connected to the same plug-in suppressor, or interconnecting wires need to go through the suppressor. External connections, like phone, also need to go through the suppressor. Connecting all wiring through the suppressor prevents damaging voltages between power and signal wires. These multiport suppressors are described in both guides.
--
bud--
.
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