Re: Lightning Strike and surge

w_tom wrote:
On Aug 11, 4:37 pm, Mark F <mark49...@xxxxxxxxx> wrote:
Very unlikely that a lightningbolt that went 1000 feet to 5 miles in
the air would be deterred by a 10 pound surge protector (or even a 100
pound surge protector) if yourcomputerwas in the direction that the
discharge was taking.
..
Direct strikes to a building require lightning rods for protection. Direct strikes are very rare unless a building is very exposed.

When lightning hits utility wires there are multiple paths to earth.

Francois Martzloff was the NIST surge guru and wrote the NIST guide. He has also written numerous technical papers on surges and surge protection. One of them looked at a lightning strike to the primary wire on top of a pole behind a house for typical urban distribution. The lightning strike was an extremely strong 100,000A. On average for the US, the estimated probability of a worse event is once in 8,000 years. Of the 100,000A, 33,000A went toward the house on the neutral. The surge that stayed on the neutral is earthed by the neutral-ground-earth connection at US services. A fraction of the 33,000A would couple to the `hot' wires. The result is more like 10,000A on a 'hot' wire for a near-worst-case lightning strike. Service panel suppressors with far higher ratings are readily available. A service panel suppressor dumps almost all of the surge energy to earth.

If there is no service panel suppressor, when the voltage from service bus bars to the enclosure reaches about 6,000V (US) there is arc-over. Once the arc is established, the voltage across the arc is hundreds of volts. Since the enclosure is connected to ground/neutral/earthing-electrode, this dumps most of the remaining surge energy to earth. (Receptacles will also arc-over at about 6,000V (US)).

In a different paper Martzloff looks at the amount of energy absorbed in a MOV on a branch circuit with no service panel suppressor. The impedance of a branch circuit greatly limits the current, and thus energy, that can reach a plug-in suppressor. With surge currents up to 10,000A (the maximum likely above), the amount of energy absorbed by the MOV was surprisingly small, 35J max. In 13 of 15 cases it was 1 Joule or less. The reason is arc-over at the service panel and the branch circuit impedance. The highest energies that reached the MOV were for short (30 meter) branch circuits and surprisingly for low surge currents. With lower surge currents the MOV could clamp the voltage at the source to below 6,000V so there was no arc-over. With arc-over the max energy absorbed was 1.1J max.

Note that neither service panel suppressors or plug-in suppressors protect by absorbing the surge energy. But both absorb energy in the process of protecting.


..
One 'whole house' protectors from responsible companies such as
Square D, Leviton, Siemens, Cutler-Hammer, Keison, Polyphaser,
Intermatic, and GE - all will earth direct lightning strikes without
damage.
..
All of these "responsible companies" but SquareD and Polyphaser also make plug-in suppressors.

For it's 'best' service panel suppressor SquareD says "electronic equipment may need additional protection by installing plug-in [suppressors] at the point of use."

And repeating from the NIST guide:
"Q - Will a surge protector installed at the service entrance be sufficient for the whole house?
A - There are two answers to than question: Yes for one-link appliances [electronic equipment], No for two-link appliances [equipment connected to power AND phone or cable or....]. Since most homes today have some kind of two-link appliances, the prudent answer to the question would be NO - but that does not mean that a surge protector installed at the service entrance is useless."
..
A protector without earth ground will somehow absorb those
megajoules? Will that silly little inch part stop what three miles of
sky could not?
..
w_ is referring to plug-in suppressors.

Repeating:
"Poor w_ can't understand how plug-in suppressors work. It is explained in the IEEE guide (starting pdf page 40) if poor w_ could only read. Plug-in suppressors work primarily by clamping the voltage on all wires to the common ground at the suppressor. The guide says they do not work primarily by earthing. And nobody but w_ says they work by stopping or absorbing. The guide explains that earthing occurs, just not primarily through the plug-in suppressor."

--
bud--
.

Relevant Pages

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