Re: How to ground electric outlets over a slab?

westom wrote:
On Apr 30, 4:23 pm, gfretw...@xxxxxxx wrote:
It isn't magic, it is just energy that gets converted to heat in the
MOV., That works until the MOV burns up. That is why MOVs are rated by
the amount of energy they can convert and how fast.

Let's view those numbers. The protector is rated for how many
hundred joules? It will somehow absorb the hundreds of thousands of
joules in a surge? That is what bud promotes.

w is not able to understand simple physics.

Francois Martzloff was the NIST guru on surges, wrote the NIST guide, and has many published technical papers. One of them looks at a MOV on a branch circuit of 10-50 meters with surges to the power service of 2,000-10,000A (the maximum with any reasonable probability of occurring, at least for a house).

Surprisingly, the maximum energy dissipated was 35 Joules. In 13 of 15 cases it was 1 Joule or less. That is because at about 6,0000V there is arc-over from service hot bus to the enclosure. After the arc is established the voltage is hundreds of volts. In US services, the enclosure is connected to the equipment ground wires, the neutral wires and the earthing system. Arc-over dumped most of the incoming energy to earth. In addition, the impedance of the branch circuit wiring greatly limits the current that can reach the MOV. Surges are very short duration, so the inductance of the wire is much more important than the resistance.

The higher energies were for a 10M branch circuit and, even more surprising, the lower current surges below 5,000A. Contrary to intuition, at all branch circuit lengths the energy dissipation at the MOV was lower as the surge current went up. That was because the MOV acted to clamp the voltage at the service panel. With the short branch circuit and lowest surge currents, the MOV prevented arc-over. Higher current surges forced the voltage up faster, causing arc-over faster and more energy was dumped to earth.

MOVs in both service panels and plug-in suppressors do not protect by absorbing energy. But they absorb some energy in the process of protecting.


Also, 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.

For the reasons above, a plug-in suppressor with high ratings is not likely to ever fail. That is one reason some manufacturers can provide protected equipment warranties.

Notice no plug-in protector even claims
to provide that protection.

Complete nonsense. Some manufacturers even have protected equipment warranties.


Still missing - a link to anyone who agrees with w that plug-in suppressors do NOT work.

Still never answered - simple questions:
- Why do the only 2 examples of protection in the IEEE guide use plug-in suppressors?
- Why does the NIST guide says plug-in suppressors are "the easiest solution"?
- Why does the NIST guide say "One effective solution is to have the consumer install" a multiport plug-in suppressor?
- How would a service panel suppressor provide any protection in the IEEE example, pdf page 42?
- Why does the IEEE guide say for distant service points "the only effective way of protecting the equipment is to use a multiport [plug-in] protector"?
- Why did Martzloff say in his paper "One solution. illustrated in this paper, is the insertion of a properly designed [multiport plug-in surge suppressor]"?
- Why do your "responsible manufacturers" make plug-in suppressors?
- Why does "responsible" manufacturer SquareD says "electronic equipment may need additional protection by installing plug-in [suppressors] at the point of use"?

For real science read the IEEE and NIST guides. Both say plug-in suppressors are effective.

--
bud--
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