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I must say I am impressed with Wes KISS and all others who have commented,
I am going to put the circuit I found into practice will see what happens. Once again thank you
The best information on surges and surge protection I have seen is at: https://www.electro-tech-online.com/custompdfs/2012/05/IEEE_Guide.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 a major organization of electrical and electronic engineers).
And also:
**broken link removed**
- "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 surge guide is aimed at people with some technical background.
What does a fuse do during a surge? This introduces another concept critical to surge protection. Destructive surges are current sources - not voltage sources. Voltage will increase as necessary so that the current will still flow. Anything that tries to stop a surge will only see voltage increase high enough to blow through. Nothing stops a destructive surge.
The normal failure mode of a MOV is it starts to conduct on normal voltages and goes into thermal runaway. Fuses (or thermal protectors) don't blow during a surge. For they open after the surge is over.
In US systems, at about 6,000V there is arc-over from service busbars to the enclosure. After the arc is established, the arc is hundreds of volts. (Since the enclosure is connected to earth that dumps most of the surge energy to earth.)
What happens when a surge on the hot wire (maybe 5000 volts) is shunted to the neutral? 5000 volts on the hot wire AND 4600 volts on a neutral wire. Where is the protection?
A plug-in protector would have one supply (hot) supply wire and two drain wires (neutral and ground). The voltage at the protector would be about 1700V, not 5,000. Read the IEEE surge guide example. The voltage between the wires going to the protected equipment is safe for the protected equipment.
The protection is what absorbs hundreds of thousands of joules. Earth ground. A protector either connects tens of thousands of amps to earth ground. Or that protector does nothing (is a profit center).
Nonsense. The IEEE surge guide explains (starting page 30) that plug-in protectors do not work primarily by earthing a surge. They work by limiting the voltage from each wire (power and signal) to the ground at the protector. The voltage between the wires going to the protected equipment is safe for the protected equipment.
When using a plug-in protector all interconnected equipment needs to be connected to the same protector. External connections, like cable, also must go through the protector. Connecting all wiring through the protector prevents damaging voltages between power and signal wires. The NIST surge guide suggests that most equipment damage is from high voltage between power and phone/cable/... wires.
The author of the NIST surge guide looked at the amount of surge current you can get on power service wires. For US systems the maximum probable current was 10,000A for each of the 2 hot wires (and another 10,000A on the neutral). That is based on a 100,000A lightning strike to a utility pole adjacent to a house with typical urban overhead power distribution. Only 5% of strikes are larger than 100kA, and the strike was extremely close. The probability of a worse event is very low.
Service panel protectors with ratings much higher than 10,000A are readily available. They are very likely to protect anything connected only to power wires from a very near very strong lightning strike (at least with services connected as is done in the US).
The author of the NIST surge guide also investigated how much energy might be absorbed in a MOV in a plug-in protector. Branch circuits were 10M and longer, and the surge on incoming power wires was up to 10,000A (the maximum probable above). The maximum energy at the MOV was a surprisingly small 35 joules. In 13 of 15 cases it was 1 joule or less. One reason is arc-over at about 6,000V at US service panels. Another is the impedance of the branch circuit to the relatively high frequency surge currents in a very short duration surge. The current that can reach a plug-in protector is quite limited, so the energy that is absorbed in a plug-in protector is very limited. Plug-in protectors with much higher ratings are readily available. As with service panel protectors, high ratings mean long life. A plug-in protector, wired correctly (as above), is very likely to protect from a very near very strong lightning strike.
(Neither service panel or plug-in protectors work by absorbing the surge. But they both absorb some energy in the process of protecting.)
Westom has a fetish about earth ground. The IEEE surge guide explains that plug-in protectors do not work primarily by earthing a surge. (Earthing occurs elsewhere.)
Contrary to the westom's opinions, which he spreads all over the internet, both the IEEE and NIST surge guides say plug-in protectors are effective.
I used to have a homemade surge protector, with MOVs and a filter. I stopped using it long ago. A competent manufacturer will carefully design protection for failing (overheating) MOVs. And commercial protectors with high ratings are not that expensive. I do not recommend making or modifying surge protectors.
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