Isolating electronics from suges - AVS Forum
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post #1 of 4 Old 01-06-2012, 10:20 PM - Thread Starter
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I like to know how reliable a whole house surge protector (lets say from a good brand) will be in protecting sensitive electronics from large surges? I live in a tropical country and lightning is frequent and large. I know this question has no definite answer, but like to see statistics if available so i can get a better idea.

Secondly, i am looking for a coaxial cable switch to switch between a low resistance earthing wire and a TV. That is, in one position, the cable will connect to the TV and in the other position it will connect to a copper code which is earthed. I know there are enough of such switches available, but the isolation is not enough between connections during surges. The whole purpose of this switch in this application is to route any surges to ground without leaking (through sparks) to the TV.
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post #2 of 4 Old 01-06-2012, 10:45 PM
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It would help if we knew what country. Electrical power distribution systems differ from country to country and it might affect the answer a bit.

No need for a switch on the coax, even if you can find one with the isolation you need. For most cases, grounding the coax shield where it enters the house with a ground block is sufficient. If you want more protection, you can use a coaxial surge protective device at the same location which will shunt a surge on the center conductor to ground, and reduce what the TV sees to safe levels.

A properly grounded whole-house surge protective device at the service entrance will reduce the surge voltage to safe levels. Most electronic and electrical gear is inherently protected to at least 600V. I think the most important thing for you will be the surge current rating. In the USA, Underwriters Laboratories(UL) tests and certifies surge protective devices up to 20KA which is considered a worst expected case surge. Devices that have higher surge current ratings will last longer. IIWY I would be looking at a 250KA device.

That takes care of surges conducted by the electrical wiring or coax. There is still the possibility that lightning could induce a surge directly on the internal wiring if the strike is close enough to the house even if it doesn't strike the power lines or coax. And of course, all bets are off if you suffer a direct hit.
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post #3 of 4 Old 01-06-2012, 11:02 PM - Thread Starter
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Thanks for the reply Colm.

Its Sri Lanka. I think the earthing system is TT.

In Sri Lanka, plenty of deaths get reported each year due to lightning strikes that come though antenna wires. Although i did not mention in my first post, apart from protecting the electronics, the system should be able to suppress such strikes to a level where the residents are protected as well. Do you think a coaxial surge protection device is capable of doing that with high reliability?
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post #4 of 4 Old 01-07-2012, 12:19 AM
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I haven't seen any statistics on that. And I think you would be hard put to find such statistics. I cannot give you any guarantees, just good practice.

Protection of the antenna starts with proper grounding of the antenna mast, and the coax shield where it enters the building. They need to be properly bonded to the ground for the electrical system. In the USA, the typical requirements can be found in the National Electrical Code (NEC). Antenna manufacturers typically list similar requirements in the documentation that comes with the antenna. A good gas tube based coaxial surge suppressor will start conducting before the voltage exceeds the insulation rating of the coaxial cable and then essentially act as a dead short (ionized gas) until the surge is gone. The inexpensive ones used on most residential installations in the USA are rated for 5000A. IIWY I would go with one rated 20KA.

If you have a direct strike to the antenna, I am pretty sure you are going to have induced voltages on all the wiring in the house because of the electromagnetic field of the lightning. How significant that is, and how to deal with it, is way beyond my knowledge.

If you have a high probability of a direct hit, you may also need to consider lightning air terminals.
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