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## [TowerTalk] whole house surge protectors

 To: Tower Talk List [TowerTalk] whole house surge protectors Jim Lux Wed, 19 Sep 2007 10:34:55 -0700
 ```I've been doing a bit of browsing Most of the whole house protectors are shunt mode (which, by the way, can actually cause some problems, making things worse) Intermatic IG1240RC Leviton 51120-1 Panamax gpp8005 Siemens various models etc. In any case, a shunt mode suppressor will also suppress transients originating within the house. There is a case where they will be of less effectiveness.. if you have a transient induced on the branch circuit between the panel and your load, then the transient propagates both directions, and, depending on the relative lengths of the wire, it will get to the load before it gets to the clamp. Once the clamp goes into effect, an inverted transient gets reflected back, so you can calculate the maximum width of the unsuppressed pulse. (you could use something like 2 ns/ft as a propagation speed... so for a 100 ft run, with the transient induced next to the load (or downstream from the load), you get half a microsecond or so before the voltage is clamped. If the transient is induced on a branch circuit other than the one your load is on, the suppressor is between the transient source and your load, so it would clamp the transient before it arrives at the load. If you put a point of use transient suppressor *with a higher voltage* than the whole house protector, it will take care of the half microsecond impulse before the whole house protector kicks in, and won't have to absorb as much energy. FWIW, statistics show that most transient damage occurs from transients originating outside the house, typically from a lightning strike or MV line / LV line fault somewhere (MV = 10-30kV, LV = 120,240,480V). That makes the rise time of the transient much slower (it's low pass filtered by the power line), and also makes the whole house protector more effective. In the event of a MV/LV short (the only kind of line transient I've had personal experience with in Southern California.. we don't have much lightning here), you've probably got a significant overvoltage that lasts 8-10 milliseconds or longer (until the MV breaker trips or fuse blows). You'd have to hope that the surge suppressor can hold on that long without blowing its internal fuses. Or, ideally, it would short, and trip your main breaker. Since most of these whole house protectors have energy absorptions in the few kilojoule range, I'm not very sanguine about their ability to protect against this kind of fault. Figure the case of a 14.4kV feeder shorting to the 240V drop into your house (this has actually happened to me). If the series impedance of the feeder, through the drop, into the grounding system, is on the order of an ohm or so, the fault current is around 10-20kA. If the surge protector is based on an MOV, the 400V MOV is going to dissipate about 4-8 MW, or, 4-8 kJ/millisecond. If it takes a half cycle for the breaker to trip/fuse blow, that's 8 ms, and about 50kJ (which is why things literally explode when this happens). A surge protector based on a spark gap, which, once it fires, has a much lower clamping voltage, will dissipate less energy in the protector, so has better survivability. _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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