ECN Forum Forums General Topics of the Trade General Discussion Area Surge Protection

A knot is a mix of the cable going in both directions within the knot (depending on the topology of whatever know was used). The magnetic field will effectively cancel out at the inner parts of the knot, and just wrap around it on the outer parts. So the current would just flow through the knot easily. A coil would be better. At best the knot would reduce some UHF and higher RF.

Trumpy makes a good point - that when the surge protection works, it could need to be replaced. I suppose it must also be robust enough to survive the duration of the surge. A lightning strike can't be safely dissipated inside a house, so it doesn't need to survive that.

With a power bar, the return path to ground (or neutral if conducting to ground isn't legal) can be quite long. Might it be too long to be effective?

The theory of the point of use protector is that it shunts transients within the protector so you need a lot of joules in the rating. Basically you are just heating up an MOV or two. The ground connection is just there to provide a path for that delta. You still should be just burning off the transients that were generated within the building there though. The bulk of the incoming transients should have been stopped at the Dmark or the service disconnect panel where you have a very short grounding path. I would drive a rod there, even if I had a Ufer, just for a local ground reference (bonded to the other electrodes).

I have had 2 direct hits to the mast where my weather station is mounted and all I ever lost was the serial port in the PC that runs it. That was the first strike. After working on that line (ferrites and a "phone line" style protector in a strip), the second strike left me unscathed.

You can make some fairly good protectors yourself if you carefully match the MOV to the expected line voltage.
Hosfelt will sell you them in all sorts of different voltages and joule ratings.

And everything else. The MOV has a low resistance when the voltage is high, so the dissipated energy is low. Unless a destructive fault current flows (like a direct strike with no alternate path to ground), the MOV is going to hold the voltage drop at the clamp voltage where it goes back down in resistance. The conductors will dissipate a lot of it, too, because it is current flowing. A fuse or breaker in the circuit to the POU protector could blow/trip, as well.


I agree.


Yup! But you won't have the advantage of it being a listed protective device and the insurance that comes with some protectors. Your own insurance might not pay out in the event of a surge too large to be protected, claiming that it wasn't so large and your unlisted protector was faulty.

I think I may need to do just that, though, because I have yet found a POU protector for a L-L 240 volt circuit (NEMA 6-15/20P and a few 6-15/20Rs although I'll take C13/C19 as an alternative). 330V MOVs on L1-G and L2-G, and 660V MOVs on L1-L2. I do have some power strip boxes with the traditional looking receptacle in the box in 5-15R form. So I just need to find 6-15R in that form, and rewire the guts for 240V and L+L+G circuit type.

I like the idea of a whole house protector that includes cable and phone surge protection. That and a point of use type protector at each piece of equipment.
We had a nearby lightning strike sneak into our house via the outside overhead phone and cable lines a few of years back and it really raised hell. It damaged the pairs in one of the phone wires in the basement and burned up a cordless phone base in the upstairs bedroom as well as our kitchen wall phone/answering machine, a 56K modem PC card, a small APC UPS unit and a couple of older 19" CRT TV’s. Our HO insurance paid the claim promptly, so at least that part went smoothly with no hassles.
I notice that most if not all surge protector manufacturers claim that in addition to the regular warranty, their product usually include some rather substantial amount of insurance protection against damage or loss, but has anyone ever actually collected from these or are they just a marketing tactic?

That insurance is buried in the price somewhere. I have never heard of anyone actually having to get it honored so I am not sure how well it works. We had a deal with Panamax (one of the first multi input protectors) and sold them. We did get a couple of Panamax units replaced but the equipment survived.