Surge protector technology?

a powerbar isnt necessarily a surge protector.

That is what I wanted but it was labeled as a surge protector.

Bill

-- Fermez le Bush

That is an MOV not a capacitor.

I have MOV protectors behind a GFCI with no problems

... only in a "better than nothing" sort of way Three MOVs is better You should also have an inductive componant.

Three MOV are not in most cases better, due to the tolerance on the MOV the lowest rated one will take all the surge. For three to make any major difference they need to be a matched set, most are not. The size of the MOV is more important, than the number unless they are matched sets.

BillB

Bill, not 3 in parallel. One going line to neutral, one line to ground and a much lower breakdown voltage one going neutral to ground. The line to neutral one is really just to make up for a bad ground. Better than nothing. All of this is made a lot more effective if you have a big iron inductor in there to eat the energy spike that gets shunted with the MOVs (as heat). A couple loops around a ferrite bead is again, better than nothing. I have had engineers tell me a couple knots in the cord will help for very short duration transients. I don't really believe it but I still seem to end up with a knot or two in my power cords and I don't untie them. ;-)

Yes I agree, but most supplier install sets of MOVs in parallel as well as between L+N, L+E and N+E and claim that they give better performance by quoting the total Joule ratings of all the installed MOVs. This is completely misleading.

BillB

I broke the disk to examine it. It sure looks like a piece of barium titanate or similar substance with leads just like a disc capacitor. Do MOVs or varistors have the same appearance?

Bill

-- Fermez le Bush

Yes, its a MOV. Google search it, you can learn how it works, etc.

We are on the same page here partner. You can get MOVs in big sizes but the cost is not a linear thing. One big one costs more than a handfull of little ones and it is false economy not to spend the extra money for the big guys. It is still chump change against the cost of stuff that blows up..

The electrical calalog guys will sell you a bag of them for the price of a good case of beer.

The manufacturer could match them, making paralleling equivalent to a single device. But unlikely in cheap stuff. I wonder how much matching is done in more expensive devices.

bud--

I never saw parallel MOVs in expensive protectors. They just used big ones but there are also other componants, along with that big chunk of iron.

Assuming one of the parallel MOV's operates and the others don't, it takes the surge *until it dies*, then the other MOV(s) come into play. That extends the duration of the protection - thus more protection, from that perspective. So in theory, 3 in parallel would last 3 times as long as a single, all other conditions being equal.

What paralleling 2 of the same MOV's does not do is lower the clamping voltage, or double the current capability. So if one clamps the voltage to 300, adding a second in parallel does not lower it to 150. Nor does it mean that if one can handle a surge of X amps, two can handle a surge of 2X amps.

Ed

The problem is you can run out of time. The big chunk of iron can slow down the shot but you have to get rid if it.

Paralleling MOVs increases that circuit's joule ratings. As joules increase, MOV life expectancy increases exponentially. As joules increase for a same transient, overall voltage across all parallel MOVs decrease. IOW as joules increase, total energy absorbed by all MOVs decreases.

For example, the MOV designed to protect a 240 AC circuit may conduct a small current at 350 volts. But as transient current increases, that MOV voltage may rise to 900 volts. MOVs do not operate with a sharp response time more commonly associated with avalanche diodes. Their volt-current response curve is quite gentle as current increases. Therefore parallel MOVs will share the current shunted.

Due to variations even within MOVs of same part number, derate the overall performance of parallel MOVs. For example, three 100 joule MOVs would not create a 300 joule protector. Because of MOV variations, we may rate that protection circuit to 240 or 270 joules.

Two MOVs > Assuming one of the parallel MOV's operates and the others

When the first MOV of the set blows it usually takes out everything in the area, if the protection circuit operates its switches out all the MOVs in that part of the circuit and switches off the power at the sockets. If the protection circuit does not operate the MOV can destroy the tracks on the PCB and any components near it and have been known to spilt the case of the power strip. They blow with a hell of a bang.

BillB