Surge protector technology?

I disassembled a switched surge protector in order to modify it. I explain
why at the end.
I found that here seemed to be no surge protection. The switch was wired to
the outlets through a fuse. A ceramic disc capacitor was across the switched
outlets. That was it!
I was surprised not to find a varistor type device. Then I thought that the
small cylindrical gizmo might be an inductor so as to form an LC filter. The
marking on this cylinder, however, read as if it were a fuse.
My question is: Does this legitimately pass as a surge protector?
The reason I was making the modification is to switch some pumps or other
electrical equipment without tripping GFIC while still retaining GFIC
protection. I have found that any capacitance to ground and possible an
inductive kick through a varistor could cause a trip.
Bill
-- Fermez le Bush
Reply to
Salmon Egg
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a powerbar isnt necessarily a surge protector.
Reply to
matt
On 9/13/06 3:28 PM, in article snipped-for-privacy@i3g2000cwc.googlegroups.com, "matt" wrote:
That is what I wanted but it was labeled as a surge protector.
Bill -- Fermez le Bush
Reply to
Salmon Egg
That is an MOV not a capacitor.
I have MOV protectors behind a GFCI with no problems
Reply to
gfretwell
... only in a "better than nothing" sort of way Three MOVs is better You should also have an inductive componant.
Reply to
gfretwell
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
Reply to
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. ;-)
Reply to
gfretwell
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
Reply to
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
Reply to
Salmon Egg
Yes, its a MOV. Google search it, you can learn how it works, etc.
Reply to
Skenny
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..
Reply to
gfretwell
The electrical calalog guys will sell you a bag of them for the price of a good case of beer.
Reply to
gfretwell
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--
Reply to
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.
Reply to
gfretwell
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
Reply to
ehsjr
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.
Reply to
gfretwell
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 in parallel clearly lowers MOV voltage as made so woefully obvious from manufacturer datasheets. For a constant current transient, MOV voltage decreases as number of parallel MOVs increase. More MOVs also means the total energy absorbed by MOVs decreases. More parallel MOVs also means life expectancy increases exponentially.
ehsjr wrote:
Reply to
w_tom
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
Reply to
billb

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