surge protection on washer??

Having MOVs in locations with impedance inbetween is the reason to do it. The first MOV takes part of the surge, if any reaches the next one, it then helps with the protection. The impedance slows the rise time of the surge and helps with the surpression. Some of the surge is dissapated in the inductance.

Reply to
Ralph Mowery
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There is no reason to slow the rise time, at least for MOVs.

Inductance stores a surge, it does not dissipate it.

If you had identical MOVs in parallel they would equally share the surge and the cumulative rating would increase (look at MOV curves for surge amps versus number of surges). With an inductance between they do not equally share the surge and you are, in effect, lowering the cumulative rating.

Manufacturers do not put inductance between MOVs. They will tell you not to daisy-chain plug-in protectors. And it is a violation of UL standards for plug-strips (which is one of the listings for most plug-in protectors).

In a building, the inductance between a service panel and plug-in protectors works much different than the inductance for wiring between 2 daisy-chained plug-in protectors.

Reply to
bud--

How is that? inductance is inductance. And how about the MOVs inside an appliance? They are a similar distance from a second cord type surge protector if you had two in series.

I'm not disagreing that the amount of surge current the first surge strip would possibly take could be larger than the subsequent one. And I'm not disputing that UL says you shoudn't daisy chain power strips, but I think that is a separate issue, ie they don't want dummies plugging 5 things in one strip, then another 5 in the next one.

Reply to
trader4

The better ones do. Here is one example.

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I did not make it clear abou the inductance. Becuse many surges will have a very steep rise time, the inductance acts similar to a resistor and prevents some of the surge from getting past it. Much like an RF choke in a radio circuit.

Reply to
Ralph Mowery

Could be one of those UL things for dummies. Not that I did it for protection, but at my computer desk there is a surge supressor strip behind it that has my cable modem and router pluged into it. It stays on all the time. Pluged into that strip is another one that is about a foot square with a switch on the frount and the outlets on the back. It is mostly empty space inside but makes a base for things to sit on. I use the switch on it for the compute, monitor and printer. It may not meet the stupid UL rules but is safe as the current drawn is not very much.

At work there was a big stink about some battery chargers for the handy talkies. There was about 3 strips plugged into each other. They all had the wall wart cubes on them. I am sure there was not a 10 amp load on the whole system if all the chargers were putting out the maximum charge. Safety department saw that and made them move the strips to seperate outlets.

Reply to
Ralph Mowery

A service panel protector is exposed to whatever comes in on the power service wires. That is, for practical purposed, up to 10,000A surge current. The protector will lower the surge voltage to a reasonable level.

Suppose there is no service panel protector and there is a large surge. At about 6kV between the busbars and enclosure there is arc-over. The voltage across the established arc is hundreds of volts. Since the enclosure is connected to the earthing system, most of the surge energy is dumped to earth. And since the building ground and neutral are connected the surge at that point is all "normal" mode (between hot and ground/neutral).

The inductance of the branch circuit for the very short duration surge caused by lightning then greatly reduces the surge current that can reach a plug-in protector. That is true whether there is a service panel protector or not. The branch circuit inductance is an intrinsic part of the protection provided by a plug-in protector**. (If you have a very short branch circuit you should have higher ratings for a plug-in protector.)

When daisy-chaining plug-in protectors, the inductance between the protectors does not have the same major effect.

But what if the L-N MOV conducts in the first protector and the L-G MOV conducts in the second protector. There is voltage drop across the inductance of the hot wire between protectors that results in a higher L-N voltage at the protected equipment. In a service panel, the lead length is very important (60 volts drop for 6 inches of lead and 500A surge current - from the IEEE surge guide). Is it a problem in a 6 ft power cord? I don't see a reason to find out.

** For plug-in protectors "if included in the manufacturer's instructions the ... connections shall be a minimum of 30 ft of conductor distance from the service...." (2011 NEC 285.25)

Ideally I would rather have all surge protection that is at the equipment at a single location. For interconnected equipment that would have to be common to all the equipment. But I manufacturers include internal protection for sensitive' equipment since users may not add external protection. It is a necessary compromise.

I don't see a reason to add another layer.

Reply to
bud--

Why are those "better ones"?

The circuits all use gas discharge tubes. Far as I know those are not used in the power circuits of plug-in protectors, and I haven't heard of them being used in power circuits of electronics. Gas discharge tubes have a short delay until they operate - the gas has to ionize. Inductors may or may not make sense with gas discharge tubes.

The article is probably aimed at Europe.

Far as I know, the inductors in plug-in protectors in the US are for noise filtering (and I am not convinced that does anything useful). MOVs are faster than surges and inductors are not necessary for protection.

An inductor is likely to lower the rise time and lengthen the surge.

I don't know of MOV based plug-in protectors that use multiple MOVs with inductors between them (in the US).

Reply to
bud--

Then read this and learn what the inductors are for in the beter surge protectors.

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This one is from a company in the US.

The inductors can provide two functions. One is the RFI protection that keeps the 'trash' from the device from going back to the power line in normal operation. When a surge comes on the line it has another function.

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Reply to
Ralph Mowery

Why are those "better"? And why were the circuits in your previous post "better ones"?

Interesting that the link is from ee times - india.

The app note is from Littelfuse. It is for using gas discharge tubes in combination with MOVs. As I wrote previously, GDTs have a time delay because the gas has to ionize. The app note uses MOVs to protect during the time delay so GDTs can be used. Coincidentally Littelfuse makes GDTs.

From my last post - "far as I know [GDTs] are not used in the power circuits of plug-in protectors, and I haven't heard of them being used in power circuits of electronics."

According to the IEEE surge guide (which has been linked to here often), "the vast majority (>90%) of both hard-wired and plug-in protectors use MOVs to perform the voltage-limiting function. In most AC protectors, they are the only significant voltage limiters." MOVs are so widespread because they have high energy dissipation capacity in a small package at relatively low cost.

And from the Littelfuse app note: "The clamp-type devices [MOVs] have faster response times but are limited in their current handling ability because most of the energy of the transient must be dissipated by the clamping device." Most of the energy of the transient is _not_ absorbed by the MOV. As I have often posted, an investigation by the surge expert at the NIST found the energy that was absorbed at a MOV in a plug-in protector was surprisingly small - 35 joules max. In 13 of 15 cases it was 1 joule or less. The service wire surges were up to

10,000A, the maximum with any reasonable probability of occurring. And the largest energy at the MOV was not caused by the largest surges. Protectors with ratings far larger than 35 joules are readily available.

Noise filters are likely real useful in electronic equipment.

I am not convinced they do anything useful in plug-in protectors.

That is if you are using Littelfuse GDTs for protection, backed up by MOVs for the hole in GDT protection.

--------------------------- I would not daisy-chain plug-in protectors. The inductance between the protectors can work to your disadvantage. And no manufacturers I know of allows daisy-chaining.

Reply to
bud--

Sure, it's not the same magnitude of effect, but it's still inductance causing a difference.

It would seem to me that there is a lower voltage at the protected eqpt, because part of the voltage drop is between the protectors.

1000 - 100 = 900

And if there were no second surge protector, the eqpt would see the full 1000V. What works on 15 ft of wire also works on 3 ft of wire, just to a differing extent.

In a service panel, the lead

Now you;re sounding like Wtom how says that without a direct connection to earth, no protection is possible. If 6 ft is a problem for one surge protector, then it's a problem for another one and it's a problem for the surge protection in the eqpt itself, which any with electronics have. How can that MOV in the TV work, but a second surge protector after the first is a problem?

But that surge protection is working with a whole house, a plug-on, two plug-ins, whatever is before it. And you haven't answered the question as to how that MOV in the appliance is different than adding a second surge protector before it.

If I already had two surge protectors that were of equal rating that I had no other use for, I see nothing in the physics that says daisychaining them to protect a $1000 TV is a bad idea.

Reply to
trader4

I ment to post this link.

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To understand how inductors work you need to understand the rise time and dv/dt.

Reply to
Ralph Mowery

Where is Wtom when we need him. :-)

Reply to
Ralph Mowery

Hi, B4 anything, we should talk about GOOD quality built product not El Cheapo junk. My idea is I'll apply protection right at the logic board. Where I live power surge is very rare and never heard it damaged. anything. Lightining is also rare, my HAM radio antenna tower never got hit(I have a protection for my gears tho). No insurance coverage?

Reply to
Tony Hwang

Where I lived before this house I had about a 40 foot ham tower up. It was also near the top of the rise of land that was near it. ANever got hit with many lightning storms.

A transformer that feeds the house let go one night during a thunder storm. There was a whole house protector about the size of a baby food jar outside the house at the meter. It did not look damaged from just looking at it. The surge did take out two differant protection strips. I think they were the Isobar 6 outlet types. One for the ham gear and one for the TV. The equipment was ok. The built in oven smoked, but all it did was burn out a trace on the circuit board and take out the MOV. Service call for the stove was the minimum they charge.

A neighbor that feeds off the same transformer lost his TV and a few other small things. All power wiring in the area was above ground.

Reply to
Ralph Mowery

So make it H-N at the first protector. That lifts N toward H. Then N-G at the second. That pulls the N at the 2nd protector away from the N at the 1st and adds to the H-N surge seen at the protected equipment. It also increases the voltage between H and signal wires referenced to G.

With no service panel protector, the voltage at the panel could be up to around 6kV. With a H-N MOV the voltage on both H and N wires at the protector could be around 3kV above the ground at the panel. (The protector still protects because, if connected correctly, the voltage between all wires going to the protected equipment is safe for the protected equipment.)

Not at all. Plug-in protectors, wired correctly, provide protection.

As I wrote below protection in the connected electronics is a necessary compromise. (And the circuits for electronic equipment I have seen do not have N-G MOVs.)

I did answer it above. It is a necessary compromise.

(And service panel is different from downstream protectors.)

Using 2 plug-in protectors is an unnecessary compromise. What manufacturer allows daisy-chaining? What manufacturer intentionally adds inductance between paralleled MOVs?

You can, of course, do what you want. Don't expect that either manufacturer will honor a warranty.

Reply to
bud--

It is the same article as above.

I understand rise time and dv/dt.

They are irrelevant for MOVs because MOVs are fast enough for surges they will see. According to the IEEE surge guide almost all protection is from MOVs.

-------------------------------- I would not daisy-chain plug-in protectors. The inductance between the protectors can work to your disadvantage. And no manufacturers I know of allow daisy-chaining.

Reply to
bud--

I think there is something about mov's in equipment. Something not permitted or something like that. I don't remember seeing any in equipment. They would have to be sealed up, because they blow up. I'd have to dig out my book, PC Power protection. You can put stuff in your own equipment.

Greg

Reply to
gregz

Insurance claim for a typical washer? Most policies have deductibles that are higher than the cost of a typical washer. Plus, I'm not sure they would cover damage from a surge anyway. We're not necessarily talking about a direct lightning strike to the house. If there was a surge on the power lines and the washer quits working, good luck proving the cause.... And you file the claim, even if you wind up getting a couple hundred bucks, then they raise your rates.

Reply to
trader4

That's kind of my point. If there's only 3 ft of wire between the MOV's, then there isn't going to be a lot of inductance. Again, I'm not saying that if you had two of the same MOVs separated by that additional 3 ft that it would be as good as having one that was twice the rating. But I don't see it as being bad either. The surge would probably get split between them, but not 50-50. I wouldn't go out and buy two surge protectors to use that way. But if I had two sitting around I don't see the downside in the physics to daisy chaining them.

The MOV will all be conducting if the clamping voltage is exceeded. And I don't see how part of the voltage drop being across the inductance of the hot wire in the cord is a bad thing. If the voltage drop is across the inductance of the cord, then it's not across the appliance. It would seem you could make exactly the same case for the interaction between a panel protector and a plug-in, or between the plug-in and the internal MOV's in the appliance. All of those are separated by wire with inductance.

In a service panel, the lead

Well, yeah because they are dealing with potentially 10K amps and the shorter the path to ground, the less impedance. But at the typical appliance you already typically have 25 - 100 ft of wire to deal with, then an appliance cord that's 6 ft, then surge protection in the appliance.

If it's a problem for a second surge protector at the end of a 6ft cord, why isn't it a problem for one surge protector followed by the MOVs that are at the end of the 6 ft appliance cord?

Except I've never seen that in any surge protector manufacturer's instructions. Have you?

Yes, but the point is, it's in fact more surge protection, MOVs, situated 6 ft down the cord from a plug-in protector. If that doesn't result in bad things happening, I don't see why a second plug-in daisy chained that can handle substantially more surge current will.

From a practical standpoint, I agree. But I don't see anything in the physics that says it's a bad thing either.

Reply to
trader4

Are all these surge protectors defective? They all have similar MOVs and they all should be conducting when the clamping voltage is exceeded.

But they are there and apparently bad things aren't happening from having a second set of MOVs 6 ft further down the appliance cord from a plug-in. So, I don't see it happening with a daisy chained external surge protector either.

Is Polyphaser adding inductance between MOVs good enough?

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Or look at all these schematics:

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How about Electronic Design News:

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I think the surge protection warranties are a joke. I've seen enough reports of people trying to collect on the alleged "protected equipment" warranties. You try to collect, send the surge protector in to them and then typical response is "The surge event exceeded the design limits of the device. It's not covered"

Reply to
trader4

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