Surge protectors in series

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If two surge protectors are connected in series, is the amount of surge protection available at the down-stream protector approximately equal to the sum of the two individual protections??
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Caesar Romano wrote:

By 'surge protector', do you mean something like plug strips with MOV peak voltage limiting? If so, the upstream device will limit an overvoltage transient and the downstream device sees normal waveform and provides added protection only if the upstream device fails. Actually, the varistors don't provide an absolute clamp at their trigger voltage, but the downstream guy will do very little protecting.
If you're referring to connecting two MOV's in series across the line, then the overvoltage clamping will begin when line voltage reaches the sum of the individual MOV clamp voltages. The same transient current will flow through each MOV, and each will dissipate part of the transient (as heat). If they have the same clamp voltage, then each MOV absorbs half of the energy.
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wrote:

You don't finish, but aren't you saying that the voltage that gets to the appliance can reach twice the voltage with only one MOV across the line, that it's much worse, much less, practically no protection with two? I don't know enough to know, but that sounds conceivable and sounds like the logical next sentence to what you wrote.
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mm wrote:

The peak let-thru voltage will be the sum of the series-connected MOV clamp voltages (a bit higher actually). They are manufactured in several clamp voltage ratings. Using a series-connected pair would probably happen only if designing protection for an unusual line voltage or to make do with what is in the junk box. Using two series-connected MOV's, each intended for 120VAC to protect a 120VAC line would be a bad idea. Using the same pair to protect a 240VAC line would be better.
By the way, parallel connection of two or more MOV's is a bad idea. If they have different clamp voltages, the first to begin conducting does all the work. Even two MOV's of the same rating will have slightly different characteristics and won't play well together.
for protection of a 120VAC line
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Nope.
wrote:

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Caesar Romano wrote:

I haven't thought of it that way. I suppose it's possible, depending on how a particular protector circuit functions.
I have a protector at my service entrance. When lightning struck my house, I had perhaps $1000 worth of damage to electronics in various rooms, but none to my my computer/telephone equipment, which was on a plug-in protector. Because the surge didn't come in on the line, it made a big difference to have that equipment plugged directly into a protector. It's possible that my computer would have been wrecked if the whole-house protector hadn't absorbed some of the energy.
I have twelve items plugged in at my computer desk. A surge protector is plugged in at the wall. That feeds a lamp, the phone, and another surge protector.
The second protector feeds my computer stuff and a third protector, which feeds my audio/video stuff. If the a/v stuff were connected to a cable or outdoor antenna, this might be unwise.
One reason to use three protectors is to be able to leave my computer stuff and my audio stuff switched off, for added protection, while still using my phone and lamp. The second protector could save my computer stuff in the event that the first protector fails and lets something through.
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I had a lightning strike and had Tripp Light units, I asked that question to their tech support and they said yes. My Tripp light units are also wired in such a way with added Movs for each outlet so that on a 6 plug unit the outlet furthest from the power plug has greater protection. But lightning can come in anywhere, 120v outlets only cover part of your problem.
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Caesar Romano wrote:

Outlet strips are not intended by anyone, including UL, to be connected in series.
Which protector does the protecting depends on which MOV clamps at a lower voltage. Voltage ratings, like 330V, are UL categories and cover a wide range. Even MOVs with the same part number that are not from the same batch would not likely have identical clamp characteristics. The upstream or downstream protector may initially do the clamping or it may be partially or evenly shared.
You would probably get a combined Joule rating equal to the sum of the individual ratings. If the clamping was actually evenly shared the combined cumulative rating would be higher than the sum of the individual ratings.
IMHO loads should only be connected to the downstream protector.
I recommend not connecting in series. Suppressors with very high ratings are readily available at relatively low cost.
And all interconnected equipment needs to be connected to the same plug-in suppressor, or interconnecting wires need to go through the suppressor. External connections, like phone, also need to go through the suppressor. Connecting all wiring through the suppressor prevents damaging voltages between power and signal wires.
--
bud--

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Tell that to Tripp Lite, they sell one of the best units made. In fact im fairly certain they were the first to offer a warranty against lightning damage.
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ransley wrote:

You aren't specific about which of the many things I said I should tell to Tripp Lite.
I presume it is that suppressors shouldn't be connected in series. From the UL White Book: "Relocatable power taps [power strips, which plug-in suppressors are a variation of] are not intended to be series connected (daisy chained) to other relocatable power taps or to extension cords."
--
bud--

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bud-- wrote:

The white book treats surge protectors as another item: Furniture Power Distribution Units. It says they, too, are not intended to be daisy chained.
It also says they are not intended to be used as Relocatable Power Taps. I wonder what it would hurt. I'm sure it doesn't mean it's unsafe to use a surge protector as a power strip. I think it means that there could be an application were a power strip would be okay but not a surge protector.
I wonder if they say daisy chaining is not intended because for some users, too many outlets could mean too many amps.
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You know UL, they gotta keep folks "safe" [from themselves], 1 Trip unit will do the job it was designed for, if you want safe, what I do is unplug when storms might be comming and I amd leaving. No surge protector can protect all that lightning can dish out on a big direct hit. I got hit bad once it was so strong it lit flourescent lights that were shut off 3 stories below where it came in when I was in the kitchen. In the attic track light bulbs were even loosened in the sockets that worked when screwed back in. It was so strong insurance pros thought it was a Plasma going through the room since circuits affected were not near the strike and the electronics damages the ins covered it cost over 20,000 to the insurance co. There wasnt even ANY entry point or exterior damage, just fire in one corner box and equipment fried 50 ft away. It must have been Plasma. A friend had ball lightning roll-float through his large room and do no damage, I guess thats Plasma. Lightning is scary stuff. Unplug for 100% saftey, its less of a hassle than a repair, and you know your stuff is safe. Im in a place hit 3 times already, and nows the storm season.
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ransley wrote:

My strike blew masonry from two chimneys as far as 100 feet. It wiped out three stereo receivers in three rooms. One wasn't plugged in or attached to anything but speakers.
It amazed me that so many items that were plugged in and running were apparently not damaged.
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Again tell that to Tripp Lite. Some of Trips units with multiple outlets have increased protection for each outlet as you move away from the power cord, daisy chaining is only like a strip with additional outlets. Stick your UL book and learn, call Tripp, mr UL book.
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ransley wrote:

It is refreshing to know that a phone tech at Tripp Lite is smarter that UL.
(Incidently I like Tripp Lite as a brand.)
Results may not be predictable when using 2 suppressors in series. Take the example in the IEEE guide <http://www.mikeholt.com/files/PDF/LightningGuide_FINALpublishedversion_May051.pdf starting pdf page 40. There is as surge coming in on the cable service. Because the ground wire from the cable entry block to the system ground at the power service is far too long (30 feet) there is 10,000V between the power ground and the cable ground. That appears at TVs connected to both power and cable. The example shows how a plug-in suppressor protects connected equipment.
Now use 2 suppressors connected in series with the 2nd connected to the TV and the cable going through the 2nd. There will be a current through cable sheath and power ground wire which lifts the ground at the suppressors away from the ground at the power service (as is clearly indicated in the IEEE example). That lifts the ground at the suppressors from the hot and neutral so the MOVs will limit the voltage H-G, N-G. If the only MOVs that conduct are in the 1st suppressor you will have the ground wire in the line cord to the 2nd suppressor (maybe 6 feet) separating the power ground reference and the cable ground reference. The voltage drop over 6 feet of the ground wire from the cable entry ground block to the power service is 2,000V. It will be far lower in the line cord but will add to the difference in voltage between the power and cable wires going to the TV. Is that a problem? Who knows - but I would rather not run the science project.
Multiple MOVs in a single suppressor do not have 6 feet between them.
Since suppressors with high ratings are readily and cheaply available I dont see a good reason to connect suppressors is series (except maybe to connect a UPS with relatively low ratings downstream from a high rated plug-in suppressor).
--
bud--

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bud-- wrote:

<http://www.mikeholt.com/files/PDF/LightningGuide_FINALpublishedversion_May051.pdf

I started at page 40 but couldn't find a diagram of what you're talking about. I will agree that there can be pitfalls when a system is connected to more than one ground.
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E Z Peaces wrote:

I stumbled across the instructions for one the 2 plug-in suppressors I use. It says: "All Belkin Surge Protectors must be plugged directly into a properly wired AC power line ... and must not be 'daisy-chained' together in serial fashion with other power strips, UPSes, other surge protectors, ... or extension cords."
Perhaps ransley could find where Tripp Lite says in writing plug-in suppressors can be daisy chained. I didn't think phone techs were held in high regard.

The example in the IEEE guide, pdf page 40, document page 31, "4.1 Ground Potential Rise within a Building".
--
bud--

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bud-- wrote:

I believe one could get into trouble daisy chaining. I wish I could see diagrams to understand what could go wrong.
Years ago, I was impressed with the argument at the website of an English manufacturer (Zero Surge?) that if your phone ground electrode wasn't bonded to your power ground electrode, it was safer not to plug your phone line into your point-of-use protector. That's the kind of thing where a diagram would refresh my memory.
In the 80s, my BIL kept having to send his modems in to have the lightning-protection fuses replaced. He was using a Radio Shack gas-tube protector for his phone line. Finally, the modem manufacturer told him to get a better protector. He got a Tripp Lite and had no more trouble. The threshold of the gas tubes was too high to protect the modem fuses.

Ahh! I was starting at document page 40.
That example uses a TV plugged into a different outlet from the cable protector. Wouldn't it be better to plug the TV into an extension cord daisy chained with the cable protector?
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E Z Peaces wrote:

If the phone grounding electrode isn't bonded to the power system ground you better not connect anything to both the power and phone lines (like a computer). A plug-in suppressor would give you a chance.
For good protection, not only must the phone entry protector connect to the "ground" at the power system, the connection must be with a short wire to prevent high voltage between power and phone lines. That is the moral of the IEEE illustration (starting pdf page 40) for cable. In the case of a wire that is too long the IEEE guide says "the only effective way of protecting the equipment is to use a multiport [plug-in] protector." (Ignored, of course, by w.)
Not bonding is a code violation in the US, and I believe all phone companies are indoctrinated into making the connection. They don't necessarily understand the importance of a short connection. And if the phone entry location is distant from the power service you can't have a short connection.

Yea - I used to have that problem a lot.

It would be better than what is shown. A lot better idea to not use an extension cord from the TV to the suppressor and use a second suppressor. They aren't real expensive (unless you only buy Monster products like w).
--
bud--




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bud-- wrote:

I was mistaken. Zero Surge is American. Now they recommend against multiport protectors. http://www.zerosurge.com/HTML/teleres.html
They don't explain it with diagrams. Switching to a multiport stopped my BIL's modem from blowing its fuses.

My SEs are 20 feet apart. I bonded them after I found 0.25VAC between the electrodes. I was online when lightning hit a tree 30 feet from my power SE. I had no damage, but the phone man had to replace the "fuses" on the telephone pole. (They call them something else.)
I told him I thought bonding had saved me. He beat around the bush for 20 minutes, then said the code requires it but it's phone-company policy not to comply. He said surges usually come in on the power company's neutral. If the electrodes are bonded, the clamping of the phone company's SE protector can send the surge into the phone line. That's why he had to replace his fuses.
The lack of bonding appears common around here. It may save the phone company a few fuses, but it puts the lives and equipment of residents at risk.
Across the street, my neighbor refused to bond his electrodes. The bolt that struck my house didn't damage any of my phone/computer equipment, but it got his modem, computer, cordless phones, and satellite receiver. He called the phone company, and there technician said there was nothing wrong with the grounding. So my neighbor told me I was wrong.
His BIL is a power-company executive. He said I was right. So my neighbor had the phone guy return. This time the phone guy admitted that the code required bonding and it was the phone company's responsibility. He said he would expedite it if my neighbor would give him free music lessons. My neighbor agreed, but the phone man never returned and the electrodes are still not bonded.

Are you talking about something other than daisy chaining?
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