Surge protectors in series

[Caesar Romano]

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??

[Bryce]

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.

[RickMeister]

Nope.

[E Z Peaces]

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.

[ransley]

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.

[mm]

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.

[bud--]

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.

[ransley]

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.

[Bryce]

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

[bud--]

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."

[westom]

You assumed protectors somehow stop or absorb surges. They don't. Do you really think that protector will stop what three miles of sky could not?.

A surge first creates a path from cloud to earthborne charges. Then surge current - electricity -flows simultaneously and equally through everyth> You cannot really suppress a surge altogether, nor

Where does surge energy get harmlessly absorbed? In earth. A protector is only a connecting device to protection - earth. Protector and protection are two separate items. A protector located too far from protection (earth ground) may divert that surge destructively in other paths inside a building.

E Z Peaces describes a 'whole house' protector. But also describes a protector apparently with insufficient earthing. One 'whole house' protector means the surge does not even enter the building; need not seek earth ground through a computer or other appliances. Again, first the path from cloud to earth is created. In his case, that connection to earth was through some appliances - destructively.

A surge that does not enter the building does not seek earth - which is what every telco everywhere in the world does. Effective earthing making the original question - connecting protectors in series - irrelevant. Your telco connected to overhead wires all over town may suffer 100 surges during each thunderstorm. How often how has your town been without phone service for four days while they replace their computer? Telcos don't daiychain protectors. Telcos locate every protector where each wire enters the building - and making the shortest possible connection to earth.

Where does surge energy get dissipated harmlessly? In earth.

What a protector connects surges to - where surge energy gets absorbed - is surge protection - earth ground. Every wire inside every incoming utility cable connects short (ie 'less than 10 feet') to earth either using wire (ie cable TV, satellite dish) or via a 'whole house' protector (AC electric, telephone).

Not just any earth ground. All must make a short connection to the same earth ground electrode.

A protector is only as effective as its earth ground. Where do your daisy chained (in series)protectors make that "low impedance" connection to earth? Why do commercial broadcast stations and ham radio operators routinely suffer direct lightning strikes and never have damage? Why do telcos not use your plug-in protectors? They need protection. Protectors connect as short as possible to earth so that surges need not enter a building. Never damage that telco switching computer. Nobody will stop or absorb what three miles of sky could not.

bud will now reply with nasty and insulting comments because he is paid to do so.

[Caesar Romano]

On Mon, 4 May 2009 14:35:22 -0700 (PDT), westom wrote Re Re: Surge protectors in series:

Who is Bud and who pays him?

[salty]

Anybody who follows Westom's advice or believes his idiocy is a prime candidate for the Darwin Awards. Westom is a long time usenet kook who likes to sprinkle just enough truth in his nonsense to fool people into doing things that could kill them.

He has changed his usenet identity once again to try and escape from his past. He used to post as w_tom.

[E Z Peaces]

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.

[ransley]

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.

[ransley]

to

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.

[westom]

It will become obvious. Meanwhile, surges are electrical connections from cloud to earth. First a path forms. Then electric current flows simultaneously through everything in that path. If anything attempts to stop that current, then voltage increases as high as necessary to blow through that obstruction.

Surge protectors do not stop and do not absorb surges. An appliance is connected directly to AC mains if using no power strip, one power strip or five power strips in series. Doubt it? Then break one open. Connection to AC mains is electrically direct. Nothing inside to obstruct a surge.

Protection means the surge does not enter a building. Protection means a surge finds earth ground before entering the building. It was done that way even 100 years ago and is still installed in any facility that can never suffer damage.

[Tony Hwang]

Hi, Never? Only on theory. On a direct mega hit nothing survives. I witnessed it first hand years ago.

[E Z Peaces]

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.

[bud--]

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

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 don?t 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).