Whole service surge protectors any good?

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wawireguy

Senior Member
Do the small 200 amp and less service surge protectors really do anything? I want to know if I should be suggesting them to customers or not. If they are marginal at best I wouldn't be comfortable upselling them unless a customer asked for one.
 
mxslick

mxslick

Senior Member
Location
SE Idaho
This has been covered before , but the answer to your question is generally yes, as long as you stick to name brands, and be aware that they are sacrificial devices and will need to be replaced after a major surge event/lightning strike.

Also, whole-house surge protection works best with additional protection at point-of-use on critical loads like computers, electronics, etc.

If the customer has expensive electronics then I would recommend it.
 
R

RFEngineer

Member
mxslick said:
If the customer has expensive electronics then I would recommend it.
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"Whole-house" TVSS devices are fine at the service entrance and/or utility meter. However, they shouldn't be used on a 120VAC branch circuit. Typically, MOV surge suppressors are advertised as secondary protection devices offering so-called "three modes of protection."

The three modes are: (1) line to neutral; (2) neutral to ground; and (3) line to ground. When working with sensitive electronic equipment, any surge should only be diverted to the neutral, and not the grounding conductor. The grounded neutral is designed to handle an impulse of surge current. This is in contrast to a fault condition where fault current is diverted to the grounding conductor.

In many instances, having a 3-mode MOV does not present a problem on a 120VAC branch circuit -- unless the premise has an alternate pathway for a surge to enter, typically a CATV coaxial line (even with its own suppressor), telco, and any sub panel located away from the main entrance panel where a branch feeds an outdoor, underground circuit. A lightning surge can easily couple to any one of these cables and the intensity of the surge may be greater at the 3-mode secondary device than at the whole-house device. Then you've got problems.

The best solution in these instances is not cheap. Three manufacturers that I know of produce 1-mode suppressors with a "store and bleed" feature. A series inductor limits the surge, then a capacitor stores the surge and slowly releases the capacitor's stored energy into the neutral. This method keeps the surge current on the neutral managed to reasonable levels. Take a look at SurgeX, Brickwall, and ZeroSurge. All three are nearly identical devices, but the owner's wallet will have deep scars.

Paul
 
tom baker

tom baker

First Chief Moderator
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Location
Bremerton, Washington
Here is what Mike Holt has to say about TVSS
More is better
You get what you pay for

What I recommend and have is a whole house TVSS, or as the 08 NEC calls them, SPDs, it was about $200.
And then I have point of use SPDs at computers, TVs, etc.
Knock down the surge at the service, and then use the impedance of the building wiring to reduce it more to where a point of use can reduce it more.

And for my desktop computer and server I have two high quality UPSs.

On the industrial side, I never install an electrical service with out SPDs. Most buildings will have two, one on the 480 side, and one on the 120/240 side. The amount of electroinc equipment failures has decreased since installing SPDs. Nearly everything I install has electronics in it....
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
RFEngineer said:
When working with sensitive electronic equipment, any surge should only be diverted to the neutral, and not the grounding conductor. The grounded neutral is designed to handle an impulse of surge current. This is in contrast to a fault condition where fault current is diverted to the grounding conductor.
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I don't see how this can matter any in a typical residence as the neutral and ground are the same size and as often as not terminate at the panelboard on the same bar.

Perhaps a diagram of what you are trying to say is in order.
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
tom baker said:
The amount of electroinc equipment failures has decreased since installing SPDs. Nearly everything I install has electronics in it....
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Maybe. It could just be that electronics have become far more resistant to damage from surges over time. Modern electronic devices are no where near as sensitive to these kinds of things as they once were.

I am a fan of installing them but I don't know that there is any correlation that can be made between installation and failure rates.
 
R

RFEngineer

Member
petersonra said:
I don't see how this can matter any in a typical residence as the neutral and ground are the same size and as often as not terminate at the panelboard on the same bar.
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Correct. They generally are of the same AWG. The issue is that a surge impulse can create a large potential difference along any conductor -- we just don't want that potential to be different on a grounding conductor.

In many electronic circuits, ground is used a circuit reference among components. Now consider two pieces of sensitive equipment, each powered and grounded by a receptacle on the same or even a different branch circuits. Here's the essence of the problem: Consider the case where two pieces of equipment have their grounded chassis interconnected with coaxial cable, video cable, or audio cabling. In most cases, the outer shielding is bonded to the equipment chassis at both ends of the cable. The shield of the cabling now creates a second surge pathway. Why? Because the 3-mode SPDs on the branch circuits are putting it there.

Now consider an inductively coupled surge on a line conductor that is diverted to the grounding conductor by the 3-mode SPD. Depending on the induction point, a huge impulse of current splits, and flows along the two stated pathways. The conductive pathways are not perfect conductors and as such, voltage is dropped along the grounded conductors, that includes the premise ground conductor and the grounded equipment cabling. The more I rises, the more E is dropped. At the moment of the surge the potential between equipment cases is then unequal, sometimes by a significant amount. That potenial difference creates real-world problems with electronic equipment.

Contrast this with a diversion of the surge only (not a safety fault) to the grounded neutral conductor. We've now diverted the surge to neutral where it is dissipated back at the common ground/neutral bonding point.

For folks who are concerned that the pathway back to the ground/neutral bond can present too much resistance, it's a fact thay the popular 3-mode SPDs already do this. Schematically, you will see an MOV from Line to Neutral, in addition to the remaining two modes (i.e., Line to Ground, and Neutral to Ground). The best solution to deal with this involves storing the surge energy, then bleeding it on to the neutral conductor.

Summary: the best premise surge protection solution involves: (1) 3-mode protection only at the service entrance; and (2) "store and release" 1-mode protection on sub-panels and select branch circuits.

The expensive hospital-grade (HG) Leviton and Hubbell 3-mode suppressors being recommended and sold by many A/V low-voltage installers? Throw them out. They have no use on a branch circuit where they're doing more harm than good. The HG grade is fine, just not with "three modes of protection." Let's keep "three modes" only at the service entrance.

A diagram? This is what I'm talking about:

http://www.zerosurge.com/howsuppressionworks.cfm

http://www.brickwall.com/how-it-works.html

http://www.surgex.com/library.html

-Paul
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
How are these any better than just having a MOV from L-N only?

I have always maintained that N-G and L-G surge suppressors serve no real purpose, but never thought about them potentially damaging anything.
 
R

RFEngineer

Member
petersonra said:
How are these any better than just having a MOV from L-N only?

I have always maintained that N-G and L-G surge suppressors serve no real purpose, but never thought about them potentially damaging anything.
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The benefit is that surge current has an opportunity to be current-limited onto the neutral, unlike an MOV where it quickly routes the surge in one impulse. But to your point, I would select a single-mode L-N MOV device on a branch circuit over an SPD that offers "all three modes of protection." I have no issues with using a 3-mode device at the service entrance panel and/or the electric meter.

-Paul
 
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