Surge Protective Devices

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Rick 0920

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If installed correctly, do Type 1 and Type 2 SPD's provide any protection from surges resulting from nearby lightning strikes or are these devices primarily designed to protect against transient voltages resulting from POCO spikes or equipment spikes within the building?
 
Both. SPD's (the electronic kind, most common for 60 Hz these days) are simply Metal Oxide Varistors (MOV's). These are simply electronic devices that "cutover" from Open Circuit below a threshold voltage to Short Circuit above that threshold voltage in fractions of a microsecond. If you had a Perfect Super-conducting (zero Ohms) connection from the SPD to the Ground that could handle unlimited current (and if the SPD could handle unlimited power forever), then surge would be clamped to 0V for the time the voltage is above cutover. This is of course not the case in reality. The biggest limitation is the power handling capability of the SPD before it dies. The "ground" connection matters very little as the SPD is in parallel with the connected equipment, so if the SPD goes to "short circuit", the voltage across the connected equipment should be close to zero, regardless of the voltage from the ground bus to the actual Earth.

Mark
 
busman said:
Both. SPD's (the electronic kind, most common for 60 Hz these days) are simply Metal Oxide Varistors (MOV's). These are simply electronic devices that "cutover" from Open Circuit below a threshold voltage to Short Circuit above that threshold voltage in fractions of a microsecond. If you had a Perfect Super-conducting (zero Ohms) connection from the SPD to the Ground that could handle unlimited current (and if the SPD could handle unlimited power forever), then surge would be clamped to 0V for the time the voltage is above cutover. This is of course not the case in reality. The biggest limitation is the power handling capability of the SPD before it dies. The "ground" connection matters very little as the SPD is in parallel with the connected equipment, so if the SPD goes to "short circuit", the voltage across the connected equipment should be close to zero, regardless of the voltage from the ground bus to the actual Earth.

Mark
Click to expand...
With the SPD's becoming mandatory in dwelling unit services in the 2020 NEC per 230.67 and an entirely new article in 242, (I know, not entirely new as Art. 285 used to be surge protectors), I am just wondering if they are designed to protect homeowners from lightning? we used to install Intermatic Lightning Arrestors in every service back in the 80's in Orlando. They were also MOV's that were designed to do the same thing I guess. Since I live in Florida with all the lightning strikes, my neighbors are all asking me what they can do to keep GFCI's, microwaves, garage door openers, etc.... from frying resulting from nearby lightning strikes. The 2020 NEC is requiring these now but I'm hoping someone here knows exactly what they are designed to protect against. I am not wanting to mislead anyone by recommending a device that I don't really know what it is designed to do. Mark, I really appreciate your input.
 
These devices do not care where the elevated voltage comes from. They are tested for transients similar to those induced by lightning.
 
All of the research that I have done indicates that a Type1 SPD can be installed either on the line or load side of the main or disconnect. A type 2 can only be installed on the load side. However, some Type 1 SPD's instructions say "line side only"????
 
The problem with MOVs is that they are sacrificial. Every tiny surge nibbles away at the protection, until the day of The Big One-- and there's a lot less protection than your planned on.
I've been using ZeroSurge point-of-use surge protectors for years, and haven't had an issue (knocking on wood as I type). They claim their units are "Mode 1 (Line-Neutral)," and caution against Mode 2 and "all mode" products. https://zerosurge.com/
They have NO MOVs!
ZeroSurge licenses their technology to BrickWall surge protectors, and possibly others.
I've been near the computer when there's a flash of lightning, and the surge protector at the computer will go HUMMMmmmmm, while the computer merrily keeps computing. Other than that, they keep protecting.
Other than being a satisfied customer, I have no affiliation with the company!
 
In my opinion, the value and caveats are whatever is written in the connected-equipment warranty.
 
Several years ago the house I’d built at the time had a QO SurgeBreaker, and P&S SPD receps at every TV location. Lighting struck directly between my house and the neighbors, which were about 30’ apart.

It took out my SurgeBreaker but I didn’t lose any electronics. It blew my neighbors receptacles behind his TV out of the wall and fried almost every electronic device in his house. My house also had an ufer ground, and I’m pretty certain his did not.


More anecdotal evidence; a house I wired for a customer about 5/yrs ago had the same setup, but four panels, each with a QO SurgeBreaker, several P&S SPD receps, as well as ufer ground. Right after they moved in a storm brought a limb down on the GA Power 12kv line that crossed their REA 7.2kv line, inducing a massive surge. Took out all of their SurgeBreakers, about 50 or so AFI/GFI/DF breakers, and all of their SPD receps. They didn’t lose a single electronic device though.

My parents house sits on top of a hill, and for years they would have lightning damage at least every other year. I finally put an SPD on their house and drove at least a half dozen ground rods around it. That was probably 15 years ago and they haven’t suffered any lightning damage since. Now that I think of it, I should probably replace their SPD.


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230712-0005 EDT

An MOV surge limiter is a nonlinear resistance that has a high shunt impedance below a threshold voltage. This threshold is not real precise, and above the threshold it has an impedance that is not very low, but still useful. An MOV does not clamp to 0 V, but rather becomes a somewhat low resistance at voltages above its threshold.

The difference between different MOVs is their threshold voltage, and physical size. Size determines peak power handling capability. Outlet strips with several sockets usually have a fuse or breaker that may trip on a large overvoltage. Thus, protecting the loads pluged into the strip two ways.


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My thoughts:
a] The ZeroSurge (and Brick Wall & SurgeX) point-of-use surge protectors, are all excellent but very pricey units.
b] MOV's have been common for over 4 decades. Much of their bad reputation is also 4 decades old. Modern MOV's have come a long way since than.
 
Speedskater said:
My thoughts:
a] The ZeroSurge (and Brick Wall & SurgeX) point-of-use surge protectors, are all excellent but very pricey units.
b] MOV's have been common for over 4 decades. Much of their bad reputation is also 4 decades old. Modern MOV's have come a long way since than.
Click to expand...
ZeroSurge also has panel-mount 30A branch-circuit models.
MOVs are still sacrificial.
 
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