Surge protection-how does it work?

[GerryB]

Just bought an Intermatic whole house surge protector for a customer and will be installing later. The instructions show coming off the main (line side) or off a 2-pole 20 breaker.(load side) I called Intermatic and asked if it made a difference and they said no, which caused me to think "what exactly does a surge protector do and how does it work"? Does it absorb a surge? If you lose the neutral does it protect against that and for how long? Thanks, I know you guys know.

 

[petersonra]

<dupe>

 

[petersonra]

Think of a surge protector as a variable resistor that is sensitive to voltage above a certain point. When the SPD sees voltage above the point it is sensitive, its resistance changes from what is close to being an open circuit to what is close to being a short circuit.

For the very short period of time the SPD is a very low resistance it conducts. Ohm's law says that while it is in a low resistance state, the voltage drop across it won't be real high despite a fair amount of current flowing through it for a short time (microseconds typically).

I think it makes very little difference if the SPD is placed right at the main or on a branch CB. It does appear that keeping the leads as short as possible and keeping them straight is important. The transients it protects from have high frequency components and even a small amount of inductance can add impedance to the wiring, which would result in the SPD still working but you could have voltage drop across the wiring due to the higher impedance caused by coiling up lead wires.

There are some interesting ramifications to how a SPD works. A lot of the energy of a surge would appear to actually be dissipated as heat in the wiring rather than being absorbed into the SPD as most of us tend to think happens.

Say you have a 1000V surge comes down from the POCO and hits the panelboard from L-L. Instead of 240V your have 1000V for a few microseconds. The SPD turns itself into a low resistance path. However, your current path is still your service wires and then thru your SPD to complete the circuit. It is likely the resistance in the service wiring far exceeds that within the SPD, so I^2R says most of the energy will be dissipated in the service wires.

 

[Cavie]

Intermatic sells $10,000 and a $25,000 dollar gauranty versions that we install. Read the paperwork closley! We have found $10,000 gauranty paperwork in the $25,000 boxes on 3 ocations. We have brought this to thier attention and they were very thankfull. I would like to know if any body has collected on the gauranty. I've had the same 10,000 unit on 2 houses for 22 years and the lights are still lit. I could never collect. Don't know what happened to the paperwork.

 

[GBShade684]

It does matter where it is installed. The surge will take the path of least resistance, as does all electricity. If the SPD is installed further down, then the upstream circuits have already seen the full surge. When the SPD begins conducting it will drop off those circuits, but damage may already have been done. Also the SPD is more to protect sensitive electronic equipment from flash over due to the increased voltage. The surge is so fast that the heat build up from the amperage spike is much less of a concern vs the flash over potential which can fry the electronics....

 

[petersonra]

It does matter where it is installed. The surge will take the path of least resistance, as does all electricity. If the SPD is installed further down, then the upstream circuits have already seen the full surge. When the SPD begins conducting it will drop off those circuits, but damage may already have been done. Also the SPD is more to protect sensitive electronic equipment from flash over due to the increased voltage. The surge is so fast that the heat build up from the amperage spike is much less of a concern vs the flash over potential which can fry the electronics....

The "path of least resistance" thing is a complete misunderstanding, almost to the point of being a myth.

Electricity takes ALL paths that are available to it. The amount of current is dependant on the amount of resistance in the path.

In any case what upstream circuits are there inside of a panel board as the OP was asking. If the SPD is installed on a branch CB, the only upstream device would be the main CB. It is going to see the surge anyway regardless of where the SPD is located.

 

[A/A Fuel GTX]

Try to install the 2P 20 ( or whatever, it really doesn't matter ) as close to the service entrance conductors as possible, like at the top of the buss.

 

[Speedskater]

Because much of the energy of a lightning surge is in the radio frequency range (about 1MHz) most of the current will take the paths of lowest "impedance" rather than "resistance". It's interesting that at 1MHz there is little impedance difference between 14AWG and 4AWG. Also flat, wide copper strap or braid works better than round wire of the same cross-section.

 

[petersonra]

Because much of the energy of a lightning surge is in the radio frequency range (about 1MHz) most of the current will take the paths of lowest "impedance" rather than "resistance". It's interesting that at 1MHz there is little impedance difference between 14AWG and 4AWG. Also flat, wide copper strap or braid works better than round wire of the same cross-section.

I have never seen a SPD with braid or strap leads. One would think if it made any difference someone would make their SPD with braided leads if just as a marketing advantage.

In any case, all of the branch circuit wires are going to have a far higher impedance than the short leads on a properly installed SPD at the panel board.

One has to wonder if the high frequency nature of at least some surges would make a line reactor a good choice as part of a surge control system. having said that, the transformer up on the pole is a pretty decent substitute for a line reactor and it does not seem to do all that good of a job at stopping transients. that makes me wonder just how much of typical transients really are of a HF nature.

 

[GBShade684]

The "path of least resistance" thing is a complete misunderstanding, almost to the point of being a myth.

Electricity takes ALL paths that are available to it. The amount of current is dependant on the amount of resistance in the path.

In any case what upstream circuits are there inside of a panel board as the OP was asking. If the SPD is installed on a branch CB, the only upstream device would be the main CB. It is going to see the surge anyway regardless of where the SPD is located.

Yes, current will flow on all paths and it depends on the overall resistance, or impedence as Speedskater points out above. But when we are considering loops that have R/Z in 5-10-15Ω range vs a conducting MOV, in the nΩ range, current through the first loop is negligible. That's what I meant. Sorry if I was unclear.

 

[Speedskater]

I have never seen a SPD with braid or strap leads. One would think if it made any difference someone would make their SPD with braided leads if just as a marketing advantage.

Neither have I in residential or commercial SPD's. But antenna towers and broadcasting building have lots of them.

In any case, all of the branch circuit wires are going to have a far higher impedance than the short leads on a properly installed SPD at the panel board.

Some writers point out that this is one of the problems with point of use SPD's.

One has to wonder if the high frequency nature of at least some surges would make a line reactor a good choice as part of a surge control system. having said that, the transformer up on the pole is a pretty decent substitute for a line reactor and it does not seem to do all that good of a job at stopping transients. that makes me wonder just how much of typical transients really are of a HF nature.

Something like series mode SPD's.

Series Mode AC Protectors
The common MOV based shunt surge protector dumps large transients currents onto the AC neutral and ground conductor increasing the local ground potential, series protectors do not. To learn more about the advantages of Series Mode Surge Protectors, click here. http://www.prosoundweb.com/studyhall/lastudyhall/surge_protect2.shtml

Some manufacturers of series mode surge suppressors are listed below:

http://www.brickwall.com/
http://www.zerosurge.com/
http://www.surgex.com/

But even small Series Mode AC Protectors are very expensive.

 

[GerryB]

Just read the instructions further. They do not cover loss of neutral. Here's what it says. "This device is not intended to provide protection during Utility voltage swells or loss of neutral conditions which are by definition not transient events..." "a Power Transient shall mean over-voltage resulting from momentary voltage spikes or surges..." This makes me wonder if a plug in protector is better. A few years ago a HO had loss of neutral from a storm. It completely blew the back out of the plug in surge protector, but it saved whatever he had plugged into it.

 

[petersonra]

Neither have I in residential or commercial SPD's. But antenna towers and broadcasting building have lots of them.

But, this was not a discussion about antennas.

Some writers point out that this is one of the problems with point of use SPD's.

I am not so sure this is truly an issue with POU protectors. When the SPD turns on you will have zero volts across the SPD terminals. If that SPD is L-N, it will work fine.

If it is the L-G or N-G unit that turns on you will raise raise the ground potential because you are shunting a large amount of current to ground and the voltage will rise on the ground wire. You will have 0 Volts L-G at the remote SPD, but you won't have zero volts from the G terminal at the remote SPD to earth.

 

[Speedskater]

But, this was not a discussion about antennas.

Actually I meant types of structures that may have strap or braid somewhere in the grounding systems.

I am not so sure this is truly an issue with POU protectors. When the SPD turns on you will have zero volts across the SPD terminals. If that SPD is L-N, it will work fine.

If it is the L-G or N-G unit that turns on you will raise raise the ground potential because you are shunting a large amount of current to ground and the voltage will rise on the ground wire. You will have 0 Volts L-G at the remote SPD, but you won't have zero volts from the G terminal at the remote SPD to earth.

If you and in components or systems with different styles of SPD's or no SPD in different areas of the building and the connect them together with signal or control wires it can get very complicated.