Ground transient reduction

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ron

Senior Member
What are the downsides of introducing a filter (inductor) in series with the equipment ground conductor for a Fire Alarm Control Panel (or any control panel for that matter). This filter will be UL listed, and would theoretically reduce incoming transients from the outside world, affecting the electronic components within the Control Panel.
I'll be talking with a manufacturers rep about this type of product, and wanted some additional ammunition.
 

don_resqcapt19

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Illinois
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retired electrician
Re: Ground transient reduction

I don't see "inductors" on the list of EGCs in 250.118 so this would be a code violation. Also I don't believe that the transients originate in the grounding system and don't see any real use for a device like this.
Don
 

ron

Senior Member
Re: Ground transient reduction

Don,
A inductor fits within the definition of "A copper or other corrosion resistant conductor. This conductor shall be .... in the form of a wire or a busbar of any shape"
It happens to be a copper conductor in the shape of a coil.
The thought is, if a lightning strike should occur, a transient may be introduced on the ground system.
My concern is that an inductor will be a high impedance to a transient, and may reduce the ampere flow through the EGC during a fault. A fault very often looks like a transient.
 

charlie b

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Location
Seattle, WA
Occupation
Electrical Engineer
Re: Ground transient reduction

Here?s my two cents worth.
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">First cent = It?s a code violation, just as Don has said.
    Second cent = It wouldn?t work anyway.</font>
<font size="2" face="Verdana, Helvetica, sans-serif">As to the ?first cent?: The NEC article that you quoted (250.118) says that the wire can be ?any shape.? That phrase refers to its cross-sectional appearance. But once you wrap the wire around itself many times (i.e., to form a coil), it ceases to be a ?wire,? and instead becomes a ?component.? The component will not behave in the same manner as would a wire. Therefore, it cannot be presumed that it will serve the function that the wire was intended to serve. Specifically, the function of an EGC is to provide a low-impedance path back to the source, so that an accidental ground fault will be able to trip the breaker and terminate the event. What you propose is to add impedance to that path. This action would increase the time it takes for the breaker to trip, and might prevent the breaker from tripping.

As to the ?second cent?: There are devices that are designed to protect various types of systems and equipment from a lightning strike. Even without knowing specific information about the filter you propose to use, I would still predict that such a filter would not be among them. A lightning strike would probably fry the filter without slowing down on its way to destroying the Fire Alarm System.

At no extra charge, here is a ?third cent?s worth?: The real and final answer to you question will boil down to this: The filter may be UL listed, but is it UL listed for the application that you are proposing?
 

dereckbc

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Staff member
Location
Plano, TX
Re: Ground transient reduction

Ron, I think you answered your own question, it will add to the overall circuit impedance.
 

ron

Senior Member
Re: Ground transient reduction

OK,
The UL Listing is as a filter. It's instructions direct its installation on the equipment ground.
One additional peice of information that I found, is that it is installed on the output of the control panels power supply and before the PC boards.
The internal impedance of the power supply will limit the amount of current that is available to act as fault current. The marketing information indicates that the inductors coil type will not act as a high impedance to a fault due to the core material is set to saturate on fault current and chosen to be a high impedance to transient voltage. (They claim the the coil will act differently to transient voltage (lightning) than transient current (fault)).
I'm attempting to debunk what I think is a bad idea, just passing ideas back and forth.
Here is one flavor http://www.9corp.com/ and another
http://www.vortextek.com/id12.html
 

ron

Senior Member
Re: Ground transient reduction

We have some clients in lightning prone areas, that feel that they have been "losing" control panels due to lightning induced transients. They have asked that we look into other options, that might be slightly "out of the box".
 

james_mcquade

Senior Member
Re: Ground transient reduction

ron,
from the articles i take it that this may be an inductor network to filter the lightning strikes.
by increasing the grounding resistance, you allow more damage to be done. the higher the ground resistance, the more likely the strike will find more than one path to ground. also, inductive circuits store energy.
 

steve66

Senior Member
Re: Ground transient reduction

Code issues asside, I am very skeptical this device will do any good. How many false fire alarms do you know of that were caused by "ground transients"? The answer is probably zero. The ground is used to clear faults, and provide a stable reference to ground. I really think fire alarm panels are probably robust enough to withstand a little noise on the ground (after all, they have a DC power supply that eliminates a large part of the AC supply). Yet, we are supposed to accept that the same power supply is helpless against a little ground noise.

If ground noise is really a problem, it is most likely from improper wiring (ground wires on the neutral bus, vice versa, multiple bonds, no ground electrodes, no bonding between systems, ect.) Don't expect this device to fix problems like those. And I agree that if the fire alarm panel really gets hit with lightning, that device won't save it.

P.S. One of those web sites had an article wrote by a MBA (Master in Business Administration??) What makes that person qualified to talk about surges and transients?

Steve
 

hurk27

Senior Member
Re: Ground transient reduction

I looked at the device's and even tho they claim that they are new technology we have been using the same technology for years. All it is is a transformer that has it's secondaries shorted. the primary is placed in series with a DC load and any AC that tries to pass through it will be shorted out some what. look at any car stereo filter and this is what they are trying to sell as a ground transient filter. will it work well in some cases it might provide some reduction of a AC voltage that tries to pass it but as others have said it would reduce the available fault current to trip a breaker.
Any body that has tried to get rid of a alternator wine in a car stereo would know how ineffective these are. The reason they think they can be used on the EGC is there is not suppose to be any AC on it we know different as most EGC's that are connected to the grid will have some current on it. and this would only make this filter produce heat. or burn up.

The electronic name for this circuit is called a choke.
 
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