The topic of lightning surge protection is always relevant, especially during these peak summer months. Residing in what has been dubbed The Lightning Strike Capital of the World — Central Florida — I have a pretty good vantage point on this subject. So this month we will review best practices, shed light on tips you may have not heard, and investigate technology that could make your lightning fighting days easier and those efforts more reliable.
Sometimes installers and technicians deploy faulty reasoning, thinking, “If I do not ground my equipment, it will be less attracted to lightning and I will have less equipment loss.” While this may appear to be true the practice is dangerous to both equipment and, even more importantly, life safety. If you do not give lightning surges direction to ground they will find their own course. Many in security have experienced this when sensitive reeds in window alarm contacts have been permanently frozen shut.
Also remember from a liability perspective that most alarm panel manufacturers recommend some sort of power connections for their internal surge suppression to work. You should always follow the manufacturer’s recommendations.
Lightning surge suppression technology is only as good as finding and verifying good electrical ground resistance. This is a particular challenge in highly active areas like Florida. While we will mainly discuss electrical surges from lightning, also be mindful that the quality of power from the utility company is one of the principal destroyers of equipment.
Solid Grounding Strategies
The most important initial element of any transient voltage surge suppression (TVSS) is a low impedance ground connection. Articles 100 and 250 of the National Electrical Code (NEC), or NFPA 70, describes an acceptable ground as being rated at 25 Ohms of resistance or less. However, our goal is to achieve less than 5 Ohms. Anything above this can start to adversely affect the performance of surge protection devices (SPDs). Remember that proper electrical grounding and bonding practices typically follow the directives of your local AHJ. So if you have not yet done so, check with your AHJ for grounding implementation guidelines.
Where are some of the best locations in a facility to find a good ground connection? They are electrical service grounds, grounded building steel, local electrical ground and dedicated driven rods. Did you notice anything missing from this list? Yes, we no longer reference the now infamous cold water pipe. Most modern cold water pipes are not metal but PVC, even though on the surface they appear to be metal.
As many dealers that live in areas such as mine will tell you, finding a good and consistent earth ground can be tricky. In Florida, sandy soil can measure good as water tables rise in the summer, but ground resistance can become high in the drier winter months when water tables drop. In sandy arid areas like the Southwest it can be even worse.
An alternative grounding method that has become popular here in Florida is an “Ufer” ground connection that is provided from concrete slab-encased or trench-laid metal rebar grids. However, an Ufer ground connection should not be considered a sole source ground connection. Bonding should also be conducted between the Ufer point and/or rods. Another alternative is the application of a low resistance, carbon-based backfill material called Ultrafill placed around the ground rod.
(Note: Amendments to the 2008 NEC have clarified some provisions of previous concrete-encased electrode language. Alt-hough the word “Ufer” is not used in the text of the code, NEC Section 250.52(A)(3) addresses Ufer grounds.)
The highly respected organization BISCI has made some ground testing guidelines available. It suggests the most accurate test, when disconnected from the utility grid, to be one known as the three-point fall of potential method. BISCI also cautions against potential misuse of popular and expensive clamp-on test meter devices. While easy to use, you must be sure they are at the only single point ground source. BICSI also notes that low resistance of the system ground can only be verified through correctly implemented testing.
Surge Protection Device Do’s/Don’ts
One of the best ways to minimize the dangers of lightning and utility surges on equipment is the implementation of SPDs. I recently reviewed the latest in surge protection at a Tri-Ed regional training session conducted by Mike Molinari, a regional account executive for Florida-based DITEK Corp. He offered some really good tips on installing SPDs that I want to pass on:
- The conductor length between a SPD and the equipment being protected should be a minimum of three feet in length. This is to allow enough time for the SPD to react to the transient surge.
- A low impedance ground path is absolutely essential when installing a SPD. Never assume you have a good ground.
- The use of a grounding bus bar is strongly recommended as a means of terminating SPD ground wires to existing electrical grounding leads. You need a good solid mechanical connection of all your grounding conductors.
- When installing multiple SPDs and terminating to a common ground, a dedicated ground wire run from each individual SPD to a common grounding bus bar is recommended. In order to get a good ground do not “daisy-chain” SPD ground wires, or use twist-on wire connectors. These practices can increase the resistance and extends the length of the ground path.
As a final note, everybody is busy using Power over Ethernet (PoE) technology on IP devices. Make sure to check out PoE SPD devices, especially for those remote IP camera installs. Check out the informative whitepapers at DITEK’s Web site (ditekcorp.com), and also the Grounding and Bonding Self-Guided Online Course based on NFPA 70 (nfpa.org).
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Systems Integration ·
Bob Dolph ·
Surge Protectors ·
Tech Talk ·