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TECH TALK When Lightning Boils Soils An interesting phenomenon associated with lightning and grounding rods is the creation of fulgurites. If a grounding rod takes a hit from lightning, the surrounding soil is heated to such a high temperature that it can turn to a form of glass. And glass happens to be a very good insulator. This reaction is more prevalent in sandy Fulgerites are the crystallized, glass-like formations left around ground rods soil areas. So, in an instant, a good low resistance ground formed by intense heat of a lightning strike. The phenomenon can turn a rod can turn in to an insulator. Periodic testing is necesgood ground to bad in literally a fash. Photo courtesy DITEK Corp. sary to confrm a system's ground resistance is still low. It has been said that in some areas of Florida the formation of fulgurites on system ground rods are prevalent enough to prompt replacing them on a regular basis as a precautionary measure. 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 backfll material called Ultraf ll placed around the ground rod. (Note: Amendments to the 2008 NEC have clarifed 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.) Te 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 verifed 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 Moli- TECH TALK nari, a regional account executive for Florida-based DITEK Corp. He ofered some really good tips on installing SPDs that I want to pass on: • Te conductor length between a SPD and the equipment being protected should be a minimum of three feet in length. Tis 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. • Te 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. Tese practices can increase the resistance and extends the length of the ground path. As a fnal 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 SelfGuided Online Course based on NFPA 70 (nfpa.org). In keeping with the theme, this month I have selected the DITEK Corp.'s Critical Load surge protection device (SPD). Up until recently, you would have needed to periodically visually inspect the presence of an LED indicator for performance confrmation. The DTK-120SRD device now has a set of contacts for alarm supervision, a favorite feature for all of us alarm people. The product's multistage hybrid design provides high quality fltering and lower clamp levels. Designed for 120V circuits, it meets both government and military specifcations for fre panel applications. TOOL TIP 24 / SECURITYSALES.COM / JULY 2013 The DTK120SD provides 120V, 20A surge protection for critical equipment, such as alarm panel circuits. It also includes dry contacts for remote notifcation of surge protection status. Photo courtesy DITEK Corp.