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Grounding Electrode Conductor
[Please note: There are no Figures / Illustrations included in this newsletter]
Grounding electrode conductor sizing and installation errors can cause the entire grounding system to fail.
In Part 6 of this series, we discussed grounding electrode systems. And, we compared them to the tires on NASCAR race cars. Now we look at the grounding electrode conductor (GEC), which you can think of as the suspension. A properly tuned suspension allows the tires to do their job and keep the car on the track. The GEC connects the "car" (grounding electrode conductor) to the "tires" (grounding electrode system).
The GEC performs this function at the service, at each building or structure (where supplied by a feeder), or at the source of a separately derived system .
The GEC can be solid or stranded, insulated or bare. Generally, it must be copper. You can use aluminum, if the GEC is not subjected to corrosive conditions and is not within 18 in. of the earth [250.64(A)] (Figure 250-117).
The NEC doesn't require you to identify the GEC. The generally accepted practice is to apply green marking tape, or not identify the GEC at all.
Using Table 250.66, size the GEC for the largest service-entrance conductor (or equivalent area for parallel conductors-unless the GEC connects to one of the three following electrode types:
Sizing the GEC is simpler than it might seem. Prove this to yourself by answering this question. What size GEC do you need for a 1,200A service supplied by three parallel sets of 600 kcmil copper conductors per phase (Figure 250-121)?
Answer: (d) 3/0 AWG. The equivalent area of three parallel 600 kcmil is 1,800 kcmil. So, you look in the far left column of Table 250.66 for the row that pertains to an 1800 kcmil conductor. You can see that the last row, "Over 1100," is the one you want. The GEC size denoted by that row is 3/0.
Installing the GEC
If your GEC runs across a surface (or behind panels that allow access), the NEC considers it "exposed" . You must provide protection for any exposed GEC [250.64(B)]. The first step in providing protection is to securely fasten the GEC to the surface on which it runs. The additional steps you take will depend on the size of the GEC. If the GEC is:
If you install the GEC in a ferrous metal raceway, you must make that raceway electrically continuous by bonding each end of the raceway to the GEC [250.64(E)].
You can run the GEC to any convenient grounding electrode [250.64(F)]. But what if your GEC isn't long enough to reach? Can you splice the GEC? Yes, but only if you use one of the methods provided in 250.64(C) (Figure 250-64C0 CC250-20.cdr):
When a service consists of multiple disconnecting means as permitted in 230.71(A), you can use a grounding electrode tap from each disconnect to a common GEC [250.64(D)]. You must size the grounding electrode tap from each disconnect to the largest ungrounded conductor serving that disconnect per 250.66.
You size the common GEC for the grounding electrode taps per 250.66 also, but you must base its size on the service conductors feeding all the service disconnects.
Each grounding electrode tap must terminate to the common GEC in such a manner that there will be no splices or joints in the common GEC. In addition, the grounding electrode tap cannot be made within the service-disconnect enclosure.
The second rule is to make the connection to the GEC in a manner that ensures a permanent and effective grounding path. If you have an underground metal water pipe electrode, you must install a bonding jumper around insulated joints and equipment likely to be disconnected for repairs or replacement [250.68(A] (Figure 250-125).
Continuity of the conductive bonding path for metal water piping as required by 250.104(A) cannot rely on water meters, filtering devices, or similar equipment [250.53(D)(1)].
The GEC must terminate to the grounding electrode by exothermic welding, listed lugs, listed pressure connectors, listed clamps, or other listed means. In addition, termination fittings must be listed for the materials of the grounding electrode. You cannot terminate more than one conductor on a single clamp or fitting, unless the clamp or fitting is listed for multiple connections [250.70] (Figure 250-126).
When the termination to a grounding electrode is encased in concrete or buried, the termination fitting must be listed and identified for this purpose. Ground fittings listed for concrete encasement or direct burial are typically made from brass or bronze, not steel or aluminum alloy-so pay attention to the color of the fittings to reduce errors in the field.
You're now well equipped to avoid mistakes in your GEC installations. You are able to ensure correct sizing, adequate protection, and proper termination. Now your grounding system won't skid off the track because of GEC errors.
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