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Grounding versus Bonding Part 7 of 12

2005 NEC®

Grounding Electrode Conductor

Mike Holt for EC&M Magazine

[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 [100].

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.

Size matters

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:

  1. Ground rod. That portion of the GEC that is the sole connection to the ground rod does not need to be larger than 6 AWG copper (Figure 250-122). Follow the ground rod installation requirements contained in 250.52(A)(5).
  2. Concrete-encased grounding electrode (Ufer ground). That portion of the GEC that is the sole connection to the concrete-encased electrode does not need to be larger than 4 AWG copper (Figure 250-123). Follow the concrete-encased electrode installation requirements contained in 250.52(A)(3).
  3. Ground ring [250.52(A)(4)]. That portion of the GEC that is the sole connection to the ground ring does not need to be larger than the conductor used for the ground ring. A ground ring encircling the building or structure in direct contact with earth must consist of not less than 20 ft of bare copper conductor not smaller than 2 AWG.

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)?

(a) 1 AWG (b) 1/0 AWG (c) 2/0 AWG (d) 3/0 AWG

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" [100]. 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:

  • 4 AWG or larger, you must protect it from physical damage [250.64(B)]. How you do that is a matter of craft and subject to the approval of the AHJ.
  • 6 AWG and free from exposure to physical damage, you can run it along the surface of the building construction without metal covering. If a 6AWG GEC is exposed to physical damage, you must run it in rigid metal conduit (RMC), intermediate metal conduit (IMC), rigid nonmetallic conduit (RNC), electrical metallic tubing (EMT), or cable armor.
  • Smaller than 6 AWG, you must run it in RMC, IMC, RNC, EMT, or cable armor.

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)].

Splices

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):

  1. Use compression-type connectors listed for grounding or exothermically weld the splice.
  2. If needed, connect sections of busbars together to form a GEC.
  3. Terminate the GEC to a busbar sized not smaller than 1/4* x 2 in. Fasten the GEC securely in place at an accessible location. Make connections exothermically or with listed connectors (Figure 250-64C3 CC250-21.cdr).

Taps

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.

Enclosures

  • Ferrous (iron/steel) raceways, boxes, and enclosures containing the GECs must have each end of the ferrous metal raceway, box, and enclosure bonded to the GEC [250.92(A)(3)].
  • Nonferrous metal raceways (such as aluminum RMC) enclosing the GEC don't need to meet the "bonding each end of the raceway to the GEC" provisions of this section.
  • If you use a bonding jumper with a bonding bushing or wedge [250.92(B)(4)] to bond the raceway to the GEC, you must size the bonding jumper no smaller than the enclosed GEC (Figure 250-64E 01 CC250-22.cdr).

The Terminator

How should you terminate your GEC to grounding electrodes? First, ensure the GEC attachment fitting remains accessible [250.68(A)]. There are two exceptions to this rule:

  1. The grounding electrode attachment fitting to an encased or buried grounding electrode isn't required to be accessible. But when the grounding electrode attachment fitting is encased in concrete or buried, it must be listed and identified for this purpose [250.70] (Figure 250-124).
  2. An exothermic or compression connection to fireproofed structural metal isn't required to be accessible.

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.

View More Mike Holt Grounding and Bonding Articles

Mike's 2005 Grounding versus Bonding Seminar Schedule

October
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October 10th thru
October 11st
Mike Holt/EC&M/Leviton: Grounding versus Bonding
Boston, MA
Boston Convention & Exhibition Center
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(617) 954-2000
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October 18th thru
October 19th
Mike Holt/EC&M/Leviton: Grounding versus Bonding
Philadelphia, PA
Pennsylvania Convention Center
1101 Arch St.
(215) 418-4700
Mike Holt Enterprises, EC&M magazine & Leviton
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Phone: (888) 632-2633
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November
 TOPIC  LOCATION  SPONSOR  INFORMATION
November 9th thru
November 10th
Mike Holt/EC&M/Leviton: Grounding versus Bonding
Seattle, WA
Meydenbauer Center
11100 NE 6th Street
(425) 637-1020
Mike Holt Enterprises, EC&M magazine & Leviton
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November 16th thru
November 17th
Mike Holt/EC&M/Leviton: Grounding versus Bonding
Chicago, IL
Midwest Conference Center
401 W Lake St
Northlake, IL
Outside Chicago - 7 Miles from Ohare
Mike Holt Enterprises, EC&M magazine & Leviton
Email Sarina Snow
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