In the 1999 National Electrical Code (NEC), and particularly in Article 250, the words "effective" and "effectively" are frequently used in relation to grounding and bonding. For example, Section 250-50(b) recognizes as part of the grounding electrode system "The metal frame of the building or structure, where effectively grounded," without any explanation of what "effectively grounded" means.
This is the sort of requirement one would expect to find in a performance-, rather than a prescriptive-type Code, of which the NEC is an example.
But in some cases, such as Section 250-50(c), Concrete-Encased Electrode, where it says "Reinforcing bars will be permitted to be bonded together by the usual steel tie wires or other effective means," one acceptable method is described, with the permission to use other effective means. This gives you something by which to judge what effective might be.
In Article 100, the definition of Grounded, Effectively is "Intentionally Connected to earth through a ground connection or connections of sufficiently low impedance and having sufficient current-carrying capacity to prevent the buildup of voltages that may result in undue hazards to connected equipment or to persons." This transfers the uncertain term from effective to the equally cloudy "sufficient," without providing anything specific.
The basic requirement for an equipment-grounding conductor is in 250-2(d): "Performance of Fault Current Path. The fault current path shall be permanent and electrically continuous, shall be capable of safely carrying the maximum fault likely to be imposed on it, and shall have sufficiently low impedance to facilitate the operation of overcurrent devices under fault conditions. The earth shall not be used as the sole equipment grounding conductor or fault current path," but again there are no specific requirements. If each fault return path is calculated for the value of resistance and impedance necessary to open the overcurrent devices in a specified time. Each path is then tested to determine its "effectiveness," but this simply isn't done on an average job. Following the rules in Art. 250, this is assumed to be sufficient. Over the years, this has proven to be true.
There are specific requirements for grounding and bonding connections in Sec. 250-8: "Connection of Grounding and Bonding Equipment. Grounding conductors and bonding jumpers shall be connected by exothermic welding, listed pressure connectors, listed clamps, or other listed means. Connection devices or fittings that depend solely on solder shall not be used. Sheet metal screws shall not be used to connect grounding conductors to enclosures." And in Sec. 250-70 for the connection of grounding electrode conductors to grounding electrodes: "Methods of Grounding Conductor Connection to Electrodes. The grounding conductor shall be connected to the grounding electrode by exothermic welding, listed lugs, listed pressure connectors, listed clamps or other listed means. Connections depending on solder shall not be used. Ground clamps shall be listed for the materials of the grounding electrode and the grounding electrode conductor and, where used on pipe, rod, or other buried electrodes, shall also be listed for direct soil burial. Not more than one connector can be connected to the grounding electrode by a single clamp or fitting unless the clamp or fitting is listed for multiple conductors. One of the following methods shall be used:
1. A listed bolted clamp of cast bronze or brass, or plain or malleable iron
2. A pipe fitting, pipe plug, or other approved device screwed into a pipe or pipefitting
3. For indoor telecommunications purposes only, a listed sheet metal strap type ground clamp having a rigid metal base that seats on the electrode and having a strap of such material and dimensions that it is not likely to stretch during or after installation
4. An equally substantial approved means."
These specific requirements are helpful in our search for the meaning of "effective." The inclusion of "listed" in these requirements brings into play Sec. 110-3(b), which requires that "listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling." Carefully following these instructions will go a long way toward making the installation "effectively" grounded or bonded.
So it can be seen that there are, after all, enough specific requirements in Article 250 to assure us of effective grounding and bonding.
Although not recommended, one certain way to determine the effectiveness of a grounding or bonding path is to depend on it to hold the voltage to a reasonable level, or to open an overcurrent device. Then, if it fails, it was evidently not "effective."
More certain in Article 250 are the rules for the size of grounding electrode conductors in Table 250-122, but even there the sizes given are minimum sizes, so it may be necessary to use larger conductors in order to achieve the objectives of the performance requirements in Sec. 250-2. There is more uncertainty about what is required.
Workmanship plays an important part in whether application of the rules results in an effective grounding or bonding installation. One loose locknut in a metal raceway run, or one set screw not tightened in a coupling or a connector, can render ineffective the fault return path of a circuit or feeder.
SCHWAN is an electrical code consultant in Hayward, Calif. He can be reached at firstname.lastname@example.org.