How many grounding electrodes are required

These are the commonly seen issues in grounding electrode system that follows the NEC, but does not satisfy project scope:. There are many considerations that need to be taken into account when designing and installing grounding electrode systems.

These are:. Figure 4: This is a service entrance main breaker with a four-wire load. The line side is at the top with the white neutral conductors and the load side is at the bottom with gray neutral conductors. Error 3: Bonding grounded conductor neutral to ground bar at multiple locations. Per Article This connection is also allowed at separately derived systems. If the grounded conductor is grounded again on the load side of the service, the connection between the grounded conductor and the EGC on the load side of the service places the EGC in a parallel circuit path with the grounded conductor.

Another issue that can arise out of multiple bonding locations is the risk the grounded conductor being disconnected on the line side of the service. This could cause the EGC and all conductive parts connected to it to become energized because the conductive path back to the source that would normally allow the overcurrent device to trip is not connected.

In this case, the potential to ground of any exposed metal parts can be raised to line voltage, which can result in arcing and severe shock hazard. One common error in grounding and bonding design is the grounding of generators and whether a three- or four-pole automatic transfer switch is used with a four-wire power system. Grounding a separately derived system is detailed in Article The error in grounding and bonding design for separately derived systems stems from understanding the definition of a separately derived system.

As shown in Figure 3, a system is considered separately derived when the system does not have a direct electrical connection to the other supply system grounded conductor neutral , other than through the bonding and equipment grounding conductor.

The generator also requires to be directly connected to ground when it is considered a separately derived system as shown below. If a four-pole ATS is used and the neutral is switched, the generator or secondary backup source becomes a separately derived system. It should be noted that a three-pole ATS can be used with a four-wire generator and also be considered a separately derived system if the electrical distribution system is a three-wire system. In this situation, the generator neutral would be connected to ground, but a grounded neutral conductor would not be brought to the ATS.

Figure 5: This is a delta-wye transformer with the high side coming in from the bottom and the secondary coming out from the top.

As shown, the grounded conductor neutral is grounded at the transformer. A common reason for confusion mainly stems from not understanding the proper definitions. Therefore, the first step to understanding Article is understanding the terminology within the NEC. Below are some terms taken from the edition of NEC Article and clarifications for mentioned terms.

Bonded bonding : Connected to establish electrical continuity and conductivity. Bonding is not to be confused with grounding. Two pieces of equipment bonded together does not necessarily mean both pieces of equipment are grounded.

However, it assures that the metallic parts of the bonded equipment can form an electrically conductive path for electrical continuity. Bonding jumper, supply side: A conductor installed on the supply side of a service or within a service equipment enclosure s or for a separately derived system that ensures the required electrical conductivity between metal parts required to be electrically connected.

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Location Westchester County, New York. What is the minimum number of Grounding Electrodes required at premise wiring systems that are required to be grounded? One scenario: A small dwelling that utilizes a Ufer concrete footing grounding electrode system.

I then 'bond' to the cold water and any other system that requires bonding. Another situation could be a storage building that has no water and utilizes the Ufer ground. Am I required to drive ground rod s? Location Indianapolis. Re: Minimum number of Grounding Electrodes " If available on the premises at each building or structure served, each item in Where none of these electrodes are available, one or more of the electrodes specified in Pierre, None of the other electrodes are required to be supplemented.

This rule is not because the water pipe is not sufficient, it is, but it is likely to be rendered useless with someone disconnecting the clamp or a plastic union being inserted. This would otherwise result in deterioration of one or the other pipes. The movement of water, acting as an electrolyte, past the two dissimilar metals causes a small DC voltage and thus current flows at the junction or coupling of the two metals.

The small DC current that results is similar to a battery one of the metals becomes an anode and the other a cathode with eventual breakdown of one of the metals due to the resultant chemical reaction.

Since the dielectric union insulates one length of pipe from the other at the connection point, a bonding conductor must be installed around the insulator.

A small amount of current may still occur with the bonding jumper, but the cathodic effect is minimized. Because the metal underground water pipe may be replaced eventually with a nonmetallic piping system, a backup or supplementary electrode has been required for the electrical system by the National Electrical Code NEC for quite some time.

This supplementary electrode can be an electrode of any type permitted by Section , such as building steel, a concrete encased electrode, or a ground ring. Because these electrodes must already be connected to the electrical system if they are available at the premises, the electrodes most likely to be used as supplementary electrodes would be man-made electrodes.

One of these man-made electrodes could be metal underground tanks or other metal piping systems described in Section b , although galvanic corrosion can occur here also, creating additional problems. Metal underground gas pipes must never be used as an electrode since any galvanic corrosion of the pipe could have disastrous results.

The two most common electrodes used to supplement the metal water pipe electrode are rod electrodes or plate electrodes as described in Sections c and d , respectively. A rod electrode must not be less than 8 feet in length and can consist of iron, steel, stainless steel, nonferrous metals metals that do not contain iron , or a combination of these materials.