What Is A Grounded Conductor

What Is A Grounded Conductor – Hailing from the great state of Texas, there’s nothing better or more reassuring than a pair of comfortable cowboy boots. The key to a good pair of shoes is choosing the right size. The lack of size significantly affects the comfort of these stylish shoes. Nothing is more uncomfortable than squeezing into a pair of boots that are too small, and a pair of boots that are too big rubs back and forth against your skin causing blisters. The same can be said about the dimensions of electrical conductors, the consequences of which are far beyond simple convenience. Choosing the wrong size conductor in an electrical installation can lead to dangerous and catastrophic results with conductors that are too small for the applied load. And who wants to pay unnecessary and extra costs for larger conductors than necessary?

If you work in the electrical industry, there are many grounding and bonding conductors that we refer to and use on a daily basis. Proper sizing of these grounding and bonding conductors is a critical component of proper electrical system installation. In this article, we will look at the proper dimensions of some of these important grounding and bonding conductors. in the village

What Is A Grounded Conductor

, there are three basic tables we use to determine the sizes of these grounding and bonding conductors. First we have Table 250.66

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It is important to use the correct terminology when discussing grinding and bonding. If someone calls my office and says:

.” In that case, the first thing we need to do is determine exactly what “grounding” they’re referring to. When dealing with grounding and bonding, it’s important to get everyone on the same page using the correct and defined terms used.

. With this in mind, let’s define what conductor we are talking about before discussing the size of these conductors. In Article 100 of Art

An important set of requirements for grounded service conductors is contained in 250.24(C). This section requires that when an alternating current system operating at 1,000 volts or less is grounded at any point, the grounded conductor

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The service conductor varies with the calculated load according to 220.61. The original calculation from 220.61 shall be the minimum size of the grounded service conductor unless modified by 250.24(C)(1) or (C)(2).

First, a load calculation must be performed in accordance with 220.61 to determine the minimum size for the assumed neutral load. Second, the size of the conductor must be determined from 250.24(C)(1) or (C)(2). Section 250.24(C)(1) requires that the service grounding conductor be sized in accordance with Table 250.102(C)(1) or Note 1 to Table 250.102(C)(1). The final minimum size of the service grounding conductor shall be the larger of the results determined from these two calculations. Using this table, the grounded service conductor size is determined based on the largest ungrounded conductor or equivalent area (AWG/kcmil) for parallel conductors. For example, a service with 250 kilometers per phase copper conductor requires a minimum grounding conductor size of 2 AWG copper conductor or 1/0 AWG aluminum conductor or copper clad aluminum conductor. If the service consists of three 250-kilometer copper conductors per phase in parallel (750 kilometers), the grounding conductor size is at least 2/0 AWG copper or 4/0 AWG aluminum or copper-clad aluminum conductor.

Note 1 to Table 250.102(C)(1) introduces the “12 ½ percent rule” if ungrounded feeder conductors are larger than 1100 kCmil in copper or 1750 kCmil in aluminum.

, the grounded conductor shall have an area not less than 12½ percent of the area of ​​the largest underground supply conductor, or an equivalent area for parallel supply conductors. An example of this is a service with six 4/0 AWG copper conductors per phase. How many round mils are in each 4/0 AWG copper conductor? For that answer we will have to visit

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Chapter 9 Table 8 This Chapter 9 table shows that a 4/0 AWG copper conductor has 211,600 circular mils. In our example, we have six conductors per phase.

Some quick math says that these (6) 4/0 AWG copper conductors equal 1,269,600 circular miles.

. This total circular value in mils exceeds the largest copper reference value of 1100 ccmils at the bottom of Table 250.102(C)(1). According to Note 1 to Table 250.102(C)(1), we must now apply the “12 ½ percent rule” to these 1,269,600 circular mills to find the minimum ground conductor size required for these six 4/0 AWG copper conductors. phase Again, our quick math shows that 12 ½ percent of 1,269,600 circular miles equals 158,700 circular miles.

. To select a grounded service conductor with a value of at least 158,700 circular mils, we must return to Table 8 in Chapter 9. According to Table 8, a 2/0 AWG conductor has 133,100 circular mils, while a 3/0 AWG conductor has 167,800 round mils, so a 3/0 AWG copper conductor is the minimum grounded conductor size for six 4/0 AWG ungrounded copper conductors per phase.

Equipment Grounding Conductors

Earth defines an electrode as “a conductive object through which direct contact with earth is made”. A grounding electrode conductor is defined as “a conductor used to connect the grounding conductor of a system or equipment to a grounding electrode or to a point in the grounding electrode system.”

A ground electrode conductor (GEC) size for single service is required to be sized according to 250.66 and Table 250.66. The minimum copper conductor size shall be 8 AWG and no larger than 3/0 AWG. Where aluminum or copper-clad aluminum grounding conductors are installed, they shall be not less than 6 AWG and not more than 250 kcmil. The size of the ground electrode conductor depends on the size of the largest ungrounded service entrance conductors or ungrounded derivative conductors.

Table 250.66 is based on the conductor size ratio, not the rating of the circuit breaker or fuse in the service equipment. For example, if a 3/0 AWG copper service conductor is installed, the minimum size ground electrode conductor is 4 AWG copper or 2 AWG aluminum. If 750 kcmil aluminum service entrance conductors are installed, a 1/0 AWG copper conductor or a 3/0 AWG aluminum ground electrode conductor is required. Any ungrounded service conductors over 1100 kCmil copper or over 1750 kCmil aluminum or copper-plated aluminum require a maximum size 3/0 AWG grounding electrode copper or 250 kCmil aluminum or copper-plated aluminum.

, a circular area of ​​parallel conductors in mils is added together and treated as a single conductor for determining the GEC size. An example of this is four 250 kcmil aluminum service conductors arranged in parallel, which are treated as one 1000 kcmil aluminum conductor. According to Table 250.66, these four 250 kcmil aluminum service conductors require a 2/0 AWG copper or 4/0 aluminum or GEC copper-clad aluminum conductor.

Use Of Equipment Grounding Conductors

For sizing grounding electrode conductors to provide multiple enclosures, 250.64(D) provides four options for this installation. Services may be installed in more than six separate enclosures installed at one location subject to certain conditions. In these cases, the method of selecting the ground electrode conductors is a matter of choice for the designer or installer. A rule of thumb is to size the ground electrode conductor for the circular area of ​​the service entrance conductor(s) at the connection point for each service disconnect, or to size the common ground electrode conductor depending on the size of the main service entrance. Conductor(s).

Section 250.64(D)(1) provides two options. One option allows the use of a single wire of the common grounding electrode type to supply individual service enclosures. This common ground electrode conductor is sized according to the main conductors at the service entrance. A second option is to use a busbar as the common conductor of the grounding electrode. The busbar should be minimum 6 mm × 50 mm (¼ in. × 2 in.) and long enough for all connections. Tires can be made of copper or aluminum. For both options, ground taps sized according to the individual service entrance conductors that feed each service disconnect are then connected to a common ground conductor, wire, or busbar from each service disconnect. It is important to understand that the alternative presented in 250.64(D)(1) applies to both conductors; The common ground electrode conductor is required to be installed unbonded or bonded (as a general rule) and the lead(s) of the ground electrode conductor are allowed to connect to the common ground electrode conductor. It should also be noted here that the conductors from the individual earth electrodes to the permitted bus are not earth electrode conductors.

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