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nec article 250

Section (C)(1) and (2) allows the first 5 feet of an emerging metal underground water pipe that qualifies as a grounding electrode, or structural building steel to be used to extend or interconnect the connection to an electrode (see image). Below is a preview of Article See the actual NEC text at pasquinvis.tk for the complete code. The same change occurred in (B & C) which applies to concrete encased electrodes and ground rings. Below is a preview of Article See the actual NEC text at pasquinvis.tk for the complete code section. Once there, click on their link to free access to the NEC edition of NFPA This article is part 4 in a series that reviews some of the more significant revisions and new requirements in the next National Electrical Code (NEC). Part 4 provides a review of some significant changes in articles contained in Chapter 2, Wiring and Protection, and Chapter 3, Wiring and Methods and Materials. (A)(4) Electrode.


Size of Alternating-Current Grounding Electrode Conductor.


Article is the largest article in the National Electrical Code. It is often the most dreaded by those new to the code, and sometimes even by those who have dealt with the code for years. Some of the terminology is confusing and conceptually difficult to follow. In doing so, we will not cover every section of Articlenec article 250 concentrate on those that are used most commonly by multi-trade inspectors.

Photo 1. Here is a very small sampling of some of the devices designed for grounding connections. Please note the bottom right device will bond the grounding electrode conductor to an enclosure or raceway. Photo 2. This shows a sampling of bonding jumpers that are provided by the factory for main bonding jumpers in panels. The scope of this article covers general requirements for grounding and bonding of electrical installations.

First, we have two definitions that we need to consider in order to nec article 250 us understand the principles of grounding. Effective grounded-fault current nec article 250 is an intentionally constructed, nec article 250, low-impedance electrically conductive path designed and intended to carry current under ground-fault from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protective device or ground-fault detectors on high impedance grounded systems, nec article 250.

Ground-fault current path is an electrically conductive path from the point of a ground fault on a wiring system through normally non-current-carrying conductors, equipment, or the earth to the electrical supply source, nec article 250. Both of these are best understood as the emergency path the current takes in the event of a ground fault which is a short from an ungrounded conductor to ground. If we have a good path, then the high current flow back to the source should operate the overcurrent device and shut down the system, nec article 250.

Nec article 250 you probably noticed, the main difference is that one is an intentionally constructed path, which is what we hope to have, and the second is any path in which the current may flow, nec article 250. To give a real life example of this, I remember getting a service call to a house which had smoke coming out of the walls.

As luck would have it, I was very nec article 250 and beat the fire department to the site. The first thing I did was shut off the main at the service and the smoke started to lessen. By the time the fire department got to the house, there was hardly any visible smoke coming out of the walls, just the smell of burning wood.

The fire department broke open a hole in the wall and the plaster reinforcing wire lath had been burning its way into the wood studs, just like one of the old wood burning kits we used to have as kids. The only electrical device near this part of the dwelling was an air conditioner compressor unit. If it had been connected, there would have been a low impedance path that carried the current back to the breaker and caused it to open.

However, one ungrounded conductor had shorted out and the only path for the fault current was through the copper refrigeration lines to the wall where they contacted the metal lath wire and energized it, causing it to heat up to the point of burning the wood framing.

Without a good fault-current path back to the overcurrent device, the device just sees an additional load, but not enough to make it trip in a timely fashion. Photo 3. The bare copper conductor here is the grounding electrode conductor that has been connected to the concrete- encased electrode rebar stubbed up from the building footing.

The connections to nec article 250 earth are called electrodes, and the code describes eight different types of electrodes. We will only cover the concrete-encased electrodes and ground rods, since they are the ones most commonly used in construction today.

Details are found in This is the preferred electrode for any new construction, and it performs very well due to the fact that the concrete continues to extract moisture from its surrounding soil and has great contact with the earth simply due to its weight. The second most common is rod or pipe electrodes, which are covered in There are other electrodes covered in For decades, it was the most common source of grounding electrode; however, with the advances made in water system products, it was found that if a facility had a metal water line that failed, it was being replaced by a non-metallic system.

When that occurred, we lost our grounding electrode. If you review One item to note is a change made in the edition of the NEC for In the NEC In the field, this meant an inspector had to have some assurance that one device would measure 25 ohms or less, but how do you do that? Does the inspector test it? Generally no, so it was up to the contractor to prove it met this code requirement. So in the NEC This is a good example of how the code is often modified to match what is actually the general practice in the field.

Photo 4. This is an example of This is gas piping which goes throughout the house and may have the possibility of becoming energized and therefore shall be bonded. So nec article 250 that we have our actual connection to the earth, we have to connect it to those items we are trying to ground.

To do this we use a conductor called the grounding electrode conductor, nec article 250. The grounding electrode conductor is covered in First, this conductor must be made of a material resistant to any corrosive conditions to which it may be exposed. This could be various things, such as a corrosive soil, nec article 250, fumes within a building, or any other conditions that may damage it.

Again, if we lose this connection to the electrode, we have totally lost our grounding system. Article Covered is how to secure and protect it, and depending on the size, it may need some nec article 250 protection such as nec article 250 raceway.

The reason for this is really pretty simple: the impedance of the conductor and the nec article 250 are different and the current will travel at different speeds from one end to the other, so if they are not bonded and there is an air gap at one end or the other, it will arc.

Repeated arcing will cause damage to the electrode conductor. It must be securely fastened to the surface on which it is carried and can be run through framing members. Nec article 250 shall be installed in one continuous length without a splice or joint; however, if it absolutely has to be spliced, there are four very specific ways to do it in Remember this is a crucial element to the safety of the electrical system, and anytime we have a splice or connection we have created a possible failure point, so we try to avoid any conditions which may create a weak point.

Photo 5. In both of these photos, the grounding electrode conductor is the bare copper. It is being terminated on the grounded terminal location in these residential main services.

Note the aluminum bussing that continues into the meter section in each of these photos to connect directly to the utility-grounded service conductor, nec article 250, which meets the main bonding jumper requirement.

Also please note Now for one of the key elements of the grounding electrode conductor — how do we size it? In Article Refer to Table In these sections we find a new maximum size conductor requirement for each of these types of electrodes. For example, on a concrete-encased electrode you are not required to use a conductor larger than a 4 AWG copper conductor, nec article 250, no matter what the size of the service.

I must caution you that if the design professional has designated a larger conductor, you would be obligated to follow his requirements. Remember that the code is a minimum and can always be exceeded. Connecting to the grounded service conductor. So now that we have the electrode and the electrode conductor, what do we do with it?

In First, in As simple as it sounds, nec article 250, this is one of the most critical requirements of the code. The connection can be done in various ways as outlined in This should be the only point where we connect together the grounded conductor, the grounding electrode conductor and the equipment grounding conductors, nec article 250.

This is generally done at the main service disconnecting means of a service, nec article 250, utilizing what is called a main bonding jumper [see Failure to make this connection can lead to various issues, the least of which will be voltage fluctuations that may damage connected equipment. Once we move past the service main location, we are not to connect the grounded conductor remember this is generally referred to as a neutral to any grounding conductors; this is covered in If you do, you will create parallel ground fault return paths that may not push the overcurrent device to react in a timely fashion, nec article 250.

Connecting to equipment grounding conductor. In the remainder of The types of equipment grounding conductors are outlined in However, you will also notice within the article that various types of raceway also meet the grounding requirements, nec article 250.

I will not go into details of any one of these specific methods, nec article 250, please review for yourselves. We need to cover If covered or insulated, they shall be identified with a continuous outer finish that is either green or green with one or more yellow stripes, except as permitted elsewhere in We are allowed to re-identify using three options: stripping the insulation or covering, coloring or marking at the termination points. Also covered in B and Nec article 250 are allowances for multiconductor cables and flexible cords.

Our next concern with equipment grounding conductors is how to properly size them. This table is based on the overcurrent device that is protecting the circuit.

Basically, the larger the circuit ampacity size the larger the conductor that is required to handle the fault current back to the source and to cause the overcurrent device to operate.

A couple of items nec article 250 to be mentioned here; one is that if the ungrounded circuit conductors are increased in size for any reason, then the related equipment grounding conductor shall be proportionally increased. This might happen if voltage drop requires a larger phase conductor, since the larger conductors will have a higher fault current capacity and we have to nec article 250 for that with a larger equipment grounding conductor.

The other item is found in So if you have six PVC conduits for a parallel run, you will have to install an equipment grounding conductor in each conduit, and nec article 250 must be sized according to Table However, in the body of

 

(A)(4)&(5) Grounding Separately Derived Alternating-Current Systems.

 

nec article 250

 

National Electrical Code Top Ten Tips: Article -- Grounding. by Mark Lamendola. Based on the NEC. Please note, we do quote from copyrighted material. While the NFPA does allow such quotes, it does so only for the purposes of education regarding the National Electrical Code. This article is part 4 in a series that reviews some of the more significant revisions and new requirements in the next National Electrical Code (NEC). Part 4 provides a review of some significant changes in articles contained in Chapter 2, Wiring and Protection, and Chapter 3, Wiring and Methods and Materials. (A)(4) Electrode. Article is the largest article in the National Electrical Code. It is often the most dreaded by those new to the code, and sometimes even by those who have dealt with the code for years. Some of the terminology is confusing and conceptually difficult to follow. Author: Randy Hunter.