Basic Concepts for a Solidly Grounded System In accordance with the 2014 NEC This presentation is meant to give an overview of grounding and bonding and it is not intended to show how to size conductors Presented by Independent Electrical Contractors Texas Gulf Coast Chapter 713-869-1976 www.iectxgulfcoast.org Revised 2-26-14

The following is from “Electrical Grounding and Bonding” 3rd Edition by Phil Simmons Electricity follows the basic laws of physics, regardless of whether it is current flow over ungrounded (“hot”) conductors, over grounded conductors (sometimes neutral conductors), or in the grounding system. “Electrical Grounding and Bonding” is used in the IEC National curriculum for apprenticeship training

The following is from “Electrical Grounding and Bonding” 3rd Edition by Phil Simmons So, if we can understand basic circuit flow, we can understand the requirements and performance rules for grounding and bonding of electrical systems and equipment. Ohms Law is as applicable to grounding and bonding as it is to power circuits

What is the purpose of system grounding?

Purpose of Grounding Systems 250.4(A)(1) Grounded systems Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

Grounding limits the voltage imposed by lightning Although potentially very destructive, the effect of a lightning strike can be reduced by proper grounding. Keep in mind that a direct hit from lightning will cause damage to electrical appliances and possible wiring but hopefully grounding will help limit the damage.

Grounding limits voltage imposed by line surges A line surge would happen on the utility supply lines.

Grounding limits the voltage imposed by unintentional contact with higher voltage lines. Unintentional contact with a higher voltage line can cause a dangerous condition in an electrical system. This is a possibility in an overhead distribution area where the primary conductors, those over 600 volts, may come in contact with the service conductors feeding the house. Grounding helps to reduce the effect of this type of condition.

Systems are grounded to stabilize the phase to earth voltage Anywhere in this system the voltage to ground will be 120 volts 120 V Grounded Conductor

120 V Systems are grounded to stabilize the phase to earth voltage Grounded Conductor

B Systems are grounded to stabilize the phase to earth voltage ≈208 V A C 120 V This is a high leg delta system 120 V Grounded Conductor

Systems are grounded to stabilize the phase to earth voltage Grounded Conductor C This is a corner grounded delta system and the phase voltage is 480. The measured voltage between line A and line B is 480. This is an excellent place to explain why the Code uses the term grounded conductor instead of neutral. Line C is the grounded conductor and it is not a neutral. Refer to the definition of Neutral Conductor and Neutral Point in Article 100. O volts

Functions of Grounding Electrodes Conducting object used to connect electrical systems and/or equipment to the earth Functions of Grounding Electrodes 1. Connect the electrical system to earth 2. Connect electrical equipment to earth Attempt to maintain equipment at earth potential Service Disconnect Have no effect in clearing ground faults The fourth item is actually “little effect” but the purpose for stating “no effect” is to get people to stop thinking that generated electricity is always trying to get to ground (earth). It will take the earth as a path but it is trying to get back to its source. It is possible to be in an area where the earth path back to the source is of a low enough impedance that the current will flow in a sufficient amount to operate an overcurrent device but this would not be the normal or most common situation.

250.4(A)(2) Grounding of Electrical Equipment. Normally non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials. Point out that the definition for “ground” is “the earth”. Grounding means connecting to earth.

Service equipment and System connected to earth The system bonding jumper is not shown in the transformer because the transformer is utility company owned and it is not covered by the NEC. Service equipment and System connected to earth

Utility company transformer Electrical System Service Equipment No Shock Hazard Utility company transformer The system bonding jumper is not shown in the transformer because the transformer is utility company owned and it is not covered by the NEC. Service equipment and System connected to earth

Accidental connection from hot to enclosure Think of this figure as a barefoot child playing outside near the electrical panel after a rain storm Accidental connection from hot to enclosure How much current flows is dependent on the resistance of the soil This is meant to stress the importance of following the NEC because practical safeguarding of people is the purpose of the Code. No one can predict when all of the conditions are right, or maybe a better word is wrong, to set up a situation where a fatality can occur. System connected to earth

250.4(A)(3) Bonding of Electrical Equipment. Normally non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path. Most people are OK with bonding electrical equipment on the load side of the service disconnect but they seem to think using the neutral (grounded) conductor is wrong and a ground rod is the way to do it. Get across that ground means connecting to earth and we just covered why we do that. Also, remember the grounded conductor is not always the neutral.

How do we bond on the supply side of the service disconnect? Check out 250.92 and 250.142 Remember this class is not a “how to” class its purpose is to get the grounding and bonding concepts understood; basically why we do the Code requirements for grounding and bonding

Usually self-contained meter sockets and meter-main combination equipment are produced with the grounded conductor terminals or bus (often a neutral) bonded directly to the enclosure The meter enclosure is then effectively bonded when the grounded conductor is connected to these terminals within the meter enclosure The self-contained meter is a good example of using the grounded conductor on the supply side of the service disconnect as a means to bond the enclosure No additional bonding conductor connection to the meter enclosure is required

Photo courtesy of Gordon Stewart with Joe Swartz Electric Neutral lugs fastened directly to meter can Photo courtesy of Gordon Stewart with Joe Swartz Electric Gordon Stewart is the current IEC National president as of January 2014

Remote metering is something we need to focus on because the current transformer enclosures (CT cans), meter enclosures and potential transformer enclosures (PT cans) also need to be bonded.

Self-contained meter Meter enclosure CT can PT can

Some electrical inspectors do not look at equipment on the supply side of the service disconnecting means because they consider that as being under the exclusive control of the electric utility company This is true in Houston, TX and our main utility company, CenterPoint Energy, is in the process of revising their service standards to require bonding in CT can, PT can and meter can. CeneterPoint will not connect service until the bonding is complete

HOWEVER 90.2(A)(3) is very clear that installations of conductors and equipment that connect to the supply of electricity is covered by the NEC

Utility Company Fuse CT Can Electricity is always trying to get back to it’s source. The only way for this ground-fault current to get back to the source is through the dirt. Some utilities require the ground rod but emphasize that it has no effect on operating the overcurrent device. This is the same as we have seen for parking lot lighting or outside area lighting. Engineers sometimes require a ground rod at the light pole which is really not needed. The light pole base in most cases is a concrete encased electrode and it will handle a lightning strike if that is the purpose of the ground rod. The NEC allows a supplemental ground rod but an equipment grounding conductor is required for the ground fault return path in the case of equipment on the load side of the service disconnect. The grounded conductor is to be used on the supply side of the service disconnect.

Hot conductor touches can Not enough current can get back to the source to blow the fuses because the impedance of the dirt is too high and the CT can is now at the same potential as the “hot” conductor that is touching the can Utility Company Fuse Hot conductor touches can CT Can Electricity is always trying to get back to it’s source. The only way for this ground-fault current to get back to the source is through the dirt. Some utilities require the ground rod but emphasize that it has no effect on operating the overcurrent device. This is the same as we have seen for parking lot lighting or outside area lighting. Engineers sometimes require a ground rod at the light pole which is really not needed. The light pole base in most cases is a concrete encased electrode and it will handle a lightning strike if that is the purpose of the ground rod. The NEC allows a supplemental ground rod but an equipment grounding conductor is required for the ground fault return path in the case of equipment on the load side of the service disconnect. The grounded conductor is to be used on the supply side of the service disconnect. CT can is grounded but not properly bonded

CT can is grounded but not properly bonded Hot conductor touches can Utility Company Fuse Not enough current can get back to the source to blow the fuses because the impedance of the dirt is too high and the CT can is now at the same potential as the “hot” conductor that is touching the can CT can is grounded but not properly bonded Hot conductor touches can CT Can Electricity is always trying to get back to it’s source. The only way for this ground-fault current to get back to the source is through the dirt. Some utilities require the ground rod but emphasize that it has no effect on operating the overcurrent device. This is the same as we have seen for parking lot lighting or outside area lighting. Engineers sometimes require a ground rod at the light pole which is really not needed. The light pole base in most cases is a concrete encased electrode and it will handle a lightning strike if that is the purpose of the ground rod. The NEC allows a supplemental ground rod but an equipment grounding conductor is required for the ground fault return path in the case of equipment on the load side of the service disconnect. The grounded conductor is to be used on the supply side of the service disconnect.

Utility Company Fuse CT Can Electricity is always trying to get back to it’s source. We have now provided a low impedance path back to the source. The current on the secondary of the utility transformer should be so high that it causes the fuse on the primary to open. A grounding electrode (ground rod) is not shown because the purpose of this slide is to show fault current through the grounded conductor. The utility company may require a ground rod and that is OK and by Code it would be an auxiliary grounding electrode (refer to 250.54). CT Can

Metal can bonded to grounded service conductor (Neutral) Utility Company Fuse Metal can bonded to grounded service conductor (Neutral) Hot conductor touches can Electricity is always trying to get back to it’s source. We have now provided a low impedance path back to the source. The current on the secondary of the utility transformer should be so high that it causes the fuse on the primary to open. A grounding electrode (ground rod) is not shown because the purpose of this slide is to show fault current through the grounded conductor. The utility company may require a ground rod and that is OK and by Code it would be an auxiliary grounding electrode (refer to 250.54). CT Can

5 1 6 1 1 1 3 2 4 2 1=Supply-side bonding jumper 2=Main Bonding Jumper 3= Equipment grounding conductor 5 IMC 1 6 1 Metallic wireway 1 IMC IMC 1 3 The purpose of this slide is for proper terminology. Code Panel 5 has worked very hard over the past several years to properly identify the different grounding and bonding conductors and jumpers by the purpose they serve. This is so that training future electricians may be a little easier. The 2011 NEC finally eliminated the term “grounding conductor” because that term was used by the electrical community as a genic term for all grounding and bonding conductors. This class will not cover all grounding and bonding terms because the focus of this class is mainly the effective fault current return path. It may need to be pointed out that this is a service gutter and metering is not shown. The IMC conduit in the top of the gutter is from the load side of the meter. 2 PVC 4 4=Equipment bonding jumper on load side of service 5=Grounded service conductor 6=Grounding electrode conductor 2 EMT

5 1 6 1 1 1 3 2 4 2 1=Supply-side bonding jumper 2=Main Bonding Jumper 3= Equipment grounding conductor 5 IMC 1 6 1 Metallic wireway 250.96 requires the removal of nonconductive paint OR fittings designed so as to make such removal unnecessary 250.12 has the same requirement for equipment to be grounded 1 IMC IMC 1 3 The purpose of this slide is for proper terminology. Code Panel 5 has worked very hard over the past several years to properly identify the different grounding and bonding conductors and jumpers by the purpose they serve. This is so that training future electricians may be a little easier. The 2011 NEC finally eliminated the term “grounding conductor” because that term was used by the electrical community as a genic term for all grounding and bonding conductors. This class will not cover all grounding and bonding terms because the focus of this class is mainly the effective fault current return path. It may need to be pointed out that this is a service gutter and metering is not shown. The IMC conduit in the top of the gutter is from the load side of the meter. 2 PVC 4 4=Equipment bonding jumper on load side of service 5=Grounded service conductor 6=Grounding electrode conductor 2 EMT

250.4(A)(4) Bonding of Electrically Conductive Materials and Other Equipment. Normally non–current-carrying electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path. Typically any metal or conductive piping system in a structure will be bonded to the electrical system. The proper Code language is “likely to become energized” and for that reason someone in the class will point out that next slide is not correct. Also, this class will not discuss how the metal piping systems are bonding. In the case of gas appliances it is acceptable to bond the gas pipe with the electrical circuit that is supplying the electrical equipment in the gas appliance. This circuit is the one most likely to energize the gas pipe.

Must Bond All Metal Piping Systems Water & Gas Piping Pneumatic Systems Waste, Drain & Vent Air & Vacuum Systems

250.4(A)(5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. This is the real focus of this class. This section of the Code is a performance requirement and the prescriptive methods contained in Article 250 shall be followed to accomplish this performance requirement. Refer to 250.4

250.4(A)(5) Effective Ground-Fault Current Path. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be considered as an effective ground-fault current path. Point out the highlighted text. Generated electricity is not trying to get in the earth! Also, even if the installation was in an area where the earth was an excellent conductor it cannot be used as an effective ground-fault return path.

Proper bonding creates the safety circuit (effective ground-fault current path) that is necessary in order for our overcurrent protective devices to operate This “safety circuit” needs to be installed in the same manner as a power circuit The term “safety circuit” seems to make sense to electricians. This is not an NEC term and it does not appear in grounding and bonding books that I am aware of but we are trying to get electricians and especially young ones to understand the reason we are connecting everything together is to create a circuit that will function properly when it is needed to clear a ground fault. If the connections are loose or poorly done the circuit may not be complete.

Loose connections in a power circuit will cause the power to be unreliable The same results will happen to the “safety circuit” because of poor or impaired connections; however when the “safety circuit” is unreliable the consequences could be fatal

Remember the “safety circuit” is how the fault current is getting back to the source in order to cause the overcurrent protective devices, such as fuses and circuit breakers, to operate and turn off the power The effective ground-fault current path must be a low-impedance circuit (“safety circuit”) in order to facilitate the operation of the overcurrent device(s)

Normal Current Flow The blue backing means the buss bars are isolated from the enclosure. Notice the neutral bar in the meter enclosure does not have blue backing. The green dot in the neutral bar in the meter enclosure means the bar is actually fastened to the can.

Accidental contact with hot conductor and metallic enclosure Ground-fault Current Flow Accidental contact with hot conductor and metallic enclosure Some of the fault current will try to take the dirt path back to the transformer. It is unlikely that the dirt will conduct much current. Remember that electricity will take all paths not just the one with the least resistance. The amount of current that flows in each path (circuit) is a function of Ohm’s Law. It would be very difficult to determine the resistance (or actually the impedance) of the earth (dirt) but always remember some amount of current will flow through the earth path, it could be micro amps but electricity has to follow the laws of physics and if there is voltage and a complete circuit there will be current flow. OFF

Accidental contact with hot conductor and metallic enclosure Without proper bonding Accidental contact with hot conductor and metallic enclosure Load may not be affected by accidental contact of hot conductor and the problem may go undetected Ground-fault current will never get back to the source because the impedance is too high and circuit breaker will not trip The light blub enclosure is grounded but not bonded and therefore the only path (circuit) available for the fault current is through the dirt. This is a good slide to point out the difference between grounding and bonding. Also tell the class that maybe the wiring method was EMT and the equipment grounding conductor is the conduit as allowed by 250.118 but a bad connection was made at the lighting outlet box (loose locknut on the connector) or couplings were not tightened.

Without proper bonding Ground-fault current will not get back to the source because the main bonding jumper has not been installed and now the fault current has to take the earth as a return path back to the source The light blub enclosure is grounded but not bonded and therefore the only path (circuit) available for the fault current is through the dirt. This is a good slide to point out the difference between grounding and bonding. Also tell the class that maybe the wiring method was EMT and the equipment grounding conductor is the conduit as allowed by 250.118 but a bad connection was made at the lighting outlet box (loose locknut on the connector) or couplings were not tightened.

250.24(A)(5) Load-Side Grounding Connections. A grounded conductor shall not be connected to normally non–current-carrying metal parts of equipment, to equipment grounding conductor(s), or be reconnected to ground on the load side of the service disconnecting means except as otherwise permitted in this article. This is done in many installations. Electricians that have not attended grounding and bonding classes do not understand why this is important. To the uneducated everything is tied together at the service therefore let’s tie it together everywhere. Remember the manufacturer of electrical panels does not know if you are installing a main panel or sub-panel and that is why the green screw (main bonding jumper) is not installed in the neutral bar by the manufacturer.

Since we connect the grounding electrode conductor, equipment grounding conductors, and the neutral at the service what’s wrong with connecting them at a sub-panel? They all go to the same place anyway!!

Utility Company Transformer Load Electric Meter This is a proper sub-panel installation. The blue backing behind the neutral bar means it is isolated from the enclosure.

Normal Current Flow

Broken neutral and no circuit

Improper Current Flow Mistake! Neutral and equipment ground connected Explain how there is a parallel path with the neutral conductor and the equipment grounding conductor. Even under normal conditions the equipment grounding conductor will carry current because the connection has been made between the neutral bar and the equipment grounding bar. The amount of current flowing in the different paths is a function of Ohm’s Law and can vary depending on resistance in each of the paths. The green line connecting the sub-panel to the main panel is the equipment grounding conductor and this may be a metallic raceway Explain how someone could get injured or killed by separating the equipment grounding conductor and becoming a part of the circuit. Also, this could lead to other parallel paths such as building steel if the conduit is used as the EGC. All this stray current in a building could affect electronic equipment such as computers and copiers.

Improper Current Flow Mistake! Neutral and equipment ground connected The amount of current flowing in the different paths is a function of Ohm’s Law and can vary depending on resistance in each of the paths. Explain how someone could get injured or killed by separating the equipment grounding conductor and becoming a part of the circuit. The heart stops beating at 100 milliamperes which is 1/10 of an amp! GFCIs are set to trip at 5 milliamps.

Severity of Electric Shock 1

Broken neutral but circuit complete Mistake! Neutral and equipment ground connected Now we have a very serious situation because the equipment grounding conductor would not be sized to carry the full load current of the sub-panel. For instance if this was a 200 amp panel the neutral would be a 200 amp conductor. The equipment grounding conductor would be sized from Table 250,122 for a 200 amp overcurrent protective device which would be a #6 AWG. The #6 would be capable of carrying 65 amps and would get very hot if it had to carry 200 amps. Remind the class that the #6 has no overload protection.

Broken neutral but circuit complete If the wiring method was possibly SE cable there is a possibility of starting a fire particularly in a wood frame structure. You can probably think of some other scenarios where this could start a fire.

Concrete-encased electrode Typical service arrangement either overhead or underground. Be sure and point out grounding and bonding connections. The gas pipe is bonded and not to be used as a grounding electrode, there are no connections on the “street side” of the meter. The water pipe may be a grounding electrode provided it has 10 feet of contact with the dirt and the connection to the service is within 5 feet of it’s entrance into the house. In Houston a ground rod is required in addition to any other grounding electrode. Concrete-encased electrode

Gas pipe is not a grounding electrode but if it is likely to become energized it shall be bonded in accordance with 250.104(B) Typical service arrangement either overhead or underground. Be sure and point out grounding and bonding connections. The gas pipe is bonded and not to be used as a grounding electrode, there are no connections on the “street side” of the meter. The water pipe may be a grounding electrode provided it has 10 feet of contact with the dirt and the connection to the service is within 5 feet of it’s entrance into the house. In Houston a ground rod is required in addition to any other grounding electrode. Metallic water pipe may or may not be a grounding electrode, refer to 250.52(A)(1), however it is required to be bonded in accordance with 250.104(A) Concrete-encased electrode

250.94 Bonding for Other Systems An intersystem bonding termination shall be provided external to enclosures at the service equipment. Intersystem means that the electrical system and other systems are bonded together to minimize the occurrence of potential differences between equipment of different systems.

Intersystem bonding termination The Intersystem bonding termination could be connected directly to the grounding electrode conductor or directly fastened to the panel can. Refer to 250.94

Cable TV ground rod not bonded to electrical system ground rod Accidental connection between coax and neutral This is just to show the importance of bonding all grounding electrodes. Cable TV ground rod

Cable TV ground rod not bonded to electrical system ground rod Accidental connection between coax and hot Cable TV ground rod

Separate Buildings Supplying one building from another is basically the same as wiring between a main panel and a sub-panel

250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s). (B) Grounded Systems. For a grounded system at the separate building or structure, an equipment grounding conductor as described in 250.118 shall be run with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).

Bldg. 2 panel Bldg. 1 with electrical service MBJ Bonding Jumper Underground or overhead feeder This was allowed before the 2008 NEC only when there is no metallic or conductive path between the buildings. Now the second building is treated in the same manner as a sub-panel. All new installations require an equipment grounding conductor from the building feeding the other building. Also, point out that the building” may not be an actual building. Refer to Article 100 for the definition of a building. An equipment grounding conductor is required to be run with the supply conductors in accordance with 250.32(B)

Utility metering not shown Building Disconnect This illustrates an installation where the first “building” is actually a structure used solely for the support of electrical equipment. Grounding Electrode To service disconnect Service raceways Feeder raceways

Proper grounding and bonding at service All conductors and conduits are not shown Service disconnect Proper grounding and bonding at service Terminology is the important part of this slide Service raceway Service raceway

Proper grounding and bonding at service All conductors and conduits are not shown Main Bonding Jumper Service disconnect Grounding Electrode Conductor Proper grounding and bonding at service Bonding Bushing Grounding Electrode Bonding Bushing Terminology is the important part of this slide Rigid metal conduit Service raceway Service raceway Rigid metal conduit

Disconnect at building All conductors and conduits are not shown Disconnect at building Proper grounding and bonding at second disconnect Point out that the grounding electrode is required but it does not connect to the neutral or equipment grounding conductors Feeder raceway Feeder raceway

Disconnect at building Neutral bar isolated from enclosure All conductors and conduits are not shown Disconnect at building Equipment grounding conductor Equipment grounding bar Equipment grounding conductor Proper grounding and bonding at second disconnect Bonding jumper Rigid metal conduit Point out that the grounding electrode is required but it does not connect to the neutral or equipment grounding conductors Feeder raceway Feeder raceway Rigid metal conduit Grounding electrode

All conductors and conduits are not shown This slide is to illustrate current flow with a properly grounded and bonded system. The current goes from the source (the transformer which is not shown but it should be assumed that the current does not start or stop at the load side of the service disconnect) to the building disconnect and then to the load and back to the source for a complete circuit (path). There is no attempt to show overcurrent protection in this slide or the following slides. All conductors and conduits are not shown Load

Load All conductors and conduits are not shown The mistake is pointed out and then the parallel path can be seen on the equipment grounding conductor. There is another parallel path with the metallic conduit and then there is another parallel path with the earth (dirt). Again it should be pointed out that there will be current flow in all of these paths (circuits) during normal operation and probably no one will be aware of a problem. Just as with the main panel and sub-panel a deadly situation is just waiting for the right conditions to happen. Load

Mistake! Neutral connected to grounding electrode and equipment grounding conductors All conductors and conduits are not shown The mistake is pointed out and then the parallel path can be seen on the equipment grounding conductor. There is another parallel path with the metallic conduit and then there is another parallel path with the earth (dirt). Again it should be pointed out that there will be current flow in all of these paths (circuits) during normal operation and probably no one will be aware of a problem. Just as with the main panel and sub-panel a deadly situation is just waiting for the right conditions to happen. Load

DISCUSSION Hopefully some good discussion will follow and the point will be made about how important it is to know the NEC and make sure the installation is in compliance. Someone’s life depends on it!