Grounding and Bonding
Grounding and bonding are often confused with each other. Both are safety related systems, but grounding is more about protecting electrical equipment and bonding is more about protecting people. Neither is used during normal daily operation of the electrical system of the house. Refer to the illustration in the basic electricity section to see how electricity flows during normal daily operation.
One of the reasons for the grounding system of the house is to help safely deal with voltage surges. If lightning strikes near the transformer belonging to the utility, or if a higher voltage wire falls on the service drop, or if there is a switching surge, some of that energy may wind up in the electrical system of the house. Without the grounding system of the house, the energy has no safe path to ground. It may find an unsafe path, perhaps arcing through branch circuit wire insulation to metal water pipes or gas pipes, or welding the wires in a motor or transformer, or damaging your new plasma TV. Damaged equipment, electrocution, and fires are all possible when voltage surges have no safe path to ground. If the voltage surge is large enough, for example from a lightning strike, even the grounding system of the house may not prevent equipment damage and fires.
While it serves other functions, the grounding system of the house acts like a surge suppressor. It limits voltage surges in the electrical distribution system of the house and shunts them safely to ground. And while grounding gets more attention, bonding is at least as important for electrical safety.
Bonding occurs when:
1.metal that could carry electricity (but is not supposed to),
2.is intentionally connected together to provide a permanent low resistance return path,
3.that is capable of conducting all electricity accidentally carried by the metal back to its source.
Note the words in bold print. They are important and we’ll return to them later.
In most houses, the source of electricity is the transformer belonging to the utility and the low resistance return path is the grounded conductor belonging to the utility. That is why you should find metal water pipe and gas pipe bonding conductors, and the equipment grounding conductors (EGCs) in electrical cable connected to the grounded terminal bar at or before the service equipment. This low resistance return path is essential. Without a low resistance path, enough current may not flow, so that the overcurrent protection device (OPD) clears the ground fault.
A ground fault occurs when electricity flows in metal (or other conductive material) that is not normally energized. Ground faults usually occur when a hot wire comes in contact with the conductive material.
How does bonding help clear ground faults? Suppose a rat sits on a copper water pipe and chews through insulation on an electrical cable. If the pipe is bonded, as it should be, the pipe and the rat become the conductive material that returns the electricity to its source. The unfortunate rat is fried, and the current in the pipe should quickly increase past the circuit breaker’s limit. The circuit breaker trips and clears the fault.
But what if the pipe were not bonded? The rat lives to chew another day because without a return path no current flows. If the cable touches the pipe, the pipe is energized even when no current flows. That is, until someone touches a metal water supply fixture. If the person is grounded, the person becomes the conductive material and the return path. Current flows through the person, and the results may be unfortunate.
A low resistance return path is critical for proper bonding because a high resistance return path may not trip the circuit breaker and clear the ground fault. Returning to the rat example, assume the water pipe is bonded, but the bonding clamp is loose or is clamped to a painted or rusted surface creating 10 ohms of resistance at the clamp. Using Ohm’s Law we know that:
I(current in amps) = E(voltage in volts) / R(resistance in ohms).
If E=120 volts and R=10 ohms, then 120/10=12 amps. This poorly bonded circuit will carry 12 amps. Twelve amps will not trip a 15 amp circuit breaker, but it is more than enough to kill the rat or anyone else.
Note that we did not mention the grounding system of the house during our discussion of bonding and ground faults. That is because the grounding system of the house has a minimal impact on clearing ground faults. Two reasons exist for this minimal impact, and they deal with two common electrical myths.
Myth one is that electricity wants to return to ground. It really wants to return to its source, which in the case of most house electrical systems is the transformer belonging to the utility, and ultimately the power generating station. If all bonded metal is connected by a low resistance path to the grounded wire belonging to the utility, that metal is the lowest resistance return path to the electricity’s source. The grounding system of the house is usually a higher resistance return path and thus has less impact on returning electricity to its source.
Myth two is that electricity takes the path of least resistance back to its source. It really takes all available paths. The current carried by each path is determined by the resistance in each path. Assume that the resistance in an effectively bonded water supply pipe is 0.5 ohms and the resistance through a person touching a metal water supply fixture connected to the pipe is 10 ohms. The current in the bonded water supply pipe is 120/0.5=240 amps and the current through the person is 120/10=12 amps. The person will certainly get lit up, but only for a fraction of a second because the current flowing through the bonded path will quickly trip the circuit breaker.
There is much more to grounding and bonding. For home inspectors, this is the easiest way to think about them.
1.The grounding system of the house acts like a voltage surge suppressor that helps safely shunt voltage surges to ground.
2.Bonding is a safety system that helps clear ground faults in normally non-current carrying materials.
The grounding system of a house is not a surge suppressor; it just acts like one in some cases. A real surge suppressor is a good idea if there are expensive and sensitive computers and other equipment in the house.
Before we move on to consider some grounding and bonding components and their installation requirements, we should distinguish between the grounding system of the house and the EGCs contained in modern electrical cable. Both use the term grounding, but the EGCs are really bonding wires. They are not part of the grounding system of the house. Their function is to provide a low resistance return path for components like metal switch plates and metal equipment cabinets that may become energized.
The grounding electrode system of a house’s electrical system consists of: (1) grounding electrode(s) and, (2) a grounding electrode conductor (GEC). Common grounding electrodes include:
•at least 20 feet of #4 rebar or #4 AWG bare copper wire encased in concrete (a ufer ground),
•a galvanized steel pipe or rod, or a copper-coated steel rod driven at least eight feet into the ground,
•a metal water service pipe (including metal well casings) in contact with the ground for at least ten feet.
Only 1 grounding electrode is usually required for older houses, however all accessible grounding electrodes around a house must be bonded together using the same size wire as the grounding electrode wire. In newer houses, metal water service pipe may not be the only grounding electrode, but if it is present it must be bonded to all other grounding electrodes. Also in newer houses, 2 grounding electrodes are now required if a rod and pipe grounding electrode is used.
The GEC should be at least #6 AWG copper for 150 amp and greater service. Number 4 AWG copper wire is required for ufer grounding electrodes with 200 amp and greater service. A number 8 AWG copper wire may be used for 125 amp and smaller services. An aluminum wire may be used, but restrictions make it impractical in most cases. In newer houses, the connection to a water pipe grounding electrode may not occur more than five feet from where the pipe enters the home.
The GEC must be connected to the grounded (neutral) wire of the utility at an accessible location between the load side of the service drop or lateral and the service equipment. No other grounding connections are permitted downstream from this connection, except for detached buildings supplied from service at another building. This is because additional grounding connections could create unintentional return paths to the source of the electricity.
Note that the grounded (neutral) wire and the EGC are connected in the distribution panelboard in the following illustration. The result is that current is flowing on all bonded metal and on the EGC, as indicated by the yellow triangles. While this current is at zero volts (thus no power) under normal conditions, there are situations when this current could be at positive voltage, and could create a hazard to both people and equipment.
The best way to remember bonding requirements is like this: if it is metal and it is or could be near electrical wires, then it probably needs to be bonded to the grounded wire of the utility. Components that may require bonding include metal:
•water and gas distribution pipes,
•electrical equipment cabinets and cases,
•framing and sheathing,
•all metal parts of the electrical service and distribution systems.
Satellite and cable TV coax cable must also be bonded. Bonding connections at electrical fittings and boxes must be physically secure and provide a low resistance electrical connection. Any non-conductive contaminants such as paint and rust must be removed at the bonding connection point. Bonding jumpers must be installed around interruptions such as plastic boxes, water meters, and sometimes components such as water softeners and filters. Bonding wires must usually be the same size as the GEC.
Electrical Service ratings (Capacity)
Minimum Voltage Almost all utility-supplied residential electrical service is 240 volt single phase. Three phase 240 volt and three phase 208 volt residential services are very uncommon for houses. single phase 120 volt service to a house is usually considered a reportable deficiency because most cooking appliances require 240 volts, and because the electrical current capacity of 120 volt service might not be adequate. Electricity service is sometimes referred to as 220 volts. This voltage is not supplied by modern electric utilities.
Minimum Current The minimum electrical service current for a modern single-family house is 100 amps. Anything smaller is considered a reportable deficiency, even if the service is original. Even 100 amps is often marginal for all but small houses with gas service for heating and clothes drying. Most newer houses have 150 or 200 amp service and large houses may have up to 400 amp service. Each unit of a two-family house or a townhouse may have as little as a 60 amp service; however, the home inspector may wish to report such a limited service to the client.
Determining Service Amperage Home inspectors are required by most standards of practice to report the service amperage to the house. The service amperage is usually the lowest amperage rated component starting at the service entrance wires and concluding at the service equipment and the panelboard. For example, if the service entrance wires are 2/0 copper (rated for 200 amps), but the service equipment and panelboard are rated for 150 amps, then the service to the house is 150 amps. Note that the nominal capacity of the electric meter or the meter base is usually not a consideration when determining service amperage.
Determining service amperage can be easy when the service equipment is a single overcurrent device; the rating on the service equipment overcurrent device is usually the service amperage, but not always. An old panelboard is sometimes replaced by a new panelboard and service equipment with a greater amperage rating, but the service entrance wires are not replaced. The service amperage in this case is limited by the rating of the service entrance wires. This is a dangerous situation because the higher amperage equipment can allow more current to flow through the service entrance wires than the wires can safely handle. Insulation can melt and an electrical fire can start.
Situations sometimes occur when it is not possible to determine the service amperage. These situations occur most often when there are multiple service equipment disconnects in multiple enclosures. It is okay to report that the home inspector could not determine the service amperage, if the home inspector recommends electrician evaluation to determine the service amperage.
Required and Dedicated Branch Circuits Certain branch circuits are required in modern houses. Older houses without these circuits are not necessarily deficient. Required individual branch circuits include:
•two-20 amp, 120 volt branch circuits that serve only kitchen countertop receptacles and receptacles in the breakfast and dining rooms; one of these circuits may serve the refrigerator,
•120 or 240 volt branch circuits that serve only one furnace or air handler,
•a 20 amp, 120 volt branch circuit that serves only receptacles in the laundry room,
•one-20 amp, 120 volt branch circuit to serve only receptacles in bathrooms (exception: one 20 amp, 120 volt branch circuit for each bathroom may serve both lights and receptacles in the bathroom).
Most 240 volt circuits are dedicated to serving one electric appliance such as a water heater, an air conditioning condenser, or a well pump. Most 240 volt circuits serving cooking appliances such as ranges, wall ovens, and cooktops are also dedicated circuits; however, there are exceptions that allow multiple cooking appliances on one circuit. If installed, the 20 amp, 120 volt branch circuit that serves the kitchen exhaust fan or microwave oven should be a dedicated circuit. A dishwasher and food-waste disposer may each need a dedicated 120 volt circuit.
Multiwire Branch Circuits A multiwire branch circuit is a three wire branch circuit with two hot (ungrounded) wires and one neutral (grounded) wire. In residential electrical systems, the voltage between the two hot (ungrounded) wires is 240 volts, and the voltage between the hot (ungrounded) wires and the neutral (grounded) wire is 120 volts. When a multiwire branch circuit is operating as intended, the voltage on the shared neutral (grounded) wire is zero. Examples of multiwire branch circuits include split-wired receptacles that provide the required two 20 amp kitchen countertop receptacle circuits, and split-wired receptacles that are sometimes used to provide electricity to a receptacle serving the dishwasher and the garbage disposer. Clothes dryer and range circuits are also examples. Water heater and air conditioning condenser circuits are usually not multiwire branch circuits because there is no neutral (ungrounded) wire in the circuit.
Circuit breakers protecting multiwire branch circuits should be connected with an approved handle tie. This is a safety requirement so that both hot legs of the circuit are disconnected simultaneously.
Service Load Calculation A qualified electrician should perform a service load calculation to determine the amperage load for a house when the house is built, and when a significant increase in amperage load is contemplated. Amperage load might increase as a result of major remodeling or the addition of new electric appliances such as heat pumps and air conditioners. A similar calculation should be performed for a subpanel before one is added. These calculations are out of scope for a home inspection; however, home inspectors should have a basic understanding of these calculations.
A load calculation assumes that all electric circuits are not active simultaneously; thus, the calculated load is less than the sum of all circuits in the house, or all circuits served by a subpanel. The calculation is the sum of the following: (1) the load of light and receptacle circuits, (2) the load of kitchen and laundry receptacle circuits, (3) the load of electric appliances such as the electric clothes dryer, water heater, and cooking appliances, (4) the load of the largest heating or cooling equipment such as all air conditioning or heat pump condensers or electric space heating. The loads for numbers 1, 2, and 3 are reduced by a factor that accounts for circuits not being active simultaneously.
Electrical Service Drop and Service Lateral
Service Description The common house electrical service consists of an overhead service drop or an underground service lateral, a service mast, service entrance conductors, an electric meter in a meter base, the service equipment, feeder conductors, and one or more panelboards. These components are configured in different ways based on the service type (underground or overhead), the age of the house, and local customs. A house may not have all these components.
Service Drop An overhead service drop is common for older houses and for houses in rural areas. The service drop conductors run from the transformer on the pole belonging to the utility to a point at the house where they connect to the service entrance conductors (usually with a visible splice). This connection point is called the service point, and usually marks the point where the responsibility of the utility ends and the homeowner’s responsibility begins.
The service drop conductors may be attached to the house or they may be attached to a service mast. A service mast is a pipe that extends above the roof. When the service drop conductors are attached to the service mast, the service entrance conductors enter the service mast through a service head (gooseneck), run inside the service mast, and then run into the meter base. Service drop conductors may be attached to the house on the fascia or on the wall. When the service drop conductors are attached to the house, the service entrance conductors usually run inside conduit or inside the service entrance cable sheathing, then into the meter base.
The service entrance conductors then run from the meter base to the service equipment. The service equipment location depends on local customs and on the age of the house. Some service equipment is located inside and some service equipment is located outside. There is no benefit to either location. The service equipment may be in one or more separate cabinets, or it may be in the same cabinet as the main panelboard. There is no benefit to either location. If the service equipment is in a different cabinet from the main panelboard, the conductors between the service equipment and the main panelboard are called feeder conductors.
Water can run down conductors and into the meter base or panelboard cabinet. Water can damage components and increase resistance at connections. Increased resistance creates heat and heat creates a fire hazard. Service entrance conductors should form drip loops below the service head so that water drains off the conductors before the conductors enter the service head. The service head should be angled down so that water does not enter through it.
The grounding electrode conductor (GEC) usually connects to the electrical system at the service equipment. All panelboards downstream from the GEC connection are subpanels. If the service equipment is in a different cabinet from the main panelboard, the main panelboard is also a subpanel.
Service Lateral An underground service lateral is common for newer houses and is more desirable because the conductors are less likely to be damaged. The service lateral conductors run from the transformer into a riser at the house, and then into the meter base. After the meter base, a service lateral system is like a service drop system.
Service Drop Clearance Above the Roof Service drop conductors can be dangerous if contacted and can be damaged if they come in contact with the roof. The minimum distance between the lowest individual service drop or service entrance conductor and a roof with a slope less than 4/12 is 8 feet. The lowest point is usually the drip loops. The minimum distance for a roof with a slope 4/12 or greater is 3 feet.
An exception reduces the minimum distance between the service drop and the roof to 18 inches if less than 6 feet of the service drop conductors extend above the roof (measured along the conductors), and if the service drop conductors extend above no more than 4 feet of the roof (measured along the roof). The 18 inch clearance is the most common distance seen in the field. Service drop clearances may be changed by additions to the house such as new rooms and porch roofs.
Service Drop Clearance Above the Ground The minimum distance between the lowest individual service drop or service entrance conductor and the ground or a pedestrian walkway is 10 feet. The lowest point is usually the drip loops. The minimum distance above a residential driveway is 12 feet. The minimum distance above a public street and above areas subject to truck traffic is 18 feet. The minimum distance above a swimming pool is 22½ feet above the water and extending 10 feet in all directions from the pool edge.
Service Drop Clearance to Building openings The minimum distance between the lowest individual service drop or service entrance conductor and the side or sill of an operable window, door, deck, balcony, or similar point is 3 feet. The lowest point is usually the drip loops. The clearance requirement is to individual conductors, not to conductors in conduit and conductors in sheathing. Clearance is not required above openings.
Service Equipment. Panelboards, and Enclosures
Service Equipment Description The service equipment is the means to disconnect all electricity to the house. More common terms include main disconnect, main breaker, and service disconnect. Service equipment may be circuit breakers, fuses, or switches that may contain fuses. Circuit breakers are common in newer houses. The service equipment is usually located in one enclosure, but it may be in more than one enclosure. If the service equipment is in separate enclosures, the enclosures should be in one location.
Disconnecting all electricity to a house should require operating or pulling no more than six circuit breakers, fuse blocks, and switches in any combination. The service equipment should be labeled to indicate its function, and it should be listed for use as service equipment. Typical service disconnects involve one or two disconnects in one enclosure. An exception is an older panelboard design known as the split-bus panel, described later. Fuse blocks are no longer allowed to be used as service equipment, but existing equipment may remain if safe and functional.
Enclosure Description Home inspectors will encounter different types of panelboard enclosures. One type is often called a meter-main enclosure because the meter base, service equipment, and the panelboard are located in one enclosure, with the meter base in one section and the service equipment and panelboard in the other section. Access to the panelboard is through a door either below or above the meter or on one side of the meter. Another type is often called a main breaker panelboard enclosure because the service equipment and the panelboard are located in one enclosure. Another type is often called a main lug panelboard enclosure because the panelboard is served by feeder conductors from the service equipment or from another panelboard. Main lug panelboards are usually configured as subpanels, even if the panelboard is the service panel for the house. Remember, panelboards downstream from the service equipment are usually configured as subpanels (neutral conductors separated and isolated from the grounding conductors).
House panelboard and service equipment enclosures are usually made from steel and some-times from plastic. Galvanized steel is used if the enclosure is listed for wet or damp area installation. Nonmetal enclosures may be allowed if listed as electrical enclosures. Panelboards, service equipment, disconnect devices, and similar equipment for residential use are usually required to be inside a listed enclosure. Some very old equipment and amateur installations may not be inside a listed enclosure; this is usually considered a reportable defect.
Enclosures should be listed for use where installed. Enclosures installed outdoors should be listed for outdoor use. This should be indicated on the enclosure label. Enclosures installed outdoors or indoors in a damp location should have at least a ¼ inch air space behind the enclosure to allow drying and to avoid condensation; this feature is usually built into the back of the cabinet by making the attachment openings protrude.
Enclosures installed in wood walls should be flush with the wall or should project from the wall. The maximum gap around an enclosure in a finished wall is ⅛ inch.
OPDs and wires generate heat, especially AFCIs and GFCIs. Enclosures should be large enough to allow sufficient air circulation around OPDs and wires to avoid excessive heat buildup that can damage components and cause an electrical fire. Exactly how much space is required is not defined, so it can be difficult to know when to report an enclosure that may be too small.
Panelboard Description Most house panelboards are single-bus panelboards. The panelboard is supplied by a main breaker on the panelboard or by lugs that supply electricity to all OPDs on the panelboard. A few older panelboards are split-bus panelboards; so named because electricity for the 15 and 20 amp branch circuits on the lower bus is supplied by a circuit breaker on the upper bus. Split-bus panelboards do not have a main circuit breaker. The upper bus has slots for five 240 volt branch circuits and one 240 volt circuit breaker that serves the lower bus. The six device service equipment limit is satisfied by shutting off the upper bus circuit breakers.
Location, Access, and working Clearances The service equipment, panelboards, and equipment disconnect devices, such as for furnaces and condensers, should be located where access is safe, and should be provided with a safe space around them for inspection and repair. this equipment should not be located in storage spaces, clothes closets, bathrooms, and above stair steps. Stair landings are an acceptable location if the working clearances are available. Indoor equipment should have an electric light nearby.
This equipment should have clear working space in front that is at least 36 inches deep, 30 inches wide, and 78 inches tall, measured from the floor. The cabinet door should be able to swing open at least 90°. The area directly above and below the enclosure is reserved for electrical system components and should not contain components such as plumbing pipes and HVAC ducts.
This equipment should be located so that circuit breakers, fuse block pulls, and switch handles are not higher than 79 inches above the adjacent walking surface. Measurement is to the handle in the up position. This requirement applies to all switches including those controlling lights and receptacles. There is no minimum height requirement.
This equipment should be readily accessible; meaning that one should be able to reach it without climbing over or moving objects or by using portable ladders. Equipment hidden by decorations such as mirrors and pictures is not usually considered readily accessible. Equipment blocked by shelves, workbenches, and similar components is not usually considered readily accessible. Equipment enclosures may be locked and may be located in a locked room; however, the key should be accessible to a qualified person. The problem with locked equipment in houses is that the key is often lost or not easily locatable.
The service equipment for manufactured homes (often incorrectly called mobile homes) is usually located on a post in the yard near the home. The panelboard in the home should be configured as a subpanel with the neutral conductors isolated from the EGCs.
Typical Defects, Electrical service Typical defects that home inspectors should report include:
1.service drop conductors in and around tree limbs,
2.damaged service drop and service entrance conductor insulation,
3.no insulation at service drop connection to service entrance conductors,
4.drip loops inadequate to drain water,
5.loose, bent, or damaged service mast or service head
6.absent, deteriorated, damaged, improperly installed service mast flashing,
7.loose or damaged service drop connection at house,
8.inadequate clearances between service drop and service entrance conductors and roofs, ground, and building openings,
9.loose, damaged, deteriorated meter bases and electrical enclosures,
10.meter bases and electrical enclosures not sealed where attached to wall coverings, this is a water infiltration point,
11.loose or damaged conduit at or around enclosures,
12.service equipment and panelboard upgraded to larger capacity, but service drop and service entrance conductors not changed.
Typical Defects, Grounding and Bonding Typical defects that home inspectors should report include:
1.damaged, disconnected, loose GEC at grounding electrode connection,
2.GEC too small for service (minimum #8 copper for under 150 amp service and #4 or #6 copper for 150 amp or larger service),
3.absent, loose grounding or bonding clamp,
4.grounding or bonding clamp connected to surfaces that are corroded, painted, dirty, or are covered by other high-resistance contaminants,
5.GEC improperly spliced; GEC may be spliced using a listed compression connector or by welding (not soldering),
6.metallic conduit connected with plastic fittings (electrical connection disrupted),
7.underground water pipe GEC connection located more than 5 feet from where water pipe enters the house (do not confuse this with the water distribution pipe bonding connection),
8.absent, loose, broken metal conduit connections (bonding path interrupted by absent or poor physical or electrical connection),
9.absent, loose, corroded metal water pipe bonding connection,
10.bonding jumper absent around water meter, water pressure regulator, water softeners and filters, and similar removable non-metallic components in metal water distribution pipes,
11.improper bonding connection installed for phone, cable, or similar services,
12.CSST gas tubing not bonded at first metal gas pipe or fitting after gas meter.
Safety Issues Additions and modifications to electrical service components usually require a permit. Typical defects found in these components may indicate unpermitted work.
Standards IRC 2018 E3405 (working clearances), E3602 (service load calculation), Table E3603.4 (conductor sizes for service entrance and GEC), E3604 (service drop and service entrance conductor clearances), E3607, E3608, E3610, E3611 (grounding), E3609 (bonding), E3703 (required branch circuits), E3705.7 (OPD locations), E3907 (enclosure installation), G2411 (gas pipe bonding).