10-114 Grounding Conductor Size (See Appendix B)

1. Except as permitted by Subrule 2), the grounding conductor shall be sized not smaller than
   1. 6 AWG if of copper; or
   2. 4 AWG if of aluminum
2. The grounding conductor shall be permitted to be sized smaller than prescribed in Subrule 1), provided that it is not smaller than the current-carrying conductor(s) of the system being grounded.

In summary, the grounding conductor (the conductor connecting the service to earth) in most residential installations will be as specified in Subrule 1) due to the normal minimum size service conductor being either No. 10 AWG copper or No. 8 AWG aluminum. 

10-116 Installation of Grounding Conductors (See Appendix B)

1. The grounding conductor shall be electrically continuous throughout its length.
2. ………..
3. ………..
4. ………..
5. A grounding conductor installed in the same raceway with service conductors shall be insulated, except that an uninsulated grounding conductor shall be permitted where the length of the raceway
   1. does not exceed 15 m between pull points; and
   2. does not contain more than the equivalent of two 90° bends between pull points.

The above Subrules are meant to ensure there are two insulation thicknesses between power and grounding conductors under normal installation practices, thereby preventing a short circuit should the insulation on the power conductor(s) be compromised due to abrasion. The conditions in Subrule 5) are considered less harsh and may allow the grounding conductor to be bare.

10-208 Conductor of an AC System to be Grounded (See Appendix B)

1. The conductor of an ac system to be grounded shall be
   1. one conductor of a single-phase, 2-wire system – the identified conductor;
   2. the mid-phase conductor of a single-phase, 3-wire system – the identified neutral conductor;
   3. the mid-phase conductor of a multi-phase system having one wire common to all phases – the identified neutral conductor;
   4. …………
   5. …………

For our study purposes, a single-phase, 2- or 3-wire system will have the black- or red-coloured wire as the current-carrying conductor (hot) to the load, and the white-coloured conductor (neutral) will be connected to ground. 3-phase systems will be explained further along in this learning guide.

10-610 Bonding Means – Fixed Equipment (See Appendix B)

1. ……….
2. ……….
3. Unless otherwise marked, the armour of flexible metal conduit and liquid-tight flexible metal conduit shall not be deemed to fulfill the requirements of a bonding conductor, and a bonding conductor shall be run within the conduit.
4. ………
5. ………

The spirally wound armour of flexible metal conduit, otherwise known as “BX” or “Teck” cable, cannot be relied upon to have a consistent, uninterrupted electrical path, as the connectors used between the cable and boxes can be either insufficiently tightened when installed, or can become loose and lose contact with movement over time. A dedicated bonding conductor must be included in the fill of the cable when using these varieties of cable.

10-612 Bonding Conductor Connection to Electrical Equipment

1. The bonding conductor to conduits, cabinets, equipment, and the like shall be attached by means of lugs, pressure connectors, clamps, or other equally substantial means.
2. Connections that depend on solder shall not be used.
3. ……….

The purpose of a bonding path is to allow any stray current that may contact metal parts of a circuit, such as boxes and enclosures, to pass through it to ground, thereby creating a short circuit that will trip the overcurrent device (fuse or circuit breaker) and deaden the circuit rather than creating a shock hazard. This usually happens instantaneously but in the event of a high resistance ground fault path, any soldered connections in that path could heat up to the point of melting the solder, causing the wires to disconnect and consequently break the continuity of the ground path, making it a possible electrocution hazard. Approved wiring connections are required to ensure an uninterrupted path to ground.

10-614 Size of System Bonding Jumper or Bonding Conductor (See Appendix B)

1. ……….
2. ……….
3. The size of a field-installed bonding conductor installed in other than service equipment shall not be less than that determined by Table 16 based on
   1. the overcurrent device protecting the ungrounded conductors; or
   2. the allowable ampacity of the largest ungrounded conductor for installations where the size of the circuit conductors is increased to compensate for voltage drop.
4. ………

Table 16 is used by first determining the amperage rating of the overcurrent protection device or largest ungrounded (hot) conductor in the circuit, using the larger of the two, and determining the minimum size of system bonding jumper or conductor based on it being either copper or aluminum. For example, a 20 A circuit breaker using copper conductors would require a minimum No. 14 AWG bonding conductor according to Table 16.

10-700 Equipotential Bonding of Non-Electrical Equipment (See Appendix B)

The following parts of non-electrical equipment shall be made equipotential with the non-current-carrying conductive parts of electrical equipment;

1. the continuous metal water piping system of a building supplied with electrical power;
2. the continuous metal waste water piping system of a building supplied with electrical power;
3. the continuous metal gas piping system of a building supplied with electrical power;
4. ………
5. ………
6. ………

A hot wire that contacts a continuous metal piping system would liven it, making it an electrocution hazard unless it is bonded to ground. It is important to note that, in old buildings where there was either a galvanized or copper water service, bonding the electrical system’s ground to it also allowed it to act as a ground path to earth for the electrical system due to its being in good contact with the earth over a long distance. Once non-metallic water services became the norm, the electrical installation leaned to using ground rods or plates to do that job, with the copper water systems of the day requiring bonding for their safety. Todays predominant PeX piping systems have very few metallic parts and are not continuous metal, so bonding them isn’t required. Gas piping systems, however, are still metallic and continuous inside buildings and so they are required to be bonded unless they are of CSST (Corugated Stainless Steel Tubing). Appendix B states that they are exempt from this requirement due to possibility of puncture by conventional bonding mechanisms or damage from arcing due to improperly secured bonding means during faults or lightning strikes.

10-704 Material for Equipotential Bonding Conductors

Equipotential bonding conductors shall be of materials permitted for grounding conductors or for bonding means.

10-708 Equipotential Bonding Conductor Size

1. Except as permitted by Subrule 2), the size of an equipotential bonding conductor shall be not smaller than
   1. 6 AWG if of copper; or
   2. AWG if of aluminum.
2. The size of an equipotential bonding conductor installed as concealed wiring and mechanically protected shall be permitted to be a minimum No. 10 AWG copper or No. 8 AWG aluminum.

10-002 states “The overall objective for grounding and bonding is to minimize the likelihood and severity of electric shock by establishing equipotentiality between exposed non-current-carrying conductive surfaces and nearby surfaces of the earth and to prevent damage to property during a fault”. Equipotential bonding simply means that there should not be any difference in electrical potential between the bonded system and any other interconnected ground. The two Code Rules above align with the requirements for grounding conductor size previously covered in Rule 10-114 and are allowed to be smaller provided Subrule 2) is followed.

Now complete Self-Test 9 and check your answers, quoting applicable Code rules.

Self-Test 9