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Proper Grounding
By - LD Tullis
Tullis Electric
mailto:pas4me@qwest.net

1/06/2000

Following are excerpts from the National electrical code on grounding etc of your RV:
Any question should be referred to the code.
Table 250-122. Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment
Rating or Setting of Automatic Overcurrent Device in Circuit Ahead of Equipment, Conduit, etc., Not Exceeding (Amperes)

Amps Copper Size (AWG or kcmil)
15 14
20 12
30 10
40 10
60 10
100 8
200 6

c) Equipment Grounding Conductors Smaller than No. 6. Equipment grounding conductors smaller than No. 6 shall be protected from physical damage by a raceway or cable armor except where run in hollow spaces of walls or partitions, where not subject to physical damage, or where protected from physical damage.

250-124. Equipment Grounding Conductor Continuity

(a) Separable Connections. Separable connections such as those provided in drawout equipment or attachment plugs and mating connectors and receptacles shall provide for first-make, last-break of the equipment grounding conductor. First-make, last-break shall not be required where interlocked equipment, plugs, receptacles, and connectors preclude energization without grounding continuity.

(b) Switches. No automatic cutout or switch shall be placed in the equipment grounding conductor of a premises wiring system unless the opening of the cutout or switch disconnects all sources of energy.

250-126. Identification of Wiring Device Terminals

The terminal for the connection of the equipment grounding conductor shall be identified by one of the following.

1. A green, not readily removable terminal screw with a hexagonal head.
2. A green, hexagonal, not readily removable terminal nut.
3. A green pressure wire connector. If the terminal for the grounding conductor is not visible, the conductor entrance hole shall be marked with the word green or ground, the letters G or GR or the grounding symbol shown in Figure 250-126, or otherwise identified by a distinctive green color. If the terminal for the equipment grounding conductor is readily removable, the area adjacent to the terminal shall be similarly marked.

Figure 250-126 Grounding symbol.

G. Methods of Equipment Grounding

250-130. Equipment Grounding Conductor Connections

Equipment grounding conductor connections at the source of separately derived systems shall be made in accordance with Section 250-30(a)(1). Equipment grounding conductor connections at service equipment shall be made as indicated in (a) or (b). For replacement of nongrounding-type receptacles with grounding type receptacles and for branch-circuit extensions only in existing installations that do not have an equipment grounding conductor in the branch circuit, connections shall be permitted as indicated in (c).

  1. For Grounded Systems. The connection shall be made by bonding the equipment grounding conductor to the grounded service conductor and the grounding electrode conductor.

250-104. Bonding of Piping Systems and Exposed Structural Steel

(a) Metal Water Piping. The interior metal water piping system shall be bonded as required in (1), (2), (3), or (4) of this section. The bonding jumper shall be installed in accordance with Section 250-64(a), (b), and (e). The points of attachment of the bonding jumper(s) shall be accessible.

  1. General. The interior metal water piping system shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used. The bonding jumper shall be sized in accordance with Table 250-66 except as permitted in (2) and (3).

551-30. Generator Installations

(a) Mounting. Generators shall be mounted in such a manner as to be effectively bonded to the recreational vehicle chassis.

(b) Generator Protection. Equipment shall be installed to ensure that the current-carrying conductors from the engine generator and from an outside source are not connected to a vehicle circuit at the same time. Receptacles used as disconnecting means shall be accessible (as applied to wiring methods) and capable of interrupting their rated current without hazard to the operator.

(c) Installation of Storage Batteries and Generators. Storage batteries and internal-combustion-driven generator units (subject to the provisions of this Code) shall be secured in place to avoid displacement from vibration and road shock.

(d) Ventilation of Generator Compartments. Compartments accommodating internal-combustion-driven generator units shall be provided with ventilation in accordance with instructions provided by the manufacturer of the generator unit.

FPN: For generator compartment construction requirements, see Standard on Recreational Vehicles, NFPA 501C-1996.

(e) Supply Conductors. The supply conductors from the engine generator to the first termination on the vehicle shall be of the stranded type and be installed in listed flexible conduit or listed liquidtight flexible conduit. The point of first termination shall be in a:

1. Panelboard,
2. Junction box with a blank cover,
3. Junction box with a receptacle,
4. Enclosed transfer switch, or
5. Receptacle assembly listed in conjunction with the generator.

The panelboard or junction box with a receptacle shall be installed within the vehicle’s interior and within 18 in. (457 mm) of the compartment wall but not inside the compartment. If the generator is below the floor level and not in a compartment, the panelboard or junction box with receptacle shall be installed within the vehicle interior within 18 in. (457 mm) of the point of entry into the vehicle. A junction box with a blank cover shall be mounted on the compartment wall and shall be permitted inside or outside the compartment. A receptacle assembly listed in conjunction with the generator shall be mounted in accordance with its listing. If the generator is below floor level and not in a compartment, the junction box with blank cover shall be mounted either to any part of the generator supporting structure (but not to the generator) or to the vehicle floor within 18 in. (457 mm) of any point directly above the generator on either the inside or outside of the floor surface. Overcurrent protection in accordance with Section 240-3 shall be provided for supply conductors as an integral part of a listed generator or shall be located within 18 in. (457 mm) of their point of entry into the vehicle.

e) Power-Supply Assembly Not Less than 30 Amperes. The external power-supply assembly shall be permitted to be less than the calculated load but not less than 30 amperes and shall have overcurrent protection not greater than the capacity of the external power-supply assembly.

551-32. Other Sources

Other sources of ac power, such as inverters or motor generators, shall be listed for use in recreational vehicles and shall be installed in accordance with the terms of the listing. Other sources of ac power shall be wired in full conformity with the requirements in Parts A, C, D, E, and F of this article covering 120-volt electrical systems.

551-33. Alternate Source Restriction

Transfer equipment, if not integral with the listed power source, shall be installed to ensure that the current-carrying conductors from other sources of ac power and from an outside source are not connected to the vehicle circuit at the same time.

Low-Voltage Wiring Methods.

1. Conductors shall be protected against physical damage and shall be secured. Where insulated conductors are clamped to the structure, the conductor insulation shall be supplemented by an additional wrap or layer of equivalent material, except that jacketed cables shall not be required to be so protected. Wiring shall be routed away from sharp edges, moving parts, or heat sources.

2. Conductors shall be spliced or joined with splicing devices that provide a secure connection or by brazing, welding, or soldering with a fusible metal or alloy. Soldered splices shall first be spliced or joined so as to be mechanically and electrically secure without solder and then soldered. All splices, joints, and free ends of conductors shall be covered with an insulation equivalent to that on the conductors.

3. Battery and dc circuits shall be physically separated by at least a -in. (12.7-mm) gap or other approved means from circuits of a different power source. Acceptable methods shall be by clamping, routing, or equivalent means that ensure permanent total separation. Where circuits of different power sources cross, the external jacket of the nonmetallic-sheathed cables shall be deemed adequate separation.

4. Ground connections to the chassis or frame shall be made in an accessible location and shall be mechanically secure. Ground connections shall be by means of copper conductors and copper or copper-alloy terminals of the solderless type identified for the size of wire used. The surface on which ground terminals make contact shall be cleaned and be free from oxide or paint or shall be electrically connected through the use of a cadmium, tin, or zinc-plated internal/external-toothed lockwasher or locking terminals. Ground terminal attaching screws, rivets or bolts, nuts, and lockwashers shall be cadmium, tin, or zinc-plated except rivets shall be permitted to be unanodized aluminum where attaching to aluminum structures.

5. The chassis-grounding terminal of the battery shall be bonded to the vehicle chassis with a minimum No. 8 copper conductor. In the event the power lead from the battery exceeds No. 8, then the bonding conductor shall be of an equal size.

(d) Battery Installations. Storage batteries subject to the provisions of this Code shall be securely attached to the vehicle and installed in an area vaportight to the interior and ventilated directly to the exterior of the vehicle. Where batteries are installed in a compartment, the compartment shall be ventilated with openings having a minimum area of 1.7 in.2 (1100 mm2) at both the top and at the bottom. Where compartment doors are equipped for ventilation, the openings shall be within 2 in. (50.8 mm) of the top and bottom. Batteries shall not be installed in a compartment containing spark- or flame-producing equipment, except that they shall be permitted to be installed in the engine generator compartment if the only charging source is from the engine generator.

(e) Overcurrent Protection.

1. Low-voltage circuit wiring shall be protected by overcurrent protective devices rated not in excess of the ampacity of copper conductors, as follows.

Table 551-10(e)(1). Low-Voltage Overcurrent Protection

Wire Size (AWG) Ampacity Wire Type

18  6 Stranded only

16  8 Stranded only

14 15 Stranded or solid

12 20 Stranded or solid

10 30 Stranded or solid

2. Circuit breakers or fuses shall be of an approved type, including automotive types. Fuseholders shall be clearly marked with maximum fuse size, and both circuit breakers and fuses shall be protected against shorting and physical damage by a cover or equivalent means.

FPN: For further information, see Standard for Electric Fuses (Cartridge Type), ANSI/SAE J554-1987; Standard for Blade Type Electric Fuses, SAE J1284-1988; and Standard for Automotive Glass Tube Fuses, UL 275-1993.

3. Higher current-consuming, dc appliances, such as pumps, compressors, heater blowers, and similar motor-driven appliances, shall be installed in accordance with the manufacturer’s instructions. Motors that are controlled by automatic switching or by latching-type manual switches shall be protected in accordance with Section 430-32(c).

4. The overcurrent protective device shall be installed in an accessible location on the vehicle within 18 in. (457 mm) of the point where the power supply connects to the vehicle circuits. If located outside the recreational vehicle, the device shall be protected against weather and physical damage.

Exception: External low-voltage supply shall be permitted to have the overcurrent protective device within 18 in. (457 mm) after entering the vehicle or after leaving a metal raceway.

(f) Switches. Switches shall have a dc rating not less than the connected load.

Voltage Converters (120-Volt Alternating Current to Low-Voltage Direct Current). The 120-volt ac side of the voltage converter shall be wired in full conformity with Parts A, C, D, E, and F requirements of this article for 120-volt electrical systems.

Exception: Converters supplied as an integral part of a listed appliance shall not be subject to the above.

All converters and transformers shall be listed for use in recreation vehicles and designed or equipped to provide over-temperature protection. To determine the converter rating, the following formula shall be applied to the total connected load, including average battery charging rate, of all 12-volt equipment:

The first 20 amperes of load at 100 percent, plus

The second 20 amperes of load at 50 percent, plus

All load above 40 amperes at 25 percent

Exception: A low-voltage appliance that is controlled by a momentary switch (normally open) that has no means for holding in the closed position shall not be considered as a connected load when determining the required converter rating. Momentarily energized appliances shall be limited to those used to prepare the vehicle for occupancy or travel.

(c) Bonding Voltage Converter Enclosures. The noncurrent-carrying metal enclosure of the voltage converter shall be bonded to the frame of the vehicle with a minimum No. 8 copper conductor. The grounding conductor for the battery and the metal enclosure shall be permitted to be the same conductor.

     In my article on RV batteries, I tell you to hook the "battery negative" to the ground, if you have a positive ground system then change that wording to be "battery positive", I intended to say to hook the normally grounded terminal of the battery to ground along with the equipment ground. (this equipment grounding conductor should conduct current only when there is a fault in the system unlike the neutral which conducts the unbalanced current between the two phase legs). Since you do not want the metal skin of your coach to act as a return path for 120v loads, you must Isolate Neutral (Always white on 120/240v wiring) from the skin or frame of the coach-hence an isolated buss or connection for the neutral and a grounded or bonded connection (always green or a green stripe)to the panel and coach frame.

     I recommend this bond be made at 2 or three places on the frame with a #6 copper wire equidistant spacing as the steel frame is not a good conductor and could give you electronic noise and possibly a little grief with some of the heavier battery powered equipment. a good ground buss for this purpose could be some scrap copper pipe hammered flat and bolted to the frame with a good oxide inhibitor (never seize for instance)I will be using a stainless bolt setup but will not use the bolt as a conductor as SS is a poor conductor.

     Pigtails will probably always have red or black for phase leg or 120v connection, but will ALWAYS have white for neutral and green for ground.

LD Tullis
Tullis Electric
mailto:pas4me@qwest.net