The terms ground and grounding refer to noncurrent-carrying , mechanical equipment grounding conductors, bonding jumpers, and circuit grounding conductors. Figure 12 and Figure 13 illustrate the general layout of typical grounded systems.
1. All grounding circuits within equipment shall ensure a resistance of one tenth ohm (0.1 W ) or less at any point.
2. To test grounding resistance, attach one lead of a digital ohmmeter at the main grounding termination and use the other to probe all conductive metal. See 5.5.
1. The main grounding conductor shall be secured to a single designated termination that will not be disturbed by any other conductor terminations.
2. Mounting hardware and cover screws the may be removed for normal servicing shall not bee used for grounding terminations.
3. All protective coating (e.g., paint, enamel) shall be removed from contact surfaces where grounding conductors and bonding conductors terminate.
4. Unless prohibited by location requirements, an external tooth lockwasher may be installed between the grounding lug and surface to be grounded to maintain the position of the lug and to insure effective penetration through any dirt or corrosion on the contact surface.
5. The disconnection or removal of any component (device) shall no interfere with or interrupt the grounding continuity to any other component (device).
6. When terminal lugs are used for grounding, they shall be a ring tongue type.
7. Terminal lugs are not required to be insulated.
8. Grounding terminations shall not depend on solder for mechanical strength nor for electrical continuity.
Exception: Multipin connectors with solder pins (subject to resistance check).
9. An insulated terminal block (barrier strip) shall not be used as a grounding bus.
10. Commercial type ground buses should be used for multiple ground connections.
1. Grounding conductors shall be green, green with a yellow tracer, or bare copper wire or braid.
2. All grounding conductors shall be stranded copper wire.
3. Grounding conductors and connectors shall be compatible in current rating to the associated ungrounded conductors and connectors.
4. Metallic bases, frames, or bonds shall not be used as current-carrying conductors between subassemblies.
5. Raceways, hinges, covers, enclosures and frames shall not be used in lieu of grounding or bonding conductors.
6. The grounding conductors shall be run with the current-carrying conductors.
7. The grounding conductor shall not be intentionally used as a current-carrying conductor.
1. The grounding conductors shall be unspliced and continuous from termination to termination.
2. A terminal block, ground lug or ground bus is acceptable for connecting two grounding conductors. Wire nuts and butt splices are unacceptable.
5.5 Conductive Metal.
1. All machine frames, enclosures, raceways, covers, doors, or panels with components having hazardous potentials require a grounding conductor termination.
2. All metal clad components mounted external to enclosures and having hazardous potentials, require a grounding conductor termination. Examples:
- Solenoid valves.
- Outlet Boxes.
The incoming ground conductor shall terminate at the device box. A grounding conductor (jumper) shall run from the termination on the box to the grounding screw on the receptacle
5.7 Interconnecting Cables.
Every cable having hazardous potentials which interconnects subassemblies, units, or equipment shall contain a grounding conductor to assure effective grounding with any combination of connected equipment.
1. Grounded conductor (neutral) shall be isolated from grounding conductors.
EXCEPTION: Reference at source transformer.
2. DC common shall be connected to a isolated bus (isolated from ground). One circuit grounding conductor shall be used to connect the isolated DC common bus to ground.
EXCEPTION: Isolated DC power systems.
3. Maximum leakage current on a grounding conductor shall not exceed 3.5 mA.
EXCEPTION: Current from an EMC filter shall not exceed 5 % of the input current or 1 A. A label stating high grounding conductor current shall be attached adjacent to the power requirement label.
1. Totally plastic encased units designed for two wire cord.
2. Double insulated units that are marked or labeled with one of the following:
Figure 12. Grounding Small Equipment
1. Dead front cap, longer grounding pin.
2. Any of the approved flexible cords with grounding conductor.
3. Approved strain relief.
4. The main equipment ground shall terminate first at the equipment frame on a stud, screw or ground bus.
5. Mounting panels for electrical / electronic components having hazardous potentials or hazardous energy levels shall be grounded with a grounding conductor.
Figure 13. Grounding Large Equipment
|Previous Page||Next Page||EHSC Home||NCSU Home|