Electrical Enclosures and Wiring Methods

6.1 General Requirements

Enclosures, raceways, wireways, and wiring ducts shall be suitable for the application and compatible with the environment that the equipment is to be operated in.

6.2 Electrical Enclosures

Electrical enclosures shall be NEMA type or equivalent. See Appendix I for a partial list of NEMA type electrical enclosures.

6.2.1 Components. The following components shall be contained in electrical enclosures:

  1. Supply circuit disconnecting means.
  2. Branch circuit protection.
  3. Control transformer.
  4. Control relays.
  5. Contactors.
  6. Motor starters.
  7. Conductors.
  8. Distribution terminal blocks (control terminals and power terminals must be segregated).

6.2.2 Requirements.

  1. Clear space for connection and testing of components.
  2. Clear space (15 % minimum) for future use.
  3. Spare terminal space (10 % minimum).
  4. Barriers for all arcing devices.
  5. Clearances between bare terminals and grounded parts as follows:

- 250 V or less: 0.5 inch

- 251 V to 600 V: 1.0 inch
  1. Sufficient wire bending space at terminals. See the National Electrical Codeã , Article 373.

6.2.3 Recommendations. Enclosures should have:

1. A removable panel for component mounting.

2. Hinged doors that swing horizontally and open a minimum of 165 degrees.

6.2.4 Restrictions. Enclosures shall not have any:

1. Components mounted on hinged doors or removable covers.

EXCEPTION: Control circuit components for operator use.

2. Piping container air, gas, or liquids.

3. Unused or ineffectively closed openings.

6.2.5 Access. Enclosures shall be provided with access covers or doors that meet the following requirements:

1. Covers or doors that allow access to hazardous potentials shall require a tool to open or shall be interlocked. See 7.3.

2. Covers or doors with an area of more than 3 ft2 shall be hinged.

6.2.6 Main Electrical Control Enclosure. When equipment geometry dictates a need for more than one power and power control device enclosure, the main electrical control enclosure shall:

  1. Contain main supply circuit disconnecting means. See Sec. 3.10 and Fig 14.
  2. Contain all components and circuits that have hazardous potentials after the operation of the EMO switche(s).
  3. Require a tool to open.

6.3 Electrical Enclosure Wiring

  1. All enclosure wiring shall be routed, harnessed, appropriately laced or in plastic wiring ducts.
  2. The maximum number of conductors allowed in wiring ducts shall comply with 4.2.6.
  3. The wiring duct material:

    4. - Shall not support combustion.

    - Shall be nonwarping.

    -Shall be an insulator.

    - Shall be rated for the highest voltage applied to any conductor contained within.

  4. Wiring ducts shall not have exposed metal parts, except for mounting screws.

6.4 Equipment Wiring

1. Installation- Conductors shall be:

a. Routed, laced, harnessed, in wiring duct, wireways or raceways when inside equipment.

b. In approved, enclosed wireways or raceways when outside of equipment.

Note: Appendix I lists acceptable raceway types.

2. Insulation- All conductors in the same bundle, harness, raceway, wireway, or wiring duct shall have insulation rated for use at the highest potential present.

3. Induced Current- When AC power conductors are installed in metal raceways or wireways, all phase conductors, the grounding conductor and, where used, the grounded conductor (neutral) shall be grouped together.

4. Conductor Size- Conductors installed in raceways shall not be smaller than #14 AWG.

5. The maximum number of conductors installed in raceways, wireways, and wiring ducts shall comply with 4.2.6 .

6.5 Mechanical Protection

1. Conductors which remain energized with the supply disconnect "OFF" shall be isolated from other conductors by jackets, conduits, or raceways.

2. Any surfaces which conductors may contact shall be free of burs, sharp edges, threads, insulation-damaging roughness and other deteriorating agents.

3. All raceways and wireways shall be supported within 1ft. of each end and at 4.5 ft. intervals.

4. There shall be at least 1 in. clearance between moving parts of equipment and flexible cable or conduit. If maintaining the clearance is impossible, a barrier shall be provided.

6.6 Conductor Length

1. The external length of power attachment cords or flexible conduit shall be as short as possible but shall not exceed 8 ft.

2. The length of the grounding conductor between the strain relief and the terminating screw shall be such that in the event of strain relief failure, the grounding conductor is the last to be under strain.

3. At least 6 in. of free conductor shall be left inside the outlet, switch, and junction boxes.

4. Wherever hardwiring makes access to a drawer or compartment difficult, wiring loops shall be provided to allow access for maintenance and inspection.

6.7 Splicing

1. Conductors and cables shall be run without splices from termination to termination.

2. Connection to leads on motors, solenoid valves, transformers, etc., shall be made within an approved enclosure or by an approved device. See 3.1.1. For ease of maintenance, terminal blocks should be used.

6.8 Strain Relief

Strain relief shall be provided for all raceways, cords and cables. The strain relief device shall comply with the following:

  1. Strength- The device shall be capable of withstanding a 35 lb. pull for one minute from any direction without allowing any movement of the raceway, cord, or cable that could damage the conductor insulation or strain the terminations.
  2. Length- the cord or cable jacket shall extend into the strain relief device at least one cable diameter.
  3. Type- The strain relief device used shall be approved for use on the raceway, cord, or cable.

See Fig 15 for examples.

Note: Type NM (two screw) connectors are not acceptable for use on flexible cords or cables.
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