Manufacturers are responsible for determining the safety of such chassis and/or enclosures and for providing documentation showing how that determination was made. Unlisted commercial equipment and in-house fabricated equipment shall be approved by the local Authority Having Jurisdiction.

9.5.1 AC POWER DISTRIBUTION

9.5.1.1 CHASSIS BONDING AND GROUNDING

Metal chassis shall be effectively bonded to a main grounding point in the rack cabinet where necessary to assure electrical continuity and shall have the capacity to conduct safely any fault current likely to be imposed on it. (NEC Section 250-75)

In a chassis with ac service connected to it, the grounding terminal of its receptacle shall be internally bonded to the chassis frame. (NEC Section 250-74)

If solder is used, the connection of the equipment grounding conductor shall not depend on solder alone. (ANSUISA-S82.01-1988 - Section 9.5.4.4 and NEC Section 250-115)

The leakage current of cord connected equipment should not be more than specified in Subclause 9.11 of ANSUISA-S82.01-1988.

9.5.1.2 CONNECTIONS, CONNECTORS, AND COUPLINGS

Input/output ac power connections to the chassis shall comply with NEC requirements.

The exposed, noncurrent carrying, metal parts of panel mount connectors operating at 50 volts or greater shall be bonded to the chassis.

Plugs and sockets for connecting any AC power source shall be NRTL approved for the application. (Ref. ISA-S82.01-1992, Section 6.10.3.a)

AC power plugs and sockets shall not be used for purposes other than the connection of AC power.

Connectors operating at 50 V or greater shall be rated or recommended for their intended use.

Any connector used to provide power at 50 V or greater shall not allow personnel to make inadvertent contact with the power source.

If plug pins of cord-connected equipment receive a charge from an internal capacitor, the pins shall not be capable of rendering an electric shock or electric burn in the normal or the single fault condition 5 seconds after disconnection of the supply. (Ref. ISA-S82.01-1992, Section 6.10.3.c)

Plug-in type connectors intended to be connected and disconnected by hand shall be designed so that the grounding conductor connection makes first and breaks last with respect to the other connections. [See ISA-S82.01-1992, Section 6.11.2.g and NEC Section 250-99(a)]

The following applies for all AC power connectors within or external to electrical/electronic enclosures:

1. There should be no exposed current-carrying parts except the prongs, blades, or pins.

2. The connector shall prohibit mating of different voltage or current rating than that for the device intended.

3. All connectors must be protected against overcurrent in accordance with their rated ampacity. (NEC Section 240-4)

4. Connectors must be NRTL approved for the application.

5. Use of MS, PT, or other non-approved connectors is not permitted except when justified to and approved by the AHJ.

If conditions require the use of a non-NRTL listed or labeled connector, such as a "MS"(military standard pin and socket type) or "PT" (similiar to "MS" but smaller) type, for input/output ac power, a warning label should be affixed next to the connector stating: "WARNING - POWER MUST BE REMOVED BEFORE CONNECTING/DISCONNECTING."

All terminals/live parts with a potential of 50 volts or greater shall be guarded to protect from accidental contact or bringing conductive objects in contact with them (NEC Section 110-17). Consult ANSI/ISA-S82.01-1988, Table 9-1 for spacing information regarding live parts.

All energized switching and control parts shall be enclosed in effectively grounded metal enclosures and shall be secured so that only authorized and qualified persons can have access.

9.5.2 DC POWER DISTRIBUTION

Guidelines for do power distribution include:

1. The metal chassis or cabinet should not be used as a return path.

2. High-current analog or switching do power supplies should use separate return paths from digital circuits.

3. All of the guidelines pertaining to ac power such as grounding, proper wire size, high voltage, etc. should apply to do circuits as well.

An accessible terminal charged by an internal capacitor should be below 50 volts within 10 seconds after interruption of the supply. (ANSI/ISA-S82.01-1988 - Section 9.3.5.2)

As with ac power, avoid contacting do parts when working on a live chassis. The use of the appropriate class gloves should be considered when performing this type of work.

9.6 PROTECTIVE DEVICES FOR ENCLOSED ELECTRICAL/ ELECTRONIC EQUIPMENT

This section deals with the various protective devices commonly found in electrical/electronic equipment not discussed elsewhere.