Enclosed Electrical/Electronic Equipment

DOE-HDBK-1092-2004

9.0 ENCLOSED ELECTRICAL/ELECTRONIC EQUIPMENT

9.1

PURPOSE

This section provides guidelines to

1. complement existing electrical codes and recommend industry standards,

2. improve electrical safety in the work environment for personnel within the DOE complex.

3. eliminate the ambiguity and misunderstanding in design, construction and implementation

requirements for electrical/electronic equipment, and

4. assist the AHJ in providing information for acceptance of equipment within the scope of this

document.

9.2

SCOPE

This section addresses enclosed electrical/electronic equipment electrical safety guidelines

which are not specifically addressed elsewhere in the Electrical Safety Handbook. These types

of equipment include: instrumentation and test consoles; enclosed electrical/electronic

equipment; other laboratory diagnostic electrical/electronic equipment (stationary or mobile)

mounted in or on an enclosure, rack or chassis; and special electrical/electronic equipment

facility requirements.

9.3

GROUNDING AND BONDING

Many ground system types exist within electrical equipment. All metal parts of electrical

equipment enclosures and chassis shall be bonded and grounded as per the NEC. The

methods chosen to avoid ground loops and reduce noise shall meet the requirements of the

NEC 250.6.

9.3.1

OBJECTIONAL CURRENT OVER GROUNDING CONDUCTORS

Enclosed Electrical/Electronic equipment has both power and signal conductors entering and

leaving these enclosures. Objectionable currents and noise may be the result of the design or

installation of conductors and equipment and their grounding locations. NEC 250.6 addresses

these objectionable currents and noise (See Section 10.9.2.1).

NEC 250.6 must be used with care because it seems to give blanket authority to do whatever is

necessary to stop objectionable currents from flowing in the grounding system. This is not the

intent. NEC 250.6D specifically indicates that the introduction of noise or data errors in

electronic equipment shall not be considered objectionable currents, as addressed therein.

Therefore, such objectionable currents must be handled in other ways. NEC Section 250.6

principally deals with objectionable currents that can flow over grounding conductors due to

severely unbalanced loads or improper installation practices. NEC 250.96(B) provides

requirements for isolation of grounding circuits to reduce electrical noise (EMI). Because of the

complexity and number of interconnections of most grounding systems, the NEC allows

modifications of the grounding system and connections in order to address such problems.

Those permitted:

9-1