The following is not intended to encompass all of the electrical design requirements which must be considered in planning electrical systems for facilities intended to accommodate testers. The information provided should, however, provide a guide to understanding for personnel who would be tasked with specifying facility electrical safety necessary to the testing environment.

Provisions for an adequate number of receptacle outlets to accommodate cord and plug connected equipment, testers, etc., in a facility must also be considered in specifying the electrical requirements.

For equipment that cannot tolerate power interruption, consideration should be given to the use of a continuously operating or standby uninterruptable power supply (UPS) or a generator.

9.11.1 AMPACITY OF FACILITY WIRING AND DISTRIBUTION EQUIPMENT

Consideration must be given to accommodating the anticipated load demand which may occur as a result of power supplied to the various possible combinations of electrical equipment connected to a particular branch circuit (See Section 9.4).

9.11.2 FACILITY GROUNDING AT REMOTE SITES

Proper grounding is considered crucial to providing the safest possible electrical installation, from the standpoint of maximizing the safety of facility occupants and minimizing property damage and loss.

Designs for equipment to be used at remote sites must take into consideration the same grounding issues which may not be accommodated due to the lack of permanent facility power wiring (See Section 9.3).

9.11.3 FACILITY LIGHTNING PROTECTION

Lightning protection is required for facilities which will house enclosed electrical/ electronic equipment while such equipment is involved with radioactive, explosive, and similarly hazardous materials. (See Section 5.1)

9.11.4 SURGE PROTECTION

In addition to facility lightning protection, the effects of surges resulting from lightning strikes to power distribution systems may be lessened by the use of lightning arrestors and suppressors installed at strategic points in the supply system to the facility. An assessment is necessary, addressing the consequences of lightning-induced surges, in order to determine the degree to which protection should be provided.

For additional information see Section 9.6.1.

9.12 ENCLOSED POWER ELECTRONICS

Power electronics equipment is equipment that uses electronic components and subsystems to control significant amounts of electrical energy. Examples of power electronics systems include:

1. Power supplies and modulators for laser systems;

2. Accelerators, magnets, x-ray systems, and other research equipment; 3. Radio and radar transmitters;

4. Variable speed motor drives; and 5. Induction heating systems.

All applicable portions of this section should be addressed due to the hazards involved with this type of equipment.

9.12.1 ENCLOSURES

Power electronics equipment should be constructed in all-metal enclosures for containment of fire, high energy, and electromagnetic radiation hazards.

The enclosures should support the housed equipment, provide strength to brace conductors against short circuit forces, and protect housed equipment against physical damage.

It is usually easier to provide barriers to protect the electronics enclosure from collision and missile hazards rather than strengthening the enclosure itself.

9.12.2 COMPONENT CLEARANCES

Enclosures must provide adequate clearance from energized parts. The required clearances depend on the shape of the conductor, the surface characteristics of the conductor and enclosure, the voltage characteristics, environmental conditions, and creepage. The breakdown strength along the surface of supporting insulators may require larger clearances than breakdown in air.

All power electronics enclosures shall provide adequate room for access to parts and subsystems for expected maintenance and modification. Consideration should be given to handling provisions for heavy parts and subsystems, access to test points and calibration adjustments, and work clearances for safe access to enclosure interiors.

Safe work on high-voltage equipment requires installation of manual grounding devices on exposed high-voltage conductors. Enclosure size shall provide adequate room to safely apply and remove grounding devices, and permit grounding devices to remain in place without interfering with expected work.

Enclosures shall be sized to allow cables to be installed and routed without infringing on required clearances from high-voltage conductors.

Subassemblies, circuits, and related equipment should be segregated to the extent possible to minimize the possibility of a fault in one device damaging another.

9.12.3 INSTRUMENTATION

Power electronics systems can involve fast pulses, high frequencies and high currents and it is common for the voltage difference between ground in one circuit and ground in another circuit to differ substantially. This difference can be hundreds or thousands of volts. Wire and cable shall be insulated to withstand these potentials. Surge arrester and capacitor protection maybe used to control these potentials. DC circuits connected to coils, solenoid valves and other inductive components should be tested for induced voltages and appropriate protection for circuits should be provided.

9.12.4 GENERAL

Test points needed for adjustment and diagnosis should be installed on the front panel or other appropriate location of power electronic systems to facilitate their use without exposure hazard to employees in the area.

Currents generated only during fault conditions or those introducing noise or data errors shall not be considered objectionable currents. Bonding and grounding connections shall not be altered to reduce the significance.

Conductors, busbars, and internal wiring should be insulated in the event objects are dropped into the equipment.

Automatic discharge devices are not a substitute for grounding devices used for personnel protection. Grounding points shall be located in the system and physically arranged to permit the attachment of adequate grounding devices for the protection of personnel working on the system.

These grounding points shall be capable of carrying the short-circuit current to which they may be subjected and applied using methods appropriate for the voltages or currents involved.