Instrumentation - hdbk109220040161

DOE-HDBK-1092-2004

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. (See Section 10.10.1.2)

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. However, Bonding and grounding may be altered to

reduce the noise or data errors, in accordance with provisions of NEC 250.96(B). Conductors,

bus bars, 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.

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