10.8.1.1 HAZARDS

1. Internal component failure can cause excessive voltages. Internal component open-circuit failure in capacitor banks and Marx generators can result in full voltages across components that may not be appropriately discharged in the usual manner.

2. Internal component shorts in capacitor banks and Marx generators can result in excessive fault current, causing extreme heat, overpressurization of capacitor cans, and explosion.

3. Overloading or improper cooling of power supplies can cause excessive temperature rise.

4. Output circuits and components can remain energized after input power is interrupted.

5. Auxiliary and control power circuits can remain energized after the main power circuit is interrupted.

6. When power supplies serve more than one experiment, errors made when switching between experiments may create hazards to personnel.

7. R&D electrical apparatus may contain large amounts of stored energy, requiring fault analysis.

8. Liquid coolant leaking from R&D electrical equipment may pose an electrical hazard to personnel.

10.8.1.2 DESIGN AND CONSTRUCTION

In design and construction of R&D equipment, it is important to remember the following cautions:

1. Install only components essential to the power supply within the power-supply enclosure.

2. Provide appropriate separation between high-voltage components and low-voltage supply and/or control circuits.

3. Provide to personnel a visible indicator that the power supply is energized.

4. Minimize the number of control stations and provide an emergency shutdown switch where needed.

5. Where possible, avoid multiple-input power sources.

6. Apply a label containing emergency shutdown instructions to equipment that is remotely controlled or unattended while energized.

10.8.1.3 OPERATION AND MAINTENANCE

Before working in a power-supply enclosure or an associated equipment enclosure, see Sections 2 and 7. Personnel should take the following precautions:

1. Implement lockout/tagout.

2. Check for auxiliary power circuits that could still be energized.

3. Inspect automatic shorting devices to verify proper operation.

4. Short the power supply from terminal to terminal and terminal to ground with grounding hooks.

10.8.2 CONDITIONS OF LOW VOLTAGE AND HIGH CURRENT

10.8.2.1 HAZARDS

It is usual for R&D facilities to have equipment that operates at less than 50 V. Although this equipment is generally regarded as nonhazardous, it is considered hazardous when high currents are involved. Examples of such equipment are a power supply rated 3 kA at 25 V, a magnet power supply with rated output of 200 A at 40 V, and a bus bar carrying 1 kA at 5 V.

Though there is a low probability of electric shock at voltages less than 50V (See Figure 10-1), there is a hazard due to arcing and heating in case of an accidental fault. For example, a tool could drop onto the terminals and initiate an arc, causing severe burns.

Figure 10-1. Process for the analysis of circuit hazards.