Every Energy Source

Isolation fails most often because an energy source was not identified, not because the identified ones were badly isolated. Build the list before touching anything.

Sources to enumerate

• Electrical — mains supply, secondary supplies, control circuits, UPS, generators, solar, capacitors holding charge, induced voltage from adjacent circuits.
• Mechanical — rotating inertia, springs under compression or tension, counterweights, suspended loads, belt tension.
• Hydraulic and pneumatic — accumulators, trapped pressure between valves, air receivers, pressurised seals.
• Process — pressure, vacuum, flow from upstream, backflow from downstream, purge and utility connections.
• Thermal — hot surfaces, steam, hot oil, cryogenic lines.
• Chemical — residues, reactive materials, spontaneous heating.
• Gravitational — anything that can fall, roll or swing when released.

The two that catch people

Stored energy and secondary supplies. An isolated machine with a charged accumulator or a compressed spring is still fully capable of killing, and an isolated motor with a separately supplied control circuit or a standby generator connection is not isolated at all.