Which statement about marking equipment in multi-source systems is correct?

Which statement about marking equipment in multi-source systems is correct?

• A. They must be clearly marked to indicate the presence of all sources
• B. They must be marked only for the highest-rated source
• C. No marking is required
• D. Marking is only required at the main disconnect

Answer: (A)

When a system can be energized from more than one source, it’s essential to clearly indicate all the possible energizing sources at the equipment. This labeling helps anyone working on or near the equipment know that more than one source could backfeed or energize the circuit, so proper isolation must be verified before service. This approach is the safest because it prevents the mistaken belief that turning off a single source guarantees de-energization. If the marking only mentions one source or leaves others unmarked, a technician might assume the equipment is safe when another source still presents a shock or backfeed risk. By clearly labeling all present sources, the marking communicates the full reality of the power supply situation and supports proper lockout/tagout and verification practices. For example, a panel that could be fed by either utility power or a standby generator should have markings that show both sources are capable of energizing the panel. Marking should be visible and durable, indicating every source that can energize the equipment, not just the largest or main source. This is why the correct approach is to clearly mark the presence of all sources.

When a system can be energized from more than one source, it’s essential to clearly indicate all the possible energizing sources at the equipment. This labeling helps anyone working on or near the equipment know that more than one source could backfeed or energize the circuit, so proper isolation must be verified before service.

This approach is the safest because it prevents the mistaken belief that turning off a single source guarantees de-energization. If the marking only mentions one source or leaves others unmarked, a technician might assume the equipment is safe when another source still presents a shock or backfeed risk. By clearly labeling all present sources, the marking communicates the full reality of the power supply situation and supports proper lockout/tagout and verification practices.

For example, a panel that could be fed by either utility power or a standby generator should have markings that show both sources are capable of energizing the panel. Marking should be visible and durable, indicating every source that can energize the equipment, not just the largest or main source. This is why the correct approach is to clearly mark the presence of all sources.