That the equipment has more than one energy source that needs to be isolated before servicing begins. This is one of the dangerous oversights in lockout/tagout situations. A worker isolates the power source, assumes the machine is safe, and gets injured by a second source they did not know about or forgot to account for.

More than most people expect. Large industrial machines often combine power with pneumatic or hydraulic systems. Equipment with power supplies, battery systems or capacitors stores energy even after the main disconnect is open. Conveyors with drive motors, presses with hydraulic and electrical inputs and automated systems with both line power and control power circuits are all common examples.

On the machine itself near the primary control panel or start point, near each individual energy isolation point, on maintenance access doors, and at any location where a worker would begin a lockout procedure. The goal is to make sure whoever is doing the work knows before they start that isolating one source is not enough.

OSHA 29 CFR 1910.147 on the Control of Hazardous Energy requires that all energy sources on a piece of equipment be identified and controlled before servicing. The written energy control procedure for each machine is supposed to list every energy source. A Multiple Power Source sign reinforces that requirement at the machine level so the information is there when it is needed.

No. The sign alerts workers to the fact that multiple sources exist. The written procedure tells them what those sources are and how to isolate each one. Both are required for a hazardous energy control program. The sign without the procedure leaves workers knowing there is a problem, but not knowing how to solve it.

The machine is not safe to service. Stored energy in a circuit, a charged capacitor, a pressurized pneumatic line or a second electrical feed can all cause serious injury even after the main disconnect is open. Multiple Power Source signs exist specifically to prevent that assumption from being made in the first place.

A sign that says "Multiple Power Sources: Electrical, Hydraulic, Pneumatic" is more useful than one that just says "Multiple Power Sources/'. Where the specific sources are known and consistent, including them on the sign or,on a label gives maintenance workers a checklist before they start.