Which Is Not an Energy Isolating Device? LO/TO Quiz

Q: Do push buttons, selector switches, or an HMI “OFF” command ever count as isolation?

For OSHA 1910.147 servicing/maintenance, those are control circuit-type devices . They may be part of the normal shutdown step, but they are not the isolation step because they only command a change of state and can be bypassed or fail in ways that allow unexpected energization.

10 – 65 Questions 16 min

This quiz applies OSHA’s Control of Hazardous Energy standard, 29 CFR 1910.147, to a high-risk judgment: separating an energy isolating device that physically blocks energy from a control circuit device that only commands “off.” The wrong choice can leave stored or backfed energy live, driving OSHA citations and per‑violation penalties that can reach six figures.

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1Which is NOT an energy isolating device?

2An energy isolating device is a mechanical means that physically prevents the transmission or release of energy.

True / False

3An emergency stop (E-stop) button is an energy isolating device under OSHA’s lockout/tagout standard.

True / False

4A technician must service a motor. Which device is typically an energy isolating device for the electrical hazard?

5After applying locks/tags to the isolating device(s), what must be done before servicing begins?

6Which is an example of stored or residual energy that may need to be released after lockout?

7Which device is typically an energy isolating device for electrical power when it is manually operated and lockable?

8Which OSHA standard is commonly referenced for Control of Hazardous Energy (lockout/tagout)?

9What is the main purpose of the “try-start” step during lockout/tagout verification?

10A solenoid-operated valve becomes an energy isolating device as long as you lock out the electrical power feeding the solenoid.

True / False

11A machine has an electric motor and a pneumatic cylinder. You lock out only the electrical disconnect. What is the key missing action?

12Arrange the basic lockout/tagout sequence from first to last.

Put in order

1Release/secure stored energy

2Isolate energy using the isolating device(s)

3Verify zero-energy state

4Apply locks/tags to isolating device(s)

5Shut down the equipment

6Prepare/notify and identify energy sources

13Select all that apply. Which items are control devices (NOT energy isolating devices)?

Select all that apply

14Which is NOT an energy isolating device?

15After lockout, the try-start shows no motion, but a meter reads 120 V at the motor terminals. What should you do?

16Select all that apply. Which are examples of stored or residual energy that may remain after the main energy source is isolated?

Select all that apply

17Select all that apply. You are servicing a press with electrical power, pneumatic supply, and a gravity-loaded ram. Which actions are appropriate for energy control?

Select all that apply

18Which device is NOT typically an energy isolating device because it is automatically actuated?

19After applying locks/tags on an electrical machine, arrange these verification actions in the best order.

Put in order

1Discharge/secure stored electrical energy (e.g., capacitors)

2Re-test to confirm zero energy

3Test for absence of voltage at the point of exposure

4Try-start using normal operating controls

5Ensure the area is clear of personnel

20A vertical pneumatic cylinder is holding a suspended load. Arrange the safest steps to control hazardous energy before servicing.

Put in order

1Apply lock/tag to the air isolating valve

2Bleed/vent trapped air from the system

3Verify zero pressure and no movement

4Close the air supply isolating valve

5Support/block the load to prevent سقوط/movement

21Arrange the steps for removing lockout/tagout and returning equipment to service (general case).

Put in order

1Reinstall guards and ensure components are intact

2Ensure controls are in a neutral/off position

3Notify affected employees and restore energy/start up

4Remove locks/tags (per procedure and authorization)

5Inspect the work area and account for tools/materials

22Which device most directly isolates pneumatic energy for lockout/tagout?

23Select all that apply. Which items are common “trap” answers that are NOT energy isolating devices?

Select all that apply

24Arrange the best-practice sequence for locking out a machine with multiple energy sources (electrical, pneumatic, hydraulic).

Put in order

1Review the procedure and identify all energy sources

2Release/secure stored energy (bleed, block, discharge)

3Verify zero energy at the point(s) of exposure

4Apply locks/tags to each isolating device

5Isolate each energy source using its isolating device

6Shut down the equipment using normal controls

25You need to enter a robot cell. The main electrical disconnect is locked out, but the end-effector is pneumatically powered and a vertical axis could drop. Which option best describes what must be done before entry?

26Select all that apply. Which are effective ways to control gravity-stored energy during servicing?

Select all that apply

27Select all that apply. When verifying electrical isolation with a meter, which practices support a reliable test?

Select all that apply

28A worker locks out a local control switch at the machine but leaves the upstream disconnect energized. What is the primary hazard?

29A machine uses electrical power and steam heat. You locked out the electrical disconnect. Which additional isolation is typically required for the steam hazard?

30Select all that apply. Which methods are appropriate for verifying a zero-energy state?

Select all that apply

31A hydraulic system includes an accumulator. After locking out the pump motor, what additional step is usually required?

Disclaimer

This quiz is for educational and training purposes only. It does not constitute professional certification or legal compliance verification.

LO/TO Misreads That Turn “Off” Into “Not Isolated” (OSHA 1910.147)

Most wrong answers to “which is not an energy isolating device?” come from treating convenient operating controls as if they were isolation points. Under OSHA 29 CFR 1910.147, the difference matters because verification can look “good” while energy can still be transmitted, reintroduced, or released.

1) Calling control-circuit devices “isolation”

What happens: A push button, selector switch, pilot light, PLC/HMI command, or an emergency stop is selected as the isolator.
How to avoid: Ask, “Does it mechanically prevent transmission/release of energy?” If it only sends a signal, it is a control device, not an isolator.

2) Locking a local station while leaving the true source available

What happens: A near-machine switch is locked while an upstream disconnect, valve, or breaker can still energize the system.
How to avoid: Trace the energy path back to the source and isolate at the point that actually blocks energy flow into the machine.

3) Treating a solenoid valve as a pneumatic/hydraulic isolator

What happens: The electrical coil/control valve is locked out, but line pressure remains and can shift actuators if the valve leaks or is overridden.
How to avoid: Use a manual, lockable line valve or blocking device to isolate the pressure source, then bleed/vent downstream.

4) Ignoring stored, residual, or potential energy

What happens: Electrical power is isolated, but gravity loads, springs, flywheels, capacitors, hydraulic accumulators, or compressed air remain hazardous.
How to avoid: Add a specific “release/secure stored energy” step (block, pin, bleed, vent, drain, discharge) before “try-start.”

5) Weak verification (or verifying the wrong hazard point)

What happens: “Try-start” is skipped, or checks are done at a convenient panel instead of at the hazard zone.
How to avoid: Verify at the point of exposure: try the normal start, test for zero (voltage/pressure/motion), and re-check after bleed-down or blocking.

6) Assuming one lock covers multi-energy equipment

What happens: Electrical is locked out while pneumatic, hydraulic, steam, chemical feed, or mechanical energy paths remain live.
How to avoid: List every energy type and identify an energy isolating device (or equivalent method) for each path.

Energy-Isolating Device vs Control Device: OSHA 1910.147 Print-Friendly Quick Reference

Print note: Save or print this page as a PDF and keep it with your written energy control procedures for pre-job review.

Core definition (what you’re deciding in this quiz)

An energy isolating device is a mechanical means that physically prevents the transmission or release of energy (electrical, mechanical, hydraulic, pneumatic, thermal, chemical, etc.). A control circuit-type device (push button, selector switch, interlock logic, PLC output) only commands a change in state and can fail, be bypassed, or be re-energized remotely.

Fast identification test (“Is it an isolator?”)

Physical separation: Does it mechanically open/close the energy path (not just signal a contactor/valve)?
Energy-blocking location: Is it placed so energy from the source cannot reach the machine?
Lock application: Can it accept a lockout device to hold it in the safe position (or, if not lockable, is there an equivalent method under your program)?
Re-energization resistance: Would a remote command, software change, or automatic restart defeat it?

Common energy isolating devices (typical examples)

Electrical: Manually operated disconnect switch; manually operated circuit breaker used as the disconnecting means; lockable switch-disconnect.
Pneumatic/hydraulic: Manual line valve that shuts off supply; bleed/vent downstream; mechanical blocks for actuators where needed.
Process piping/fluids: Line valve plus blank flange/slip blind where required by procedure and hazard level.
Mechanical/potential energy: Blocks, pins, chocks, or restraints that physically prevent motion from gravity, spring force, or stored mechanical energy.

Devices that are commonly not energy isolating devices

Push button start/stop stations and selector switches
Emergency stop buttons and safety relays (they stop; they don’t isolate)
PLC/HMI “OFF,” software commands, key switches used only as control logic
Contactors, motor starters, control relays
Solenoid valves used as the only shutoff for air/hydraulic supply
Indicator lights, alarms, status screens

Mini-procedure (sequence you should be able to defend)

Prepare: Identify all energy sources and the correct energy isolating device(s) for each.
Shutdown: Stop the machine using normal controls.
Isolate: Operate the energy isolating device(s) to block energy from the source.
Apply LO/TO: Apply locks (or tags-plus controls when lockout isn’t possible under your program).
Release/secure stored energy: Bleed, vent, drain, block, pin, discharge, or restrain.
Verify: Try-start and test for zero energy at the hazard point (voltage/pressure/zero motion).

On-the-Job Drills: Picking the Correct Energy-Isolating Device

Use these short prompts to practice the exact judgment the quiz targets: identifying what physically isolates energy versus what merely commands a stop. For each scenario, name (1) the energy isolating device, (2) the “tempting but wrong” control device, and (3) one stored-energy step you must not skip.

Conveyor jam cleanout: The operator hits the red E-stop; the motor stops. There is a lockable fused disconnect on the wall, and the conveyor can coast for several seconds after power removal.
Air cylinder on a packaging machine: The HMI has a “Maintenance Mode” that disables outputs. The air supply feeds a bank of solenoid valves; upstream there is a manual quarter-turn valve with a lockout hasp, plus a dump/bleed port.
Hydraulic press: A keyed selector switch prevents the press from cycling. The hydraulic power unit has an electrical disconnect, and the system has an accumulator with a pressure gauge and bleed-down valve.
Two power sources: A machine has a main disconnect and a separate 120V convenience receptacle feeding task lighting inside the guard. The “Stop” push button drops out the contactor, but lights remain energized.
Backfeed risk: A VFD-controlled motor stops when the local control switch is turned off. The cabinet has capacitors and a waiting period label; there is also a lockable disconnect upstream.
Gravity hazard: A raised platen is held by hydraulic pressure. Electrical power to the pump can be locked out, but the load can still descend if a valve leaks.
Shared energy source: Three machines are fed from one disconnect; each machine also has a local operator station. Two authorized employees will service different machines at the same time.

Debrief checklist (use after each prompt)

Did you pick a device that blocks energy from the source?
Did you identify at least one stored-energy hazard?
Could a remote command or automatic restart defeat your chosen device?

Five Non‑Negotiables for Answering “Which Is Not an Energy Isolating Device?”

Energy isolating devices physically block energy. If a device only sends a signal (to a starter, relay, drive, or solenoid), it is a control element—not isolation.
“Stops motion” is not the same as “prevents energization.” Emergency stops, interlocks, and software modes can stop equipment but can still allow unexpected restart or release of stored energy.
Isolate at the source, not the convenience point. Choose the disconnect/valve/blind/block that prevents energy from reaching the hazard zone, even if it’s farther upstream than the operator station.
Account for stored and residual energy every time. Bleed, vent, block, pin, drain, discharge, and restrain as applicable before you claim a “zero energy” state.
Verification must match the hazard. Try-start plus objective testing (voltage/pressure/zero motion) at the exposure point is how you prove the isolator selection was correct.

Glossary: LO/TO Terms Used in Energy-Isolating Device Decisions

Energy isolating device (EID): A mechanical device that physically prevents the transmission or release of energy. Example: Locking a manually operated disconnect switch open so power cannot reach the motor circuit.
Control circuit-type device: A device that controls equipment operation by command or logic but does not physically isolate energy. Example: Pressing a stop push button that drops a contactor while upstream power remains available.
Stored (residual) energy: Energy that remains after shutdown/isolation and can still cause motion or exposure. Example: Pressure in an air receiver that must be vented after the supply valve is closed.
Backfeed: Energy flowing into equipment from an alternate source or path. Example: A separate lighting circuit or secondary feed energizing parts of a cabinet even when the main motor disconnect is open.
Try-start (verification): An attempt to start equipment using normal controls after applying LO/TO to confirm the isolator selection is effective. Example: After locking the disconnect, pressing “Start” and confirming no motion occurs, then resetting controls to neutral.
Tags-plus: A tagout approach that adds extra physical protections when a device cannot be locked out, to provide protection equivalent to lockout. Example: A tag plus removal of an isolating element, blocking, or additional control measures specified by procedure.

Authoritative References for OSHA 1910.147 and Energy-Isolating Devices

OSHA 29 CFR 1910.147 — The control of hazardous energy (lockout/tagout) — The regulatory text, definitions, and required program elements used to determine what qualifies as an energy isolating device.
OSHA Publication 3120 — Control of Hazardous Energy (Lockout/Tagout) — Plain-language guidance and examples, including the distinction between isolation and control-circuit devices.
OSHA Directive CPL 02-00-147 — Enforcement policy and inspection procedures that clarify common noncompliant practices (including misuse of push buttons/selector switches as “isolation”).
NIOSH (CDC) — Hazardous Energy Control — Program-focused guidance, including periodic procedure inspections and practical prevention strategies.
OSHA eTool — Hazardous Energy Control (Lockout/Tagout) — Task-oriented examples and explanations that reinforce why lockout physically restrains the energy isolating device.

FAQ: Energy-Isolating Devices Under OSHA 29 CFR 1910.147

Why isn’t an emergency stop (E-stop) an energy isolating device?

An E-stop is designed to stop hazardous motion quickly, typically by opening a control circuit that drops out a contactor or control relay. It does not usually physically prevent energy from being transmitted or reintroduced (including remote restart, control failure, or backfeed), and it does not address stored energy (coast-down, gravity, pressure, capacitors). For LO/TO, you generally must isolate with a disconnect/valve/blocking method that holds the system in a safe state.

Do push buttons, selector switches, or an HMI “OFF” command ever count as isolation?

For OSHA 1910.147 servicing/maintenance, those are control circuit-type devices. They may be part of the normal shutdown step, but they are not the isolation step because they only command a change of state and can be bypassed or fail in ways that allow unexpected energization.

Is a solenoid valve an energy isolating device for air or hydraulics?

Usually no. A solenoid valve is typically a control device that can leak, be overridden, or be re-energized electrically. Isolation is normally achieved with a manual, lockable line valve (plus bleed/vent) and, where needed, mechanical blocking or restraints to control stored and potential energy.

What if the disconnect or valve can’t accept a lock?

When an energy isolating device is capable of being locked out, lockout is expected. If it is not capable, employers typically must use a tagout approach that provides equivalent protection—often requiring additional physical measures (for example, removing an isolating element, blocking, or other procedure-defined safeguards). The key is that the method must still prevent unexpected energization and must be verifiable.

How do I handle equipment with multiple energy sources or backfeed?

List every energy type and every feed path (including auxiliary circuits, stored energy devices, and shared utilities). Then isolate each path with the correct energy isolating device and verify at the hazard point. If one system can energize another (electrical backfeed, tied pneumatics, shared hydraulics), treat it as a multi-source lockout problem—not a single-switch shutdown.