24VDC Lockout Requirements: What OSHA Actually Says

Estimated Reading Time: 7 minutes

TL;DR: The 24VDC control power lockout question trips up even experienced safety professionals. OSHA’s 29 CFR 1910.147 does not give you a voltage exemption. If 24VDC control circuits create a hazardous energy exposure, LOTO applies. Low voltage does not equal low risk when actuators, solenoids, and servo drives are in the picture.

24VDC control power lockout requirements come up constantly in manufacturing plants. The debate is almost always the same. A maintenance tech needs to troubleshoot a conveyor. The supervisor says, “It’s only 24 volts – just go in there.” The safety manager pushes back. Here’s the thing: the voltage number alone doesn’t determine whether lockout/tagout applies. What matters is whether unexpected energization could injure someone. And with 24VDC control circuits, that happens more often than people realize.

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Key Takeaways

• OSHA 1910.147 has no voltage threshold that automatically exempts a circuit from lockout/tagout requirements
• 24VDC can drive actuators, solenoids, and servo drives that cause amputations, crush injuries, and fatalities even when the voltage poses no shock risk
• Stored energy in 24VDC systems – including capacitors and batteries – must be dissipated before declaring a zero-energy state
• The “it’s only 24 volts” argument is not an OSHA defense and has resulted in citations and fatalities
• NFPA 70E and 1910.333 govern qualified electrical work, but 1910.147 still applies to mechanical hazards created by 24VDC-controlled equipment
• Machine-specific written procedures must address each energy source, including control circuits

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What Is 24VDC Control Power?

24VDC control power is a low-voltage direct current circuit used to power the control systems of industrial machinery. It’s the operating voltage of most PLCs, HMIs, sensors, solenoid valves, and relay coils in manufacturing environments. The appeal is clear. 24VDC doesn’t pose the same shock risk as 480V or even 120V circuits. Workers can touch live 24VDC terminals without the same electrical danger. But that’s where the confusion starts.

Why Facilities Use 24VDC Control Circuits

Most modern industrial equipment runs on a split architecture. The main drive power – 480V three-phase, for example – handles motors and heavy loads. The control side, typically 24VDC, handles the logic: when to start, when to stop, which valve to open. Think of it as the nerve system of the machine. The 24VDC circuit tells the machine what to do. Disconnect the 480V side and the machine has no muscle. Disconnect the 24VDC side and the machine has no brain. Both matter for energy control.

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Does 24VDC Require Lockout Tagout Under OSHA 1910.147?

Under OSHA 29 CFR 1910.147, lockout/tagout is required any time servicing or maintenance creates exposure to hazardous energy – regardless of voltage level. The standard defines hazardous energy broadly: any electrical, mechanical, hydraulic, pneumatic, chemical, thermal, or other energy capable of causing injury. 24VDC control power falls into this category whenever it controls equipment that could move, actuate, or energize in a way that could injure a worker. OSHA’s 1910.147 standard is clear: the key question is whether unexpected startup, energization, or release of stored energy could cause injury. If yes, LOTO applies.

The “Low Voltage” Myth Costs Lives

Here’s a pattern I’ve seen in more than a few facilities. A maintenance tech knows that 24 volts won’t shock them. So they start treating 24VDC control circuits as safe to work on live. No lockout. No verification. Then a solenoid valve opens. Or a cylinder extends. Or a conveyor jogs. The voltage didn’t cause the injury. The machine did – because 24VDC control power was still telling it what to do. OSHA’s control of hazardous energy overview covers “any source of electrical, mechanical, hydraulic, pneumatic, chemical, thermal, or other energy.” The only question is whether a hazard exists. Not whether the specific voltage is high enough to shock. LOTO violations consistently rank in OSHA’s top 10 most cited standards. According to OSHA, this standard prevents approximately 120 fatalities and 50,000 injuries every year. Those numbers include incidents from low-voltage control circuits.

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When 24VDC Creates Hazardous Energy

24VDC is hazardous whenever it controls a device capable of causing unexpected movement, release, or activation. Here’s what that looks like in practice.

Solenoid Valves and Pneumatic Cylinders

A solenoid valve on a pneumatic cylinder runs on 24VDC signal power. The air pressure doing the work might be 100 psi. But that valve stays closed or opens based entirely on 24VDC control. If you’re working inside a press or at the point of operation and 24VDC is still live, that cylinder can actuate. The voltage won’t shock you. The cylinder will crush you.

Servo Drives and Motion Control

Servo drives receive position and velocity commands through 24VDC control signals. The drive amplifies those signals into actual motor power. But the motion is triggered by the 24VDC side. A technician troubleshooting a servo axis on a live system can trigger unexpected movement just by interrupting and restoring the control signal – or by a PLC program continuing to run.

Stored Energy in Capacitors

Many 24VDC power supplies and drives contain capacitors that store charge. When you de-energize the 480V main supply, those capacitors don’t discharge instantly. They can hold enough energy to energize control circuits – and trigger actuators – for seconds to minutes after shutdown. OSHA’s lockout/tagout enforcement directive requires verification of zero-energy state before work begins. De-energizing the source is step one. Verifying that stored energy has dissipated is what actually makes it safe.

How to Properly Isolate 24VDC Control Circuits

Proper lockout of 24VDC control power follows the same six steps as any other energy source in your written energy control procedure. The steps don’t change based on voltage. The isolation points do. Here’s what machine-specific LOTO procedures need to address for 24VDC control circuits:

1. Identify all 24VDC power supply sources feeding control circuits on the machine. One machine may have multiple 24VDC power supplies serving different subsystems.
2. Locate the energy-isolating device for each 24VDC source – typically a circuit breaker, disconnect, or power supply switch capable of accepting a lockout device.
3. Apply a lockout device to each energy-isolating device. If the device cannot be locked, tagout is used – but the standard strongly prefers lockout wherever locking is feasible.
4. Release or restrain all stored energy. For 24VDC systems, allow capacitors to discharge fully. Some facilities add a discharge verification with a voltmeter as a procedural step.
5. Verify zero-energy state by attempting to operate the control device and confirming no response.
6. Test the effectiveness of the isolation before beginning work. Don’t assume – verify.

If you’re building or updating machine-specific procedures, the LOTO energy control procedures templates on this site include documented procedure frameworks that cover multiple energy sources, including control circuits.

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The 1910.147 vs 1910.333 Debate for 24VDC Systems

When electrical work is being performed – as opposed to mechanical maintenance – the governing standard shifts from 1910.147 to 1910.333 and NFPA 70E. This distinction matters for how you classify the work. Here’s a comparison that clears up most of the confusion:

Task	Standard That Applies	Why
Replacing a 24VDC solenoid with power on	OSHA 1910.147 (LOTO required)	Motion hazard from actuators
PLC program troubleshooting on live panel	NFPA 70E / 1910.333	Qualified electrical work, live conductors
Entering a machine’s hazard zone for repairs	OSHA 1910.147 (LOTO required)	Any source of hazardous energy present
Signal testing 24VDC wiring with voltmeter	NFPA 70E / 1910.333	Electrical safety work by qualified person
Both exposures exist simultaneously	Both standards may apply	Procedure must address each task separately

The mistake I see facilities make: they classify any 24VDC task as “electrical work” to justify skipping LOTO. That’s not how this works. The work type AND the exposure determine which standard governs. As E-Hazard’s analysis of 1910.147 vs electrical safety standards points out, both standards can apply to the same machine depending on what’s being done. Your energy control procedures need to address which standard governs which tasks. If you’ve seen LOTO violations come up in your facility, the breakdown of common LOTO mistakes and how to avoid them walks through the patterns behind most citations.

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Frequently Asked Questions About 24VDC Control Power Lockout Requirements

Does OSHA require lockout on 24VDC circuits?

Yes, when 24VDC control circuits create exposure to hazardous energy. OSHA 1910.147 has no voltage exemption. The standard applies whenever unexpected energization could cause injury – and 24VDC systems controlling pneumatic actuators, servo drives, and solenoid valves clearly qualify. Voltage doesn’t determine risk; movement potential does.

What if we can’t lock out the 24VDC power supply?

If the energy-isolating device cannot accept a lockout device, tagout is required. The standard is explicit that lockout is preferred when locking is feasible. If lockout cannot be achieved, additional protective measures must compensate – including removing isolation handles or adding blocking devices. Review OSHA 1910.147(c)(3) for alternative protection requirements.

Can we use a tagout-only approach for 24VDC circuits?

Only if the energy-isolating device cannot be locked. Even then, the standard requires additional safety measures beyond just tagging. Many facilities that tag only 24VDC circuits are out of compliance. A lockout hasp or small circuit breaker lockout device is available for most control panel breakers and achieves lockout rather than tagout.

Who needs training on 24VDC lockout requirements?

All authorized employees who perform lockout on equipment with 24VDC control circuits, and all affected employees who work in the area when lockout is being performed. Authorized employees need hands-on training specific to the equipment they service. The lockout tagout training requirements for authorized vs. affected employees differ – make sure your program addresses both roles.

What’s the difference between 24VDC lockout and full machine lockout?

There is no separate “24VDC lockout.” Energy control requires isolating ALL hazardous energy sources on the machine, including 24VDC control power. A written machine-specific procedure lists every energy source – 480V drives, compressed air, hydraulics, and 24VDC control power – with a lockout point for each. Locking only the main 480V disconnect and leaving 24VDC live is incomplete lockout.

Do we need a written procedure for every machine with 24VDC control power?

Yes, if that machine has any hazardous energy sources and employees service it. OSHA 1910.147(c)(4)(i) requires documented procedures where energy isolation is not obvious. 24VDC control circuits – because they’re often overlooked – absolutely warrant documentation in your lockout tagout program.

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Now It’s Your Turn

The 24VDC control power debate usually comes down to one assumption: low voltage means no hazard. It doesn’t. Your LOTO program needs to address control circuit energy sources the same way it addresses any other energy type. That means written procedures, trained authorized employees, and actual lockout devices applied to 24VDC energy-isolating devices. Here’s where to start this week:

1. Pull your machine-specific LOTO procedures and check whether 24VDC control power is listed as an energy source. If it’s not, your procedures are incomplete.
2. Walk your floor and identify every energy-isolating device for 24VDC control circuits on the machines your team services most often.
3. Confirm your authorized employees can identify 24VDC energy sources, know the isolation points, and understand why control circuits matter even at low voltage.
4. Add 24VDC verification steps to your written procedures – specifically, a voltmeter check or control test to verify zero-energy state after lockout.

If you need a starting point for your LOTO procedures, the All-Access Resource Library has done-for-you templates you can customize for your facility’s specific equipment.