Safety Made Simple With a Proving Unit
- Brian Hall
- Nov 10
- 3 min read
A better way to verify absence of voltage
It’s easy to trust a familiar tool, especially one you use every day. But even the most reliable voltmeter can fail without warning, so it's important to know what to do if it happens.
Risks of Voltmeter Failure
A damaged lead, a wrong setting, or an internal fault can turn a routine task into a life-threatening situation. Many shocks, arc flashes, and electrocutions have occurred because a voltmeter gave a false “zero” reading — indicating the circuit was dead when it was still energized.
That’s why NFPA 70E® Article 120.6 requires workers to verify that their test instruments function properly both before and after testing conductors or circuit parts they believe are de-energized. OSHA also expects employers to provide the tools, training, and procedures workers need to verify the absence of voltage safely.
Why Meter Verification Matters
In most cases, your technicians must perform what’s known as a Live-Dead-Live (L-D-L) test:
Test the meter on a known live source.
Test the circuit to confirm it’s de-energized.
Re-test on the live source to ensure the meter still works.
If the meter doesn’t read the expected voltage during the first or last step, it’s unsafe to rely on it: the meter or leads could be damaged.
Unfortunately, finding a known live source isn’t always simple. In some facilities, 120-volt outlets aren’t nearby or may not even exist in the work zone. This, in turn, can lead to unsafe shortcuts, like removing guards or using improvised connections to find a live source, and these actions can introduce even greater hazards.
The Smarter, Safer Option: Proving Units
A proving unit eliminates the need to search for a live source. Compact and battery-powered, it produces both AC and DC output voltages (typically between 50 and 240 volts) that allow workers to verify their meters quickly and safely.
By using a proving unit, an electrician can:
Confirm the meter is functional before and after every test.
Eliminate unnecessary exposure to live circuits.
Complete the L-D-L process anywhere, even in remote or restricted areas.
Proving units fit easily in a tool bag, add almost no time to the job, and remove one of the most common excuses for skipping verification.
Supervisors: Build It Into the Routine
Even the best workers can forget steps when they’re under time pressure. This is where supervisors and safety leaders play a key role in creating habits that make safety second nature.
By including proving units and L-D-L verification in daily procedures and checklists, supervisors send a clear message: Safety isn’t optional — it’s how we work.
A strong safety culture means giving workers tools that make compliance easier, not harder. The proving unit does exactly that.
Quick Checklist: Verifying Absence of Voltage Safely
Inspect your voltmeter and leads before each use for cracks, wear, or damage.
Perform a Live-Dead-Live test — or use a proving unit — before and after testing.
Confirm the meter’s settings match the expected voltage type (AC or DC).
Never skip verification due to time pressure or convenience.
Report and replace any damaged instruments immediately.
Supervisors: ensure workers are trained and have access to proving units on every job.
Keep It Simple, Keep It Safe With Proving Units
Electrical safety doesn’t always depend on complex technology. Sometimes, it’s the simplest tools and habits that prevent the worst outcomes.
Proving units make compliance easier, reduce errors, and keep workers safer, one test at a time.
If you haven’t reviewed your team’s absence-of-voltage verification process recently, now is the time.
Small investments in the right tools and training make a big difference when it matters most.
Guidant Power is here to help you. Contact us to simplify electrical safety — with training, evaluations, and insights designed for real-world work.
70E®, Standard for Electrical Safety in the Workplace®, NFPA 70®, NEC®, and National Electrical Code® are registered trademarks of the National Fire Protection Association, Quincy, MA. All rights reserved. This informational material is not affiliated with nor has it been reviewed or approved by the NFPA.
