The Step that Carries Risk

The lockout/tagout sequence is well understood: identify all sources, shut down, isolate, apply locks and tags, release stored energy, and then verify that no voltage is present. Every step can be performed from outside the enclosure up until verification.

To test for absence of voltage with a portable meter, qualified personnel have to open the equipment, work inside an enclosure that is still assumed to be energized, place probes on each conductor, and confirm the reading phase-to-phase, phase-to-ground, and phase-to-neutral where applicable. The meter itself must be checked against a known source before and after the test. This step happens in full arc flash and shock PPE, because at that moment the electrically safe work condition has not yet been established.

That is the paradox of the traditional sequence. The single step whose purpose is to confirm safety is the step with the highest exposure.

What Standards Allow

NFPA 70E requires that an electrically safe work condition be verified by testing for the absence of voltage before a circuit is treated as de-energized. It also recognizes permanently mounted absence of voltage testers as an acceptable means of performing the test, provided the device is listed and installed for the purpose.

The listing standard is what makes this defensible. UL 1436 sets the requirements for permanently mounted absence of voltage testers, including the self-verification behaviour that a portable meter can never provide on its own: before indicating absence of voltage, the device tests its own measurement path, verifies the connection to each conductor, and confirms it can still detect voltage if voltage were present. A dead meter and a dead bus look identical to a technician. A listed AVT is required to tell them apart and to fail to a non-indicating state when it cannot.

Every other element of the lockout/tagout program stays in force: sources identified, locks applied, stored energy released, program documented, workers qualified. What changes is that the verification result is read from outside the enclosure.

Side by Side

Not only does HRG technology allow for process continuity during a single phase to ground fault, thereby avoiding unnecessary process interruptions, there is evidence that changing from a solidly grounded system, where ground fault levels are excessive and damaging to equipment such as motors to a HRG system where ground faults are controlled to a low level, reduces motor repair costs.

The second factor to consider when reviewing operational costs is the hourly cost of process interruptions which varies by industry:

Where the Work Changes

One insurance company reported 228 instances of ground faults leading to losses over a 7 year period. There were 156 losses involving industrial facilities with an average loss of $769,230. The losses including costs associated with equipment damage, process interruptions, spoiled product, employee retraining and medical costs.

Three Misconceptions

What to Confirm Before You Specify