What You’ll Learn
- When a written discharge procedure is required: circuit parts operating at 100 volts and 10 joules or above
- The five minimum contents every procedure must specify — voltage, energy, steps, tools, and test instruments
- How the procedure is built on the capacitor risk assessment, including the wait time and what to do if energy remains
- The seven-step sequence that layers the discharge procedure onto the electrically safe work condition process of 120.6
- Why shorting wires stay connected during the work — and why a capacitor can quietly recharge if they are removed
The Source You Cannot Switch Off
Lockout/tagout and the electrically safe work condition process are built around sources you can open, lock, and verify. A capacitor breaks that model: it is a source that stays after the disconnect opens. Opening the switch removes the supply, but the stored charge sits in the bank, silent and invisible, waiting for a path out. That is why Informative Annex R calls for a written discharge procedure for capacitor work — a document, much like a complex lockout/tagout procedure, that spells out exactly how this specific equipment is brought to an electrically safe work condition, stored energy and all. It turns a sequence that lives in one experienced worker’s head into a sequence anyone qualified can follow, check, and repeat.
When the Procedure Is Required: 100 Volts and 10 Joules
The threshold for the written procedure is stated in R.13: where a conductor or circuit part is operating at or above 100 volts and holds 10 joules or more of stored energy, a written discharge procedure should be used to document the steps needed to place the equipment in an electrically safe work condition. Both numbers must be met — voltage alone does not trigger it, and neither does energy alone. Below those thresholds the annex’s shock framework treats the stored charge as a lesser hazard; at or above them, improvisation is no longer acceptable and the discharge gets written down before the job begins.
Built on the Risk Assessment: What the Document Must Capture
The procedure’s foundation is the capacitor risk assessment of R.6. The written procedure incorporates the results of that assessment, and R.6.9 describes what it must capture: the amount of stored energy available, how long to wait after de-energization before opening the enclosure, how to test for the absence of energy, and what to do if stored energy is still present when the testing is done. That last item is the one experience teaches: bleed systems fail, discharge paths break, and a procedure that only describes the happy path leaves the crew inventing steps at exactly the wrong moment. A good written procedure reads like the risk assessment turned into instructions — every hazard the assessment found has a step that answers it.
The Five Minimum Contents
Section R.13.1 sets the minimum contents the written discharge procedure must specify:
- The voltage, in volts
- The energy, in joules
- The specific steps to safely discharge the capacitor, or to verify that it is discharged
- The specific tool or tools — for example, a ground stick — or the engineering system used to discharge the capacitors, where one is necessary
- The specific test instruments — for example, a digital voltmeter — or engineered systems used to verify the de-energized state
Notice what the list demands: numbers first, then actions, then named hardware. A procedure that says “discharge the capacitor and test it” without stating the voltage, the joules, the ground stick, and the meter has not met the annex’s minimum — it has described the idea of a procedure rather than a procedure.
The Sequence: Seven Steps onto 120.6
The step sequence in R.13.2 layers the discharge procedure onto the standard process: a qualified person follows the steps of 120.6 for establishing an electrically safe work condition, together with the specific sequence in the written discharge procedure. Removing the stored energy is one part of that overall process. The combined sequence runs as follows:
- Review the scope of work and the written discharge procedure. Determine all safe approach boundaries and the PPE and tools the task requires.
- Hold a job briefing with the personnel involved, and notify affected persons that the equipment will be de-energized.
- After properly interrupting the load current, open the disconnecting device for each source feeding the equipment.
- Wherever possible, visually verify that all blades of the disconnecting devices are fully open, or that drawout-type circuit breakers are withdrawn to the fully disconnected position.
- Apply lockout/tagout devices in accordance with a documented and established policy — or use plug control on smaller equipment.
- Where bleed resistors or automatic discharge systems apply, wait the prescribed time for the capacitors to discharge below the thresholds in 360.3.
- Perform the test and ground method selected under R.11.
The capacitor-specific steps are the last two, and they are the reason the written procedure exists. Steps 1 through 5 make the equipment safe from its supply; steps 6 and 7 make it safe from itself.
After the Last Step: Keep It Shorted, Because Charge Can Creep Back
The shorting requirement closes the sequence. To make sure recharging does not occur, all of the capacitor’s terminals should be connected together — shorted — and grounded with a non-insulated wire of sufficient gauge to withstand handling. For capacitors in series, a shorting wire goes across each individual capacitor and to the case; for a single capacitor or a parallel bank, the grounding device, such as a ground stick or hook, is permitted to be left hanging on the terminal while the work proceeds. The caution behind this is dielectric absorption: not all of a capacitor’s energy leaves when it is first shorted, and polarization in the dielectric can rebuild a voltage of up to 10 percent within a few minutes after the ground is removed. A capacitor that tested dead can quietly come back to life on the shelf of the enclosure — which is why the shorts are applied and left in place, not applied, checked, and taken away.
Worked Scenario
A plant electrician is assigned to replace a failed unit in a power factor correction bank. The equipment label and the risk assessment agree on the numbers: the bank operates at 480 volts with a stored energy well into the hundreds of joules — far above the 100-volt, 10-joule threshold — so the written discharge procedure governs the job. The procedure she pulls states the voltage and energy, names the soft grounding stick and the digital voltmeter to be used, and gives the prescribed wait after de-energization. She reviews the scope and the procedure, confirms the boundaries and PPE, and briefs her helper. She interrupts the load, opens the disconnect, and visually verifies the blades are fully open. Lockout/tagout devices go on. Then she waits the full prescribed time for the bank’s bleed system to bring the stored energy down — and does not trust it: following the procedure’s test steps, she verifies the discharge with the meter, applies the test and ground method the procedure specifies, and leaves the terminals shorted together and grounded with the shorting wire while the replacement work is done. When the failed unit comes out, it is handled as an item that can recharge — because, as the procedure accounts for, it can.
Common Mistakes and Safety Notes
- Using a generic lockout procedure alone. Locking out the supply does nothing about stored charge. At 100 volts and 10 joules or above, the discharge itself gets a written procedure.
- Writing a procedure without numbers. The document must state the voltage in volts and the energy in joules, and name the specific tools and test instruments — “discharge and test” is not a procedure.
- Skipping the prescribed wait because the bank “has bleeders.” Step 6 waits for the discharge to finish; bleed systems can fail, which is why step 7 tests and grounds rather than assuming.
- Leaving out the failure branch. The procedure must say what to do if stored energy is still present after the discharge steps — that is the moment the crew most needs instructions.
- Removing the shorting wires once the meter reads zero. Dielectric absorption can rebuild up to 10 percent of the voltage within minutes. Terminals stay shorted and grounded during the work.
- Shorting only the bank terminals on a series string. Each capacitor in series gets its own shorting wire, connected to the case — charge can transfer between series capacitors instead of draining away.
Summary
Where a conductor or circuit part operates at or above 100 volts with 10 joules or more of stored energy, Annex R calls for a written discharge procedure — built on the R.6 risk assessment — to document how the equipment reaches an electrically safe work condition. The procedure records the stored energy available, the wait after de-energization before the enclosure is opened, how absence of energy is tested, and what to do if energy remains; at minimum it specifies the voltage, the energy, the discharge steps, the discharge tools, and the test instruments. A qualified person then works the 120.6 process together with the procedure’s sequence: review and boundaries, job briefing, open the disconnects, visually verify, lock out and tag out, wait the prescribed discharge time, and perform the selected test and ground method. Finally, the terminals are shorted together and grounded and left that way — because dielectric absorption can return up to 10 percent of the voltage to a capacitor whose ground was removed too soon.
Quick-Check Questions
1. At what voltage and energy levels does Annex R call for a written discharge procedure?
Answer: Where a conductor or circuit part is operating at or above 100 volts and contains 10 joules or more of stored energy.
2. What are the five minimum contents the procedure must specify?
Answer: The voltage in volts; the energy in joules; the specific steps to safely discharge the capacitor or verify it is discharged; the specific tools or engineering system used to discharge it; and the specific test instruments or engineered systems used to verify the de-energized state.
3. What four pieces of information does R.6.9 say the procedure should include?
Answer: The amount of stored energy available, how long to wait after de-energization before opening the enclosure, how to test for absence of energy, and what to do if stored energy is still present.
4. In the R.13.2 sequence, what happens between applying lockout/tagout and performing the test and ground method?
Answer: Where bleed resistors or automatic discharge systems apply, the worker waits the prescribed time for the capacitors to discharge to below the thresholds in 360.3.
5. Why are shorting wires left connected to the capacitor terminals during the work?
Answer: To ensure recharging does not occur — dielectric absorption can rebuild a voltage of up to 10 percent after a ground is removed, so the terminals stay shorted together and grounded.
Based on NFPA 70E (2024), Informative Annex R, paraphrased for study.
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