4.2 How a circuit is actually made safe
"It's off" is not a state a standard recognizes. 29 CFR 1910.333(b)(2) sets out how a circuit is actually made safe, and it does something few OSHA paragraphs do: it says the steps must be followed in the order in which they are presented. This chapter walks that order, and explains the sentence that catches out the most experienced people — the one about induced voltage and backfeed.
1 Deenergized is not safe until it is locked or tagged
1910.333(b)(1) makes the point before the procedure starts: "Conductors and parts of electric equipment that have been deenergized but have not been locked out or tagged in accordance with paragraph (b) of this section shall be treated as energized parts, and paragraph (c) of this section applies to work on or near them."
Read that as the field rule it is. A breaker somebody switched off, with nothing on it, is an energized circuit for the purposes of this standard — which means only a qualified person may work on it, and all the energized-work practices apply. The lock is not paperwork. It is what changes the legal and physical status of the circuit.
And (b)(2) requires a written copy of the procedures, available for inspection by employees and by OSHA. A note allows the written procedure to be, quite literally, a copy of paragraph (b).
2 Step one: deenergizing, and what may not be used to do it
1910.333(b)(2)(ii) has four parts. (A): safe procedures for deenergizing are determined before circuits or equipment are deenergized. (B): the circuits and equipment to be worked on are disconnected from all electric energy sources — and then the sentence that matters most on a plant floor: "Control circuit devices, such as push buttons, selector switches, and interlocks, may not be used as the sole means for deenergizing circuits or equipment. Interlocks for electric equipment may not be used as a substitute for lockout and tagging procedures."
(C): stored electric energy that might endanger personnel is released — capacitors discharged, high capacitance elements short-circuited and grounded. A note adds that if the capacitors or associated equipment are handled to meet this requirement, they are treated as energized. (D): stored non-electrical energy in devices that could reenergize the circuit is blocked or relieved.
3 Step two: locks and tags, and the rules for using one without the other
| Paragraph | Requirement |
|---|---|
| (A) | A lock and a tag on each disconnecting means used to deenergize, attached so that persons cannot operate the disconnect without undue force or the use of tools. |
| (B) | Each tag contains a statement prohibiting unauthorized operation of the disconnecting means and removal of the tag. |
| (C) | A tag may be used without a lock if a lock cannot be applied, or if the employer can demonstrate that tagging gives a level of safety equivalent to a lock. |
| (D) | A tag used without a lock must be supplemented by at least one additional safety measure giving equivalent safety — the standard's examples are removing an isolating circuit element, blocking a controlling switch, or opening an extra disconnecting device. |
| (E) | A lock may be placed without a tag only if all three are true: only one circuit or piece of equipment is deenergized; the lockout does not extend beyond the work shift; and employees exposed to the hazards of reenergizing are familiar with the procedure. |
The default is both. Everything else is an exception with conditions attached, and (D) is the one that gets skipped: a tag on its own is not a lighter version of a lock, it is a lock's worth of protection assembled out of other measures.
On construction sites, 1926.417 states the same idea in three short paragraphs: controls to be deactivated during work are tagged (a); deenergized equipment is rendered inoperative and has tags attached at all points where it can be energized (b); and tags are placed to identify plainly the equipment or circuits being worked on (c).
4 Step three: verification, and the sentence that catches everyone
1910.333(b)(2)(iv) opens with a condition: "The requirements of this paragraph shall be met before any circuits or equipment can be considered and worked as deenergized." Not "should be". Before.
- 1(A) A qualified person operates the equipment operating controls or otherwise verifies that the equipment cannot be restarted.
- 2(B) A qualified person uses test equipment to test the circuit elements and electrical parts to which employees will be exposed, and verifies they are deenergized.
- 3The test must also look for what nobody switched off: "The test shall also determine if any energized condition exists as a result of inadvertently induced voltage or unrelated voltage backfeed even though specific parts of the circuit have been deenergized and presumed to be safe."
- 4Above 600 volts nominal, the test equipment is checked for proper operation immediately before and immediately after the test — the live-dead-live check, written into the standard.
Backfeed is the reason a circuit can be dead at the panel and alive at the work. A generator someone connected without a transfer switch, a control transformer fed from another panel, a shared neutral, a UPS, a second feed to the same equipment. Induced voltage arrives from conductors running alongside. Neither of them is visible at the disconnect, and neither is caught by "I turned it off myself."
5 Step four: reenergizing, in order, even temporarily
1910.333(b)(2)(v) sets four requirements to be met "in the order given, before circuits or equipment are reenergized, even temporarily" — that last phrase aimed squarely at the quick bump test.
| Order | Requirement |
|---|---|
| (A) | A qualified person conducts tests and visual inspections as necessary to verify that all tools, electrical jumpers, shorts, grounds and similar devices have been removed. |
| (B) | Employees exposed to the hazards of reenergizing are warned to stay clear. |
| (C) | Each lock and tag is removed by the employee who applied it, or under their direct supervision. If that employee is absent, a qualified person designated for the task may remove it, provided the employer ensures the employee is not available at the workplace and is made aware the lock or tag was removed before resuming work there. |
| (D) | There is a visual determination that all employees are clear of the circuits and equipment. |
6 How this fits with 1910.147
Most plants already run a lockout/tagout program under 1910.147, the control of hazardous energy standard. Note 2 to 1910.333(b)(2) handles the overlap: procedures that comply with paragraphs (c) through (f) of 1910.147 "will also be deemed to comply with paragraph (b)(2) of this section" provided the procedures address the electrical safety hazards covered by Subpart S and incorporate the requirements of (b)(2)(iii)(D) — the additional safety measure with a tag used alone — and (b)(2)(iv)(B) — the qualified person's test, including induced voltage and backfeed.
In plain terms: your LOTO program can cover this, but only if it includes those two electrical specifics. A generic machine lockout procedure that never mentions testing for backfeed does not.
7 Where the sources hide
Disconnecting "from all electric energy sources", as (b)(2)(ii)(B) puts it, assumes somebody knows how many there are. On real equipment the count is often higher than the drawing suggests, and every extra source is a way for a locked-out circuit to be alive at the work.
- 1A second feed. Equipment fed from two panels, an automatic transfer switch, or a tie breaker that was closed years ago and never reopened.
- 2Control power from elsewhere. A control transformer or interlock circuit fed from a different panel than the power circuit — which is one reason control devices may never be the means of deenergizing.
- 3Stored energy. Capacitors and high capacitance elements, addressed directly by (b)(2)(ii)(C), and stored non-electrical energy — springs, hydraulics, elevated masses — addressed by (D).
- 4Backfeed from a generator or inverter. A portable generator connected without a transfer switch, a UPS, a solar inverter. This is the case (b)(2)(iv)(B) names by name.
- 5Induced voltage. Conductors running parallel to energized circuits pick up voltage without being connected to anything.
Only the last two are invisible at the disconnect, and both are exactly what the verification test is required to find. That is why the standard reserves the test to a qualified person with instruments rather than to the person who threw the switch.
- Deenergized but not locked or tagged is treated as energized (1910.333(b)(1)) — the lock changes the status of the circuit.
- The steps of (b)(2) must be followed in the order presented, and a written copy of the procedure must be available to employees and OSHA.
- Push buttons, selector switches and interlocks may never be the sole means of deenergizing; stored electrical and non-electrical energy must be released or blocked.
- The default is a lock and a tag. A tag alone requires an additional safety measure of equivalent protection; a lock alone requires all three conditions of (b)(2)(iii)(E).
- A qualified person verifies with test equipment, and the test must find induced voltage and unrelated backfeed — above 600 V, the tester is checked before and after.
- Reenergizing has its own ordered list, including removing every jumper and ground, warning exposed employees, and a visual determination that everyone is clear.
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