The UPS article, hiding under a number nobody expects.
The 2024 edition had Article 340 — Power Electronic Equipment. In 2027 that article is gone by name. Its content now sits inside a new Article 330, organised by frequency rather than by equipment type. Anyone searching the standard for "power electronic equipment" will not find an article by that name.
It now means Article 330. And the article is no longer titled after the equipment — it is titled after a frequency band, 1 Hz to 110 MHz, excluding dc and 50/60 Hz. A technician told to "follow Article 340 for the UPS" will land somewhere with nothing in it.
A deleted article number fails loudly. Someone looks it up, finds nothing, and asks a question.
Article 340 still exists in the 2027 edition. It is titled Electrical Hazards for Mixed Frequencies and it is reserved — the number is being held open and there is no technical content under it. A procedure citing Article 340 now points at a real article that says nothing, which reads like the requirement was relaxed rather than moved.
§ What moved where
| 2024 edition | 2027 edition | What happened |
|---|---|---|
| 340 Power Electronic Equipment | 330 | Content absorbed into the new frequency-based article |
| 330 Lasers | — | DELETED No counterpart in 2027 |
| — | 340 | NEW Mixed frequencies — reserved, no content |
Two article numbers changed meaning in opposite directions at the same time. That is the worst case for a document set that cites article numbers rather than titles.
§ What Article 330 actually covers
The scope at 330.1 is explicit about the equipment it captures, and the list is unusually helpful — it names the equipment rather than describing it abstractly:
- Equipment that includes rectifiers and inverters — this is the phrase that pulls in the entire critical power chain.
- Motor drives — every VFD on the mechanical plant.
- Uninterruptible power supply systems — named explicitly in the scope.
- Lighting controllers.
- Arc welding equipment.
- Radio-frequency induction heaters.
- Transmitting towers.
- High-voltage vacuum devices.
Read that list again with a data center in mind. UPS systems and rectifiers/inverters are named in the scope text — this is not an article about welding shops that happens to catch a UPS by implication. The committee wrote the critical power chain into the scope.
Between Article 330 and Article 360 you have the whole UPS: 330 covers the electronics — the rectifier, the inverter, the static switch — and 360 covers the battery behind it. Neither article covers the whole machine on its own, and a procedure written against only one of them has a gap.
The mechanical plant is in scope too. Every VFD on a chilled water pump or CRAH fan is a motor drive under 330.1.
§ Why the committee organised it by frequency
The old Chapter 3 grew article by article, each written for a piece of equipment, each developed largely in isolation. The result was overlap and gaps — equipment that fit two articles, and equipment that fit none.
Frequency is a property of the hazard rather than a property of the machine. A rectifier, a welder and an induction heater have nothing in common as equipment, but the physiological effect of current in the 1 Hz to 110 MHz band is the same regardless of what produced it. Organising the article around the band means new equipment types do not need new articles — a drive topology that did not exist in 2024 is already covered.
The exclusions matter as much as the inclusion. dc is excluded — that is Article 310, new in 2027. 50/60 Hz is excluded — that is ordinary power-frequency work under Chapter 1. Article 330 is specifically the band in between and above.
§ The thresholds at 330.4
330.4 sets exposure levels that shall not be exceeded unless risk control measures from the hierarchy of risk control are selected and implemented. They are stated as current, and they change with frequency:
| Frequency band | Threshold | Note |
|---|---|---|
| 1 Hz – 3 kHz (sub-RF) | 50 V and 3 mA | Explicitly not including 50/60 Hz — that is Chapter 1 work |
| 3 kHz – 100 kHz | 1 × f mA, f in kHz | Rises linearly with frequency — 10 mA at 10 kHz, 100 mA at 100 kHz |
| 100 kHz – 3 MHz | 100 mA | Flat |
| 3 MHz – 30 MHz | 100 (f/3)0.3 mA, f in MHz | Continuous with the bands either side |
| 30 MHz – 110 MHz | 200 mA | Flat |
The Informational Note to 330.4 states it plainly: RF electric shock thresholds depend on current and frequency, not voltage. Every instinct a qualified person has built around a voltage threshold — 50 volts, 100 volts, the limited approach boundary — is the wrong instrument here. Above 3 kHz the standard stops asking what the voltage is.
§ What 330.5 actually requires
330.5 routes the general obligations through 110.4 and then adds three requirements that are specific to this band. All three have teeth in a data center.
Adequately rated meters. Meters used for safety purposes, including zero-energy verification, shall be rated for the frequency of measurement. A meter that is accurate at 60 Hz is not automatically valid on the output of an inverter.
Dielectric PPE shall be derated when used to protect against frequencies greater than 100 kHz. Your rubber insulating gloves do not carry their nameplate rating in this band.
Workers exposed to EM hazards shall be trained to identify and protect themselves from them. The Informational Note to 330.5 adds that equipment containing RF electrical hazards could also produce nonionizing radiation hazards, and that a risk assessment should determine whether an EM exposure risk exists.
330.5(A) requires the meter to be rated for the frequency of measurement, and it names zero-energy verification specifically. Establishing an electrically safe work condition on equipment inside this band with a meter chosen for 60 Hz work is exactly the failure the section is written against — and it is a failure that returns a confident, wrong answer rather than an obvious error.
§ How the article is built
Scope. The equipment list above.
Application. Stated purpose: to guide safety personnel in preparing specific safety-related work practices for sub-RF and RF electrical hazards within their industry or laboratory.
Electrical hazard thresholds. The five frequency bands above.
Specific measures for personnel safety. Routed through 110.4, plus 330.5(A), (B) and (C).
§ What to update, in order
Search every document for "Article 340." Every hit is either a UPS/drive procedure that now means 330, or it is nothing. There is no case where a 2024-era citation of 340 is still correct.
Search for "power electronic equipment." The phrase no longer names an article. Anywhere it appears as a citation, replace it with Article 330.
UPS procedures — split the reference. Electronics under 330, battery under 360. One citation no longer covers the machine.
VFD and mechanical plant procedures — motor drives are named in 330.1. If your drive work was written against Chapter 1 alone, it now has a Chapter 3 article to answer to.
Training material — every deck that showed "340 Power Electronic Equipment" on a Chapter 3 slide.
Procedures get searched for the article number and updated mechanically. Because 340 still exists as a reserved article, a find-and-replace pass that only looks for broken references will not flag it — the number resolves, it just resolves to nothing. The reliable check is to search for the title, "power electronic equipment," which genuinely no longer exists anywhere in the standard.
The full Chapter 3 map →
Every article that moved in 2027, verified against NFPA LiNK.
Article 360 — batteries →
The other half of the UPS. Four hazard categories and the thresholds.
Walk the UPS room →
What the hazards look like in the space itself.
Chapter 3 in the 16-hour class
Article 330 for the electronics, Article 360 for the battery, and the renumbering traps that will outlive the transition — worked against real critical power configurations.
See the 16-hour class Bring it onsite