National Electrical Code Articles and Information
National Electrical Code Top Ten Tips: Article 110 -- Installation Requirements
by Mark Lamendola
Based on the 2023 NEC
Our remarks in are parentheses. Please note, we do quote from
copyrighted material. While the NFPA does allow such quotes, it does so
only for the purposes of education regarding the National Electrical
Code. This article is not a substitute for the NEC.
These are the 10 NEC Article 110 items we deem most important, based
on the pervasiveness of confusion and the potential costs of same.
- 110.3. Examination, Identification, and Use of Equipment. This
section gives 9 requirements for examination in part (A) (Number 8,cybersecurity, was added with the 2023 NEC where the former number 8 was). In (B), it
says "Listed or Labeled equipment shall be installed and used
in accordance with any instructions included in the Listing or
Labeling." In other words, use the product as intended.
Unauthorized modifications void the Listing and expose the modifier
to civil, and potentially criminal, litigation and liability.
- 110.12. Mechanical Execution of Work. The last part of the long-standing "Electrical
equipment shall be installed in a neat and workmanlike manner" has been changed to "...in a professional and skillful manner." This doesn't make things any more clear than before. Why is the NEC so vague on this? Well, it’s hard to quantify and
describe something like that. The Code is basically giving the
Authority Having Jurisdiction (AHJ) the power to reject work that
doesn’t meet industry standards. It’s a situation where
"everyone knows the rules," and the AHJ can make sure
those rules get followed. One reason contractors back such language
is they can use this rule to level the competitive playing field
against "fly by night outfits" that do sloppy work. The
costs associated with work that isn’t "neat and
workmanlike" are enormous—a small investment in upfront costs
saves the customer big money over the life of the equipment. One
requirement many people often overlook is that of filling unused
openings in enclosures—the omission of which is potentially
- 110.13. Mounting and Cooling of Equipment. This requirement is
always in dispute, it seems. Cramming equipment into an overcrowded
arrangement to maximize revenue per square foot sounds like a really
good idea until that equipment starts failing left and right, or the
whole place just burns down.
- 110.18. Arcing parts. This is one of several code requirements
that rule out using an electrical equipment room as a storage area
for combustible materials.
- 110.23. Current Transformers. "Unused current transformers
associated with potentially energized circuits shall be
short-circuited." Leaving the leads to dangle is an invitation
for disaster. A testing firm will always insist on leaving these
shorted—this is why.
- 110.26. Spaces about electrical equipment (600V or less). Most
people wrongly assume working clearances (depth of working space)
are three feet. Under some circumstances, the NEC requires them to
be more. Beyond simply safety, good engineering or maintenance
practices may require more still. Don’t assume just because you
have 2 feet and 10 inches you are "good enough" or if you
have 3 feet 2 inches you must fill in that 2 inches so you don’t
exceed the Code. Also, the Code has minimums for the width and
height of working spaces. These widths are outdated, as they are
based on an earlier era of less "girth endowed" workers.
Use common sense, with safety as your goal. Also with the 2023 revision, new text emphasizes the need to not block access and egress. Technically, they should say ingress and egress, but I digress.
- 110.27. Guarding of live parts. Various methods exist, including
construction of a mezzanine level, restricted access to an area (via
locked door), and so on. It is more than just ensuring the factory
covers are in place. When desiging or installing guard systems, think more in terms of idiot protection than code compliance. That is, anticipate human error rather than merely seek to check off the box for code compliance.
- 110.54 (A). Grounded and Bonded. This requires "effective
grounding," which is defined in Article 100. It does not
include the common practice of connecting to a ground rod that is
not bonded to the grounding system. Always be thinking of the actual current path. Remember, electricity is always trying to get back to its source (thus making a circuit). If you provide a low resistance (metallic) path, much less current will flow through the other paths available. Electricity does not take "the path of least resistance," it takes all paths before it in inverse relationship to their impedance (Kirckoff's Law of Parallel Circuits).
- 110.54(B). Equipment Grounding Conductors. This requires you to
run a grounding conductor "with circuit conductors inside the
metal raceway or inside the multiconductor cable jacket."
- 110.58. Disconnecting Means. You must have a disconnect within
sight of each transformer or motor. This allows a person to lock out
the transformer or motor for maintenance, or to shut it off quickly
in case of misoperation.
Note that the last three items discussed are in Part IV Tunnel Installations over 1000 Volts, Nominal. Yet, they apply to all installations generally. For example, a disconnect is required within sight of a motor regardless of the voltage. And bonding isn't grounding or vice-versa.