National Electrical Code Top Ten Tips: Article 280 -- Surge Arresters
Based on the 2020 NEC
by Mark Lamendola
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.
With the 2020 revision, Articles 280 and 285 were deleted and replaced by Article 242. Below is information that was current as of the 2017 NEC. It is no longer current as of the 2020 NEC.
These are the 10 NEC Article 280 items we deem most important, based
on the pervasiveness of confusion and the potential costs of same.
- Article 280 addresses surge arresters while NEC Article 285
addresses transient voltage surge suppressors (TVSSs). These are not
the same, though they both provide surge protection.
- Surge arresters apply to (in most cases) just the supply side
(line side) of the meter (280.22). TVSS devices apply to just the
load side (285.21). Some devices are listed for use in either
location, but typically surge protection devices are designed for
use in only one or the other.
- Surge protection devices (SPDs) reduce potentially damaging
short-duration spikes on data networks, cable lines, phone lines,
and other power or control lines connected to electrical equipment.
They are not a substitute for lightning protection--they address
voltage levels that lightning protection does not, and therefore are
complementary to it.
- The general hierarchy is this: lightning protection (service),
TVSS (service and feeders), surge arrester (feeder and branch
circuits), point of use surge protection (provided by plug-in
devices, UPS systems, line conditioners, and so on).
- When you use a surge arrestor, you must connect it to each
ungrounded conductor. The logic here is pretty obvious.
- Requirements differ between circuits of less than 1,000V and those
of 1,000V or over.
- You can put surge arrestors indoors or outdoors [280.11]. It simply is not
true that the NEC prohibits locating them outdoors.
- Surge arrestor wiring has a minimum size. Do not apply the
ampacity tables or make your wiring match that of the rest of the
system if doing so causes you to be below the minimums.
- Connecting your surge arrestor to a ground rod driven into the
dirt is not sufficient. The electricity is always trying to get back
to the source--that's why electricity works. You must use one of the
four types of "ground sources" specified in Article 280.
If you don't understand what these are--and most people do
not--refer to Article 250.
- A surge arrester is essentially useless without good grounding and
Check out this grounding