Eaton NEC Article 240 User manual

Application Paper AP158002EN Effective August 2015
Installing surge protective devices with
NEC Article 240 and Feeder Tap Rule
Introduction
This technical application note addresses the
installation requirements for a surge protective
device (SPD) when used with an overcurrent
protection device (OCPD). Applicable NFPAT
70 standards, National Electrical CodeTrules
(NECT), Authority Having Jurisdiction (AHJ), ANSI/
ULT1449 ratings, and installation practices are
discussed.
NEC Article 240.4 (overcurrent
protection) protection of
conductors
Article 240.4 states all conductors, other than
flexible cords, flexible cables, and fixture wires
shall be protected with an OCPD in accordance
with their ampacity rating specified in Article
301.15, unless otherwise permitted or required in
Article 240.4(A) through (G). This article applies to
conductors extending beyond the switchboard,
switchgear, or panelboard that are used to connect
an SPD to an electrical system. Connecting an
externally mounted or side mounted SPD directly
to a system bus without an OCPD is a direct
violation of the NEC and can lead to safety and
liability concerns. Acceptable OCPDs are listed
circuit breakers and fuses. There are exceptions to
this rule, see paragraph below titled SPDs
containing an internal OCPD and the Feeder
Tap Rule.
NEC Article 310.15 (conductors
for general wiring) ampacities
for conductors rated 0–2000 V
Article 310.15(B)(16) defines the rating of the
conductor ampacity that drives the maximum
rating of the OCPD to be used to protect the
electrical conductors. For example, #10 AWG
conductors 60 °C rated will require an
OCPD of 30 A.
ANSI/UL 1449 short circuit
current rating and
NEC Article 285.6
SPDs must comply with the ANSI/UL 1449
Standards for Safety Surge Protective Devices.
The SPDs short-circuit current rating (SCCR) is
determined as part of the ANSI/UL 1449 testing.
The SCCR defines the suitability of an SPD for use
on an AC power circuit that is capable of delivering
not more than a declared rms symmetrical current
during a short-circuit condition. This specification
defines the maximum level of available fault
current to which an SPD can be safely connected.
Article 285.6 requires that an SPD be marked with
its SCCR rating and the SPD shall not be installed
at a point on the system where the available fault
current capable of being delivered to the system
is greater than the SCCR of the SPD. For example,
an SPD marked with an SCCR of 50 kA shall not
be installed on a system capable of delivering
65 kA of fault current.
ANSI/UL 1449 testing with and
without an OCPD
When installing an externally mounted SPD,
the NEC requires that SPDs use an OCPD,
when Feeder Tap Rule is not utilized. Some
manufacturers may choose the use of an OCPD
to obtain their SCCR rating or successfully pass
the withstand test. For these devices that require
an OCPD, the installer must match the rating and
type of OCPD (breaker or fuses) that was used
during UL testing. For example, if a circuit breaker
was used during UL testing, the same circuit
breaker type (current limiting or non-current
limiting) and ampere rating must be installed in
the distribution equipment during the installation
of an externally mounted SPD. If fuses were used,
the fuse class and ampere rating must be the
same as used during UL testing. The OCPD
must be utilized in the installation to retain the
UL Listing.
Conversely, some manufacturers may not choose
the use of an OCPD to obtain their UL 1449
Listing. When installing these units, UL 1449
may not require the use of an OCPD but NEC
may require an OCPD. Some installers assume
and some manufacturers incorrectly promote that
such externally mounted units can be connected
directly to an electrical bus without overcurrent
protection. This practice is incorrect and is a direct
violation of the NEC. The conductors of these units
must be protected with an OCPD that is properly
rated according to NEC Article 310.15. The fact
that an SPD does not require a particular OCPD
to pass the UL 1449 testing does not negate the
need for one upon installation.

Eaton
1000 Eaton Boulevard
Cleveland, OH 44122
United States
Eaton.com
© 2015 Eaton
All Rights Reserved
Printed in USA
Publication No. AP158002EN / Z16961
August 2015
Eaton is a registered trademark.
All other trademarks are property
of their respective owners.
Installing surge protective devices with
NEC Article 240 and FeederTap Rule
Application Paper AP158002EN
Effective August 2015
SPDs containing an internal OCPD and the
Feeder Tap Rule
There are SPDs that contain an internally mounted OCPD such
as a circuit breaker or fuses. A common misconception is that
because of the internally wired OCPD, an externally mounted unit
can always be connected directly to the electrical bus without
additional overcurrent protection. Failure to protect the conductors
connecting the SPD to the system bus is a direct violation of the
NEC and could lead to safety and liability concerns.
There are certain conditions or exceptions that allow for the
installation of an externally mounted SPD without an OCPD within
the power distribution equipment at the point of connection. These
conditions are outlined in NEC Article 240.21(B)(1) known as the 10
ft Feeder Tap Rule.
In order to apply the Feeder Tap Rule to the installation of an SPD,
with an internal OCPD, all of the following conditions must be met:
1. The length of the tap conductors must not exceed 10 ft, e.g.,
the SPDs connecting leads cannot be greater than 10 ft. Rules
also exist for taps that exceed 10 ft, but discussing them would
be impractical for an SPD installation application. When installing
an SPD, the goal for the best performance is to keep the
connecting leads as short as possible (much less than 10 ft
whenever practical) and avoid sharp bends.
2. The ampacity of the tap conductors must not be less than the
rating of the OCPD at the termination of the tap conductors,
e.g., the ampacity of the SPDs connecting leads cannot be less
than the rating of its internal OCPD. At a minimum, #10 AWG
conductors would have to be used to connect an SPD
containing an internal 30 A OCPD. Using #12 AWG conductors
(ampacity = 20 A) would be a code violation and could not be
used to connect an SPD containing an internal 30 A OCPD.
However, a code exception permits tap conductors for specific
listed devices, such as SPDs to be sized in accordance with the
manufacturer’s instructions.
Exception to #2: “Where a Listed SPD is provided with
specific instructions on minimum conductor sizing, the
ampacity of the tap conductors supplying that SPD shall be
permitted to be determined based on the
manufacturer’s instructions”.
3. For field installations, if the tap conductors exit the enclosure
where the tap is made, the rating of the OCPD on the line side
of the tap conductors must not exceed 10 times the ampacity of
those tap conductors. For example, the upstream OCPD in the
panelboard, switchboard, etc. where the SPD was tapped from
cannot be rated at more than 10 times the ampacity of the SPD’s
conductors. Therefore, if the switchboard main bus is rated at
1200 A, the cable to the SPD conductor must be rated to carry at
least 120 A. For most installations this would mean a #1/0 AWG
conductor.
Summary
When installing SPDs, NEC and UL requirements must be followed.
The proper OCPD must be used in order to meet the NEC
requirements and maintain the ANSI/UL 1449 listing of the SPD.
If an external OCPD was not used during UL testing, the size and
type will not be listed on the manufacturer’s product label. Under
this condition, it is the responsibility of the installer to ensure that
the conductors of the SPD are protected with a suitable OCPD per
the NEC and the local AHJ.
If the SPD was submitted for ANSI/UL 1449 testing with an external
OCPD, the size and type required for installation will be listed in the
manufacturer’s product installation manual and must be installed
accordingly.
SPDs containing an internal OCPD can be connected directly to the
electrical bus only if the installation meets all of the requirements
defined in the NEC Article 240.12(B)(1), the Feeder Tap Rule, or by
strictly following the manufacturer’s installations instructions and
OCPD recommendations.