Requirements for use of Surge Protective Devices (SPDs) in Industrial Control Panels
Surge Protective Devices (SPDs) are commonly used in industrial control panels. The table below is an itemization of SPD
types and how they can be used in panels where no Procedure description is required. The requirements for the Voltage and
Nominal Discharge Current (NDC) ratings of the SPD are indicated in the table below. SPDs that are used outside the
guidelines of this table require Procedure description. Depending on the evaluation of the SPD, these guidelines can be
exceeded if an engineering evaluation is conducted.
Type of SPD – One Port+
Usage of Panel /
Location of SPD
in circuit
Listed - Type 1
Listed - Type 2
Listed - Type 32
R/C* - Type 1
Component
Assembly
R/C* - Type 2
Component
Assembly
R/C* - Type 3
Component
Assembly2
R/C* - Type 4
for use in Type 1
Applications2
R/C* - Type 4
for use in Type 2
Applications2
R/C* - Type 4
for use in Type 3
Applications2
Service Equip1 /
Supply Side of
Overcurrent
Protection
OK
Further evaluation
and procedure
description is
required
Further evaluation
and procedure
description is
required
Further evaluation
and procedure
description is
required
Further evaluation
and procedure
description is
required
Further evaluation
and procedure
description is
required
Service Equip1 /
Load Side of
Overcurrent
Protection
OK
OK
OK
OK
NDC:
Current > 10kA
Further evaluation
and procedure
description is
required
NDC:
Current > 10kA
NDC:
Current > 10kA
Further evaluation
and procedure
description is
required
Non-Service
Equip /
Feeder or Branch
Circuits
OK
OK
OK
OK
OK
NDC:
Current > 3kA
NDC:
Current > 3kA
OK
OK
NDC:
Current > 3kA
NDC:
Current > 3kA
All Panels /
OK
OK
OK
Control Circuits
R/C* - Type 4
Component
Assembly2
R/C* - Type 52
R/C* - Type 4
for use in
"Other"
Applications
Further evaluation
and procedure
description is
required
Further evaluation
and procedure
description is
required
+
The table applies to "One-Port" SPDs, which are most common. Where a "Two-Port" SPD is used, it shall be a
permitted type in the table above, based on the panel usage, and be used within its marked ratings, including the
Short Circuit Current Rating (SCCR). When two-port Type 3 SPDs are not marked with an SCCR, it is assumed to
be 1000A. If the Two-Port device is Recognized with a Note 4 in the Listing Information Page (indicating that
external overcurrent protection is required), this SPD needs to be procedure described.
*
R/C denotes Recognized Component
1
Includes panels marked "Suitable for Use as Service Equipment"
2
The voltage rating of the SPD shall be at least that of the circuit’s full phase (L-L) voltage for all modes (i.e. L-N, L-L,
L-G). For example, panels rated 277/480V shall use SPD rated 480V in all modes; panels rated 120 or 120/240
shall use SPD rated 240V in all modes.
SPD Terminology:
One Port - SPD is across-the-line.
Two Port - SPD is across-the-line, plus additional circuitry in series with a load. Current flow through this device shall not
exceed its marked current rating.
Notes – Clarification of requirements:


Where rated Voltage is specified, MCOV (Maximum Continuous Operating Voltage) values may be used.
Nominal Discharge Current (NDC): May also be referred to as I N. The typical ratings are 3kA, 5kA, 10kA, or 20kA.
Definitions - from UL1449 (informative)
Type Ratings (applicable to certifications before April 2010):
Type 1 - Permanently connected SPDs intended for installation between the secondary of the service transformer and the
line side of the service equipment overcurrent device, as well as the load side, including watt-hour meter socket enclosures
and intended to be installed without an external overcurrent protective device.
These devices are Listed.
Type 2 - Permanently connected SPDs intended for installation on the load side of the service equipment overcurrent device;
including SPDs located at the branch panel.
These devices are Listed.
Type 3 - Point of utilization SPDs, installed at a minimum conductor length of 10 meters (30 feet) from the electrical service
panel to the point of utilization, for example cord connected, direct plug-in, receptacle type and SPDs installed at the
utilization equipment being protected. See marking in 64.2. The distance (10 meters) is exclusive of conductors provided with
or used to attach SPDs.
These devices are Listed.
Type 4 Component SPDs, including discrete components as well as component assemblies.
These devices are Recognized as “Type 4 for use in xxx applications” where xxx may be 1, 2, 3, or “other” .
Type ratings (applicable to certifications after April 2010):
Type 1 - Permanently connected SPDs intended for installation between the secondary of the service transformer and the
line side of the service equipment overcurrent device, as well as the load side, including watt-hour meter socket enclosures
and intended to be installed without an external overcurrent protective device.
These devices are Listed.
Type 2 - Permanently connected SPDs intended for installation on the load side of the service equipment overcurrent device;
including SPDs located at the branch panel.
These devices are Listed.
Type 3 - Point of utilization SPDs, installed at a minimum conductor length of 10 meters (30 feet) from the electrical service
panel to the point of utilization, for example cord connected, direct plug-in, receptacle type and SPDs installed at the
utilization equipment being protected.
These devices are Listed.
Type 1, 2, 3 Component Assemblies - Consists of a Type 4 component assembly with internal or external short circuit
protection.
These are assemblies that are similar to UL508’s “Open Type Devices.” They may be DIN rail mounted for panel installation.
Type 1 and 2 component assemblies have undergone short circuit testing.
Type 4 Component Assemblies - Component assembly consisting of one or more Type 5 components together with a
disconnect (integral or external) or a means of complying with the limited current tests in UL1449 section 44.4 (4th edition).
These devices are Recognized, typically discrete having some sort of thermal protection. They may or may not have
undergone short circuit testing.
Type 5 - Discrete component surge suppressors, such as MOVs that may be mounted on a PWB, connected by its leads or
provided within an enclosure with mounting means and wiring terminations.
These devices are Recognized, typically discrete having no thermal protection.
Rev: 1/2015