Use of Surge Protective Devices (SPDs) in Panels
Surge protective devices (SPDs) are commonly used in industrial control panels. SPDs are covered in product categories VZCA/2. They have replaced transient voltage surge suppressors and surge arresters previously covered under product categories XUHT2 and OWHX respectively. The table below is an itemization of (VZCA/2) SPD types and how they can be used in panels where no Procedure description is required. The Voltage and Nominal Discharge Current (NDC) ratings as noted below need to be verified. SPDs that are used outside the guidelines of this table require Procedure description.
| Type of SPD - One Port Only + | ||||||
|---|---|---|---|---|---|---|
| Location of SPD See also NEC Article 285 | Listed - Type 1 R/C* - Type 1 Component Assemby R/C* - Type 4 for use in Type 1 Applications | Listed - Type 2 | Listed - Type 3 R/C* - Type 3 Component Assembly R/C* - Type 4 for use in Type 3 Applications | R/C* - Type 4 Component Assembly | R/C* - Type 5 | R/C* - Type 4 for use in "Other" Applications |
Service Equipment ICP** Supply Side of Overcurrent Protection | V | ++ | ++ | ++ | ++ | ++ |
Service Equip ICP** Load Side of Overcurrent Protection | V | V, | ++ | NDC > 10kA | NDC > 10kA | ++ |
Non-Service Equipment - | V | V | V | V, | V, | ++ |
Control Circuits | V | V | V | V, | V,NDC > 3kA | ++ |
* R/C denotes Recognized Component
** Including panels marked, "Suitable for Use as Service Equipment"
+ A Two-Port SPD shall be Listed and comply with the ratings in the table. In addition, it shall have an appropriate short circuit current rating (SCCR) rating.
++ Further evaluation and procedure description is required for this application
Ratings:
V - Rated Voltage (can alternately use MCOV - Maximum Continuous Operating Voltage): Voltage or MCOV ratings shall be > the circuit L-L (full phase) voltage. For example, panels rated 277/480V shall use SPD rated 480V; panels rated 120 or 120/240 shall use SPD rated 240V.
NDC (IN) - Nominal Discharge Current: Typical ratings are 3kA, 5kA, 10kA, or 20kA. Ratings shall be as specified in the table.
SPD Terminology:
One Port - SPD across-the-line.
Two Port - SPD across-the-line, plus additional circuitry in series with a load. Current flow through this device shall not exceed its marked current rating.
Definitions - from UL1449 (informative)
Configurations:
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 39.4.
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.
