Surge Protection for Switchgears (UL1558)

UL1558 Switchgears


Today's increased reliance on very sensitive electronics makes surge protection an important topic for Switchgears listed to UL1558. The Insurance Institute for Business & Home Safety study found that $26 billion dollars was lost due to non-lightning power surges. In addition, there are about 25 million lightning strikes in the US each year that cause between $650M to $1B in losses according to the Insurance Information Institute, State Farm©.

Selecting SPD for UL1558 Switchgears

NEC/NFPA 70 require that Surge Protective Devices (SPDs) shall be UL1449 Listed. This means selecting a surge protector is easier than it has ever been. There are only a few choices available for SPDs that are UL Listed for any of the most commonly used surge standards including UL1449 5th Edition, UL497B, and UL497E. Being a key component of most of the power distribution network throughout an entire facility, the surge protection will provide 2 critical functions: protection of the switchgear itself and first layer of protection for that actual equipment and branch panels feeding from that gear.

Recommended SPD for Switchgears

LocationEquipmentSystemSurge Protector Model#Link
Service Entrance switchgears480Vac MDS600E-480D MDS750E-480D

Secondary switchgears480Vac MS200-480D MS200-120Y

Branch Circuit switchgears277/480Vac MP100-277Y

Local Equipment switchgears120/208Vac M50-120Y-A M50-A

Determining the acceptability of an SPD
for UL 1558 Switchgears and All Other UL Listed Equipment

The UL inspector will first consider the SPD type when determining it’s acceptability for a given application or piece of equipment. This will include UL1558 as well as all other UL Listed equipment. The first level compliance is based on the UL Approval (LISTED or RECOGNIZED) of the SPD or UL SPD Type and it’s Suitable Ratings. This means that it has to meet all safety, performance, environmental and electrical system ratings of the application. If any of these criteria are not fully met, it will require a Procedure Description, a File Update and/or Additional Testing. These actions will require additional costs that may be substantial. For this reason, it is in the interest of the specifier to use UL LISTED SPD’s to eliminate any uncertainty or to make sure the UL RECOGNIZED SPD is selected at the time of UL submittal of the equipment.

Approval Considerations Table based on UL SPD Type

SPD Type
Update or

YesNoNoThe only requirement is that the SPD must match electrical and environmental ratings of the UL 67 Control Panel.

A UL field inspection of the control panel with the SPD installed is required as a part of a standard follow-up service visit.



YesYesYesYes – All UL recognized SPD’s require a UL engineering evaluation of the SPD’s existing UL1449 E–file.

This will result, at a minimum, in a cost to update the UL file and may also require testing that would result in additional costs.

Contact us to develop a surge mitigation solution for your application

Where to purchase Citel SPD's