Surge Protection for Power Supply



Today’s increased reliance on very sensitive electronics makes surge protection an important topic for most industries. 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©.

Power supplies are a key component of any UL 508A control panel (also known as an Industrial Control Panel or ICP). However, they are usually overlooked due to their limited cost in the overall system. The power supply is usually the main source of power for control circuits and Programmable Logic Controllers (PLC). Its failure causes complete equipment shutdown.

The evolution from transformer-based power supply to Switch Mode Power Supply (SMPS) increases the vulnerability of this device to electrical transients. As more solid-state components keep being added, now to remotely program and control the power supplies through RS232 or Ethernet, surge protection has become critical part for any electrical system.

This section will identify the UL 1449 5th Edition Surge Protective Device (SPD) to efficiently protection your equipment and increase its reliability.


Power Supply AC Input | Power Supply DC Output | Power Supply Communication I/O

Power Supply AC Input

The main AC incoming will be the primary location to protect the power supply against electrical surges. There can be a multitude of AC input voltages of power supplies ranging from 120Vac Single Phase up to 600Vac 3Phase. However, most of the power supplies will fall under 2 categories (2W+G and 3W+G). Based on the built-in withstand of the equipment, most of the power supplies can be protected using SPDs shown below :
LocationSystemSurge Protector Model #Link
AC Incoming Power120 to 240Vac (2W+G)DS72US-240T/NN DS72US-240TNN
AC Incoming Power277 to 480Vac (2W+G)DS42S-480 DS42S-400
AC Incoming Power120 to 240Vac (3W+G)DS73US-277Y/NN DS73US-277YNN
AC Incoming Power277up to 480Vac (3W+G)DS74US-480D DS74US-480D

Power Supply DC Output

The DC side of the power supply, especially when self-contained inside the UL 508A control cabinet, is one of the most overlooked parts in the system, leaving this part of the system vulnerable. The most common DC voltages would usually fall under two main voltages for unipolar and bi-polar power supplies, 24Vdc and 48Vdc.
LocationSystemSurge Protector Model #Link
DC Output Power24Vdc (2W+G)DS220S-24DC DS220S-24DC
DC Output Power48Vdc (2W+G)DS230S-48DC

Power Supply Communication I/O

Power supplies have evolved and will become more sophisticated than they are now, the latest generations allow an end-user to remotely access the power supply. Besides getting expected Internet Of Things (IoT) power data (wattage, input/output voltage, input/output voltage current), the remote access also provides full control and programming of the actual power delivered to the equipment. This new technological achievement comes at an extra cost. The external communication circuit of the power supply presents new vulnerabilities to electrical surges. The main protocols presently used is RS232, through multiple interfaces : twisted-pair wire and serial connector.
LocationSystemSurge Protector Model #Link
Communication circuitRS232 (1-pair wire)DLA-12D3 DLA-24D3
Communication circuitRS232 (9-pin Serial DD connector)DD9-24V DD9-24
Communication circuitRS232 (Ethernet / RJ45)MJ8-CAT6A MJ8-C6A v.2

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Where to purchase Citel SPD's