Three phase surge suppressors or surge protection devices (SPD) protect equipment from transient overvoltages present on AC power lines. Surge suppressors may operate by absorbing the surge (the shunt type suppressor) or by blocking the surge from flowing (the series type suppressor) or by a combination of the two. The shunt type suppressor has a characteristic clamping voltage that is normally chosen to be around the maximum safe operating voltage of the circuit. The performance of a surge suppressor is measured by applying a known test surge (such as described by the domestic IEEE 587 standard or the international IEC 61643-1 standard) and measuring the maximum voltage that is let through to the device to be protected.

Mounting choices for surge suppressors, three phase include wall, panel or backboard mount, hard-wired or device mount, DIN rail or other rail mount, and PCB mount.  A wall panel or backboard mount is a stand-alone panel, where surge protection components are mounted within enclosure. Usually components are module based, along for easy maintenance. The main service panel consists of the wiring and circuit breaker box within a building from which utility outlet receptacle wiring originates. The main service panel in a building is fed from the outside power line. The main panel may feed one or more optional departmental sub-panels.  A hard-wired or device mount suppressor is physically mounted on or within the device to be protected from the surge.  Rail mount suppressors are meant to mount on a DIN rail. PCB mounted suppressors need to be mounted on a PCB (printed circuit board), to provide the device with surge suppression.

Precise identification of the electrical system is critical in the proper selection and application of a surge protection device. Phase refers to difference between two or more alternating current waveforms. There are 360 degrees in a complete cycle (as a generator completes one rotation). 3-phase systems produce three sets of sine waves that are 120 degrees apart or "out of phase" from each other (3 x 120 = 360). That is phase a-b, b-c, and a-c are 120 degrees apart from each other. However, when you use only two of the legs of a 3-phase system, it is single phase since there is no other phase that it is "out of phase" with. The term two-phase is a misnomer, although many electricians use it. There is only ONE sine wave hence it is single-phase. The voltage options listed are the most common electrical systems utilized. Where single values are given, this is the L-N value. Where multiple values are given (i.e. X/Y), the first listing is the L-N value, and the second listing is the L-L value.  Three phase configurations include 3-phase WYE, 3-phase delta, 3-phase international, 4-wire WYE: 120/280 VAC, 4-wire WYE: 220/380 VAC, 4-wire WYE: 227/480 VAC, 4-wire WYE: 347-600 VAC, 3-Wire Delta: 240 VAC, 3-Wire Delta: 380 VAC, 3-Wire Delta: 480 VAC, 3-Wire Delta: 600 VAC, 4-Wire Delta: 120/240 VAC, and International: 220/380 VAC.

UL specifications to consider when searching for surge suppressors, three phase include UL 1449 L-N rating, UL 1449 N-G rating, UL 1449 L-G rating, and UL 1449 L-L rating.  Important performance specifications to consider include maximum surge current and rated AC energy absorption.  The maximum surge current is the peak surge current a surge protective device can withstand.  Rated AC energy absorption is the measurement of a surge protective device's ability to absorb heat energy created by transient surges.

Common features for surge suppressors, single phase include self-diagnostics, visual indicators or LEDs, graphical display, thermal fusing, integral disconnect, audible alarm, sine wave tracking, surge counter, and NC/NO dry contacts.  Technology choices for surge suppressors, three phase include MOV (Metal Oxide Varistor), silicon avalanche diode, silicone thyristor diode, gas tube, and hybrid. An important environmental parameter to consider when specifying surge suppressors, three phase is the operating temperature.

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