IMSU Permanent Overvoltage Protection Coil UNE-EN 50550

The Schneider Electric Acti9 iMSU A9A26500 permanent overvoltage protection coil is an electrical auxiliary device designed to monitor the voltage between phase and neutral and trigger the opening of the associated protection device when it detects a permanent overvoltage. It operates at 230 V AC and 50/60 Hz and is especially suitable for protecting equipment and installations against dangerous situations caused, among other reasons, by the breakage or loss of the neutral conductor.

The iMSU is combined with compatible Acti9 modular devices and acts on them when the phase-to-neutral voltage exceeds the set limits. Its tripping curve complies with UNE-EN 50550, providing a progressive response: the higher the detected overvoltage, the shorter the time required to trigger disconnection.

Protection against permanent overvoltages

Reference A9A26500 is specifically designed to protect installations against permanent overvoltages, that is, voltage rises that remain for a sufficiently long period to damage electrical and electronic equipment.

One of the situations that can generate this type of anomaly is the loss of the neutral conductor in an installation. The coil continuously monitors the voltage between phase and neutral and, if an overvoltage condition is reached, it acts on the associated circuit breaker to disconnect the supply.

The A9A26500 does not replace a transient surge protector. To protect against very short-duration impulses caused, for example, by lightning strikes or electrical switching operations, the appropriate transient surge protection device must also be used.

Tripping curve in accordance with UNE-EN 50550

The iMSU does not operate with a single instantaneous threshold, but rather through a voltage-time curve. In this way, the higher the voltage detected between phase and neutral, the faster the operation occurs.

• 255 V AC: no trip.
• 275 V AC: trip between 3 and 15 seconds.
• 300 V AC: trip between 1 and 5 seconds.
• 350 V AC: trip between 0.25 and 0.75 seconds.
• 400 V AC: trip between 0.07 and 0.20 seconds.

This progressive response helps avoid unnecessary tripping due to small, short-lived voltage variations and, at the same time, speeds up disconnection when the overvoltage reaches high values.

Operation associated with Acti9 devices

The iMSU maximum voltage coil is designed to work with compatible Schneider Electric Acti9 protection and switching devices. When it detects a permanent overvoltage, it causes the mechanical opening of the device to which it is coupled, interrupting the circuit supply.

Schneider Electric indicates compatibility, depending on the corresponding configuration, with families such as:

• Acti9 iC60.
• Acti9 iID.
• Acti9 iDPN Vigi.
• Acti9 iSW-NA.
• Acti9 iC40.
• Acti9 iCV40.
• Compatible RCA and ARA.
• Certain compatible Acti9 RCBO versions.

Exact compatibility must always be verified according to the main device, its number of poles, and the electrical panel configuration.

Mandatory connection between phase and neutral

Schneider Electric specifies that the iMSU coil must be installed between phase and neutral. It must not be connected between two phases, as in that configuration it would not be able to correctly detect an overvoltage caused by a neutral loss.

In the event of neutral failure, phase-to-neutral voltages can vary considerably and reach dangerous values for connected loads. The function of the iMSU is precisely to detect this anomaly and order the disconnection of the associated switch.

Use in single-phase and three-phase networks

In a single-phase installation, one iMSU coil is used connected between phase and neutral. For a three-phase network with neutral, Schneider Electric indicates using three iMSU coils, one to monitor each phase with respect to neutral.

This configuration makes it possible to individually monitor the voltage of each phase and trigger the opening of the associated protection if a permanent overvoltage is detected.

Mechanical trip indicator

The Schneider Electric A9A26500 includes a red mechanical indicator on the front that allows visual identification of the auxiliary operation and the tripping of the associated device.

This signaling makes diagnosis and maintenance tasks easier, especially in electrical panels that incorporate several protection devices.

Compact 18 mm modular format

The iMSU coil has a compact format for installation in modular panels. It occupies 2 modules of 9 mm, equivalent to 18 mm in width, allowing permanent overvoltage protection to be added without requiring much additional space.

• Height: 82.5 mm.
• Width: 18 mm.
• Depth: 68 mm.
• Modular width: 2 modules of 9 mm.
• Color: white.

DIN rail mounting

The device uses a clip-on DIN rail mounting system, making installation alongside the compatible switch inside the electrical panel easier.

Its format belongs to Schneider Electric's Acti9 modular ecosystem, allowing compact protection and switching assemblies to be formed with other elements in the same range.

Electrical connection

The A9A26500 includes connection terminals prepared for rigid and flexible conductors:

• Flexible conductor: 0.5 to 4 mm².
• Rigid conductor: 1 to 6 mm².
• Strip length: 10 mm.
• Tightening torque: 1 Nm.

The auxiliary supply is 230 V AC at 50/60 Hz.

Wide operating temperature range

The iMSU auxiliary is designed to operate over a wide temperature range, allowing installation in electrical panels exposed to different environmental conditions.

• Operating ambient temperature: -35 to 70 °C.
• Storage temperature: -40 to 85 °C.
• Relative humidity: up to 95% at 55 °C.

Schneider Electric A9A26500 technical features

• Brand: Schneider Electric.
• Range: Acti9.
• Reference: A9A26500.
• Device name: iMSU.
• Type: protection coil / permanent overvoltage trip coil.
• Application: protection against permanent overvoltages.
• Monitoring: voltage between phase and neutral.
• Protection especially associated with: loss or breakage of the neutral conductor.
• Control voltage: 230 V AC.
• Frequency: 50/60 Hz.
• Curve at 255 V AC: no trip.
• Operating time at 275 V AC: 3-15 s.
• Operating time at 300 V AC: 1-5 s.
• Operating time at 350 V AC: 0.25-0.75 s.
• Operating time at 400 V AC: 0.07-0.20 s.
• Indicator: mechanical front operation indicator.
• Mounting: clip-on DIN rail mounting.
• Modular width: 2 modules of 9 mm.
• Dimensions: 82.5 x 18 x 68 mm.
• Flexible conductor: 0.5-4 mm².
• Rigid conductor: 1-6 mm².
• Strip length: 10 mm.
• Tightening torque: 1 Nm.
• Operating temperature: -35 to 70 °C.
• Storage temperature: -40 to 85 °C.
• Standards: UNE-EN 50550 and EN/IEC 60947-5-1.
• Marking: CE.

The Schneider Electric Acti9 iMSU A9A26500 makes it possible to add permanent overvoltage protection to installations equipped with compatible Acti9 devices. Its phase-to-neutral monitoring, tripping curve in accordance with UNE-EN 50550, mechanical indicator, and compact 18 mm modular format provide a compact solution to reduce the risk of damage to electrical equipment due to prolonged voltage rises, especially those caused by a loss of the neutral conductor.