Surge Arrestor 20kA, 2-4 Pole, 275V/385V | Onesto SPD

The Onesto BY7-20T Surge Protection Device is a Class II (Type 2) surge arrestor rated at 20kA, designed to protect electrical installations, distribution boards and connected equipment from transient overvoltage caused by lightning strikes and switching surges. It is suitable for domestic, commercial and light industrial TN and TT power supply networks, and offers a visual pass/fail status indicator so installers and maintenance teams can check protection status at a glance. Available in 2, 3 and 4 pole configurations for 275V or 385V systems, it is a practical mid-range choice for boards needing more protection than a standard 10kA unit.

• Application: Suitable for domestic, commercial and light industrial distribution board surge protection on TN/TT networks
• Key specification: 20kA maximum discharge current (Imax), Class II / Type 2 SPD
• Configuration: Available in 2, 3 and 4 pole versions
• Voltage: 275V or 385V operating voltage options
• Status indicator: Green/red indication window shows functional or failed status
• Mounting: 35mm DIN rail, IP20 enclosure

Key Features

• 20kA maximum discharge current (8/20µs) suited to properties with a higher exposure to surge events
• Visual green (functional) / red (failed) indication window means the device can be checked without removing it from the DIN rail
• PA66 UL94-V0 flame-retardant housing suited to enclosure and distribution board installation
• Compact DIN rail mounting saves space in distribution boards
• Suitable for TN and TT earthing systems
• 2, 3 and 4 pole configurations to match single-phase or three-phase boards

Typical Applications

• Domestic and small commercial distribution board protection
• Farm and rural property protection where lightning exposure is higher
• Isolator and pump control panel protection
• Protection of sensitive electronic equipment against transient overvoltage
• Upgrading boards from a 10kA to a 20kA SPD

Technical Specifications

What's Included

• 1 x Onesto BY7-20T Surge Protection Device (voltage and pole configuration as selected)

Please note: DIN rail, distribution board wiring, circuit breakers and installation accessories are not included unless specifically listed above.

Installation & Compatibility Notes

• Confirm your board's earthing system (TN or TT) and system voltage (275V or 385V) before ordering.
• Select the pole configuration (2P, 3P or 4P) that matches your distribution board and phase configuration.
• Installation should be carried out by a suitably qualified electrician in line with local wiring regulations.
• Check the status indicator periodically — a red window means the SPD has operated and must be replaced.

Warranty & Support

This product is supplied with the applicable manufacturer or supplier warranty, subject to correct installation, correct application, and warranty terms.

Zisabo supplies quality plumbing, pump, filtration and electrical products with practical support to help customers choose the correct item for their application. If you are unsure whether this product is suitable, contact us before ordering and our team will assist where possible.

Need help choosing? If you are unsure whether this product is suitable for your board, contact Zisabo with your system voltage, earthing type and pole configuration, and we will assist where possible.