100 mA Time-Delay RCDs for Selective & Fire Protection
100 mA time-delay RCDs—often referred to as S-type RCDs—are designed for selective tripping and enhanced fire protection on distribution circuits. They are typically used upstream of 30 mA devices to ensure proper discrimination, preventing unnecessary power loss across an entire installation when only a downstream circuit has a fault.
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These RCDs incorporate a built-in delay, allowing downstream RCBOs or RCDs time to trip first. This makes them essential for multi-board setups, sub-mains, outbuildings, workshops and any installation where avoiding nuisance disconnection is critical.
- 100 mA sensitivity for fire protection and discrimination
- Time-delay operation to ensure correct tripping sequence
- S-type performance for stable fault handling
- Ideal for sub-mains feeding garage boards or secondary consumer units
- Supports downstream 30 mA protection without unwanted disconnection
100 mA time-delay RCDs are widely used in commercial and domestic environments where fire protection and selectivity are required by design. Each model clearly specifies rating, pole configuration and delay characteristics.
A Type Time Delay RCD – 80A 100mA, 4 Pole (WARTD480-100)
£38.75
The WARTD480-100 A-Type 100mA Time Delay RCD is a 4 Pole S-Type device rated at 80A, designed for selective upstream protection. Its built-in delay ensures only downstream RCDs disconnect under fault, maintaining continuity on unaffected circuits. Commonly used in three-phase distribution systems, EV charging installations,...
A Type Time Delay RCD – 80A 100mA, 2 Pole (WARTD280-100)
£30.25
The WARTD280-100 A-Type 100mA Time Delay RCD is a 2 Pole S-Type device rated at 80A. Designed for upstream use in selective coordination systems, its built-in time delay ensures only the RCD closest to the fault disconnects, avoiding unnecessary shutdowns of healthy circuits. Ideal for...
A Type Time Delay RCD – 63A 100mA, 4 Pole (WARTD463-100)
£30.25
The WARTD463-100 A-Type 100mA Time Delay RCD is a 4 Pole S-Type device rated at 63A. Its built-in time delay ensures upstream discrimination, allowing downstream RCDs to trip first and preventing unnecessary power loss. Ideal for three-phase distribution boards, EV charging hubs, and renewable installs...
A Type Time Delay RCD – 63A 100mA, 2 Pole (WARTD263-100)
£25.35
The WARTD263-100 A-Type 100mA Time Delay RCD is a 2 Pole S-Type device designed for upstream fault protection in dual-RCD or selective coordination setups. With its built-in delay, it ensures that downstream devices trip first, maintaining supply integrity across unaffected circuits. Ideal for EV charging...
A Type Time Delay RCD – 100A 100mA, 4 Pole (WARTD4100-100)
£38.85
The WARTD4100-100 A-Type 100mA Time Delay RCD is a 4 Pole S-Type device rated at 100A for large-scale three-phase boards. Designed for upstream use, its time delay ensures proper discrimination, allowing downstream RCDs to trip first and keeping supply integrity across unaffected circuits. It’s a...
What Is a 100 mA Time-Delay RCD?
A 100 mA time-delay RCD is a residual current device designed to provide upstream protection with a deliberate delay before tripping. This delay ensures downstream 30 mA devices have priority, maintaining selectivity and preventing full installation shutdowns.
When Time-Delay RCDs Are Used
- Sub-main feeds supplying garages, garden offices or outbuildings
- Commercial installations where discrimination is necessary
- Fire protection circuits requiring 100 mA sensitivity
- Feeds to secondary consumer units in larger properties
- Any upstream circuit supporting multiple downstream RCD/RCBO devices
Why Use a Time-Delay (S-Type) RCD?
Without an S-type delay, both upstream and downstream devices may trip during a fault, leaving properties without power unnecessarily. A time-delay RCD guarantees only the correct device trips, keeping the rest of the installation live.
- Proper discrimination between upstream and downstream devices
- Reduced nuisance tripping during localised faults
- Enhanced fire protection on higher-level circuits
Compliance & Standards
All 100 mA time-delay RCDs meet the requirements of BS 7671 (18th Edition) and follow the performance characteristics of IEC/EN 61008 or IEC/EN 61009. They are suitable for domestic and commercial installations requiring selective RCD protection.
Choosing the Correct Rating
These RCDs are available in a range of current ratings, typically 40A, 63A, 80A and 100A. The correct choice depends on the supply size, distribution design and maximum demand of the downstream circuits.
Installer Benefits
100 mA time-delay RCDs ensure stable and predictable operation across multi-board installations. They maintain uptime, simplify fault-finding and provide reliable fire protection without risking full circuit shutdowns during minor downstream issues.