Why Are RCDs Rated at 30mA for Additional Protection?

If you’ve ever looked inside your consumer unit or read an electrical certificate, you’ll have noticed that Residual Current Devices (RCDs) are typically rated at 30mA when used for additional protection. But why exactly 30 milliamps, and what does this figure mean for electrical safety?

What Does an RCD Do?

An RCD is designed to protect people from electric shock by monitoring the balance of current flowing in and out of a circuit. If even a small leakage of current is detected – for example, through a person who has accidentally touched a live part – the RCD disconnects the supply in milliseconds.

This is different from an MCB or fuse, which protect against overcurrent or short circuits. RCDs are specifically about life safety.

Why 30mA?

The 30mA figure isn’t random – it comes from medical research into how electric current affects the human body: • 1–10 mA: Tingling sensation, generally not dangerous. • 10–30 mA: Muscular contraction, difficulty letting go of live conductors. • Above 30 mA: Risk of ventricular fibrillation (a potentially fatal disturbance of the heart).

The International Electrotechnical Commission (IEC) and UK regulations (BS 7671:2024) define 30mA as the maximum current that can pass through a person without a high risk of fatal injury, provided it is cut off quickly.

That’s why RCDs disconnect the circuit if leakage exceeds 30mA – typically within 40 milliseconds – giving essential life protection.

Different Ratings for Different Purposes • 30mA RCDs – Used for additional protection of sockets, outdoor equipment, bathrooms, lighting circuits, and areas accessible to ordinary persons. • 100mA or 300mA RCDs – Often used for fire protection or equipment protection in commercial/industrial settings. • 10mA RCDs – Found in specialist locations like medical areas where extra-sensitive protection is needed.

Where You’ll Find 30mA RCDs in the Home • Socket circuits (especially those that may be used outdoors) • Bathroom circuits • Lighting circuits in modern homes • EV charging points • Within RCBOs (devices combining RCD + MCB protection) used in many new consumer units

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✅ In summary: RCDs are rated at 30mA for additional protection because this strikes the balance between electrical safety and practicality. It’s sensitive enough to protect against fatal shocks, but not so sensitive that it causes nuisance tripping from minor natural leakages.

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How Switch Electrical & Mechanical Services Ltd Can Help

At Switch Electrical & Mechanical Services Ltd, we provide: • RCD and RCBO upgrades • Consumer unit replacements • Full and partial rewires • EICRs (Electrical Installation Condition Reports) • Ongoing safety and maintenance checks

We are NICEIC Approved Contractors, and all work is carried out to the latest wiring regulations (BS 7671:2024).

📞 Call us: 0191 9052723 💬 WhatsApp us: 07388 439427 📧 Email us: switchtoday@mail.com 🌐 Visit us: switchelectrical.uk

Frequently Asked Questions (North East UK)

What are my legal electrical responsibilities as a Landlord in Newcastle? As a landlord in the North East, you are legally required to ensure that all electrical installations in your rental property are safe when tenants move in and are maintained in a safe condition throughout the duration of the tenancy. This includes obtaining a satisfactory Electrical Installation Condition Report (EICR) every 5 years or at the start of a new tenancy. Switch Electrical & Mechanical Services provides comprehensive EICR audits for landlords across Newcastle, Sunderland, and Gateshead.

How much does an EICR cost for a standard property in the North East? The cost of an EICR depends on the size of the property and the number of circuits. Switch Electrical & Mechanical Services provides highly competitive, transparent pricing for landlords in the North East. We also offer discounted rates for landlords with multiple properties or HMOs requiring block certification.

What happens if my rental property fails an EICR? If an EICR identifies 'C1' (Danger Present) or 'C2' (Potentially Dangerous) codes, the installation is deemed 'Unsatisfactory'. Landlords have exactly 28 days to complete the necessary remedial work. Our team at Switch Electrical & Mechanical Services can provide immediate, fixed-price quotes for all remedial work following an inspection to ensure you remain legally compliant.