When you install new electrical equipment in your home - whether it’s a modern shower, a new induction hob, solar equipment, or even an EV charger - you may be told that your RCD (Residual Current Device) needs upgrading.
Many homeowners understandably wonder, “Why? It’s been working fine for years.”
The truth is that today’s household appliances contain far more electronics than the ones we grew up with. That means they produce different types of electrical currents, and your existing RCD might not be designed to detect the faults those appliances can create.
This blog will explain, in simple terms, why an upgrade from a “Type AC” RCD to a “Type A” RCD is often essential, what the differences are, and how this keeps your home and family safe.
First Things First - What Does an RCD Actually Do?
Think of an RCD as a safety device that constantly monitors the flow of electricity in your home. Its job is to disconnect the power instantly if it detects electricity leaking somewhere it shouldn’t - for example, through a loose cable, damaged appliance, or even through a person.
A working RCD dramatically reduces the risk of electric shock and electrical fires.
But not all RCDs detect the same types of faults. That’s where the difference between “Type AC” and “Type A” becomes important.
What Is a “Type AC” RCD?
“Type AC” RCDs are the oldest and most basic type. They were designed decades ago when most electrical items had simple motors or heating elements.
They detect AC residual currents - the standard type of current that flows in your home.
However, modern appliances don’t always create simple AC currents. Many now use electronics that chop, smooth, or convert electricity using internal circuits. This can create pulsating DC residual currents.
And “Type AC” RCDs cannot reliably detect these faults.
What Is a “Type A” RCD?
A “Type A” RCD is designed to detect:
- AC residual currents, and
- Pulsating DC residual currents - the type created by many modern electronic devices.
This makes them compatible with today’s appliances, which often include circuitry that can mask a fault from a “Type AC” RCD.
In simple terms:
A “Type A” RCD sees danger that a “Type AC” RCD cannot.
So, Why Does Modern Equipment Require a “Type A” RCD?
As households upgrade to more sophisticated technology, many new appliances produce DC components in fault conditions. This can blind a “Type AC” RCD, meaning it may:
- Delay tripping
- Trip inconsistently
- Or not trip at all
This leaves you at risk of undetected faults, overheating cables, and electric shock.
Examples of equipment that can generate DC residual currents include:
- Electric vehicle chargers
- TVs, Game consoles, Computers, Laptops
- Modern showers
- LED lighting drivers
- Induction hobs
- Heat pumps
- Washing machines and dishwashers with electronic control boards
- Solar PV inverters
- Smart home devices, chargers, and power supplies
Because of this, BS 7671 - the UK wiring regulations - specifically states under Regulation 531.3.4 and 534.7.3 that the RCD must be suitable for the type of residual current produced.
This is why electricians must sometimes upgrade the RCD when installing new equipment. It’s not an upsell - it’s a safety requirement and a compliance issue.
What Happens If You Don’t Upgrade?
If the wrong type of RCD is installed, two problems can occur:
1. The RCD may fail to trip during a fault
If DC residual currents are present and you’re relying on a “Type AC” RCD, the device may not detect the fault. That means the circuit could remain live where there is a shock risk.
2. You have no protection even though you think you do
Your consumer unit might look compliant, but the RCD may not actually be capable of doing its job with the equipment you’re using.
In short, it’s like having a smoke alarm with no batteries - it’s there, but it won’t protect you when you need it.
Why You Might Not Have Needed a Type A RCD Before
Many older homes in Grimsby and surrounding areas still have “Type AC” RCDs because:
- The regulations were different at the time
- Older equipment didn’t generate DC components
- The property simply hasn’t been upgraded for a while
But as soon as you add equipment that needs a “Type A” RCD, the installation must be updated to match modern safety requirements.
How Does Your Electrician Decide What RCD You Need?
A qualified electrician will assess:
- The type of equipment being installed
- The manufacturer’s recommendations
- Whether the existing RCD can detect the necessary fault currents
- Compliance with BS 7671 (Regulations 531.3.4 and 534.7.3)
- The age and capacity of your consumer unit
If the installation demands a “Type A” RCD, upgrading is not optional - it’s essential for safety.
What Does an RCD Upgrade Involve?
Upgrading from a “Type AC” to a “Type A” RCD typically involves:
- Replacing the existing RCD in your consumer unit
- Checking circuit compatibility
- Testing disconnection times and safety functions
- Ensuring the entire system meets current regulations
- Issuing certification to show the installation is safe and compliant
The work is usually quick, tidy, and minimally disruptive.
Final Thoughts - Safety Moves With Technology
Our homes are changing. We now use appliances that didn’t exist 20 years ago, and electrical safety devices must evolve alongside them.
A Type A RCD offers better protection, is required by modern regulations for many installations, and ensures your home remains safe as technology advances.
If your electrician recommends upgrading your RCD during a new installation, they’re doing it to protect your family and keep your home compliant with the latest safety standards - not to inflate the job.
