Arc Fault Detection Devices (AFDDs) and BS7671

AFDDs: Do You Really Need Them? A Straight-Talking Guide for Electricians 

Introduction 

AFDDs (Arc Fault Detection Devices) – are they the future of circuit protection or just another over-the-top regulation? If you’ve been keeping up with BS 7671, you’ll know the latest regs are pushing for AFDDs in certain installations. But what exactly do they do, and do you really need to start fitting them everywhere?

Let’s cut through the noise and break it down in a way that actually makes sense for us electricians—without the waffle you’d get from a manufacturer’s sales rep.

What Is an AFDD and What Does It Do? 

AFDDs are designed to detect dangerous arc faults in electrical circuits and disconnect the supply before things go up in flames. Unlike an MCB (which protects against overcurrent) or an RCD (which detects earth faults), an AFDD looks for unwanted arcing that could start a fire.

🔹 Common causes of arc faults: 

✔ Loose connections (like the ones you find in a dodgy DIY job)

✔ Damaged or deteriorated cables

✔ Rodents chewing through wiring (mice don’t respect BS 7671)

✔ Overloaded or faulty appliances

Think of it like this: RCDs stop shocks, MCBs stop overloads, and AFDDs stop fires. Like a good apprentice, they’re watching out for problems before they get worse.

What Does BS 7671 Say About AFDDs? 

The 18th Edition Amendment 2 (2022) made some big changes regarding AFDDs. Here’s what the regs actually say(in plain English):

📌 Regulation 421.1.7 – AFDDs must be installed on socket circuits in:

✔ HMOs (Houses of Multiple Occupation)

✔ Higher-risk residential buildings (HRRBs)

✔ Student accommodation

✔ Care homes

For other buildings (like normal houses), AFDDs are recommended but not strictly required. So if you’re on-site and the customer asks, “Do I need these?” The answer is probably, “Not unless you’re running a dodgy bedsit.”

📌 Where should they be installed? 

AFDDs should be fitted at the consumer unit, protecting socket circuits. However, the regs also say that a risk assessment can be used to decide if they’re necessary elsewhere. In other words, it’s down to your judgement—and how much the customer wants to spend.

Are AFDDs Worth It? 

Alright, so they help prevent fires, but they’re also expensive – sometimes adding £100+ per circuit. So the real question is: are they worth installing everywhere? 

✅ When I’d Definitely Fit AFDDs: 

 • Care homes, student lets, or HMOs – because BS 7671 says so 

 • Old or damaged wiring – where arc faults are more likely

 • High-risk environments – wooden buildings, thatched roofs, etc.

 • If the customer wants maximum safety – some clients like to future-proof

❌ When I’d Think Twice About AFDDs: 

 • A modern, well-installed domestic installation – not required by regs

 • Where the customer is price-sensitive – they’ll bump up the cost

To put it bluntly, you wouldn’t go fitting high-end security alarms on a garden shed, would you? Same principle.

How to Explain AFDDs to Customers 

If you’re recommending AFDDs, keep it simple. Most customers won’t care about BS 7671 – they just want to know if their home will be safe and how much it’s going to cost.

Here’s how I’d explain it:

🔹 Option 1: Standard Protection (MCBs + RCDs) – Good safety, meets regulations.

🔹 Option 2: Enhanced Protection (AFDDs) – Extra fire prevention, detects faults other devices miss, reduces risk of electrical fires.

If they ask whether they need it, just be honest: “For your type of property, it’s not required, but it does provide extra protection against fires.” 

And if they say, “Will it stop my dodgy toaster setting off the smoke alarm?” Well… maybe suggest a new toaster instead.

Final Thoughts: Should You Start Installing AFDDs? 

BS 7671 has made them mandatory in some cases, and they do offer extra protection. But they aren’t needed in every home – at least not yet.

Here’s my takeaway:

✔ Know where they’re required (student lets, HMOs, care homes, HRRBs).

✔ Use a risk-based approach for other properties – they’re good, but expensive.

✔ Educate customers so they can make an informed decision.

AFDDs might become the norm in future updates of BS 7671, so it’s worth getting familiar with them now. But for most standard domestic installs, a well-installed circuit with good terminations and proper protection is still the priority.

What’s Your Take on AFDDs? 

Are you fitting them everywhere, or only when necessary? Had any jobs where they actually caught a real fault? Let’s hear your experiences—drop a comment below!