Loop impedance testing is part of every electrician’s job. It keeps people safe and makes sure installs pass the Wiring Regs. But there’s one headache that keeps cropping up — RCD uplift.
If you’ve ever tested a circuit and got higher readings than expected, chances are uplift was the reason.
Here’s what RCD uplift is, why it matters, and how Megger’s True Loop® technology takes the problem off your hands — so you can just get on with the job.
What Is RCD Uplift?
RCD uplift happens when a loop test shows a higher reading than expected, just because there’s an RCD (Residual Current Device) or RCBO in the circuit.
During a non-trip loop test, the tester applies a small current to prevent tripping the RCD. But that current interacts with the RCD’s magnetic coil. Instead of behaving like a simple conductor, the coil adds its own resistance into the test.
The tester can’t tell the difference between the circuit impedance and the coil’s added impedance, so it lumps them together in the final number.
Example:
True circuit impedance = 0.7 Ω
RCD coil adds 0.5 Ω
Tester shows 1.2 Ω
On paper, that fails the 1.1 Ω limit in the Wiring Regs, even though the installation is actually fine.
And because not all RCDs behave the same way, uplift can appear on one job and not the next. That unpredictability is what makes it so frustrating.
Why Does RCD Uplift Matter?
Safety
Loop impedance (Zs) is used to calculate Prospective Fault Current (PFC). If Zs looks too high, PFC looks too low. That can make you think a breaker will trip in time, when really it might not.
Compliance
False high readings can push circuits beyond the Wiring Regs limit. You end up with a “fail” on a safe installation. Run the test again, and you might get a different number. That inconsistency makes sign-off tricky.
Time
Chasing false failures wastes hours. Electricians often go back through connections or retest the same circuits again and again, only to realise the uplift was to blame. That’s time you’ll never get back.
The Fix: Megger’s True Loop® Technology
Megger developed True Loop® technology to strip uplift out of the measurement. It’s built into testers like the MFT-X1.
Here’s how it works: the tester runs the non-trip loop test as normal, but it uses a smarter measuring technique that can identify the resistance coming from the RCD coil. That “extra” resistance is taken out of the result.
The number you see on screen is the true loop impedance of the circuit — nothing more, nothing less.
Confidence from the Confidence Meter®
The MFT-X1 also comes with the Confidence Meter®.
When noise or uplift is bouncing your reading around, the screen shows an arc. As the tester refines the measurement, that arc closes in until it becomes a single point.
That’s your cue — the reading is stable, accurate, and ready to trust.
What’s in It for You?
Accurate results – No more false fails caused by uplift.
Consistent readings – Reliable numbers across different circuits and devices.
Less wasted time – Stop retesting and fault-finding for no reason.
Safer installs – Fault current calculations you can trust, proving protective devices will trip when needed.
Wrapping Up
RCD uplift has been winding electricians up for years. It’s wasted hours, failed tests, and raised questions about safety. With True Loop®, that’s finished.
Accurate loop measurements, no false fails, just proper results you can rely on.