If you’ve ever tested a circuit and thought, “That reading can’t be right,” you’ve most likely run into a Residual Current Device (RCD). It’s one of those recurring frustrations, especially when a perfectly good circuit looks like it’s failed.
Loop impedance testing is essential for every install and inspection under the 18th Edition Wiring Regulations, but RCD uplift can throw your readings off.
Here’s why it happens and how Megger’s True Loop™ technology fixes it for good.
What Exactly Is RCD Uplift?
RCD uplift happens when your loop impedance test shows a higher result than expected because there’s an RCD or RCBO (Residual Current Breaker with Overcurrent protection) in the circuit.
During a non-trip test, the small current from your tester interacts with the RCD’s magnetic coil, which behaves like an extra resistor. The tester can’t separate the two values, so it adds them together.
Example:
- True impedance: 0.7 Ω
- RCD coil adds: 0.5 Ω
- Tester shows: 1.2 Ω
That can make a circuit seem non-compliant when it’s actually safe. To make matters worse, not all RCDs behave the same way, so uplift might appear on one test and not the next.
Why RCD Uplift Actually Matters
Safety: If loop impedance (Zs) looks too high, your Prospective Fault Current (PFC) will look too low, which could mean an incorrect assumption about breaker performance.
Compliance: False highs can show safe circuits as failing the Wiring Regs, making certification messy and inconsistent.
Time: You waste hours retesting, chasing faults and double-checking connections, all because uplift has distorted your readings.
The Solution: Megger True Loop™
Megger’s True Loop™ technology, built into testers like the MFT-X1, removes uplift automatically. It identifies the resistance caused by the RCD coil and takes it out of the result, leaving you with the true loop impedance, accurate, compliant and ready to record.
No false fails. No second-guessing. Just proper results.
Confidence from the Confidence Meter™
The Confidence Meter™ built into the MFT-X1 adds another layer of reassurance. When there’s electrical noise or instability affecting the reading, the screen displays an arc that gradually narrows as the measurement stabilises.
Once it locks into a single point, that’s your confirmation, your reading is accurate and ready to record. It’s simple, visual and genuinely helpful when you’re working under pressure.
Why It Makes a Difference
- Accurate readings – eliminates uplift errors and false fails
- Consistent results – reliable data across circuits and devices
- Less wasted time – no more unnecessary retests or chasing non-existent faults
- Safer installs – dependable Zs and PFC values
Trusted by UK electricians for fast, compliant loop testing.
RCD uplift has been tripping up electricians (figuratively, thankfully) for years. It’s caused confusion, retests and unnecessary work.
With True Loop™, that’s history.
Accurate loop readings, real compliance and zero guesswork, finally a solution that lets you just get on with the job.
Explore our Megger True Loop™ Range
