Learn why low impedance testing is tricky, what can throw your readings off and how True Loop® technology with Confidence Meter® makes it simple.
If you’ve ever tested low impedance close to the supply, you know it’s not always straightforward. Near the transformer, there’s more noise, more interference, and more chances for your tester to wobble. Instead of a steady number, you get bouncing digits that don’t seem to settle — and that can put safety and compliance at risk.
This article cuts through the confusion. Here’s why low impedance testing is tricky, what can throw your readings off, and how Megger’s True Loop® technology with Confidence Meter® makes it simple.
Why Accurate Low Impedance Matters
Low loop impedance means high fault current. That’s what makes sure a fuse or breaker trips fast enough to protect people and equipment.
If your reading’s off — maybe because of interference or the wrong tester — your fault current calculation will be wrong too. Pick the wrong breaker, and you could end up with nuisance trips, damaged kit, or worse, a real safety hazard. Good readings also keep you in line with the regs, so your paperwork stands up without the stress.
Testing Near the Supply: What Gets in the Way
Electrical noise
Close to the transformer, circuits are full of noise — harmonics, spikes, switching loads. Testers using low currents are especially vulnerable. The result? Numbers that never settle.
RCD uplift
If the circuit’s got an RCD or RCBO, some testers mistake the device’s internal resistance as part of the loop. That pushes the reading up, even though the wiring is fine. It’s not a real fault — it’s uplift.
The Hidden Costs of Bad Readings
Wrong breaker choice → unsafe protection or nuisance trips.
Failed paperwork → circuits that are safe can look like they’ve failed.
Time wasted → chasing dodgy numbers, retesting, and second-guessing yourself.
Megger’s Fix: True Loop® and the Confidence Meter®
Megger built True Loop® technology into testers like the MFT-X1 to deal with all of this.
How True Loop® does it
The tester runs dozens of rapid tests, filters out the noise, and strips away the uplift caused by RCDs. What you see is the true loop impedance — not a best guess, but the real value.
Confidence Meter®
The Confidence Meter® gives you a quick visual check. At first you’ll see an arc on screen as the tester works. When it pulls into a single point, the reading is solid. No more waiting, no more retesting — just a glance and you know you can trust it.
Why It’s a Game Changer
Trust the result – No more chasing numbers that never settle.
Work faster – One solid reading and you’re on to the next circuit.
Cut the hassle – Less time wasted second-guessing.
Keep it safe – PFC calculations you can rely on, with protection devices sized right.
The Takeaway: Accuracy Without the Hassle
Low impedance testing doesn’t have to be a headache. With Megger’s True Loop® and Confidence Meter®, you can cut through the noise, forget about uplift, and get readings you can trust every time.