https://www.electricaltechnology.org/2025/10/gfci-breaker-gfci-receptacle-outlet.html

Residual Current Devices, or RCDs, are an essential form of protection for most circuits in modern electrical installations. In this video, we explain how an RCD works and the protection they offer to electrical installations and the people who use them.

http://hub.efixx.co.uk/SE-cprotection

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00:00 Schneider circuit protection series
00:20 What is a residual current device (RCD)?
00:50 What protection does an RCD provide?
02:06 Electric shock protection
03:20 How does an RCD work?
04:30 Where are RCDs used?
04:50 Fault protection with RCDs
06:30 Using RCDs with TT earthing systems
07:50 RCBOs
09:29 Different types of RCD – AC, A, B, F
10:16 Special electrical locations
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In this video, I will walk you through the reason a GFCI outlet still provides ground fault protection with or without a ground wire. I will also outline why I have used this installation in the past to make my properties safer.

This old Wylex RCD /GFCI is the simplest I have ever seen. The sensing core is especially unusual.

It’s worth mentioning that the unit is marked as an ELCB (Earth Leakage Circuit Breaker), but these days it would be called an RCD (Residual Current Device) in the UK or a GFCI (Ground Fault Circuit Interrupter) in other countries.
The term ELCB was dropped a long time ago due to the risk of confusion between voltage operated units (a coil detects a voltage difference between metalwork) and current operated units that detect a difference between the current flowing out and back through the breaker. The modern current operated versions are much safer as they detect more fault conditions than the old voltage operated devices.

This one was used in a TT electrical system where the house is supplied from overhead lines with a single phase and neutral, but no earth. It relies on an earth electrode at the substation (bonded to neutral) and a local earth electrode at the house to provide a path for fault current. Because the impedance (resistance) of the path through the ground is higher than a direct wired link it requires that the installation be protected by one or more RCDs/GFCIs to ensure that any significant current leakage from live to earth/ground trips out the power for safety.

This unit was retired from use after it failed to trip with a significant live to earth fault that passed 8A continuously (suggesting a 30 ohm earth loop impedance). It was replaced with an isolator and a new distribution board with two separate sections, each with its own 30mA RCD.

I recommend testing RCDs at least once a year by pressing the test button. It emulates a fault and does a full test of sensing and tripping the breaker. If the breaker does not trip instantly or after the designated time delay for programmable units, then do not hold the button in for longer as it may result in failure of the test resistor with unpredictable results.

Overview of a testing arrangement and some quick tests to demonstrate the effect of pulsed DC on a type AC RCD.
The black box is used to create a fault to earth, equivalent to the insulation in the heater being defective. Fault current shown on the multimeter in mA.
This test places a single diode in series with the heater, effectively running it on half power on pulses of DC at 50Hz. This arrangement was commonly used in heaters to provide a full/half power option with a single switch.

This breaker is a combined overcurrent and leakage device. It had a fault where it wouldn’t reset, and the issue was annoyingly trivial.

Ground Fault Circuit Interrupter or GFCI outlet is the hero in the washrooms! Make sure you have it installed, and you plug your electronics in GFCI.

Paul decided to bring in a rig that simulates the possible DC saturation aka shock/stun/feedback onto a RCD within an installation.

Given modern electrical installations contain many ways to manipulate wave forms to utilise low energy, this naturally can lead to various harmonic effects from the load and leakage from poor quality product via design or poor install or failure.

This video seeks to stir the grey matter and shine some light on the concept that DC feedback as per the 18th edition (APPENDIX 5) classification of external influences AM7.

One of the most interesting things about this RCD/GFCI is that it is a type-A designed to detect pulsing DC from a mains voltage rectifier. Something that can defeat standard AC RCD’s/GFI’s in some fault scenarios.
It appears that Rolec have had quite a lot of these breakers fail in the same way, including the single phase ones, and usually on the same terminal.