GFCI and RCD

Yes.

GFCI = American RCD = English

The English name was a result of a campaign by "Which?" magazine and "That's Life!" TV program. When the devices first appeared, every manufacturer had their own name for them (although none used GFI or GFCI), and these different names were confusing the public over just which safety device to install. The official name (in so far as there was one) in the Wiring Regulations was "Current Operated Earth Leakage Circuit Breaker" which was considered too complicated for public consumption, and was too confusing in comparison to the "Voltage Operated Earth Leakage Circuit Breakers" which had been around for years, and were previously known as just "Earth Leakage Circuit Breakers". So the industry all agreed to switch to the name RCD "Residual Current Device". The other name you do still see is RCCB "Residual Current Circuit Breaker", although that tends to be used only for the type installed in a Consumer Unit (a panel, for US readers), whereas RCD applies to the devices installed in any location. Another variation is the RCBO but this is different -- it is a regular breaker combined with RCD functionality, "Residual Current Breaker with Overload protection", which replaces a standard breaker in the Consumer Unit to provide RCD protection to a whole circuit.

I don't know the background behind the American choice of name.

Other countries use different names.

As far as I know earth leakage monitoring (current to earth) is regarded as different from monitoring curent flow in and out of the device and deducing earth leakage if it differs (RCD).

This is the reason why the voltage operated, earth leakage unit is no longer recommended in the UK, since it requires a functional earth to be present, an RCD (generic term) doesn't. Jaymack in UK

The typical American GFCI Device exists as a replacement circuit-breaker plug-in model or an individual duplex outlet model that has a pass-through feature for wiring downstream outlets. It is set to trip at a fixed value of 0.005A (5 mA)

It trips on either of two modes:

1. The difference between the neutral and hot wire current exceeds the 5 mA threshhold.

1. If a short (fault) is sensed between neutral and the protective ground.

The NEC requires GFCI's to be installed on all bathroom and kitchen countertop appliance circuits (but not refrigerator circuits), outdoor outlets and garage outlets.

I believe the British RCD is or can be set for a higher threshold and it is most-often installed to protect more than one circuit.

Beachcomber

In article , "John McLean" writes:

Well, neither of these devices directly monitor current to earth.

The old "Voltage Operated Earth Leakage Circuit Breakers" monitor the voltage between a dedicated ground rod, and the earth conductors of the installation. They are required to trip before this reaches 50V (on a 240V supply), although the tripping voltage was normally significantly lower than this. The reason for such a voltage appearing would be that a current is flowing to earth which is generating a significant voltage drop across the installation's ground rod resistance (due either to excessive current flow or a poor ground rod). We refer to as a high earth fault loop impedance (other faults can give rise to high earth fault loop impedance too). The "Voltage Operated Earth Leakage Circuit Breaker" (VOELCB) is designed to detect this condition and disconnect the supply, as the overcurrent protective device may not be seeing enough current to trip it quickly enough, or even at all. Note that there do not need to be ground connections in a VOELCB installation other than the dedicated VOELCB ground connection, in which case it will trip at quite low leakage currents as the earth rod resistance is effectively increased by the resistance of the the VOELCB's sense coil. On the other hand, you can have as many additional ground connections as you like, and if you have enough to generate a low total earth rod resistance, then the installation's earthing conductors may never reach 50V above real ground, and the VOELCB has no need to trip as the overcurrent device will do so instead. These devices are now much misunderstood nowadays, as electricians haven't been taught about them for some time, but they are still in service, although never newly fitted anymore.

Also, the VOELCB is not designed to protect against electrocution, only too high a ground rod impedance which might prevent the overcurrent protective device tripping on a short circuit to earth. The RCD does this, but in addition it provides protection against electrocution. It is also much easier to install, without having to install a dedicated ground rod and ensuring it doesn't have an overlapping earth resistance area with any other ground connection, including things like water/gas service pipes.

These are available in the UK too, but not often used (and consequently rather expensive). They never have the pass-through feature you find on US ones.

1. is not required in the UK/EU AFAIK, but some do check for it. Even with no explicit check in the device (which is done by modulating the neutral voltage relative to protective ground so it can detect any connection), any connection usually generates more than enough current to trip the device due to small voltage differences between neutral and protective ground anyway in the UK. The other (non-required) checks some UK RCDs do is to trip on live and neutral reversed, neutral feed broken, or protective ground feed broken. They are also required to trip on half wave rectified earth leakage in the UK (and I think across all the EU).

In UK, bath/shower room appliance circuits are forbidden (except for shaver outlets on a isolating transformer). Circuits which might be used to power outdoor portable appliances must be RCD protected, as must an appliance circuits in a room which is not a shower room, but contains a shower (such as a bedroom). In all these cases where the RCD is protecting against electrocution, the RCD must be rated no more than 30mA (and it trips at between 50% and

When an RCD is being used instead of an old VOELCB to protect against high ground rod resistance and not electrocution, then is should be rated at 100mA or higher.

Our circuits are different size, but the relevant factor is that an RCD is likely to be protecting very many appliances. Personally, I install them one per circuit, but that's a more expensive option which you are only likely to find in DIY installations; electricians would rarely do this because it bumps up the cost.

In the US, GFCIs are now required to trip (or not reset) under all of those conditions... N-G fault downstream, L-N reversed, or any imbalance in current. They must sense the N-G fault actively, rather than waiting for a connected load (which would trip it due to an imbalance).

Ben Miller

Just a note on costs for a standard "duplex outlet" type GFCI in the USA.

Individually these retail for about $10 or so. In quantities, I have seen them as low as $5 or even lower sold as lots on eBay. Dirt cheap, as far as I am concerned, for the services that they provide.

The more elaborate GFCI's sold for 240V. 3-wire protection of hot tubs and spas are more expensive, of course. The range seems to be $60-$100.

Beachcomber