Maker Pro
Maker Pro

GFCI and RCD

K

Kissi Asiedu

Jan 1, 1970
0
Is Ground Fault Circuit Interrupter(GFCI) the same as Residual Current
Device(RCD)? If they are why call it different names?

Thanks.
 
A

Andrew Gabriel

Jan 1, 1970
0
Is Ground Fault Circuit Interrupter(GFCI) the same as Residual Current
Device(RCD)?
Yes.

If they are why call it different names?

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.
 
R

Rheilly Phoull

Jan 1, 1970
0
Andrew said:
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).
 
J

John McLean

Jan 1, 1970
0
Rheilly Phoull said:
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
 
B

Beachcomber

Jan 1, 1970
0
:
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.

2. 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
 
A

Andrew Gabriel

Jan 1, 1970
0
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.
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.

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.
 
A

Andrew Gabriel

Jan 1, 1970
0
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

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.
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.

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

2. 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).
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.

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
100% of its trip rating).

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.
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.

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.
 
B

Ben Miller

Jan 1, 1970
0
Andrew Gabriel said:
2. 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 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
 
B

Beachcomber

Jan 1, 1970
0
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.

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
 
Top