But because you use radial circuits with unfused plugs, you have to have
limits on the number of sockets on a circuit, and thus a large number of
We can have unlimited sockets on a 32A ring (or radial) circuit, subject
to floor area and anticipated load. Our Wiring Regulations don't specify
the minutiae of where to put sockets on a kitchen counter; that's left
to the designer to ensure the installation is adequate.
Of course, the superiority of the British ring circuit is another topic
Same here; the requirement for flexible cords to be short enough that a
a 20A breaker provides adequate fault protection is thanks to European
Actually, we can't either. Individual appliances are limited to 13A (the
fused plug rating).
I think the South Africans used *our* round-pin plugs, and still
do (as do we in certain circumstances).
Ours have to be a bit hefty, to accommodate the fuse.
I read somewhere they originally started life as connectors for
christmas tree lights.
Oooh no, you'd need the earth pin to actuate the socket shutter, and the
3-pin arrangement means theyre' not phase-neutral reversable.
Do the UK whole house RCD's shut off the whole house power when they
If so, that sounds like it might be awfully inconvenient at best and
possible dangerous if they should trip at night and leave the
occupants stumbling around in the dark.
In the North American System, they are called GFI's (sometimes GFCI's)
Ground Fault Circuit Interrupters and standard practice is to place
them on individual branch circuits (15 or 20 A) as combo GFI/circuit
breakers or as stand alone units that are also duplex outlets. The
latter may be wired to protect other downstream devices. There is a
special, very expensive, GFI that must be used for hot tub
The point is...this allows the system to be selective about what to
protect with a GFI. Generally, critical loads such as refrigerators,
sump pumps, and fire pumps are never wired with GFI's to prevent
nuisance tripping from current leakage caused by old wiring. The
trip point on these standard devices is set at 5 ma and is normally
Other outlets and devices are required by the code to be wired with a
GFI including bathroom and kitchen outlets, plus outdoor and garage
receptacles. There is a new rule that bedroom outlets must be wired
with arc-fault protectors.
Apart from older installations, no.
Not applicable...see abive.
Exactly. Same here.
I have also installed battery backed lighting in critical areas; lights
can fail for other reasons than a trip (e.g. supply power failure).
In article , Beachcomber
Well we've had them for the past 25 odd years in two separate houses and
they've only tripped twice, and that was due to immersion heater leakage
and a duff element on the electric cooker.
They have tripped Twice in anger between those times.
In some rented houses we have they've tripped three times twice because
of leakage and once due to accidental contact.
Not really a big problem is it?, and its never happened during the hours
of darkness BUT we have had power cuts during the hours of darkness and
remarkably we have survived those!......
If old wiring is causing tripping, then the old wiring should become new
Transmission wasn't mentioned only what power would be best for houses.
You can do some nice stuff if you have a higher frequency supply than
Like controlling motors is easier, transformers are smaller, SMPS are
I'm not convinced that it would be worse for distribution either, but you
probably want a ~2kV - 100V ferrite transformer near the home.
RCDs have more than one type of use in the UK. An RCD which shuts
off the the whole house power should be >= 100mA trip current, and
is usually time-delayed. They are not for protecting against
electrocution, but against high earth fault loop impedance.
RCDs which protect against electrocution ( In the North American System, they are called GFI's (sometimes GFCI's)
This is what I and a number of DIYers do. However, it's not what
you'll get an electrician do who's working to a budget. Combo RCD
and breakers are called RCBO's.
I'm not very sure exactly what you mean by hot tub. We have hot
tubs in the UK, but I'm far from sure it means the same thing.
However, fixed apparatus designed for use in bathrooms has to be
safe without the use of an RCD in the UK. You can fit an RCD, but
it's not required.
We don't permit any outlets or portable appliances in bath/shower rooms,
except for sockets with isolating transformers built in for shavers.
(Apparently, we have the lowest figure for bath/shower room electrocutions
per capita anywhere in the world.) Outlets in a bedroom which contains a
shower must be RCD protected and they have to be some considerable
distance from the shower. All outdoor outlets and other outlets which
might be used to power outdoor portable appliances must be RCD protected
No. conventional practice is to organise the consumer unit with some
magnetic circuit breakers immediately after the incoming main circuit
breaker. These are used for lighting and other critical circuits.
There is then a 30mA RCD followed by MCBs for remaining circuits such
as those that could be potentially used to feed portable equipment
Alternatively, but not commonly, RCBOs are used - one per circuit.
These effectively combine MCB and RCD functionality.
Another approach is that individual wall outlets can have an RCD built
in to them.
I think its more an advantage than a reason. 12v makes for more
efficiency again, but really filament lamps arent the way forward
Yes, we dont have that requirement here, but I still dont see any
extension leads in kitchens. Appliances with 3' leads would be a right
A fair few houses were still like that in the 70s here, and I
volunteered in a workplace in the 80s still wired like that. How it
escaped the safety inspectors eyes I'm not sure, but evidently it had.
It had twisted pair cotton flex strung across the ceiling.
that would be a big fryer! They dont fwliw, the point of 7.2kW is to be
able to run a large number of appliances rather than one bigun. There
is usually a lot more total load than 7.2kW on a ring, with diversity
and short term versus long term ratings all making it work. Our rings
are a much misunderstood system. I'm not going to add up what I've got
on the kitchen circuit but its well over 7.2kW.
Yes, familiar stuff. Thankfully we dont have to live like that these
check out Joe Tedesco's forum.
Do you have figures? I dont for the US. But I do know far more deaths
are the result of fire than electrocution, and 240 is demonstrably
better in that department.
We seem to have very different approaches to achieving bathroom safety.
Nothing odd about it, its lower cost. The joints are fully under the
control of a large power co that can ensure appropriate types of joints
are used, can measure line R and R fluctuation etc, and can maintain as
needed. But as already said, it has proven to be not such a hot idea.
Copper coated ali cable has also been tried, I was offered some in the
80s for commercial work. I cant think why that wouldnt work, but its so
rare it must have its problems too.
So if I understand this correctly... If you have a direct short of the
hot wire to the earth connection... and the earth connection is of
high impedance for whatever reason and does not permit sufficient
current to trip the overload breaker... the RCD will sense that the
fault current is over 100 mA and trip after a time delay... Is that
Are you saying that the whole house RCD is the minimum permitted and
that additional RCD's are optional, at the discretion of the
Sorry.. I'm not always sure what is and what isn't American lingo :)
I believe hot tubs are also called spas. In the US, it's generally
an oversize tub mounted indoors or outdoors where the water is heated
to about 101 F. It contains jet pumps and filtration pumps,
ozonators, etc. The water is normally left in the tub, partially
heated and filtered when the tub is not in use. In California and
the west, Redwood hot tubs are popular.
There are also Jaccuzi's and Whirlpool baths which are generally
regular or oversize bathtubs that have pressure jets and heaters, but
are designed to be drained after use.
Because of all the electricity in close proximity to naked, wet
people, special GFI's are required. A popular model is made by
Just my opinion... Arcing is not a big problem in the US as far as I
know, either. I believe that during a certain year, there were just
one or two instances of a fire being caused in a bedroom because the
plug somehow got smashed by a bedframe. Despite the greater odds of
winning bigtime in a lottery than dying from an arc fault fire, the US
Code authorities decided to require arc fault protectors for bedroom
circuits, just in case.
That is one less outlet that I can plug my Tesla coil into. :) I
hate it when the do that.
On 18 Mar 2006 12:13:35 -0800,it is alleged that "Nehmo"
spake thusly in uk.d-i-y:
As others have noted, it's been done to death already, but 110/120v
centre tapped [55-60v to earth] has advantages on safety grounds for
No; whole-house RCD (as the only RCD protection) is deprecated, because
of the unneccessary loss of light.
Certain circuits, such as those for sockets which might be used for
portable equipment outdoors, must have RCD protection.
What is usually done is a split-load consumer unit:
=====> MAIN ------------------MCB---> Lights
SWITCH | |
| |-----MCB---> Lights
| |-----MCB---> Fridge/freezer socket
However, on a TT (earth rod) installation, or where the earth impedance
is too high for the MCBs to provide sufficiently fast disconnection, all
circuits are RCD protected. This may be by RCBOs on individual circuits,
but is usually done by having a 100mA time-delay RCD as the main switch.
The 100mA rating and time-delay provide discrimination such that a fault
on a socket circuit trips only that circuit's MCB.
=====> MAIN ------------------MCB---> Lights
SWITCH | |
100 mA | |-----MCB---> Lights
time- | |
delay | |-----MCB---> Fridge/freezer socket
This additional protection is not at the discretion of the electrician;
the correct means of protection for circuits must be proven by
calculation during the installation design process.