Which Residential Voltage & Frequency Arrangement Is Best?

[tony sayer]

In article , Tony Williams writes

Wonder why such a high voltage, its not that transmission losses will be all that great ?....

[Owain]

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 circuits.

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 altogether.

Same here; the requirement for flexible cords to be short enough that a a 20A breaker provides adequate fault protection is thanks to European unfused plugs.

Actually, we can't either. Individual appliances are limited to 13A (the fused plug rating).

Owain

[Owain]

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.

Owain

[sanjian]

Except that, for the same function, AC motors are smaller, lighter, and cheaper. Which means you're unlikely to see DC in use.

[Beachcomber]

Do the UK whole house RCD's shut off the whole house power when they trip?

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 installations.

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 not adjustable.

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.

Beachcomber

[Bob Eager]

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).

[dennis]

That was a mistake that wont be repeated.

The prefered method is copper with a steel core to carry the weight. It doesn't corrode as quickly as alu/steel.

[dennis]

Thats why I said 100V at 400Hz earlier. You can make good SMPS with ferrite cores easily.

[Bob Eager]

OK, apart from the transmission problem.

[tony sayer]

In article , Beachcomber writes

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 wiring ASAP....

[dennis]

Half serious. 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

50/60hz. Like controlling motors is easier, transformers are smaller, SMPS are smaller.

I'm not convinced that it would be worse for distribution either, but you probably want a ~2kV - 100V ferrite transformer near the home.

[Andrew Gabriel]

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 at

[Andy Hall]

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 outside.

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.

[meow2222]

I think its more an advantage than a reason. 12v makes for more efficiency again, but really filament lamps arent the way forward anyway.

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 pain though!

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 days :)

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.

NT

[meow2222]

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.

NT

[Beachcomber]

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 right?

Are you saying that the whole house RCD is the minimum permitted and that additional RCD's are optional, at the discretion of the electrician?

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 Seimens.

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.

Beachcomber

[sQuick]

Not true, I've installed a fryer that took 25A. You can get 13A,16A & 32A

240v plugs & sockets.

sQuick..

[Chip]

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 portable appliances.

[Owain]

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 | 30mA RCD | |------------MCB---> sockets | |------------MCB---> sockets

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 RCD | 30mA RCD | |------------MCB---> sockets | |------------MCB---> sockets

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.

Owain

[Owain]

You can, but not for use on 32A ring circuits using BS1636 13A fused plugs. The BS4343 unfused plugs (for various voltages and currents) are for use on application-specific circuits. Connecting such a socket to a

32A ring circuit would present an unacceptably high point load on the ring, upset the principle of diversity, and possibly mean that an appliance was insufficiently protected by the circuit MCB.

Owain