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#133774 - 09/24/02 11:39 AM Standard residential wiring
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
Hello all!

I started thinking about this with residential wiring: The UK uses 32A ring mains, rest of Europe 10, 13, 16 or even 20A radials. (What is the norm down under?)

I came up with this concept:

20A radials for general purpose sockets. 20A @ 230V gives 4600 W, which is more heat than can dissipate from most rooms. Therefore very few appliances will use the full capacity of the circuit.

The IEE regulations allow a 32A ring main to serve a maximum of 100 sqm, i.e. 70W per sqm. If we assume a power need of 100W per sqm. the 20A circuit would be sufficent for 46 sqm. Let's say 50 sqm just to keep things simple.

The cable would be 2.5 sqmm (13 AWG) or in some cases 4 sqmm. Maximum length with 2.5 sq.mm at 4% voltage drop is 32 metres (100 feet). 4 sqmm allows for 50 m. This is sufficient for most homes, I think. A 30x30 m house is 900 sqm, i.e. 10000 sqft. Double that if it is a two story house... (I'd sure like to own that house!)

20A type B MCB:s should be sufficient to protect the 0.75 sqmm (18 AWG) cords used for small appliances. (I have done a few calculations on this)

Separate lighting circuits would be optional.

A few appliances like washing machines, tumble dryers, storage heater etc. will have dedicated 20A circuits.

Now for the RCD:s. With 20A circuits the number of grounded appliances per circuit will be rather limited. This means little current leaking back through the earth conductor. I think (without knowing) that this will allow 10 mA RCD:s to be used. One RCD per circuit, not one or two for the whole house.

This arrangement has two benefits:
10 mA is low enough to save children.
And a fault on one circuit will not turn the whole house black.

Unlike the US where the GFI/RCD is mounted in the receptables, RCD:s in the consumer unit will also protect people from faults in the wiring. The drawback is of course the high price of a combined MCB/RCD:s (RCBO).

Here's another good thing: 20A is enough for any appliance used in a home, except for the cooker. This means that the same appliance could be sold and used in entire Europe, without having to make different versions for the single phase and the 3-phase countries.

Ideas, suggestions, opinions?

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#133775 - 09/24/02 03:46 PM Re: Standard residential wiring
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
I agree with you entirely. I would like to see the U.K. abandon the ring circuit completely and move toward using radials. The Regs. today still provide for 20 or 30/32A radial circuits, serving limited floor areas.

If we could get dedicated circuits for major appliances -- as you say, the washing machine, dryer, dishwasher, etc. -- then a few 15/16A or 20A radial circuits would be ample for the rest of the house. It might be a good idea to specify one or more such circuits specifically for general-purpose outlets in the kitchen area, as does the American NEC.

As for lighting, I think most of you in Continental Europe combine lights and receptacles on the same 15 or 16A branches, don't you? (I know France is the main exception to this as they seem to use separate 10A lighting circuits.)

Although 5A lighting circuits are the norm for residential wiring in England, the Regs. actually allow standard BC lampholders to be connected on any circuit up to 16A, so if radial receptacle circuits were set at that level then I don't see a problem with incorporating lighting on the same circuits. (I'm assuming that you do this in Sweden, right?)

The main RCD employed in houses with TT earthing systems here is something I don't like, for the reasons you've mentioned. One ground fault anywhere in the house and you're plunged into total darkness.

I too would like to see RCD/GFI protection split to a per-circuit basis, although as you hinted, with the cost of combined breakers as they stand at present it would get very expensive. (I'm sure costs would drop as production increased if individual RCDs became more widely accepted.)

By the way, although GFI receptacles are quite common in the States they do use individual GFI breakers at the main distribution panel as well (and I don't think the new AFCI types are available in receptacle versions yet either).

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#133776 - 09/24/02 05:20 PM Re: Standard residential wiring
ChrisO Offline
Member

Registered: 07/31/02
Posts: 22
Loc: St Ives, Cornwall, UK
I too would like to see RCD/GFI protection split to a per-circuit basis, although as you hinted, with the cost of combined breakers as they stand at present it would get very expensive.

I tried using single way RCBO's (with the neutral piggy back wire) and apart from the high price had little success with them actually working.

Now use double pole RCDs mounted in a 2/3 way DIN box (one for an MCB if needed) as they are only UK £25 odd with the box.

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#133777 - 09/25/02 12:48 AM Re: Standard residential wiring
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
C-H,
Just some comments on wiring, "Down-Under",we
use all Radial circuits, over here in NZ,they
are fed directly from the switchboard.
A "normal" set-up, in NZ would be:
10A lighting circuits
16-20A socket outlet circuits, depending on length of run and final loading.
25A Air Con circuits
32A Range circuit, this can also be split
with 2x 4mm2 for a seperate hob and wall-oven, these are protected by two 25A MCB's.
Why the arbitary figure of 4% v.drop?, we use a figure of 5% @ 230V and a figure of 10%
@ 400V.
Over here, with respect to RCD's, we use a trip current of 30mA, for personal protection,in domestic houses,10 mA, is normally used in hospital patient-care areas.
We normally only use ring circuits for areas like caravan parks, where every socket-outlet
has an RCBO on it, 30mA, of course, but I like the idea of the protection being at the
tap off point from the fixed wiring.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#133778 - 09/25/02 09:54 AM Re: Standard residential wiring
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
 Quote:
From Pauluk:
If we could get dedicated circuits for major appliances -- as you say, the washing machine, dryer, dishwasher, etc. -- then a few 15/16A or 20A radial circuits would be ample for the rest of the house. It might be a good idea to specify one or more such circuits specifically for general-purpose outlets in the kitchen area, as does the American NEC.


The kitchen has indeed become the biggest power consumer in the past decades. A dedicated circuit is definitely a must.

 Quote:

As for lighting, I think most of you in Continental Europe combine lights and receptacles on the same 15 or 16A branches, don't you?


Yes. In fact in my flat the wiring is centered at the ceiling lights. Above each lamp is a 6A socket.The (large) box behind it is used as a junction box for the wires coming from wall sockets and switches. This makes it easy to knock down walls. It was also easy to move a switch from one end of the flat to the other. I simply ran a cable (surface mounted) to the nearest socket and an extra wire in the existing conduit up to the lamp.

When I described this arrangement to a Brit he told me it would have violated just about every rule in the UK regs...

 Quote:
From ChrisO:
I tried using single way RCBO's (with the neutral piggy back wire) and apart from the high price had little success with them actually working.


Interesting. What was the problem with the RCBO? (I take it to be a RCBO with solid neutral.)

 Quote:
From Trumpy:
A "normal" set-up, in NZ would be:
10A lighting circuits
16-20A socket outlet circuits, depending on length of run and final loading.
25A Air Con circuits
32A Range circuit, this can also be split
with 2x 4mm2 for a seperate hob and wall-oven, these are protected by two 25A MCB's.


Thanks Trumpy!

The layout you describe sounds very much like what I was proposing. Unlike you we don't have ACs, but often electrical heating. Do you use European style DIN MCB:s? If so, what type is used for the above circuits?

 Quote:

Why the arbitary figure of 4% v.drop?, we use a figure of 5% @ 230V and a figure of 10%
@ 400V.


It wasn't entirely arbitrary: Some countries specify a voltage drop as low as 3% and some 5% or more. I thought 4% would be reasonable, but 5% could be a better choice.

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#133779 - 09/25/02 12:33 PM Re: Standard residential wiring
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Trumpy,

Thanks for the run-down on typical circuit arrangements (it answers the question I posed in another thread!). How many lighting circuits and general-purpose radial receptacle circuits would be found in the average NZ house?

Chris,
I echo the question above -- What exactly did you find to be the problem with the RCBO? I've come across them occasionally and not had problems beyond those one would normally associate with an RCD. All the RCBOs I've seen have a switched neutral, by the way.

C-H,
The only real problem I see with the "breaks every rule in the (U.K.) book" arrangement you described is that under our current Regs. it would be hard to combine the lights and sockets on the same circuit. Standard lampholders may not be wired to a circuit rated over 16A, but the lowest rated receptacle circuit arrangement recognized by the IEE Regs. is a 20A radial type (assuming it feeds more than one socket).

I certainly don't see any safety problem with your arrangement, and as we've already mentioned, the kitchen is the area which has the greatest current demand these days. A 16A radial circuit for other areas should be adequate, and still allows a 3kW heater to be run on it if necessary.

I'm afraid that the British IEE is so attached to the ring circuit that they sometimes don't seem to realize that other arrangement are perfectly acceptable.

On the voltage drop question, 4% is also specified as the maximum acceptable drop here, as measured from service entrance to farthest point of utilization under full load. In combination with the accepted supply voltage tolerance of 6%, it insures that the voltage available at any outlet will be no more than 10% below nominal.



[This message has been edited by pauluk (edited 09-25-2002).]

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#133780 - 09/25/02 05:23 PM Re: Standard residential wiring
ChrisO Offline
Member

Registered: 07/31/02
Posts: 22
Loc: St Ives, Cornwall, UK
Paul & C-H
I echo the question above -- What exactly did you find to be the problem with the RCBO? I've come across them occasionally and not had problems beyond those one would normally associate with an RCD. All the RCBOs I've seen have a switched neutral, by the way.

These are single width single pole devices that have a pigtail wire that goes to the neutral bus - mounted in the c/u they (invariably) did't hold in - gave up and used remote 2 pole RCDs, RCD sockets & RCD fused spurs - expensive(ish) but reliable.

Senate electrical are now selling latching RCD twin 13A outlets for UK 21 pounds, the Spurs are for some reason more expensive

Chris - enlightening himself about harmonics and their effect on neutral currents in 3 phase systems - I am really out of date !

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#133781 - 09/26/02 12:48 PM Re: Standard residential wiring
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Don't think I've come across the single-width RCBO devices. The regular double-width bolt-on types have been fine.

I think one of the latest Crabtree or MK range has clip-on breakers, but I've not run across any of them as yet. Call me old-fashioned, but I prefer C/Bs which are securely bolted to the busbar. Do you know the old Crabtree C50 range? Well-built, solid, and reliable.

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#133782 - 10/13/02 09:00 AM Re: Standard residential wiring
Belgian Offline
Member

Registered: 10/10/02
Posts: 177
Loc: antwerp
Here the AREI (which is the Belgian code) says:
Minimum wire section for residential installations:
1.5mm2 Lights
2.5mm2 sockets
4 mm2 washing machine (in practice everyone uses 2.5mm2)
6 mm2 electric cooker (stove)

Minimum 2 light circuits per residence.
Maximum 8 sockets per circuit.
Lights can be combined in a socket circuit and have to be considered as a socket (eg. 7 sockets and 1 light).

We have only TT systems (residential) and we use 2 GFI's
one main GFI 300mA and one 30mA for moist areas i.e. Bathrooms, dishwashers, washing machine, outdoor, boiler

Concerning the main GFI tripping and the whole house being in the dark: Well, we switch of all the fuses and switch on the GFI then switch on 1 fuse at a time untill the GFI trips and then we know in which circuit is the fault!

[This message has been edited by Belgian (edited 10-13-2002).]

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#133783 - 10/13/02 09:27 AM Re: Standard residential wiring
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
>4 mm2 washing machine

Why? Do you have some type of high power industrial washing machines in homes? Perhaps, Belgians have very clean clothes or Belgium is very dirty?

(The semi-commercial one we have in my house, draws only 3.6 kW (@400V), whereas household ones draw no more than 2.2 kW.)

>6 mm2 electric cooker (stove)

I take it that you use 230V cookers in Belgium? Are Belgian houses supplied with all three phases or just single-phase 230V?

> Maximum 8 sockets per circuit.
>Lights can be combined in a socket circuit >and have to be considered as a socket
>(eg. 7 sockets and 1 light).

This sound like stone age to me. Why is there a limit on the number of sockets and lights? The more sockets you have in a room, the fewer extension cords are needed with less risk of fire as the result. Not to mention fewer broken bones... A maximum number of rooms or floor area per circuit makes sense, not a maximum number of sockets.

>Concerning the main GFI tripping and
>the whole house being in the dark:
>Well, we switch of all the fuses and
>switch on the GFI then switch on 1
>fuse at a time untill the GFI trips
>and then we know in which circuit is
>the fault!

This procedure is the same in all systems where over-all RCD:s are used. However, it tends to be an obstacle to people. It doesn't make very much sense having to take out all the fuses and then start putting them back, one by one. Except to an electrican or engineer, that is.

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