Why are lights & GPO's on different circuits?

Kid's school science question as per subject line.

Anyone got any answers - google's not co-operating and other than spreading the load when we used to have 3ph into houses or to separate ELCB loads which is a much more recent thing.

Ideas?

Reply to
McKavity
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Err, 2c, lights are generally in the ceiling, whilst GPOs are generally supplied from under the floor boards. Also, lights usually draw less current,socan have a lowervalue fuseand thus safer in the event of a short.

Reply to
terryc

"McKavity"

** The reasons are partly historical, partly practical and partly human safety.
  1. When homes were first supplied with mains electricity, circa 100 years ago, the ONLY purpose was lighting - as appliances came along ( radios, vacuum cleaners, room heaters etc) they were plugged into the light sockets.
  2. Appliances typically draw far more power than lighting does, so will easily exceed the capacity of the cables fitted in the ceiling for ighting - means a separate ( higher capacity) power circuit for appliances is needed, preferably fitted at floor level.
  3. If the ( now independent) power circuit is over-loaded and causes the fuse to blow, it does not plunge the house into darkness - which would be very unsafe for the people inside at night.

Then there is the issue of safety grounding, essential for appliances but not required for ordinary lighting fixtures. So power circuits have three pin sockets and 3 wire conductors, unlike typical lighting.

BTW:

Is your Christian name " Phil " by any chance .................

Are you a dentist ?

..... Phil

Reply to
Phil Allison

Safety. Do you want to be in the dark, when the outlets in a room fail?

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Reply to
Michael A. Terrell

Lights need to stay operational in the event of appliance overloading (which can be fairly common), so it makes sense from that safety perspective.

Also, when electricity was first introduced, I believe lighting was the only application. Light wiring would have been low current capacity, so when higher current power points were added later it was most likely essential to put them on a new separate circuit. And hence it remained for ever more.

Dave.

Reply to
David L. Jones

Yes - physical location is valid - suspect teacher is looking for a more technical reason. Fuse rating could be the answer however that would be far in advance of what they have covered (yr 8). thanks

Reply to
Den

Cheers Phil - all good reasons. Terry also suggested circuit fuse rating differences. Overloading & lights out is another. Mmmm, I must have "over thought" the question and was looking for something more fundamental. \\

Reply to
Den

Cheers Dave.

PS dont you, pa & some of the other regulars here ever go to sleep!

Reply to
Den

The wiring rules have required that all metal luminares be earthed (except for double insulated and ELV ones), and in any case an earth wire must be provided at the lighting point. This has been the law now for over 20 years. Lighting circuits now also require RCD protection (as do all circuits supplying socket outlets).

The main reason for separate lights and power is cost. Under the wiring rules the minimum size conductor allowed for lighting circuits is

1.0mm^2, while for socket outlets (power points etc), the minimum conductor allowed is 2.5mm^2, which costs more. In a typical installation, you would use more cable for lighting than socket outlets, as you have to run cables down the walls to switches, and you have two way switches etc, further increasing the cable runs. All the conductors on one circuit has to be rated to carry the current of the protective device.

Note: Lights can be on the same circuit as socket outlets. This is a called a mixed circuit. Only requirement is that the conductors to the lighting points has to be the same size an current rating as the rest of the circuit, to enable protection by the circuit breaker (or fuse).

David

Reply to
David

The Australian wiring rules require that there be (at least) two circuits for lighting and two for GPOs.

Main reason is safety. So you're not left in the dark, and you have always have some power.

Lighting circuits not only have lower current rating fuses but also lower current rated wire.

Earth wiring has to be supplied to light fittings whether the lights need an earth connection or not.

Safety is everything in the wiring rules. Wiring rules were initiated by insurance companies.

Reply to
Davo

Not true under current rules, and never has been.

The old rules strongly encouraged at least two power circuits in domestic installations, by severely limiting the number of GPOs (as they were called in those days) allowed for an installation with only one circuit, but it was not compulsory.

New rules (AS/NZS3000:2007) leave it to the designer and cover it under the General Design of an Electrical Installation : Rule 1.6.1 (d) - minimize inconvenience in the event of a fault, and Rule 1.6.5 - Every electrical installation shall be divided into circuits as necessary to - (a) avoid danger and minimize inconvenience in the event of a fault; and (b) facilitate safe operation, inspection, testing and maintenance.

There has never been a requirement for at least two lighting circuits.

David

Reply to
David

At least get your childish insults correct Phil, that wasn't my post.

Dave.

Reply to
David L. Jones

You're the first to mention *inconvenience* (as well as danger) when losing power.

I never bought the safety bullshit angle. We've lost power due to blackouts numerous times, and the ONLY safety issue was getting bored to death by lack of television, and lately, perhaps lack of a computer and internet connection. Complete blackouts aren't unheard of, even some of the more major *cities* here in Australia still have regular blackouts (even if that IS another story).

I don't know about others, but I have torches within easy reach of a couple of rooms. I still don't buy the safety bullshit angle. What's going happen? Some old fart will fall over in the dark? Or is it a surprise the old fart didn't keel over when they stuck their knife in the toaster which caused the power loss in the first place?

Or have they never heard of candles and kerosine lamps like they used to use in the 'olde days before electrickery? Or is the safety angle just that? The risk of fire of candles and kerosine lamps the reason everyone says electricity is "safe"? Though, it HAS been nearly two entire generations since kero lamps have vanished, and candles have been redelagated to the task of aromatherapy.

That's like saying it's safe to use wired electricity in the house because cave people used to light indoors fires and burn their bloody caves down.

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Reply to
John Tserkezis

Current rules require at least two RCDs in a domestic installation (unless there is only one circuit). Also, to mimimize the impact of an operation of a single RCD, a maximum of three final sub circuits shall be protected by one RCD, and lighting circuits shall be distributed between RCDs

And will only get more frequent, with no new power stations being built in NSW.

If there is a danger, you could fit battery operated emergency lights. These are required in most public and non residential buildings.

David

Reply to
David

No matter, there is more than enough work in this area on for everyone concerned when it comes to the rest of the country. And around the world...

When the government can fund and fit those #%&!^# CFLs to everyone's place, all for no more than single digit percentage savings, why can't they supply a cheap torch (with batteries supplied!!) and really improve things?

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Reply to
John Tserkezis

"David L. Jones" "Phil Allison"

** Too many Daves in this tread.

..... Phil

Reply to
Phil Allison

"John Tserkezis"

** This loon posts straight out of a mental asylum - easy to see that.

Wot a psycho.

Reply to
Phil Allison

How about you pull your head in and be quite philthy befoer you get a solution you wont like ?

Reply to
atec77

Go with fuse rating. I don't see it as beyound Yr8. Really it is just applied resistor and they usually cover resistance as one of the early parts of electrical circuits.

OTOH, I'm only guessing based on life experience.

Reply to
terryc

"Den"

** The problem is that teacher likely THINKS he or she knows the right answer - when they do not.

..... Phil

Reply to
Phil Allison

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