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As an electrician in Australia, I am horribly confused with all you American talk. As a curiosity, anyone care to give me a low-down on the following: 1. Nominal Voltages; Why is it that Americans use 120v system, and the Centre tap transformer system? In Australia we use 240v/415v (although Distributors now are converting to 230/400 systems) where 240v is Single phase, 415 is 3 phase. On the street we have 11kv 3-wire Delta circuits transformed into a 415v Phase-Phase Voltage with a neutral to create a Phase to Neutral (single phase) voltage of 240v. 240v powers up a majority of household appliances (Power, Lighting, Ranges, Dishwashers and small air conditioners) while 415v is used for large air conditioning, and other larger appliances. Most domestic sites will only have 240v available. 2. Main Switch Current Ratings; Why so high? 250A is a lot of power. Is it because of the lower Voltages? If so, wouldn't it be smarter to have a system in place where all houses are fed with a higher voltage (eg 240v) to limit the current draw. The main advantage is a smaller conductor size? Again in Australia 2.5mm cable is used for power circuits and is general (depending on factors such as installation conditions, cable length, etc.) can happily supply 20-25A to a circuit. Same with lighting being run in 1.5mm to supply 10-16A. Our Main Switches are 100A. 3. Cable Gauge/Size; What size are your cables, What is #6 gauge? Australia uses cable sizes in the mm^2 system. sort of Insulation do you use? What wires are inside a normal household cables? Australian Common Cables:  Click here for the full 872x590 image. Do American cables look like this? 4. Earthing/Grounding: What is your system? Again Australia uses a Multiple-Earthed Neutral (MEN) system which looks like this:  Click here for the full 872x590 image. How it works: 1: 240v Supply from Supply Authority comes in 2x16mm^2 XLPE (SDI) cable 2. Supply Authority Neutral link is sealed with only authorised electricians allowed to touch, is used for metering purposes. 3. Consumers Neutral Link is linked to the SA N/L where all Final Sub Circuit Neutrals are connected. 4. The N/L has a MEN link to the Earth Bar. This is to prevent the Neutral having a voltage but connecting it to the general mass of earth (deemed to have 0v) 5. Bonding to an Earth Electrode to provide the 0v reference 6. Bonding to Water Pipes to prevent a harmful voltage to the pipe and to protect plumbers. 5. Use of Residual Current Devices (RCD); Do you use them? They are used to provide automatic disconnection of supply in the case of Active to Earth faults. I'm sure this is a gob full, but I'm curious. They may be follow-up questions.
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Apr 27, 2009 02:39
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OK, I'm starting to get it. With the Centre tap:  BTW; That's how we draw transformers with a primary coil on the left, magnetic circuit in the centre followed by secondary coils with a centre tap. So are houses normally wired up in this arrangement? Are all houses provided with the 3 cables? 1. Fair enough, I'm sure the cost of changing every bit of equipment in the country will be far too much cost. But it will be a good way to create jobs. Quick inform Obama. 2. Thought so, Older houses in Australia have 40A Main Switches but anything built after 1980 will have 100A. 3. Onto my other picture of the 3 different cables. The 2nd cable is mostly used in domestic wiring, there was a while where the Earth was unsheathed but that's been the design for quite some time. The 3rd one I don't even see much of, usually when 3 phase is required, the insulation needs to be stronger so we use a Orange Circular Cable. The second one is also available in Orange Circular. 4 (or is it 5?): Ground Fault Circuit Interrupters? try saying that underwater with a mouth full of marbles. RCD's are compulsary on all lighting and power circuits.
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Apr 27, 2009 07:45
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Lucid Smog posted:
De-rating of cables is a mixture of several factors: Whether it is installed underground, in conduit, surrounded by thermal insulation and bunching with other circuits. That picture is something I have been taught not to do, I would usually run 2 cables in a 25mm hole and then other circuits run in parallel in their own holes. That prevents 2 things; overheating and de-rating of the cables, and when running the cables they will tend to rub against the insulation of the other cables which could cause damage to the insulation of the cables.
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Apr 28, 2009 04:09
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Cheesemaster200 posted:NEC states you do not have to derate if you are running through a nipple which is less than 24" in length as long as you still meet required fill. I'm reading from the AS/NZS3008 (Australian/New Zealand Selection of Cable) I'm assuming that the yellow cable is a power cable There is 6 cables bunched together would require a derating factor of 0.57 x Current Carrying Capacity of the cable. So for a cable which has a C.C.C of 25A, you can only get approx 14A from that cable (25 x 0.57 = 14.25.) But the all depends on the length that the cable is bunched together, my rule book says that to avoid derating of the cable, bunching must not exceed half the length of the cable. For example; lets say each cable run is 30 metres. If all 6 of those cables were straight from a switchboard bunched like that for 20 metres and then branch out to different locations in the last 10m, since the bunching occurs for greater than half of the run, the appropriate derating factor occurs. If that yellow cable is a data cable. It should be at least 300mm (from memory) away from power cables. That is so data cables do not induce Voltage from the power
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Apr 29, 2009 03:44
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skoobert posted:I have a non-grounding outlet that I would like to replace with a grounding outlet. The outlet is fed by 12/2 NM without ground. Because of the location of the outlet in relation to the panel, coupled with the fact that the basement is partially finished, it would be somewhat difficult to run a new circuit. It would be very easy, however, to fish a grounding wire from the outlet down into an unfinished part of the basement and attach it to an accessible junction box with a grounding clip or screw. That junction box is part of a separate circuit and is fed via EMT back to the panel. There is not a separate grounding wire in the EMT - the conduit is used to provide grounding. In Australia it's fairly common to use the same earthing cable for different circuits since earth cable are all connected at the Switchboard anyway. I'm guessing that the conduit is metal? Just make sure the resistance is low enough to conduct the fault current, that means really good connections. Using a multimeter on the ohms scale use a "trailing lead" (a roll of cable that has one end attached to the earthing in the switchboard, the other end on one probe of the meter. The remaining probe to be inserting into the earth terminal on the switch). Not sure on U.S. code but the reading should be less than 2 Ohms
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May 12, 2009 08:23
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