:roflmao::roflmao::roflmao::roflmao:
Urgent, need advice please. What's the difference between 1, 2 and 3 phase power?
- Thread starter Gone
- Start date
Yes Rob voltage drop, + or - 5% varable supply voltage would make it roughly 50v.
Isn't that what I was saying. If you calculate with 230 or 400v by your load current or maximum demand, AMPS, your actual voltage at 5%+/- is pointless.
Isn't that what I was saying. If you calculate with 230 or 400v by your load current or maximum demand, AMPS, your actual voltage at 5%+/- is pointless.
Rob if you want to read the regs you wont find it at ecables, I have a copy of AS 3008 you could borrow.
Very true Ollie. Radox cable was being used a lot too.
All Cinema wiring at that time had to be fireproof. Which meant all cables had to be enclosed in steel ducting, screwed steel conduit, steel flex or pyrotenax used.
Pyro was great for exit lights and aisle lights in cinemas because it was only 4mm or in diameter and could almost be surface clipped to the slab under the underlay.
Plus much cinema work was upgrades from the 40s era. One helluva of lot of pyro sub mains and mains in that era.
I'm coming up 60 and was doing this work shortly after qualifying in my mid 20s. So decades is quite true.
Ask me about a certain electrical inspector being "lubricated" to approve an installation that had a ramset nail, mid slab, in what became the neutral of the pyro mains!
Pyro has gone out of favor, probably a good thing. Difficult to work, impossible to repair and too prone to damage during building. But once it's in and not disturbed it's there for ever.
For those who wish to know what pyrotenax it essentially copper pipe with with the wires enclosed in magnesium mineral insulation. It's major benefit is it's ability to survive in fire for a long period of time.
It also very compact for it's current capacity.
http://en.wikipedia.org/wiki/Mineral-insulated_copper-clad_cable
As I've stated to you before Rob, I have done ovet a dozen cimemas in Melb and I asways do the bio box, all very interesting stuff.
I would hope a manufacturer of cable to an AS would know what they talking about.
Anyway post the pages out AS 3008 which refutes my method of calculating cable size!
Which of the over 200 do you want, as there is a number of factors to take into consideration not just the ones you quoted. If you want to borrow and have a read fell free to go to my place in Melb and pick up as I'm in Collie WA at the moment.
OK I have pdf of AS 3008
See the attached excerpt pdf.
When specifying cable size there are three major factors, one related to load current, one related to percentage voltage drop of the cable and the other related to short circuit current which is essentially temperature rise of the cable under short circuit conditions.
I believe my original design brief pretty well covered it.
Do you mean this? Compared to this
(b) Voltage drop-- dependant upon the impedance of the cable, the magnitude of the load current and the load power factor.
Rob you mention two things that are in part (b) there is still parts (a & c), and cable de-rating I can't see that mentioned.
Really though Rob, you are a clever person but to keep referring to documents is a bit unfair, I'm only going on with what my drug and alcohol infected brain can remember twenty odd years ago.
John,
Your practical experience is acknowledged.
However, when you take me task about factors that have been mention in both post #55 and #60
I feel cheated.
The only factor that wasn't mention specifically was fault current, but that is largely covered by "heat".
Impedance of cable is essentially the ac resistance factoring power factor and load current but result is cable voltage drop.
Anyway let's agree or agree to disagree either way it's getting boring for both you and I and others.
I'm going to have a Scotch! If you were you would be welcome to have one as well.
cheers
Rob
Rob I thought we were finished this afternoon, but really I don't disagree with you, I'm just surprised you would persist with something when all I was trying to relay was that variations in supply voltage are not considered and voltages stated as standard are what is needed to do any calculations within the industry. Yes the actual voltage is important under certain conditions or faults to be used for calculations but generally speaking it is 230V and 400V, which is what you would not acknowledge.
So if you can accept that 230V and 400V are Australian Standards, I'll admit that I didn't always quote all that you said when you were in the ball park. Thank you for acknowledging my practical experience or what ever you meant by that since we were speaking in theory.
So if you can accept that 230V and 400V are Australian Standards, I'll admit that I didn't always quote all that you said when you were in the ball park. Thank you for acknowledging my practical experience or what ever you meant by that since we were speaking in theory.
i still dont understand this line of thinking. if the purpose of these calculations is to determine the size of cables required to safely do the job, how can you possibly ignore what the numbers are in fact, and instead use nominal standards? what i'm getting as a reader of this thread is the 230v/400v are national standards, but not actually used in most states, and likely a fiction in the states where they are used. surely noone is basing safety related calculations on fictional numbers?
Let me try to explain this a little differently.
Lets say we had 230 litres of water and I poured this over you from a large open topped barrel, the pressure at which this hit you would hurt but not be dangerous.
Now lets get 230 litres of water and spray you with a high pressure hose, the pressure of this would be dangerous and even kill you.
Now lets transpose this, 230v and 10amp for barrelled water and 100amp for high pressure hose.
It does not matter if it is 230v or 250v but the 10 amps will give you a tingle.
Now same thing 230v or 250v but the 100 amps will really hurt or kill you.
It is the current or amps that hurt not the voltage.
I am speaking about single phase, touching two or three phases at once is a game I have never played and never wish to, blowing up two phases in my face once in my life was enough and I don't wish to go there again, I've learnt my lesson the hard way.
Lets say we had 230 litres of water and I poured this over you from a large open topped barrel, the pressure at which this hit you would hurt but not be dangerous.
Now lets get 230 litres of water and spray you with a high pressure hose, the pressure of this would be dangerous and even kill you.
Now lets transpose this, 230v and 10amp for barrelled water and 100amp for high pressure hose.
It does not matter if it is 230v or 250v but the 10 amps will give you a tingle.
Now same thing 230v or 250v but the 100 amps will really hurt or kill you.
It is the current or amps that hurt not the voltage.
I am speaking about single phase, touching two or three phases at once is a game I have never played and never wish to, blowing up two phases in my face once in my life was enough and I don't wish to go there again, I've learnt my lesson the hard way.
There is no doubt the calculations are done at 230volts.
Australian Standards are over specced to blazers so there no real risk anyway. Asia uses much smaller cables.
And if the cable is specified by the formula/chart/software is marginal (my guideline -within 10% of maximum rating) in size then most sparkies will go a size up.
The real risk is fact that many novices rate a cable a the ideal current and then enclose it and fuse it at the maximum. Cable needs to de-rated depending on how it installed and for length. In short run , less than 50 meters it seldom causes a problem. But 220 metre run to the workshop should be calculated for size and likely load.
The important cable sizing issue relates more street mains (from the supply company to the main switch board) and sub-mains (from the main switch board board to the sub boards). These cables can have serious continuous load on them. Anyone who has seen what happens to a loose connection on a main switch on 250 amp main board will agree with this
For sub circuits (circuits form the switch board to the load) , especially for short runs it's not as critical.
I should say industrial installations are a bit different to the above.
thanks, chaps.
these are just two irrelevant asides...
the corner substation next to my house was refitted about 4 years ago. the guys were here every day for 3 weeks or so, and told me the hardware had not been changed for something like 50 years. i did see the cables which fed the substation under the street, and boy were they huge! i was amazed by how much manpower, time and hardware can be absorbed by a substation measuring about 10m x 8m (with 2 levels in side). their final push was a 36 hour marathon non stop. i was away at the time, but they told me when i got back at the tail end of it, that someone had made a noise complaint to the police in the middle of the night! you have to wonder if some people have a brain at all...
last year, a truck hooked the power cables at the family home of my former partner. pulled the barge board off the house etc. she went outside to find the cables on the ground, and the truck driver, who decamped quite quickly told her that it wasnt a problem, as they couldnt be live if they were on the ground!! she called me and of course i said dont go anywhere near them, and to call the police immediately.
apparently, live power cables on the ground wasnt a good enough reason for the police to attend! so they sat there for an hour till the power guys arrived. unbelievable on all counts.
these are just two irrelevant asides...
the corner substation next to my house was refitted about 4 years ago. the guys were here every day for 3 weeks or so, and told me the hardware had not been changed for something like 50 years. i did see the cables which fed the substation under the street, and boy were they huge! i was amazed by how much manpower, time and hardware can be absorbed by a substation measuring about 10m x 8m (with 2 levels in side). their final push was a 36 hour marathon non stop. i was away at the time, but they told me when i got back at the tail end of it, that someone had made a noise complaint to the police in the middle of the night! you have to wonder if some people have a brain at all...
last year, a truck hooked the power cables at the family home of my former partner. pulled the barge board off the house etc. she went outside to find the cables on the ground, and the truck driver, who decamped quite quickly told her that it wasnt a problem, as they couldnt be live if they were on the ground!! she called me and of course i said dont go anywhere near them, and to call the police immediately.
apparently, live power cables on the ground wasnt a good enough reason for the police to attend! so they sat there for an hour till the power guys arrived. unbelievable on all counts.
I can tell a similar story about Telstra.
About 6 years ago both our Telstra phone lines went off the air. I rang Telsta and ask WTF and they gave a repair time of 4 weeks.
So I immediately ported the numbers to my Optus cable CAU. There are still there.
It transpires that some feral had put a corkscrew digger through four of main exchange trunk cables to the Caulfield area.
I found out where whilst walking the dog.
Telsta had to install underground kiosks (the type two lineys climb into which are about 3 m deep) either side of the damage and re-join thousands of cable pairs.
The earth works took a week because of the concrete form works. Then there was a rotating shift of 6 lineys working 24/7 for at least another 2 weeks.
I hope the dude who did it had insurance.
just imagine what the internal tingle would feel like when you raise the auger, and there are hundreds of coloured wires hanging off it! probably something like a one week long bungee jump.
like that guy who hooked some big fibre cable between sydney and brisvegas some years back.
like that guy who hooked some big fibre cable between sydney and brisvegas some years back.
If you want the power people to turn up really fast, don't just tell them there are live wires on the ground. Tell them you have just had a tingle, then you discovered the live wires.
Roger
Or ask the question, " There are powerlines down and the ground is steaming...Is this OK?"
Before you can replace the handset you should hear the sirens in most Metro area's.
Rob, you say short runs seldum cause problems. Well, one the the guys here is your age and well experianced, he put a scenario out for the boys one day to see who could get it. I'm not sure this is up your alley, but give it a go. I was the only one who got it but I'm a bit older than the others and knew straight out and didn't have to think.
Problem- Sub-station supplies a main board at a large complex. It has three sets of 240mm2 SDI's per phase run in parallel. The run is only 11m long and the cables are run flat on cable tray. The cables were running very hot so thermal imaging was taken. There was no hot spot at fixing point as thought but the entire cables were red hot. Why?