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Old 07.07.2015, 21:31
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Re: help uninstalling ceiling lamp

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Umm... 220 and 110 GFIs and CBs have the same trip latency. Both North America and Europe use 2 leg house service 220, is _also_ single phase, here. 220 certainly seems to hurt more than 110. My main issue with 220 is that because the wire sizes are smaller, screw type terminal blocks tend to have a higher point load, so hot joints are a LOT more common. That is just my profession opinion, feel free to disregard as you see fit.


By the way, the reason trams use 600 DC has NOTHING to do with safety. Fact is, when trams were first being installed, the only motors available which you could control the torque and speed on were series wound DC motors at 600V. Although you could run these "Universal motors" on either AC or DC, they didn't work well at the 50/60 Hz frequency of either distribution grid. In most of the German speaking world, and a few other places, trains DO run these motors on 15 kV AC, but at 1/3 of the "normal" 50 Hz, which means they spend a huge amount of money on generating plant to provide this frequency.


At the turn of the century Synchronous machines were fixed speed with low start torque, which is unsuitable for a traction motor. Once a system commits to a distribution grid and rolling stock at a certain voltage the cost to switch becomes prohibitive, as there is no way to run AC and DC on the same grid. Yes, you can run an invertor on each tram and use a VFD to drive a modern AC traction motor (As I think the Cobra Tram does, but I am not certain), but that is VERY expensive.
This is not entirely correct.

In many cities (including London, Brussels, New York) in the early days trams didn't have overload lines but there was an electrical conduit, so basically a live conductor buried between two guard rails. If you stuck your fingers between the guard rails you could get a shock off the 600V. Of course in those days before elfin safety and the nanny state the attitude was that if you were stupid enough to do that you had it coming to you. However, naughty boys used to play games by dropping nails into the conduit and waiting until a cart horse inadvertently put their hoof on the nail head which would give the horse a massive shock (but wouldn't kill it) but might cause the horse to reel up backwards upsetting the cart. 600V were considered a reasonable compromise between survivability and reasonable power transfer. In the USA there was even an academic commission that did experiments with pigs to obtain statistical data on survivability at different voltages and 600V emerged as being a reasonable cut-off point. The impedance on the feeder lines was so catastrophic that when you were trying to accelerate at full power, the available voltage might drop to less that 400V meaning the light bulbs (which were in fact 120 V bulbs five of which were daisy chained in series) almost went completely black so in the early days they went on using paraffin lamps. These paraffin lamps were the cause of the first major accident on the Paris Metro by the way. The train caught fire but people were able to get out, only to be killed by the smoke that was filling the tunnels and adjacent station. Because of the high impedance, the protection breaker couldn't distinguish between an accelerating tram and a short circuit which was why they used very slow fuses.

Modern technology is miles better in many respects, but the 600V has been cemented into perpetuity as anything that's new needs to be compatible with what's old. Some systems have since moved onto 750V, but if they were to design from scratch they'd go for much more than that.

AC electrification began at about the same time as DC but in the early years DC was preferred as it was simpler. Early AC projects also used 600V, in three-phase actually and using synchronous traction motors, but the fixed speed nature of the motors led to lots of problems that could be solved but just added to complexity and weren't really worth it. It was until a generation or so later that high voltage AC caught on for railway electrification but by then they had moved towards single phase which was far more sensible.

Last edited by amogles; 07.07.2015 at 21:42.
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  #42  
Old 07.07.2015, 22:00
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Re: help uninstalling ceiling lamp

Now where did I read this?
“Fooling around with alternating current is just a waste of time. Nobody will use it, ever.” — Thomas Edison, American inventor, 1889 (Edison often ridiculed the arguments of competitor George Westinghouse for AC power).
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  #43  
Old 07.07.2015, 22:33
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Re: help uninstalling ceiling lamp

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well, I prefer to break that lil plastic box than spend 100+CHF on an electrician to uninstall one lamp, as they start charging when they leave the depot.. too much..

Did you tried a hammer
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Old 07.07.2015, 22:47
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Re: help uninstalling ceiling lamp

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I just replaced a dual switch in my kitchen, two red wires, one green.

Didn't work the first try, silly me, I assumed that the green was live, and the reds went to the two wall lamps.

On of the reds was live, though I did disconnect the breaker, but had to turn it back on to find out which was live.

Tom

Try this
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  #45  
Old 07.07.2015, 23:29
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Re: help uninstalling ceiling lamp

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Try this
Ummm, if the breaker is off, NONE are live.

Tom
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  #46  
Old 07.07.2015, 23:36
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Re: help uninstalling ceiling lamp

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Umm... 220 and 110 GFIs and CBs have the same trip latency.
I'm NOT talking about breaker trip latency, rather of the fact that an untripped line will more readily kick you off the higher the voltage, thus a lower voltage line is more dangerous.

Tom
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Old 08.07.2015, 01:25
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Re: help uninstalling ceiling lamp

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I'm NOT talking about breaker trip latency, rather of the fact that an untripped line will more readily kick you off the higher the voltage, thus a lower voltage line is more dangerous.

Tom


Sorry, That is rubbish. Please point me to some physics. My trip latency remark was in response to


"110V is dangerous primarily because of the impedances caused by very long single phase feeders, and because the protection / breakers cannot always distinguish between a real short circuit and normal load and so sometimes fail to trip"
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Old 08.07.2015, 08:54
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Re: help uninstalling ceiling lamp

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Qualified electricians, with VERY few exceptions won't do it wrong. On the one hand, they risk their license,on the other hand, they spend a lot of time putting stuff done by amateurs right. This is very frustrating work, as you end up having to check every damned thing in the whole house, which takes a long time and the customer then moans "5 hours??? To replace a switch???"

They screwed up some of the wiring on our new build - and all the neighbours too.
After a few visits, they still couldn't work out what was wrong so I had to work it out and explain it - to their boss when I called him in to explain himself.
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Old 08.07.2015, 09:49
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Re: help uninstalling ceiling lamp

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They screwed up some of the wiring on our new build - and all the neighbours too.
After a few visits, they still couldn't work out what was wrong so I had to work it out and explain it - to their boss when I called him in to explain himself.
Sadly, all too often the case in construction. I sometimes think that the combination of price pressure as well as the companies margin leads straight to this. I am astounded at how many trades regard callbacks for rectification as par for the course. I was an industrial electrician, Different world. Most of the electricians I know here do industrial/commercial work, but if it is a larger company they end up going on rectificaion calls for residential work. They HATE it.


The "Sind Sie Fachmann?" response is one of the few things that has browned me off since day one here in CH. I find it tiresome to explain to a plumber that toilet flushes should not occaisionally "hang up" when it is a new installation, to a maurer supposedly fixing a leak that water will not flow uphill etc, etc, etc.
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Old 08.07.2015, 09:54
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Re: help uninstalling ceiling lamp

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The "Sind Sie Fachmann?" response is one of the few things that has browned me off since day one here in CH. I find it tiresome to explain ... to a maurer supposedly fixing a leak that water will not flow uphill etc, etc, etc.
If you have a Maurer fixing your leaks I'm not surprised that he has problems with the properties of water.
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Old 08.07.2015, 09:59
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Re: help uninstalling ceiling lamp

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If you have a Maurer fixing your leaks I'm not surprised that he has problems with the properties of water.


If it is the flex joint between two slabs, the maurer is the one to look at it first.
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