120 V or 240 V Mains - which voltage is better?

[Hellbound]

What do you mean by "IF"? Under your pet theory, what voltage is on the American lines?

Depends on where you are. Typically, on the lines running directly by a house it's NOT 7200V. Typically 120/240 or 120/208.

https://en.wikipedia.org/wiki/Distribution_transformer

The number of customers fed by a single distribution transformer varies depending on the number of customers in an area. Several homes may be fed off a single transformer in urban areas; rural distribution may require one transformer per customer. A large commercial or industrial complex will have multiple distribution transformers.

All depends on where you are.

 

[psionl0]

That's not true, though. There aren't transformers at every house, except in rural areas where houses are far enough apart that it's cost effective. Transformers typically server several houses in an area, usually a block or so (depending on the density of dwellings and the type of building, an apartment or large office building might be served by its own transformer, for example).

My source says, "At each house, there is a transformer drum attached to the pole". However, if you know different then I am prepared to be guided by your knowledge. Certainly, an apartment complex is a different kettle of fish If it is large enough then it might be fed with the full three phase electricity and contain a network of distribution transformers.

A single pole top transformer may serve more than one house. Possibly 2-4 houses if they all run off the same pole. However, I am skeptical that such a transformer could supply an entire block.

 

[psionl0]

Ninja'd

Depends on where you are. Typically, on the lines running directly by a house it's NOT 7200V. Typically 120/240 or 120/208.

https://en.wikipedia.org/wiki/Distribution_transformer

All depends on where you are.

According to your link: "The high voltage primary windings are brought out to bushings on the top of the case".

It is the secondary (not the primary) that is at 120/240V. As for 120/208, this seems to be a rare practice in the US for residential customers. https://en.wikipedia.org/wiki/Distribution_transformer#Secondary

 

[Hellbound]

Ninja'd

According to your link: "The high voltage primary windings are brought out to bushings on the top of the case".

It is the secondary (not the primary) that is at 120/240V. As for 120/208, this seems to be a rare practice in the US for residential customers. https://en.wikipedia.org/wiki/Distribution_transformer#Secondary

Hmm. I'd have to check on how our neighborhood runs, then. We have NO power poles near our house (our lines are underground).

That being said, I know for a fact that transformers often feed multiple dwellings. We've had our whole street knocked out before when a pole-mounted distribution transformer has blown.

You may be right that the actual pole-mounted lines are all higher voltage. Hard to find any references that give a clear-cut answer, but I'm leaning towards the pole wire=higher voltage side.

 

[psionl0]

We've had our whole street knocked out before when a pole-mounted distribution transformer has blown.

A short circuited pole top transformer could cause electricity to the primary side to be cut off which would plunge the whole neighbourhood into darkness.

 

[Hellbound]

A short circuited pole top transformer could cause electricity to the primary side to be cut off which would plunge the whole neighbourhood into darkness.

Yes, but there's no transformers near any house on our street, nor any poles. The nearest pole is ~200ft away.

By the way, here's a picture of that pole from google street view. It's not the best, but you can see the secondary line coming down the pole (inside the PVC pipe), and no transformer at the top, where it comes off the wire.
.

That being said, the round metal cylinder at the bottom may be some type of device, but I wouldn't expect a transformer to be ground-mounted.

ETA: Also, meant to provide this link as well:
http://electrical-engineering-portal.com/north-american-versus-european-distribution-systems

They clearly show that even U.S. systems have multiple places per transformer. They do point out it's fewer customers per transformer in the U.S. system, because they can only run about 250 ft due to voltage drops. The European system can do runs up to about a mile form a transformer.

 

[lomiller]

A single pole top transformer may serve more than one house. Possibly 2-4 houses if they all run off the same pole. However, I am skeptical that such a transformer could supply an entire block.

Pole top transformers are available to at least 360 kVA which could supply 15 100A services drawing their max current. Since that rarely happens I’d expect more like 25-30 homes, but electric companies would have their own rules and take customer need into account. Pad mount transformers for places with underground cables could be considerably larger, but in practice probably not much due to wire diameter and current limits.

 

[psionl0]

That being said, the round metal cylinder at the bottom may be some type of device, but I wouldn't expect a transformer to be ground-mounted.

If a neighbourhood is supplied with underground power then the only two logical places for a transformer would be ground mounted or underground mounted.

ETA: Also, meant to provide this link as well:
http://electrical-engineering-portal.com/north-american-versus-european-distribution-systems

Now THAT is a reference.* Thanks for that. It lists a comparison of the advantages and disadvantages of the North American and the European systems.

* The web site has "engineering" in its name so it must be good.

 

[jsfisher]

Maybe this will help: https://earth.google.com/web/@42.73...r/data=IhoKFkJwaWtNWjdVU1RSQURkRFJlaW1qdkEQAg

If that link works for you, you should have a Street View of a pole with a transformer. You can explore around to the left and the side street to get an idea of how many residences are feed from that one transformer.

By the way, the top-most cables on knob-insulators are the high-voltage feeders. Below that a twist of three wires (two hot and an uninsulated neutral) for domestic 240/120V. The bottom-most two cables are cable TV and telephone below that.

 

[lomiller]

As for 120/208, this seems to be a rare practice in the US for residential customers. https://en.wikipedia.org/wiki/Distribution_transformer#Secondary

Rare for houses, but my understanding is that it happens. Much more common for apartments, which are also residential.

 

[Hellbound]

Maybe this will help: https://earth.google.com/web/@42.73...r/data=IhoKFkJwaWtNWjdVU1RSQURkRFJlaW1qdkEQAg

If that link works for you, you should have a Street View of a pole with a transformer. You can explore around to the left and the side street to get an idea of how many residences are feed from that one transformer.

By the way, the top-most cables on knob-insulators are the high-voltage feeders. Below that a twist of three wires (two hot and an uninsulated neutral) for domestic 240/120V. The bottom-most two cables are cable TV and telephone below that.

There we go! That makes more sense

 

[Hellbound]

If a neighbourhood is supplied with underground power then the only two logical places for a transformer would be ground mounted or underground mounted.

Except this is the point where it goes from above ground to underground, and those cylinders aren't in front of any other houses. So it has to be transformed here and fed at 120/240 from this point on (if that's a transformer), and if that's the case why not do it at the pole, where it's protected better form the elements, the nearby road, and the homeowner's lawnmower? Plus, I've never seen a transformer that looks like that. A quick image search for ground-mounted distribution transformers shows they don't look like that at all:
https://www.google.com/search?q=gro...h9_VAhXk6YMKHa2aBDIQ_AUICigB&biw=1680&bih=944

Now THAT is a reference.* Thanks for that. It lists a comparison of the advantages and disadvantages of the North American and the European systems.

* The web site has "engineering" in its name so it must be good.

Heh. Thanks. I knew there had to be some better info out there, but it's hard to find. Not in the least because of a stupid series of movies that keeps getting in the way of my searches (no, a ground mounted transformer is not a legless Optimus Prime!).

 

[Dabop]

Hmm. I'd have to check on how our neighborhood runs, then. We have NO power poles near our house (our lines are underground).

That being said, I know for a fact that transformers often feed multiple dwellings. We've had our whole street knocked out before when a pole-mounted distribution transformer has blown.

You may be right that the actual pole-mounted lines are all higher voltage. Hard to find any references that give a clear-cut answer, but I'm leaning towards the pole wire=higher voltage side.

Another source I read says that where underground wiring is common (like newer housing estates) there are 'green boxes' every few houses, these are the transformers that do the job of the poletoppers in aboveground wiring areas

 

[Dabop]

Yes, but there's no transformers near any house on our street, nor any poles. The nearest pole is ~200ft away.

By the way, here's a picture of that pole from google street view. It's not the best, but you can see the secondary line coming down the pole (inside the PVC pipe), and no transformer at the top, where it comes off the wire.
.[qimg]http://www.internationalskeptics.com/forums/imagehosting/thum_6875995ec370b4b5.jpg[/qimg]

That being said, the round metal cylinder at the bottom may be some type of device, but I wouldn't expect a transformer to be ground-mounted.

ETA: Also, meant to provide this link as well:
http://electrical-engineering-portal.com/north-american-versus-european-distribution-systems

They clearly show that even U.S. systems have multiple places per transformer. They do point out it's fewer customers per transformer in the U.S. system, because they can only run about 250 ft due to voltage drops. The European system can do runs up to about a mile form a transformer.

Hmmm theres too many insulators on that top wire to be a lousy 110v- I suspect that that is indeed your 7Kv supply, and that green cylinder is indeed pretty much the green box I referred to in my previous post- ie the 7kv to 120/240v two phase transformer supplying the underground feet to the house (possibly 2 or 3 houses according to some places)
And yes it looks horribly vulnerable where it is, considering the size and voltages involved, I would have expected it to be pole mounted

edit to add
from your link http://electrical-engineering-portal.com/north-american-versus-european-distribution-systems
It shows in the first diagram (North American Layout) that the HV is supplied (they say its 12.47Kv, rather than the 7Kv in the OP article) as a 3 phase, 4 wire feeder, that splits to 12Kv single phase street feeders (they called them single phase laterals), with local transformers that can supply several houses (note only up to 250ft away as mentioned further down the article) that convert the single phase 12.47Kv to a split/ two phase supply of 240/120v
Pretty much as I was expecting and as PsionIO and I were both putting forward
Anyone still want to disagree with that diagram? (glad you posted it Hellbound as I was actually drawing up pretty much an identical one)

 

[Dabop]

Pole top transformers are available to at least 360 kVA which could supply 15 100A services drawing their max current. Since that rarely happens I’d expect more like 25-30 homes, but electric companies would have their own rules and take customer need into account. Pad mount transformers for places with underground cables could be considerably larger, but in practice probably not much due to wire diameter and current limits.

The link kindly provided by Hellbound also puts this idea to bed, as due to voltage drop issues, the maximum length of cabling between the transformer and the houses can apparently only be about 250ft...
Packing 25-30 houses into a circle so that all are less than 250ft away would be called a caravan park here (trailer park as the USAians call em), even the cheapest of housing estates would be struggling to have house blocks that small!

 

[Hellbound]

Eh, I dunno. There's close to 20 houses within 250 ft of that pole, and that's just down into the cul-de-sac where my house is (not counting the other three streets leading away from that intersection). A 250ft distance would be a circle 500 ft in diameter.

Or, if you look at it another way, there's 4 streets leading away from the intersection where that is. If you figure a house every 80 feet along each street, on both sides, that still comes to 24 houses along the four streets (well, 20 anyway, if you remember the corners count along two streets each). In more densely packed areas, I could easily see 25 to 30.

All that being said, I'll look around the neighborhood a bit and see what I can see. I still don't think that small green cylinder is a transformer (no image searches for ground-mount transformers returned anything similar), but I'll check it. There are some green ground-mount boxes the next street over, but they're cable/phone (I've seen the trucks working them). I'll take some pics if I find anything useful

 

[EHocking]

Nigel : You see, most houses will be powered up to 120. You’re on 120, all the way up, all the way up...Where can you go from there? Nowhere. What we do, is if we need that extra push over the cliff...240. One hundred and twenty more.

DiBergi : Why don’t you just make 120 more powerful and make 120 be the top number, and make that a little more powerful?

Nigel : These go to 240.​

In Australia, the standard for nominal voltage (since 2000 (AS 60038) ) is actually supposed to be 230 volts with a +10%, -6% range.
I had a sparky out sorting a new rangehood that kept blowing, and was told that it is not uncommon that the delivered voltage is usually closer to 260 - ours read 270. So stuff you Nige.

 

[John Jones]

Got a wife and kids in Baltimore, jack.
I went out for a ride, and I never went back
Like a river that don't know where its flowing
I took a wrong turn and I just kept going.

 

[Modified]

Another source I read says that where underground wiring is common (like newer housing estates) there are 'green boxes' every few houses, these are the transformers that do the job of the poletoppers in aboveground wiring areas

That is what we have here, a green box for every five to six houses.

 

[Dabop]

In Australia, the standard for nominal voltage (since 2000 (AS 60038) ) is actually supposed to be 230 volts with a +10%, -6% range.
I had a sparky out sorting a new rangehood that kept blowing, and was told that it is not uncommon that the delivered voltage is usually closer to 260 - ours read 270. So stuff you Nige.

Thats the difference between the real world and the fantasy world a lot of these bureaucrats live in lol
With a stroke of a pen, they can change it to whatever they want- 240 not enough, lets make it a billion volts

Back in the real world, changing the voltage (even by ten volts) can be a major exercise, in some transformers they can adjust the voltage output by changing tapoff points (the ones used in some country areas have this facility to overcome line loses, voltage is a little low, bump it up to the next tap to compensate), others would need to be pulled out and either rewound or replaced... costing millions if not 100's of millions of dollars if not more

A costly exercise, and one that either the taxpayer or the consumer would end up having to shoulder- so basically everyone says 'good job bernie' pats him on the head and simply goes about business as usual with a nod - "we arent 240Vac anymore, we are 'nominally' 230 +- 10% ok"