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Boswell

Well-known member
Joined
Apr 29, 2006
Messages
222
Location
U.K.
Neutral is tied to earth at the substation. It's usually a volt or so above earth by the time it reaches a domestic meter because of the line impedances.
 
In the UK the substation (i.e. the local transformer) is often the size of a small house. Much larger than the US 'pole-pig' that feeds a small number of residences.

Local substations are 3-phase and generally quite colossal. I think the local substation when I was growing up fed something in the order of 500-600 houses, so imagine the size...

One side-effect is that they can end up being some distance from the residence, and the neutral can modulate a little bit. However, Current is generally halved for the same given power consupmtion, and the outlawing of certain methods & practices deemed quite acceptable in the US (such as the use of wire-nuts) and the more stringent low-resistance connection junction methods used in place, and higher cable-gauge-per-unit-current means that neutral modulation is actually generally quite low.

I've often measured more neutral-to-ground difference voltage at many US loactions than is common (no pun intended) in the UK.

-And yes, Light switches and power switches are indeed Down-for-on. -Only yesterday I was switching on an SSL for someone for the first time, and they were baffled by why the power switches were "down-for-on". -I told tham it's because we drive on the left in Britain, and that suddenly seemed to make sense to them, for some reason!

ALL power plugs are fused, the only permissable exception is for X-ray machines in hospitals, and those plugs must be clearly marked as unfused, and the cable armoured... The vast majority of power outlets have power switches on them for each single outlet.

They're not afraid of high voltages over there... Supergrid is 750KV... that's three-quarters of a million volts! When I started work after I left school, our studio was close to a grid-switching station that used 'snuffer' jets to blow out the arc when the contacts swung open... talk about loud!!! 3-phase comes to your house or workplace as 415V AC between lives. Just to complicate thingts, Liverpool histoprically had a different phase sequence to the rest of Britain, and motors often ended up getting mis-wired and running backwards... :shock:

Keith
 
Funny, I never thought of Liverpool as running backwards..

One more thing to mention: supplies to domestic premises in the UK are always single-phase, never 2-phase with grounded centre-tap. If you want more power, e.g. for a large kiln, it's really quite difficult to get a 3-phase 415V feed unless you register as industrial premises.
 
No, you're not allowed to bond the neutral to ground. However, you can bury your own earth plate and use that for the earth as long as it's also connected to the armoured shield of the incoming mains service.
 
> I think one of the reasons that we have 120V circuits in domestic situations here was the due to the original smear campaign Edison launched against Tesla/Westinghouse promoting the "safety" of DC power.

That was a royal mess. It is hard to figure what really happened.

> Our 120V (240 CT) system is probably the result of a compromise.

No, it came about very simply.

Edison invented the Electric Bill. Of course you should have something to sell before you present the bill, so he set up some generators and wired a few blocks of NYC.

He did not have good insulation. He went camping with rubber moguls, but most wiring was semi-exposed. He knew his workers died around electricity, and didn't want his customers dying. He knew that workers rarely if ever died around 100V machinery, so he settled 100V as his distribution voltage.

Edison did not invent the Electric Light, but he did commercialize a lamp that would work on 100V power.

Although Tommy's installations did not cover a lot of area (due to the expense of distributing power at low voltages), his lamps and plugs and sockets became The US Standard. We got stuck with about-100-Volt systems.

The economics of higher voltage are compelling. But the market has great inertia. Historically the wall-outlet voltage has snuck up 2 volts per decade.

AC of course was necessary to make broad distribution possible. And AC motors can be cheaper and more reliable than DC motors. But basically we wire the home as if it were ~100V DC lamps.

Oh: Tommy used split-phase DC. He ran three wires, one +100, one -100V, one at zero. Each small building was fed one side; large buildings got both sides. Loads were almost all 100V. This gave twice the total power for only 1.5 times the copper cost, and only 100V shocks (except around very large motors which would be attended by trained workers).

There was less of a rush to electrify in the UK and Europe. Also smart men like Siemens saw more clearly than Tommy. Better insulation and plugs were developed. The key development was improved incandescent filaments that could be made in low powers and high voltages. (There are at least three major generations of incandescent lamps; Tommy's lamps really sucked.) UK/Euro residential installations generally favored ~200V rather than ~100V wall power.

> Is the neutral connection normally tied to ground or does it float relative to earth?

In general: the system has to be tied to earth somewhere. If it truly floated, stray leakage would develop huge voltage and punch-through insulation. More important, transformer breakdown or lightning could send sparks flying out of walls.

Where and how the system is tied to earth is a matter of local custom and regulations. As you say, in the US we pretend to ground the Service Entrance, and maybe also the pole transformer and 13KV lines. This can cause its own sort of problem. It might be reasonable, in dense service areas, to ban earthing at the premises and do it professionally at a distribution point.
 
. It might be reasonable, in dense service areas, to ban earthing at the premises and do it professionally at a distribution point.
But not in the lightning capital of North America. We ground locally.

It can jump between cable tv, phone and mains drop along your siding, so best to try to find somewhere to put it.
 
Lots of double-insulation required in the UK/Europe. Anything sold without a ground connection HAS to be double-insulated. -So too does anything which will reasonably be forseen to be run along greatly-extended cable runs.

I must say I have difficulty calling the US domestic AC system 'two-phase'. -To me it's a single phase, two-pole or two-leg system, but the TIMING is still single phase. -I really have a hard time twisting my mind to think of DC as being any kind of phase at all! :shock: -I can think of it as two-pole, but not two-phase, though I understand the reasoning behind the 'phase' terminology being adopted. -Grudginly...

-I believe that the reason for double-insulation on European building sites is that reliance on 3rd-wire safety ground means relying on a third conductor which is never tested until someone's life depends on it. -When either a live or a neutral conductor is damaged, the problem is noticed immediately and the extension cable is either repaired or replaced. -If the safety conductor is damaged, you may not know about it until you are standing in a puddle of water and something goes horribly wrong... For that reason, building sites require hermetically sealed plastic housings containing double-insulated step-down trannies, feeding 100Volt distribution systems.

Yes Liverpool is a strange place (electrically speaking) at times. Beneath Exchange Street in the city centre (near Dale Street and the town hall) there are still some bussbars from the old downtown DC distribution system that was tried and abandoned.

I left Liverpool when I saw the writing on the wall: The price of bricks went up, and the bottom fell out of the alloy-wheel market... No way to make a living in that town any more... :wink:

Keith
 
[quote author="SSLtech"]
I left Liverpool when I saw the writing on the wall: The price of bricks went up, and the bottom fell out of the alloy-wheel market... No way to make a living in that town any more... :wink:

Keith[/quote]
Would that be about the time somebody held a flower festival there and it was open season on old people sniffing roses
 
-That was the 1984 Garden Festival. -They held it at the bottom of the road where I lived. They renovated the 'cast-iron shore' and built all sorts of new buildings.

-'Urban Regeneration' they called it. 'Wasted money' I called it. Now there's a lot of abandoned ruins from the 1980's at the bottom of my mum's road.

http://www.bbc.co.uk/liverpool/capital_culture/2004/04/garden_festival/index.shtml

Anyway... back to electrickery: Be careful if you ever have to install 3-phase gear into any place in Liverpool, and check the phase sequence before powering on anything 3-phase!!! -Phase rotation testers are a must in older places!

Keith
 
Just a note, I now remember that with a three phase delta, they have to bring out a neutral/ground so that the breakers will trip in case of a fault.

I believe this neutral/ground is the one used on the pri, which is probably a wye system.
But ask an electrician to be sure.

Then there's that three phase delta with a "stinger", which always screws things up.
 
"Two-phase" is exactly what it is. If you were to put two beams of a scope on the two 120V phases and look at them with respect to neutral, you would see a pair of sine waves 180 degrees apart. Similarly, if you look at a 3-phase system (star connected) with respect to neutral you see three sinewaves 120 degrees apart. The centre-tap of the 2-phase system is equivalent to the star connection in 3-phase.

Many stepper motors are 4-phase, and so it goes on.
 
Yes, I suppose that's right.

What confuses me is that it's derived from a single phase of the three, and then effectively polarity-inverted... which on a sine wave of course produces exactly the same result.

-I get so wrapped up in the means that I forget the end... perhhaps it's a 'MAINS' to an end...

...I'll stop now...

:wink:

Keef
 
When coordinating with electricians for shore power hookups for our TV truck, we ask for "240 volts, centertapped neutral, 50 amps" and they always seem know what we mean :green:
 
I should probably aplogise, I certainly meant to cause no dispute on the issue, however it appears that I'm not the only one who is conflicted with the terminology.

I certainly now better appreciate the "other" way of referring to the same thing. I also suppose that it's an easy way to generate a 6-phase power feed: the 3 primary phases and the three (polarity inverted) secondary phases... -interesting!

Keith
 
You can have a 120-0-120 two phase.

Take a 208 three phase xfmr wired in a wye.
The neutral to any phase will be 120, but the three 120 legs will be shifted.
I am not sure if it would be 120 degrees shift or something else.

Phase to phase voltage will be 208, instead of 240.
This is due to the phase angle.
 
Yes.

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&#8747 = ∫
&#8706 = ∂
&#8773 = ≅
&#8800 = ≠
&#8804 = ≤
&#8805 = ≥
&#931 = Σ
&#8240 = ?
&#916 = Δ
&#402 = ?
&#937 = Ω
&#710 = ?
&#185 = ¹
&$178 = ²
&#179 = ³
&#215= ×
&#247 = ÷
&#188 = ¼
&#189 = ½
&#190 = ¾
&#177 = ±
&#960 = π
&#8260 = ⁄
 
Code:
&#937 ;= Ω

Hey, thats cool. I always wondered about that.....

Now, how do you do actually do it?
 
I've been in this business for 35 years. Only in the past 5-10 years have I become "Muncy" and "Whitlock" enlightened, so my powering and audio wiring practices have evolved considerably from telescoping shields and potential pin 1 problems to considerably more enlightened approaches.

So now I'm wiring a new room. In the past I learned that running audio equipment on two phases invited trouble and so I tended to put a whole room on a single phase. But maybe that was just because I wasn't paying attention to loop area (thank you Neil Muncy). If you feed some audio equipment from one outlet which is on phase 1 coming from one side of the room and some other audio equipment from another outlet which is on phase 2 coming from the other side of the room, then you are looking for loop area-based troubles!

So, my question is just to confirm my conclusions: It seems to me it should be perfectly ok, and actually preferable to "balance your loads". My new Topaz transformer produces two single phase 110 volt circuits on its secondary. If I divide that into two strips, one on each phase, all centrally located at the transformer, and then split up the audio equipment, is this asking for trouble?

BK
 
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