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#132677 - 09/23/01 04:51 PM 120 vs. 240V
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
All of you in North America are used to having residential services where nothing is more than 120V to ground. Mr. Joe Have-A-Go could get shocked at 240V by grabbing both hot legs together, but he's more likely to get hit with 120V.

How do you like the idea of normal homes having 240V to ground as in Britain? Do you see it as a potential problem for the average householder? (Excuse the pun!)

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#132678 - 09/23/01 05:23 PM Re: 120 vs. 240V
Nick Offline
Member

Registered: 08/13/01
Posts: 603
Loc: Riverside, CA
I think if everything were suddenly changed to 240V (hypothetically speaking of course) less electrocutions would result for a short time. This is until everyone got used to it. There is an overwhelming opinion in this country that "Oh, it's only 120V"
Because of this many people take it forgranted and get hurt. 240V usually scares the average DIY er and would tend to make them shy away.

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#132679 - 09/24/01 12:08 AM Re: 120 vs. 240V
Dan-aw Offline
Junior Member

Registered: 09/12/01
Posts: 3
Loc: Florence, NJ USA
Paul,
The following was primarily pertaining to your last post. It may also be relevant here.

Very interesting. Sorry I missed out on the guessing. Just a couple questions or comments: Is it not true, that 100mA is enough to kill you? If so, who decided to set your GFCI protection at 100mA? What is the purpose? It sounds like a good idea to protect the entire house and it would be easy to do with your straight 240V system, but does that mean every time an element burns out, the entire house loses power or are there lower rated, faster acting GFCIs on some of the branch circuits? Comes to mind because, when I worked at a production plant once, we had material dryers that would lose an element ever now and again. It would take out half the floor. Had to turn the settings so high. What was the sense in having the GFCI protection? I did work with the engineers to solve the heater element failure problem but my point is that not every Ground Fault is a potential danger to human life. Sometimes we need to separate the life threatening protection and the simple over-current protection. How do you handle that? Oh yes, one other thing, for those of you who had noticed my “stolen tools” post, I had a wonderful tracer kit that would have brought you to that short in about five minutes. Sorry, had to B#!@%&#! Do you have a separate grounding path? Is one leg a “neutral” or a grounded leg? If you don’t have an effective grounding path how do you clear faults? Is it done with GFCI? That may not work all the time. I could go on. Obviously, I’ve never been there. My curiosity has risen.
God bless,
Dan

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#132680 - 09/24/01 03:37 AM Re: 120 vs. 240V
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
well...... i would imagine voltage drop to be less of a consideration on service laterals

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#132681 - 09/24/01 01:12 PM Re: 120 vs. 240V
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
"It's only 120V" eh? Famous last words!

The lower current at 240V for any given power (and thus lower drop and/or smaller cables) is what most people here would probably state as being our main advantage over 120V countries. It's possibly overstated though, because many of them don't realize that American homes have 240V for the "big stuff."

Main GFIs: Yes, one big problem with our "whole-house" GFIs is that a ground fault anywhere knocks out power to the entire installation. This is something that bugs me.

On old urban distribution systems where the house ground was via the cable armor or on PME systems where the ground is bonded to the neutral, GFIs weren't normally used in the past.

It was with overhead rural distribution that the problem arose, as the house was grounded only by a local earth rod. The relatively high impedance ground path meant that even with a direct hot-ground short there most likely wouldn't be enough current to blow a 15 or 30A fuse and, of course, the "grounded" metalwork would be left live. In some areas it was difficult to get enough ground current to blow a 5A lighting fuse.

It was this problem that led to a "whole-house" or main breaker being installed, the term here being ELCB (Earth Leakage Circuit Breaker). Early types were usually set to trip at 500mA or, more likely in residential, were the voltage-operated type (cheaper).

The only other way to provide the necessary protection on these systems would be for each branch C/B to be the ELCB/GFI type.

So the main GFI was never really intended to guard against direct shock. Sensitivities have increased in the last 20 years or so, and 100mA is now common, with 30mA found in some homes.

The main GFI is now also being installed on systems where it isn't strictly necessary to give added protection. In recognition of the problems of a trip taking out everything, however, some panels are available with a split busbar, so that some circuits are tapped off ahead of the GFI (most often for lights).

If a local ground rod is used so that a GFI is necessary for all circuits, the only way to achieve this separation is to use two GFI main breakers.

Individual 10 or 30mA branch GFIs can be used as well, say for an outside outlet, but they're rare in domestic wiring.

Sockets (receptacles) incorporating a GFI are becoming more common for such applications, but still fairly rare. (They protect only the outlet in question; they don't have the feed-thru capability of American GFI recepts.)

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#132682 - 09/24/01 01:26 PM Re: 120 vs. 240V
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Dan:

Sorry, I forgot your other questions. Yes, normal residential service in the U.K. is 240V 50Hz 2-wire with a grounded neutral.

Except for a few single-phase lines to remote properties, all low-voltage local distribution is 3-phase 240/415V Wye with a domestic service just tapped off one phase.

Three different grounding ("earthing" in British terminology) arrangements are in use. Take a look at "Non U.S. Visitors - A question" (currently pg. 4 General area) where I explained them.

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#132683 - 09/26/01 04:37 PM Re: 120 vs. 240V
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
I guess I should have mentioned that there is one small use of the lower voltage here, and that's on building sites where hand-hend power tools are generally 110V due to the "Health & Safety at Work" legislation.

Normal DIY-type tools are only available in 240V versions, but heavy-duty professional drills, saws, etc. are often available as 110V as well.

They're run from a 110V transformer with a grounded center-tap on the secondary so that each line is only 55V to earth. (Really big construction sites use 3-ph xfmrs so each line is 63V to ground.)

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#132684 - 09/27/01 05:54 PM Re: 120 vs. 240V
Steve Miller Offline
Member

Registered: 08/30/01
Posts: 322
Loc: Loudoun Cty, VA
I used to say "it's only 120" also ... until the day I was sitting on a bathroom sink changing a GFI (hot). Then I touched the BK wire. Guess what part of my anatomy felt likr a pin was stuck in it?

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#132685 - 01/02/02 12:01 PM Re: 120 vs. 240V
Texas_Ranger Offline
Member

Registered: 12/17/01
Posts: 2343
Loc: Vienna, Austria
Some addition from Austria: What I see as the main problems of 120V is: Higher loss due to the lower voltage and the higher currents, hence lower maximum wattages per circuit. It's really hard to get a 230V/16A circuit with a maximum load of 3680W to overload, but quite easy to do the same with a 120V/15A circuit which uses the same wiring.
Would rather fit the violations section, but I once saw an American making 12 receptacles out of a standard duplex recptacle, using various extension cords, power strips and taps, most of that stuff ungrounded, only the last extension strip in his chain grounded. No idea where the ground prong had gone...
i had to live in that room so my first thing was to look for the breaker panel. Just in case...
It was really scary.
In facz you could really add that statement to the "famous last words"-collection. There should really be surveys about how many people die stating "But it's only 120 Volts..."
Especially when they hold a black and a red wire in their hand...
*sarcasm*

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#132686 - 01/02/02 02:02 PM Re: 120 vs. 240V
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
I seen it mentioned that the lowest voltage on record as having proved fatal is just 32 volts. Makes you wonder why they sometimes need more than one jolt of 2kV on the chair, doesn't it?!

Tex,
Don't forget that in America grabbing a black and red simultaneously you'd be more likely to get 240 or 208V than 120.

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