American electrics



They have thermal trip only. They cost about 1.3p to make in some sweatshop and are as reliable as a clingfilm condom.
The US electrical system is simply unsafe compared to the rest of the world. It largely comes down to:
Lower voltage. 110V is much more dangerous than 230V. This isn't obvious to the non-technical, but the US went with "common sense" (aka thick people's prejudices) rather than sound scientific analysis. The basic issue is that very few people die of electrocution, whilst loads of people die from electrical fires. The electrical fires largely stem from high currents. If you halve the voltage, you double the current.
The high voltage has other safety benefits, too. For example, during an earth fault, the higher voltage leads to much higher current flow. An overcurrent safety device is, thus, much more effective, leading to much more rapid disconnect of the circuit.
Some numbers. Take a hypothetical circuit rated for a bit over 3kW. In the US, this would be 110V, 30A. If the breaker requires 5x current to trip immediately, this requires an earth impedence of 0.73 ohm right back to the substation. Of course, most US circuit breakers are thermal anyway, so trip is never immediate. With less than about 0.73 ohm, it will take much longer to trip (or perhaps it never trips, if the earth loop impedence is too high). A slightly higher energy circuit in the UK would be 230V, 15A. The required earth impedence is now 3.8 ohms. This is extremely easy to achieve, unlike the 0.73 ohm, which might even be impossible.
Another effect of the low voltage is that "respect" for electricity is lower. The lower voltage leads to lower quality insulation on fittings, cheaper parts and a blase attitude of users to electrocution. The result of this is that the US actually has a higher electrocution death rate per capita than the UK, despite the lower voltage! When you compare the incidence of electrical fires, the differences become much more scary.
Other differences in the US:
1. Low quality cables that have arcing failure modes, leading to fires. 2. Use of wirenuts. 3. Combination of neutral to earth (i.e. effectively TN-C earthing) leading to electrocution in the event of polarisation swap, or some open circuit conditions. TN-C earthing in banned in Europe, except in special (non-domestic) cases. 4. Provision of socket outlets in bathrooms, so users dry their hair in the bath.
Christian.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Actually, the choice of mains voltage on either side of the pond was not decided on safety grounds. The safety issues were largely unknown at the time.

and quadruple the overheating effect.

You missed: 5. the crap quality of their socket outlets, responsible for many fires. 6. building regulations which hinder people modernising their wiring, so extremely old wiring still in use is very much more common. Oh hang on, scratch that one, we just introduced the same regulations here.
--
Andrew Gabriel


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Actually I included that under the low voltage section, as it is the low voltage that makes them think they can get away with it, although I suspect it is just a cheap as possible, don't care attitude, really.
Christian.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Andrew Gabriel wrote:

Even with Prat P we dont rent out apartments and blocks all wired a la 1930s in 2005... its either legal over there or not enforced. I suspect legal, given the litigius society and wide spread of 30s electrics, waaaaaaaay past their scrap by date. What people often dont stop to think is that a typical 1930s install today would even fail a /1930s/ safety inspection, due to deterioration and additions leading to overloading.
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

No it is not legal. On a large Middle East US site I was at, it was all conduit and 1930s electrics. In plants rooms not a bit of mineral insulated cable to be seen (the norm in Europe). I asked why mineral insulated cable had not been used, and none of them had heard of it. One knowledgeable man said mineral insulated is used in the US, but infrequently because of cost. This I found strange as installing metal conduit is not cheap. The merits of conduit were given to me and how cheap is just to pull though extra wires or to replace. I asked them how often do you replace wires? Slapping pyro around the walls is not that expensive in comparison. The US appears habitual in many aspects, although they did abandon fuses to a large extent.

_________________________________________ Usenet Zone Free Binaries Usenet Server More than 120,000 groups Unlimited download http://www.usenetzone.com to open account
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 1 Jun 2005 17:21:13 +0100, "Doctor Evil"

He might not have been talking about the same stuff..
Visiting a company Boston I did some work for, I noticed an electronic service engineer colleague up a pair of step ladders working above the suspended ceiling. He explained he was also a state registered electrician so they had him do the electrical odd jobs around the factory. He was installing a length of flexible metal sheathed cable which was corrugated like flexible copper tap connectors. He went on to say that this stuff can be used anywhere without restriction, didn't have to be fastened down, and any surplus could just be just thrown into the void in the suspended ceiling. I got the impression BICBW it came pre-terminated and was sold in standard lengths, I suppose that might make it expensive.
DG
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 01 Jun 2005 18:04:44 +0100, Derek Geldard

It is called flexible conduit and there are actually quite a few restrictions. In this application a six foot max length is a big one. It is primarily used to connect the fixture in the suspended ceiling to the fixed wiring of the building. Six foot long pre wired assemblies are sold and some fluorescent suspended ceiling fixtures come with the whip pre-attached.
A similar but different product, BX or armored cable, is sold in rolls and is the equivalent of metal jacketed 2T&E and is installed similar to 2T&E it is popular in NYC because Rats can't chew through it.
Jim Remove SPAMX from email address
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 1 Jun 2005 10:31:18 +0100, "Christian McArdle"
The electrical fires largely stem from high currents. If

...For a given power rating... :-)
(Just to avoid confusing beginners!)
--
Frank Erskine

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Christian McArdle wrote:

Theres a famous picture of an American extension lead made by someone who remarkably survived. He put 2 sockets into a cut open shampoo bottle and taped it all up. The idea was it would float. Yep, float, in his pool. Appaerntly it was so he could watch tv while in the pool.
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hi,
I will assume that your post is not bait and is serious
On Wed, 1 Jun 2005 10:31:18 +0100, "Christian McArdle"

NOT TRUE 1.General use U.S. Circuit breakers have always been thermal/Magnetic. 2. They cost less due to mass production. 3. Except for a bad run of Federal Pacific breakers 20plus years ago reliability has been high.

Not True. Mr. Edison picked a voltage and he used that voltage (Direct Current, of course). Edison's first great central station, supplying power for three thousand lamps, was erected at Holborn Viaduct, London, in 1882. Does anyone know the voltage that was used? In any case the U.S. Voltage is due to historical factors. I am sure the British voltage was not selected much more recently.

NOT TRUE. You are making multiple invalid assumptions. 1. That U.S. wiring has the same number of circuits for the same load. 2. That U.S. circuits are not designed for their load. 3. That electrical fires occur in properly designed circuits simply due to higher currents. 4. You claim lower voltage equals higher current, then you say...

It seems you contradict yourself.

Not True. In the U.S. this would be a 240V 15A circuit! Except for special use such as a medium sized Caravan. or some other use that REQUIRED less than 240V.

I would be very surprised to find an impedance that high. Reasonable scenario: 500' feeder cable to building .063 ohm (3/0 Aluminum, approx. 68mm) 200' circuit wiring .242 ohm (10gauge, approx 5.25mm) comes out to .305 ohm providing about a 400amp fault. The voltage drop at the distribution transformer would be much less than 5% and therefore would have little influence. This is low enough to still be in the thermal range of the Circuit breakers trip curve and would open in less than .7 seconds.
Example of real world circuit (an outlet in my Kitchen): 20amp circuit breaker Underground feeder cable from transformer .00605 ohm (100' 350kcm Aluminum, approx 177mm) Feeder from Main to Sub Panel .006128 (80' 3/0 Copper approx 85mm) Circuit wire to outlet .198 ohms (100' 12 gauge approx 3.3mm) Total impedance .210 ohms fault current 570amps (about 28x rating) Circuit breaker is in magnetic area of curve and will open in maximum 1 cycle (1/60th of a second)

ALL U.S. general purpose circuit breakers are Thermal/Magnetic!
Note: Our circuit breakers magnetic trip are similar to your type D

Slightly Lower. The U.S. nominal was raised to115V/230V before WWII It was re raised to 120V/240V in the 70's and is now specified as a maximum of 125V/250V Nominally 120V/240V unloaded voltages near 125V are common.

Again, in the U.S. a 3kW circuit would be 240V 15amp and the same benefits would apply.

Please quote sources for statistics.

The common cable in the U.S. is the same PVC stuff you use except for color. We are more conservative in ratings 14gauge (2.08mm) is rated at 15amps, 12 gauge (3.31mm) is rated at 20amps. These are used for residential general use circuits. A cooker would use 6gauge (13.3mm) at 50amps (240V). The trend is to premium 90degreeC rated cables used at these same ratings.

Why Not?

Huh?
We have what you call TN-C-S or PME
Earth is Earth, Neutral is Neutral, they are bonded at the Service Entrance ONLY!
In the past it was permitted for the neutral to be used to ground the frames of ranges and dryers. This came about as Interim Amendment No. 53 put into effect on July 10, 1942. This was to allow the neutral to ground the frames by means of a bonding jumper from the frame to the neutral. The reason for the amendment was to save raw materials like rubber and copper for the effort of WWII. This special amendment however was not removed from the NEC until the 1996 code cycle. This one amendment has caused quite a bit of problems for the DIY. Some have assumed that the neutral and ground must be the same and have used them as such. Others have never given a thought about the bonding jumper and left it intact in a 4 wire circuit. This results in parallel current flow on the neutral and ground. In a sub panel this can be troublesome. Note: the proceeding three paragraphs are from the Internet (not my writing)
Don't ever accuse us of not making sacrifices ;<)
I really don't understand why it was not repealed 50 years earlier. However, it did not seem to cause too much trouble. Keep in mind that in our ranges and dryers very little current flows in the Neutral conductor and in some models NO current flows in the neutral conductor making it actually only an earth conductor.

Why would anyone dry their hair in the bath (or shower). Everyone I know, who uses a hair dryer, does so in front of the sink looking at themselves in the mirror!

Jim. Remove SPAMX from email address
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jim Michaels wrote:

You make some good points, but there are a few I'll pick up on:

true, at least compared to UK. Maybe not the world, US seems the model of good practice compared to African practices, and that of many other countries.

but this doesnt change the fact that 110 is inherently more dangerous than 240. With 240v we treat it with respect, with 110v people relax since it wont electrocute them, and hurts waaay less if they get bit. They worry less about cord grips etc. The result is fires, which are the prime killer, not electrocution.

still cant figure out what you mean there. For a given load you do have higher i with lower v, and each load is on 1 circuit as far as i can see.

I dont think that was the assumption: the problem is simply theyre designed to have a higher incidence of faults. The practice of push-in connection on mains sockets is something considered unthinkable here, for good reason. Use of single insulated mains flex has been illegal for decades, etc etc.

we know its due to many factors.

no contradiction there that i see, just an example of how higher v gives a safety benefit.

should give less nuisance trips, ours sometimes trip on bulb failures.

In US IIUC it would be called 240v, but in fact be 120-0-120, so the voltage from earth is 120 ac, not 240. In which case the fault clearance benefit of genuinely 240v would sometimes apply and sometimes not. Some faults that smoulder at 120 can arc over and trip at 240.

they were banned here long ago because they cause connection failures and fires. They dont provide anywhere near the clamping pressures of our screw connections.

snip
that much is fair enough, but...

remarkable. At least not something normally permitted here. But we do have a permited 2 conductor wiring system, I forget the details, ISTR maybe it uses MICC? I'm not sure, but I'm pretty positive there still is one here, but it is not AFAIK permitted in domestic premises.

I think the general complaint was that America makes more sacrifices, unnecessary human ones unfortunately.
FWIW we had 110 dc here as well in the 50s, but this has universally disappeared now.
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@meeow.co.uk wrote: > remarkable. At least not something normally permitted here. But we do

TN-C. Earthed concentric wiring (MICC). Very limited applications, usually restricted to private generating plant or private transformer supply. Not necessarily banned in domestic premises though, AFAIK.
Owain
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 18 Jun 2005 03:30:22 -0700, snipped-for-privacy@meeow.co.uk wrote:

UK Ten 100watt lamps at 240V equal 4.166 amps on circuit rated at 6 amps with 1mm wire.
US Five 100 watt lamps at 120V equals 4.166 amps on 15amp rated circuit with 14gauge (2.08mm) wire.
In this example the US system has a massively greater safety margin.

The proof is that you keep saying "for a given load" and the loads are NOT the same, we have many more circuits in typical dwelling.

Simply a system with more smaller circuits each with an equal or greater degree of safety margin.
As an example a modest 3 bedroom suburban home normally has a 200amp 40 way main panel (CU). That is 200amps in each leg of the incoming feed using three 85mm cables. this provides 48kW of power. This is a home with gas space heating, gas water heating, gas clothes drying,, and often gas cooking. Even with our maniacal excess it would be hard to overload such a system to the point of combustion.

They are a homeowner/shoddy contractor item and are frowned upon. We also would never consider it on a 30/32amp circuit.

And some that would not cause a fire at 120V will burst into flames at 240V.

Why snip the explanation?

Remove SPAMX from email address
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Not so - it's the current that causes a fire. If low voltage was safer from the fire point of view, cars would never suffer electrical fires.
--
*Many people quit looking for work when they find a job *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 04 Jul 2005 11:14:32 +0100, "Dave Plowman (News)"

Actually it is the energy current times voltage.
For a given fault twice the voltage equals twice the current!

safer does not equal never.
British cars from the 60's were notorious for electrical fires.
I never claimed lower voltage was inherently safer, I said with similar safety margins, it is similar in fire safety. When deployed with greater safety margins it is safer.
Remove SPAMX from email address
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jim Michaels wrote:

No again. Faults are not normally ohmic. Higher v creates much higher i, and of course higher v means lower i breakers... result is a big difference in fire rates, favouring 240. 240 clears faults much better.
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 6 Jul 2005 13:02:33 -0700, snipped-for-privacy@meeow.co.uk wrote:

Ring mains have less than 20amp breakers?
Remove SPAMX from email address
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Although lighting circuits are normally protected at 6A, the 1mm wiring is actually rated at 12A. The lower value protection is required because of the choice of lampholders on the circuits.

Fires tend to start at wiring accessories, cable joins, etc, and not so much in the middle of a length of wire.

Normal UK home has a 100A (24kW) supply. If you want any more than this, you have to have a 3-phase supply, but that's quite unusual in a home unless it was very big.
--
Andrew Gabriel

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jim Michaels wrote:

Your analysis is too simplistic. The load current / cable rating is not something that causes any significant number of fires in either case, it is a nonissue in reality.
Also I assume you realise 1mm2 is capable of much more than 6A, it is merely fused at 5A or MCBed at 6A.
Safety margin is determined by looking at what in the system causes safety failures, and how often. Cable rating doesnt come into it. Your heavy US cables are merely a waste of resources, achieving nothing afaics.
Unless you can explain how 4A on 32A capable cable tripped at 15A is safer than 4A on 15A cable tripped at 6A. (figures are examples, not calculated)

to be honest I dont know what youre referring to, youve snipped the relevant stuff out.
But I remember just enough to be fairly sure the assumption above didnt come into it, that IIRC you misunderstood what was being said.

Youre not understanding safety margin. Size of cable has nothing to do with it, once the cables big enough not to overload. Ours are big enough and much more. Yours are even bigger, but for what? Its just poor engineering.

Above ground supply or buried? 85mm2 is awful big, even for 200A. Or is it aluminium?

Again you miss it. Your systems are overloaded day in day out, not at the service entrance but at the wall plugs that get too hot, and the wirenuts that cant reliably maintain their ratings. The result is a high level of fires.

precisely, here theyre illegal and unheard of. There isnt even a black market in such junk, its just off the scale. Even the occasional 50 year old install isnt that bad.

yup. the question is which is the greater number. 240 gives much better clearance rate than 120.

if you could quote all relevant material I might be able to answer.
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
     snipped-for-privacy@meeow.co.uk writes:

Because voltage drop is a serious issue for 120V supplies. It's not for 240V supplies.
--
Andrew Gabriel

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.