From a reference in an earlier thread
Starting January 1, 2002, The National Electrical Code , Section 210-12,
requires that all branch circuits supplying 125V, single phase, 15 and
20 ampere outlets installed in dwelling unit bedrooms be protected by an
arc-fault Circuit interrupter.
Eventually they will be in more areas but the NEC selected to require
them on bedroom circuits first because a CPSC study showed many home
fire deaths were related to bedroom circuits.
The AFCI (Arc Fault Circuit Interrupter) breaker, will shut off a
circuit in a fraction of a second if arcing develops. The current inside
of an arc is not always high enough to trip a regular breaker. You must
have noticed a cut or worn piece of a cord or a loose connection in a
junction box or receptacle arcing and burnt without tripping the regular
breaker. As you can guess this is a major cause of fires in a dwelling.
There is a difference between AFCIs and GFCIs[RCD's to us]. AFCIs are
intended to reduce the likelihood of fire caused by electrical arcing
faults; whereas, GFCIs are personnel protection intended to reduce the
likelihood of electric shock hazard.
Expect to pay between $20 and $50 for each AFCI.
Google has hundreds of refs in the USA, but none in the UK
Sounds a good idea in principle, and clearly lots of US fire-safety folk
are keen on them.
Are they known in Europe?
Do they trigger when an incandescent bulb fails, or a switch is slow to
I've never heard of them before.
Here's my guess, which could be total balls.
I suspect the problem they purport to solve is more common in the US. This
is, paradoxically, because of their lower voltage. At 230V, the current
produced in a given fault condition is twice as high compared to 115V.
Meanwhile, the circuit breaker trip current could be half as much for the
same circuit power rating. This means that a conventional MCB will be far
more effective at detecting such a fault on a 230V nominal voltage system. I
also suspect this is why they are only required on 115V lines in the US.
Anyone else like to make a suggestion?
P.S. I notice that reading those links, a far higher proportion of US house
fires are electrical in origin compared to the UK, probably as a direct
result of the so-called "safety" of having lower voltages, although fused
plugs probably help too.
Especially as organic-material related faults can be non-linear.
I recall a line fault which showed up as about 200k on a standard 500V
Megger, but which we were able to burn a way in a few seconds with
1,000V, running IIRC 20mA or so into it = 50k.
Indeed, electrical fire in the US is a bigger problem than most
other places. I think there are many reasons...
o Half the mains voltage means equivalent power appliances require
twice the current, and a poor contact/connection will be giving
of 4 times the heat it does on 240V, and thus getting much hotter.
o Use of aluminium wiring is extensive in the US, but was never
common in the UK in premises wiring. (I've only ever seen one
piece of aluminium T&E in the UK.)
o Anyone who has browsed the electrical section of Home Depot or
similar US outlets will know what complete crap their electrical
fittings are compared with ours or any I've seen elsewhere in the
EU. There's plenty more scope for poor contact/connections than
there is with most other country's electrical accessories.
As one manufacturer said to me about the US market once, "no one
will buy our $1 sockets, because someone else sells sockets for
o Wirenuts (screwits) and pigtails -- just don't go there. ;-)
o Appliance leads which routinely run warm, and plugs and sockets
which run hot are not considered anything out of the ordinary.
o Their breakers have no fault current (fast) trip, only the thermal
(slow) overcurrent trip component.
o Reliance on dirt cheap low quality RCD's for safety (e.g. you are
allowed to fit an earthed socket with no earth connection, relying
on the RCD only).
o US homes are more often built purely from timber, so once a fire
starts, particularly in the building fabric, it spreads much more
Anyone wanting follow USA opinion on this
the discussion forums are here
The 'Non-US Electrical Systems & trades'
is mostly a UK/European forum
Which really buggers up some medical equipment in the USA,
and also results in some needed equipment not being given out
or ironically given out in 230V form since those sockets are
earthed properly but usually connected to cooker/dryer/similar.
Lighting cords are frequently dreadful in USA, and often suffer
broken conductors part way along the conductor due to flexion
or overcompression under bed/furniture feet/castors. That then
overheats and creates a slow burning fire, and toxic smoke.
The USA allows a lot of suspect wiring practices, but ironically
if you fit certain plastics structurally (acrylic & others) you have
to fit notices for the fire department re the (very) toxic smoke. So
ironically you can screw yourself intentionally just not someone
else. That's the governments job and it's proud of it :-)
Their breakers are a major problem re slow thermal trip, altho a
huge number of places suffer old wiring (and aluminium as you
say) and old fuseboards AND a lot of electrical overloading.
There is also cable routing along studding, nailguns & uh oh...
Then again, I've seen 3 UK vacuum cleaner "arc fault smoke & fire"
myself with failing cord near the plug. The moulded on plugs with
strain relief should reduce this, but often have poor grip moulding so
It's An Adventure unplugging the thing. Fit a finger-hole plug, and
the thing will not retract into the cleaner (tried, even a dead blow
hammer nearly when I found the loose plug one morning in bare feet).
I didn't call it a Miele at the time, think I called it something else.
Perhaps Miele is a swear word in German and they never told us.
A big problem in the USA is people believe 110V is low voltage.
Well it is ELV if you're talking about 33kV and such.
The AFCI's are a good idea for the USA, in the UK I'd start with
getting every home with (working) smoke alarms on each floor level.
www.stores.ebay.co.uk/panaflofan for fans, books & other items
Is alumnium used for internal wiring ? When I worked as an electrician
in Connecticut as a summer job, in the early 80s, all the internal stuff
was copper, but the Triplex drop cables were aluminium. Terminating
triplex used a special compound which was driven into the wire with a
wire brush and then aluminium bolts treated similarly. A whole roll of
"insulting" tape completed the job
A significant number of Fire Stations in the UK use retained
Our local one is a retained station, single pump/rescue tender, the
next nearest is 20+miles away; 40+mins in a car along twisty roads
I sometimes wonder how long it would take to get another appliance in.
And for the next 4 months or so it might not be possible to get in
anyway due to snow closing the roads...
Dave. pam is missing e-mail
"Dave Liquorice" wrote
| A significant number of Fire Stations in the UK use retained
| Our local one is a retained station, single pump/rescue tender,
| the next nearest is 20+miles away; 40+mins in a car along twisty
| roads with hills.
| I sometimes wonder how long it would take to get another appliance
If there's a strike on and they try it in a Green Goddess, they might as
well bring a picnic and make a day trip of it.
On Thu, 18 Dec 2003 15:35:12 -0000, "Christian McArdle"
That's exactly it AFAIK. There is a statistical relationship between
supply voltage, electrical fires, and electrocutions. UK opted for
240V: fewer fires, more electrocutions, the USA went the other way.
This leads to various peculiarities such as electric kettles being
less common because they are slower to boil (max current is about the
same defined by the need to keep flex/ connector size reasonable), and
the need for various fixed appliances to have a 230V circuit.
But since the US also has more electrocutions per capita than the UK,
that commonly held assumption that 240V leads to more electrocutions
is clearly completely wrong.
Actually, you might infer the higher voltage leads to more caution
and fewer incidents as a result. I had some US children's books on
electricity since I lived in the US for some of my childhood, and I
recall a couple of them had comments like "mains voltage can burn you".
That sure isn't the way any similar UK books would convey the danger,
and my parents took the trouble to point out to me that some of the
comments like that in my US books didn't apply in the same way UK!
However, I can think of other reasons than just this for the difference
in the figures from what one might expect.
On 19 Dec 2003 01:51:14 GMT, firstname.lastname@example.org (Andrew
As you say I think that part of that is that many Americans assume
110V is safe - normally you just get a nasty belt from it - so live
wire working (even DIY) is common. However most homes also have 220V
for devices like washing machines and cookers - and it this which
often gives them a very surprised look of late understanding - even
if only for a short time.
On 19 Dec 2003 01:51:14 GMT, email@example.com (Andrew
I think the decision was based on the likely outcome of actual contact
with the supply, as you say in reality the likelyhood of *coming into
contact* with the supply will in practice vary due to other factors
including the very fact that the lower voltage is percieved to be
intrinsically safer. The actual system employed seems less safe; AFAIK
shrouded plugs which are now mandatory for new appliances and second
hand when sold in UK are unheard of in US, also earthed outlets are
far from universal.
On 19 Dec 2003 01:51:14 GMT, Andrew Gabriel wrote:
I actually think that "burn" is a good way of explaining to children that
they shouln't mess with it - every child gets burnt at some point (even if
its just a hot radiator) and they can relate to the terms "burn", "hot",
etc. Saying that electricity can kill you doesn't mean a lot to a child
that is too young to understand death.
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