Arc Fault Circuit Interruptors

[roger]

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 break?

[Christian McArdle]

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?

Christian.

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.

[roger]

Christian McArdle writes

Interesting thought. 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.

[Andy Dingley]

not all the refs are positive.

The fault that an AFCI detects is also (by and large) found in aluminium wiring, which is prone to connector problems. Fortunately the UK was spared this abomination

[Steven Briggs]

In message , Andy Dingley writes

And those stupid little "wire nut" things the yanks use for joining wires.

[Andrew Gabriel]

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 75c." 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 easily.

[Niall]

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.

[Chris Oates]

Anyone wanting follow USA opinion on this

discussion forums are here 'Non-US Electrical Systems & trades' is mostly a UK/European forum

[Andrew Gabriel]

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.

[Peter Parry]

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.

[Peter Parry]

Not commonly.

No. As Andrew has said they are designed to overcome a number of deficiencies which are almost confined to the USA. The combination of low voltage means higher currents and in conjunction with what we would consider to be poor standards of wiring, components and particularly jointing makes the system vulnerable.

The most common fault is an overheating connection which simply sits and arcs away gently (often for weeks) until things degrade sufficiently for it to fail (The American series "CSI" featured such a theme in one program). When it fails it fails by getting very hot and melting/burning. American houses are commonly timber frame built with little regard for fire prevention or control and fires can develop within the wall spaces with great speed.

[Niall]

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.

[dorothy.bradbury]

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.

-- Dorothy Bradbury

for fans, books & other items

[Huge]

[25 lines snipped]

You forgot one;

o Volunteer fire brigades. Often a long way away.

[Huge]

Ah, thank you. That explains the stickers I've seen on American medical equipment about the type of socket it must be plugged into.

[Dave Liquorice]

A significant number of Fire Stations in the UK use retained Firefighters.

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 in. And for the next 4 months or so it might not be possible to get in anyway due to snow closing the roads...

[Steve]

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

Steve

[Owain]

"Dave Liquorice" wrote | A significant number of Fire Stations in the UK use retained | Firefighters. | 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 | in.

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.

Owain

[N. Thornton]

Hi

So how do AFCIs work? do they detect higher frequencies than the 60Hz? Do they detect current flowing at cycle peaks but not near zero? Anyone know?

Regards, NT

[Mike Tomlinson]

In article , Christian McArdle writes

They made extensive use of aluminium wiring. The wire cores are prone to "creep" and develop high-resistance connections which become hot and start fires.

probably as a direct

quite. also appliance flexes ("cords" in Merkia) tend to be single- insulated.