Help... I was sleeping in the middle of the night and all of a sudden my
UPS (uninterrupted powered supply) started to beep, I thought it was normal
power interruption but after I while it didn't go away. So I went to
basement and checked, my Bedroom fuse has tripped.
Now, here is something interesting. My bedroom is equipped with a special
fuse called "AFCI" (by Siemens) 15A. Something like this:
http://www.sea.siemens.com/reselec/product/rzafci.html I reset by pushing
the handle and everything worked again!!!!! Then, I pressed the "test"
button, it tripped and I assumed that's normal, right?
My questions are:
1. What causes the fuse to tripped all of a sudden???? doesn't make sense
when I was sleeping.
2. Why is this special fuse in my bedroom? When I bought the house, I
thought the builder guy told me it is for bathroom plugs GFCI protection.
Apparently it is not, because when the fuse was tripped my night light was
still on in my bathroom.
3. Does that mean my bathroom is not GFCI protected! That's not good..
should I do something?
A AFCI is a device (circuit breaker) that is designed to detect arc faults,
and is superior protection against overcurrent or arcing problems. To my
knowledge, all four US manufacturers that make AFCI breakers incorporate
GFCI (ground fault) protection circuitry into their AFCI devices.
Code requires AFCI protection in bedrooms on new construction. The logic was
that this is an area of the home where elderly, disabled or young people
spend a lot of time.
Unlike a standard GFCI, an AFCI device will not trip on ground fault until
the faulting load is connected. Nuisance tripping (something like you
described here) often occurs when you plug in something new or turn a switch
on. The device will not trip again until the load is re-energized (turned
The breaker could have tripped for any number of reasons. The advice I
always give people is to accept one trip, that will promptly reset, as a
fluke. More than one.... more investigation needs to be done. It could have
tripped on a ground fault OR a arc fault. Both are dangerous conditions if
Have you recently plugged anything new into this circuit, or changed/moved
something around that is plugged into it? That's a good place to start
New electrical code requires bedroom outlets to be AFCI protected.
An AFCI breaker detects arc faults and will trip. Arcing (sparking) is
believed to be a common cause of house fires and would occur if you did
something like pinch an extension cord with something metal or hit a
cable when hammering a nail into a wall.
The AFCI breaker also protects for overcurrent situations, just like a
It depends on what is on the circuit, or maybe it doesn't. When the
inspector was in for our final inspection, we were talking about AFCIs.
I was under the impression that AFCIs only protected against "parallel"
arcs, like the shorts I mentioned above. I thought they did not detect
"series" arcs, like what can happen when you turn a light switch on or
off. He told me that one problem with the current technology is that it
cannot tell the difference, so our code only requires them on the outlet
circuts and recommends that they not be used on lighting as false trips
may occur when a light is turned on or off.
So, one explanation might be that something that cycles on an off on its
own may have caused the trip. I would not likely suspect this unless you
were seeing it a little more often, though.
Another possible explanation may be along the lines of why a GFCI can
sometimes trip for no reason. AFCIs sense arcs between line and neutral
and between line and ground. The sensing between line and ground is
actually done using the same technique as GFCIs (see below), except that
many AFCI breakers have a 60 mA sensitivity -- meaning that they do not
provide the 5 mA sensitivity needed for true GFCI protection. We have two
bedrooms that have sinks in them, and though the near-the-sink outlets are
AFCI protected, they had to be GFCI outlets as the AFCI breaker was not
sufficient. I understand that some manufacturers are now producing
AFCI breakers that also provide true GFCI protection.
Back to the explanation: GFCI protection is provided by measuring the
current between the line and neutral. If they differ by more than some
threshold (the 5 mA and 60 mA levels mentioned above), then it trips.
The theory behind this is that ALL the current passing through the line
should be returning through the neutral. If it isn't, then you have a
ground fault providing an alternative return path.
One problem with GFCI detection (though this appears to be much less of
a problem these days than 20 years ago), is that transients on the power
line can cause them to trip. Transients are narrow spikes of high voltage
and are the reason why we buy surge suppressors (both power bar, as well
as whole service - the prevalance of these these days may be one reason
why I see far less false GFCI trips than 20 years ago!).
Transients are high frequency (the narrower the width, the higher the
frequency) and their movement along a power line is not unlike a signal
on a transmission line. Their movement is relatively slow (to the speed
of light) and this means that current flow due to a transient will not
appear on the line and neutral at the same moment. Depending on the size
(width and amplitude) of a transient, various wiring characteristics, and
the sensitivity of a GFCI, a transient could cause it to trip for what
appears to be no reason.
Unless you have a whole-house surge suppressor, any surge suppression in
or at your UPS would not stop the effects that could trip an AFCI or GFCI.
I suspect that this was the cause and if it is not seen regularly, it may
be because the one transient that caused it was unusually large, especially
I covered this at the top.
A quick check would be to plug in an outlet tester that has a GFCI test
button on it and press it to see if it trips the power. The electrical
inspector SHOULD have done this when the final inspection was done.
"Never ascribe to malice what can equally be explained by incompetence."
ARC fault is a crock of S###. It has been studied in depth and proven not to
be accurate. Just another scare tactic. Makes the dishonest electrician
wealthier and protects you no better. But it is code! I'm not making this
up. There is a lab currently fighting the mandatory use of arc fault
breakers because they are false protection. I'll find the study and repost.
Mike Holt.... who is THE premier fighter of BS in the National Electric
Code, had the following:
Read the whole thing, and if you don't understand it....let us know.
Right, the reason that AFCI breakers are a crock isn't that
the breakers don't protect against that kind of fault,
"...the likely hood of a line-to-neutral fault in branch-circuit
wiring causing a fire is very rare"
The threat against they protect is almost nonexistant.
Some People die in fires.
Some Fires are caused by electrical problems.
Some electrical problems are Arc faults.
Some Arc faults are prevented by AFCI's.
But Some^4 is approximately zero.
The number of deaths caused by
fires caused by electrical failures that
are arc faults which would have been
cleared by an AFCI is too small
to worry about.
Is this just your opinion, or is it substantiated somewhere?
Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?
It's an assertion based on a limited amount of research.
The TOTAL number of deaths by fire in residences is
something under 4000/year, in the US.
Those that are ascribed, somehow, to anything at all
to do with the electrical system, work out to
Filtering out the ones that aren't
started on bedroom circuts,
ones that wouldn't have been prevented
by an AFCI breaker anyway, and the
rate of failure of the breakers is beyond
my resources, but given the population
of the US in excess as somewhere
in the 260 million range (for the same years
as the above statistics), and arbitrarily picking 50%
for the percentage of lives saved, by AFCIs
that makes the threat to me, personally,
at the most pessimistic,
somewhere around 1.7 million to one.
Even less, when you consider that most
deaths by residential fires kill babys,
mobility impaired elders, and people who
are to drunk or stoned to notice the
Whether that's worth worrying about is,
of course, a matter of opinion, but I've got
things I'd rather spend money on than
eliminating 2 million to one risks, thanks.
A AFCI protects against more than "line-to-neutral" faults. Did you read the
WHOLE article as I suggested:
"The performance tests comparing AFCI/GFI with a standard circuit breaker
demonstrated that AFCI/GFCI circuit breakers will save lives under the
conditions identified by the manufacturers, including from loose terminals
or connections. The comparison test was simple; there were two outlet boxes
each containing a duplex receptacle with loose terminals. A 1,500W load was
applied to each, and after an hour or so, the receptacles melted and the
AFCI/GFI circuit breaker opened within three to eight half-cycles, whereas
the standard circuit breaker did not trip."
Ahh... loose terminals or connections=HEAT=FIRE!
Read the whole article, please!
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