Nate Nagel wrote:
Nate Nagel wrote:
John Grabowski wrote:
"Nate Nagel" wrote in message
...
John Grabowski wrote:
"Nate Nagel" wrote in message
...
Hi all,
got a weird issue. In an upstairs bedroom, I have a computer that is
running off a UPS. After investigating the wiring in the house, I
have
found a significant number of grounds "bootlegged." Little by
little I
am picking away at them, but until spring, the upstairs will
remain as
is because it's darn cold in the attic at the moment.
So here's the deal. I have determined that there is one properly
grounded outlet in the room where the computer is, because that
outlet
is fed directly from the breaker panel, and that homerun is in BX not
the cloth covered Romex that the rest of the concealed wiring is.
So as
a stopgap until I get around to fixing everything correctly I
wanted to
make sure that the computer's UPS was plugged into that particular
outlet for proper surge protection. I bought a heavy extension cord,
unplugged the UPS from the outlet that it was plugged into,
plugged the
extension cord into the correct outlet. Then I plugged the UPS
into the
extension cord, and the lights went out. Reset the breaker, figuring
that I just made an arc, if I plugged it in faster it would be
OK. Same
effect. Reset the breaker, plugged the UPS back into the outlet
that it
was using before, and everything is fine. This is a less than
year old
APC unit.
Is there some fundamental incompatibility between this UPS and the
AFCI?
I'm wondering if the UPS tests for the presence of an earth ground
(there is a "building wiring fault" light on it) and if so does that
cause enough current to trip the AFCI? (I wouldn't have found this
before, because the outlet into which it's currently plugged is not
grounded but has the ground bootlegged to the neutral.) I've
heard that
some AFCIs are also GFCIs is why I'm asking. The AFCI is a Siemens
Q115AF breaker in the breaker panel.
I'll replace the receptacle in the morning (once it's light out)
and see
if that solves the problem, but I'm not sure what kind of fault
could be
in a receptacle that would cause a breaker, AFCI or not, to trip only
when a load is connected to it but not when a plug is inserted.
Does this mean also that I run the risk of having the AFCI trip if
the
surge protection of the UPS kicks in?
Should I just give up the idea of having everything "to code" and
ditch
the AFCI and/or investigate the possibility of running a dedicated
circuit to that bedroom to feed an outlet solely for the computer,
not
protected by the AFCI?
any thoughts greatly appreciated...
nate
Is that circuit part of a three wire cable (Black, red, white) used
for
two
circuits or is it just a two wire bx with the armor as the grounding
conductor?
It's two conductor BX with the armor grounded.
AFCI circuit breakers are not required here in New Jersey, so I don't
have
much experience diagnosing problems with them. My thoughts are that
your
AFCI does not like the BX armor ground, there is something else going on
with the BX cable, or it does not like your UPS. Have you tried
plugging in
another three prong appliance into the outlet?
No, that outlet has been unused since we've moved in. It is however
the first one in the circuit so the only possibilities I can see are
that the AFCI is actually a GFCI as well (anyone know?) and there's
enough current flowing through the real ground due to the UPS's fault
sensing circuit, OR that there is a physical problem with that
receptacle, which I'll be attempting to rule out shortly, now that the
sun is up. (I've been on a program of replacing all the receptacles
as soon as wiring "issues" are cleared, because a lot of the old
receptacles were loose as well.)
nate
Update:
I replaced the receptacle. when I turned the breaker back on it tripped
immediately. I popped the cover on the panel and ohmed everything out,
seemed OK although the resistance hot to ground was lower than I thought
(~1 meg; nothing plugged in) although granted my meter is very old and
possibly inaccurate. Everything seemed OK so I tried pulling the wires
*leaving* the receptacle I'd just replaced. Then reset the breaker.
Fine. Plugged in UPS. Fine. Reattached wires and replaced breaker
with regular 15A breaker. Fine. Tried another AFCI breaker (I just so
happened to have one laying around because I wanted to split the
upstairs into two circuits eventually.) Tripped immediately. Removed
the wires leaving the receptacle again, new AFCI did not trip.
So what I apparently have is something is causing the AFCI to
electronically trip but not because of overcurrent. It's got to be a
wiring fault because I have everything unplugged. and all I know is
that it is somewhere upstairs - one circuit serves the whole second
floor, except for one outlet in the hallway (apparently intended for an
air conditioner.)
I'm not sure why it tripped only when I plugged the UPS in before,
coincidence, or just reached some kind of threshold? who knows?
F'ing great. Of course it's about 10 degrees outside, and I assume most
of this wiring is in the attic. I'm a little too paranoid to just leave
the regular 15A breaker in... or are the Siemens AFCI breakers known to
be problematic?
nate
Heh... all right, I feel dumb now.
When I started to replace the receptacle, I plugged the UPS and the
associated extension cord into a receptacle in the hallway which was on
a different circuit.
I just went upstairs to start pulling receptacles out of the wall to
inspect the wiring/try to track down the presumed ground fault. Despite
the fact that I thought I'd unplugged every appliance upstairs, what did
I see at the first receptacle I came to, but a printer plugged in to a
wall receptacle. It, of course, was connected (by a USB cable) to the
computer that was connected to the UPS. I feel obligated to point out
at this point that I did *not* connect it this way, and in fact, the
reason that I feel particularly stupid is I was just explaining
yesterday why it was important to connect all peripherals of a computer
to either the same power strip or the same UPS so there's no issues with
floating grounds etc. and voltage imbalances that end up going through
USB or other ports. (was actually on my list of things to rectify.)
I dug out another extension cord (the reason the printer was plugged
into a different receptacle is that it is on the other side of the room
from the computer desk) and plugged the printer into the back of the UPS
on one of the "surge only" receptacles. All appears to be good now.
I'm still not sure why the breaker tripped when I simply tried to move
the UPS' power feed from one receptacle to another, unless the fact that
the UPS now had a proper ground while the printer still had a bootlegged
ground was enough to cause a problem.
I ASSume that this little exercise does indeed confirm that the Siemens
AFCI is also a GFCI...
nate
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