GFCI works by comparing the current on the hot side and the neutral
side. If they are different by more than a very small amount, it trips.
Even the static discharge from walking across the carpet and touch a
protected device can create enough current on the neutral side to trip
some devices.
The water in the tub doesn't have to be ground if the hair dryer has a 3
wire cord. There can be current through the water to the dryer's
ground, thus creating the imbalance needed to trip the device.
The last time I read the NEC, you can string outlets off a GFCI outlet,
up to a maximum of 4. After that you need another GFCI.
On 3/17/2012 9:41 PM, Jonathan Schmidt wrote:
GFCIs...you can't live with them and can't live without them.
A real problem is that they wear out...something that isn't well
known. Old GFCIs may pop prematurely or fail to pop. TEST THEM YEARLY!
About the hair dryer in the bathtub...assuming the water is ground, I
can't imagine that exactly the same current from the "hot" side will
100% flow back on the neutral because, if it isn't, the thing will pop.
What am I missing about the bridge and the sensitivity?
I had my sister have all her old house sockets (at least the head of a
string) equipped with GFCIs. I took a cheap tester to her house and
almost 50% of the AC sockets were wired wrong so they needed fixing,
too. Many had grounded outlets that had no ground, and ½ had the pins
backwards! I guess the folks who sold them the house in 1985 did a
band-aid job.
If you have customers with older houses and old GFCIs supplying their
modem/router, you should encourage them to test and replace before
calling you.
Anyway, every time my sister had a thunderstorm, the office GFCI would
pop...probably because the computer was grounded through the cable
router and cable modem. The socket was behind a very large, heavy
bookcase. I'm proud of her, because, by the second time, she got a
drill with a ¾" bit and put a hole in the backboard to allow pushing
the reset with a pencil eraser. Hence, my recommendation to have your
customers understand this since the GFCI that runs your service is the
most likely to pop in a thunderstorm.
. . . j o n a t h a n
------------------------------------------------------------------------
*From:*wireless-boun...@wispa.org [mailto:wireless-boun...@wispa.org]
*On Behalf Of *Blair Davis
*Sent:* Saturday, March 17, 2012 1:37 AM
*To:* WISPA General List
*Subject:* Re: [WISPA] Preventing stupid outages
GFCI's are to detect and prevent leakage currents.
They monitor the current in the hot and the neutral lines.
Ever stood barefoot on the ground and held a drill or saw and gotten
shocked? A GFCI, working properly, will prevent that from killing
you, or even shocking you for more than a few mS
In properly working equipment, basic electrical theory shows that the
current in the hot line and current in the neutral lines must be equal.
If the currents are not equal, then current is 'leaking;' out of the
circuit.
The GFCI senses the imbalance and interrupts the circuit to stop the
leakage.
They are not perfect, though.
You can hook up an old 2 prong hair dryer and drop it in a bathtub
full of water without tripping the GFCI if you know how.
I was an electrician for the Navy for years...
I won't plug a tower into one. Every time the lighting flashes for 30
miles around, they trip...
On 3/16/2012 11:45 AM, DJ Anderson wrote:
I thought GFCI's were to protect circuits from moisture mainly, AFAIK
they do not provide any type of protection for devices other than
cutting the circuit if it senses a ground fault.
DJ Anderson
Shelby Broadband
On Fri, Mar 16, 2012 at 11:38 AM, Ben West <b...@gowasabi.net
<mailto:b...@gowasabi.net>> wrote:
To add to the anecdotal evidence against cheap GFCI outlets, I had to
remove one in a building when spontaneous trips started occurring
randomly (e.g. once every couple weeks) after an adjacent building
received a direct lightening strike.
For that matter, the GFCI contributed nothing to lightening
protection, still lost a bunch of equipment.
--
Ben West
http://gowasabi.net
b...@gowasabi.net <mailto:b...@gowasabi.net>
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