Ground Fault Circuit Interrupters (GFCI)
Contents:
- Ballast grounding & GFIs
by "Torsten Tiedtke" <ttiedtke/bfree.on.ca> (Thu, 13 Jan 2000)
- More GFCI
by Scott Hieber <shiebernet/netscape.net> (22 Aug 00)
by "Torsten Tiedtke" <ttiedtke/bfree.on.ca>
Date: Thu, 13 Jan 2000
In Aquatic Plants Digest Volume 04 : Number 026,
Jamie Noble brought up some points about flu.lamp ballasts and
GFI outlets that I feel should be clarified...
1. Magnetic ballasts require the bulbs be mounted within a certain
distance of a grounded surface to help start the lamps under
certain conditions (mainly cold temps.). This will not prevent
electric shock.
2. I feel than the basic operation of GFIs is generally not
understood...leading to potentially serious consequences.
In North American homes the power provided is ground referenced.
What this means is that one of the conductors (the 'neutral') is
actually connected to ground. This is allowed to occur in only one
place per home - at the breaker panel. Since the electricity flows
between the 'line' and 'neutral' conductors, one can be electrocuted
by touching the 'line' and something grounded (since the electricity
would return to the 'neutral' conductor through the ground path).
The is where GFI protected systems provide benefit. Ground Fault
Interrupters operate by monitoring the current flowing in both the
'line' and 'neutral' conductors. Under 'safe' conditions, the currents
in the 'line' and 'neutral' should be equal. An unsafe condition
exists with there is an imbalance between the two currents. This
can occur when contact is made with the 'line' conductor and a
grounded object. The current is now partially/completely flowing
between the 'line' conductor being contacted, through ground, and
back to the grounded 'neutral' conductor at the breaker panel. The
GFI is designed to turn off the power when this, and ONLY this,
condition occurs.
The GFI will NOT protect you under the following conditions(just a
sample):
-Contacting both the 'line' and 'neutral' conductors.
-Contacting the output of a ballast or transformer (since they
isolate)
QED
Torsten's 2cents from snow covered
Lynden, Ontario
by Scott Hieber <shiebernet/netscape.net>
Date: 22 Aug 00
To: erik/thekrib.com
Here's a little more info to throw into the talk about GFCIs.
Under UL standards, for a device to be called a "GFCI" it must break the
connections to BOTH the Hot and Neutral power supply lines under each of two
conditions:
1) an imbalance in the current in the Hot and Neutral wires supplying current
through the GFCI to a load;
2) a leakage of current between the Neutral and Ground wires downstream from
the GFCI. Properly installed, a GFCI will trip under a shorted Neutral-Ground
condition even if no load is connected to the circuit -- that is, no load
other than the short between Neutral and Ground.
Some protection devices on the market mention that they detect ground faults
but do not explicitly call themselves GFCIs; the reason for this is that they
test for the first condition but not the second. GFCIs provide more protection
than ground fault detectors that do not meet the "GFCI" standard.
Some devices manufactured under the TRC ground fault device patents meet only
the first test.
It is worth noting that some GFCI devices require a manual reset if the power
supply TO the GFCI is stopped -- for example, by a power outage that might
occur during a thunderstorm. GFCI receptacles that are installed as wall
sockets are designed NOT to require a manual reset after a power outage --
when the power comes back on, the GFCI is still send power to operate a load.
Portable GFCIs, such as on extension cords that comply with OSHA standards
require a manual reset after even a momentary power outage -- these cords
are usually the heavier cords that might be found on a construction sight or
at Home Depot. On a construction job site, this feature prevents your circular
saw, for example, from starting up accidentally when the power supply is
restored after an outage. If your aquarium filters, heaters, etc. are
connected downstream from such a GFCI extension cord, you will lose life
support for your fish after a power outage until you manually reset the GFCI.
I have seen some devices marketed for about $50-$90 dollars that trip when
power is interrupted and require a manual reset. These "Magnetic ON/OFF"
switches protect against accidental startup just like most portable GFCIs.
But portable GFCI extension cords can be purchased for a lot less money and
they accomplish the same thing for those cases where you want a manual reset
after outages.
All GFCIs require a manual reset after detecting a ground fault or shorted
Neutral-Ground condition.
The most comprehensive web site around for GFCIs is probably
http://www.codecheck.com/gfci_principal.htm
S. Hieber
The Krib
Tank Hardware
The Krib