| Mark Lloyd wrote:
|>>GFCIs (5mA) are now required to not work with reverse load-line terminal
|> Even when that's exactly what you want.
| When the supply wires are connected to the LOAD terminals on old GFCIs,
| the GFCI receptacle is not protected - it is live even if the GFCI is
| tripped. (I believe the downstream circuit, which would be connected to
| the LINE terminals, is protected.)
| Under the new UL standard, which I think was adopted about 2 years ago,
| if you connect supply wires to the LOAD terminals the GFCI receptacle
| and LOAD terminals will always be dead.
| I may have tried to say that with too few words.
Someone once told me that the GFCI receptacles that I found were DANGEROUSLY
susceptible to strong radio fields, must have been wired in reverse. But I
do know they did cut off the power to its own outlets, so I am convinced
that they were wired correctly. Maybe they are defective products and the
internal solenoid that trips the mechanism was wired on the LINE side and
should have been wired on the LOAD side.
What happens is that when a strong radio field is introduced, the GFCI sees
this somehow as leakage current. Other than for it being the wrong frequency
this is understandable, as the induced currents would be in common mode, with
the same direction on hot and neutral.
The DANGEROUS part is that even though the solenoid has opened the circuit
and cut off the power from the outlets (and presumably upstream, which was
not present for the ones I did this with), as long as the radio current was
present, the solenoid continued to activate. I believe that these solenoids
would be operating from the 120 volts AND are not designed for the heat that
would result from continuous operation. They would have been designed with
the idea in mind that as soon as the circuit opened, the leakage current
would no longer be present.
This creates TWO hazard conditions.
The first is that if a radio field that caused this was external, it might
not be known to the radio operator that there was a problem. It could cause
the solenoid to overheat, melt insulation, short circuit, arc, catch fire,
burn the house down, and KILL PEOPLE. I did NOT leave the radio field on
for a long period of time when I did this test. Even for the very first
time I discovered this, the loud buzzing of the solenoid in the GFCI was
loud enough to get my quick attention and realize the radio was triggering
the problem. So I was never doing this for more than a second or two.
The second hazard exists if the GFCI breaker does NOT open the neutral.
A neutral could have some low voltages present as a result of voltage drop
between various L-N 120 volt loads and the point of bonding neutral to
ground. A short circuit from neutral to ground might not have a great
spectacular arc flash, but it could draw enough current to activate a GFCI
at the 5ma level. The type of GFCI that allowed the radio current to trip
the solenoid continuously would also result in continuous activation of the
solenoid in this neutral-only leakage situation because the neutral would
not be opened, and the GFCI control circuitry would still be powered.
I believe a proper GFCI design must cut off its own power when tripped, so
it is not doing a continuous trip. This could be done by powering the GFCI
control circuitry, including the solenoid, from the LOAD side. When I
suggested this in a posting somewhere a long time ago, someone said that
it may be needed to power the solenoid from the LINE side to ensure that
it completes its operation to full open the contacts. I can agree that
leaving the contacts stuck in a partial open state where they may arc
across is not a good thing. But this should be accomplished through the
mechanical energy stored in the unfatiguable spring mechanism that gets
charged when the unit is reset. The solenoid should just be releasing
DO NOT DO THIS AT HOME OR WORK. There is the risk that some of these units
may be so defective that even a short period of operation could result in
I also do not know if GFCI breakers have this risk. If their internal
circuitry remains energized from the bus contacts in the panel, a radio
field could cause the very same problem. Although they clearly do have
the proper spring loading mechanism, being a part of a circuit breaker,
the solenoid that releases that mechanism when leakage current is detected
would potentially be under continuous operation if the power remains and
the apparent leakage issue remains. This would not only be a problem
with a continuous radio field, but it could also be a problem when the
neutral has enough voltage to make a leak to ground, such as in a subpanel.
So DO NOT DO THIS NEAR A BREAKER PANEL.
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
Click to see the full signature.