My occupation is Electrical Engineering. I lead a team of mostly
Tradesman / Technicians who maintain a range of electrical equipment.
tex1 wrote:
>
> At 02:55 AM 1/27/97 GMT, you wrote:
> >In The Dawn of the Third Age tex1 <tex1 at airmail.net> woke me from my
> >contemplation by writing:
> >>Actually... the way a ground fault circuit interupter operates is it
> >>monitors the ground path. any leakage to ground (as little as 1/1000th of an
> >>amp) will cause it to trip.
See below!
> >
> >For those who don't want to read further, you do not need a grounded
> >plug to be protected by a GFI. The ground has no effect on how a GFI
> >works!!!
This is a fact!
> >
> >Close but not quite right Kurt. It does monitor the current but not to
> >ground. It really doesn't matter where the current is being drained
> >to, what matters is the imbalance in current between the hot line and
> >the neutral line. It doesn't matter if there is a ground on the heater
> >or not, the GFI will still protect you. The current could be running
> >between the 120 volt line to a higher voltage or a lower voltage (such
> >as ground). The current running through both the hot leg and the
> >neutral leg are both ran through their own shut resistor creating a
> >slight voltage drop.
Never seen one that uses a resistor but the principal is correct. BTW
they are called Earth Leakage Circuit Breakers in 240V land. It is law
to fit them to new homes in many places so check before you go and buy
one. You may already be protected, my whole house is.
>If these voltages do not cancel themselves out
> >within the operation margin (or dead band) then the GFI trips and
> >opens the circuit. So you are safe no matter what type of plug you put
> >in them. Since in most cases the diverted current is passed to ground
> >via some accident they are know as Ground Fault Interrupts.
<snip>
True. (well currents but if the use resistors instread of current
transformer than voltages)
>If you still think a ground is required
> >to trip these then try this - Take a single conductor and stick one
> >end in the line input and the other in the neutral.
PLEASE DON'T ANYONE DO THIS!!! Anyone that has seen the results will
know that you may well get hurt. At least burned fingers from the melted
copper.
And YES it will trip the circuit breaker but not due to earth
leakage......see below!
> (you could even put
> >a 10Kohm resistor in this path). Now why did it trip with no ground on
> >the plug? (in fact what plug ;~)
Yes this is a test that could be done by someone that knows what they
are doing. No it will not trip!! Sorry but that is a fact!! (well unless
you are hanging onto the live wire, in which case you may trip as well)
The test is a 10Kohm resistor from the active / line (or whatever you
want to call it) to earth either via the lead or directly. In this case
it should trip. I don't recommend anyone try this, just use the test
button, it does it for you! I am just getting to know you, don't want
you dieing yet :)
> >
> >By USA law all blow driers (and few other appliances used around
> >bathroom sinks) must now come equipped with their own GFI and they
> >don't even have a grounded plug. That's because in reality ground has
> >nothing to do with how a GFI works, its only the flow of current that
> >matters and not where its going.
The out-of-balance between Active and Neutral is what matters.
> >
> >For you folks with 220VAC power, just replace hot with L1 and neutral
> >with L2 to make this explanation relevant to you.
or Active and Neutral for the 240V users.
> Cary, I will have to say I can find no fault in your statement. I based my
> statement on text material which was used in a technical school for
> electricians. As for the test you mentioned I would have to agree that a
> directed short between the grounded and ungrounded conductors would trip the
> breaker, as well as melt some copper. I admit to being a little off target
> in saying that the GFI would not trip with no grounding electrode conductor
> attached... Why I said that I could not really tell you. I was in such a
> hurry to poke Roy in the ribs that I did not fully contemplate the situation
> before getting mouthy. As for that (as little as 1/1000th of an amp to
> ground will cause it to trip). That is what the text said. I never have
> stopped to think why you can't test for voltage hot to ground on a GFI
> circuit even if the ground is a water pipe or driven rod not directly
> attached to the recepticle. I always accepted it the way it was taught. Your
> explaination sheds a little light on why it is so difficult to use a GFI on
> a magnetic load such as a transformer or flourescent ballast.
>
> Kurt
Cool Kurt, but the problem with inductive loads like fluro's and
transformers has more to do with the current detection circuits in the
ELCB or GFI.
Some comments from other emails on the subject.
I never let the top of my heaters go below the water and recommend the
same to others. As they heat up and cool down the suck water in. (except
sometimes when they are new) If nothing else the water shortens their
life and may shorten yours. If you follow this rule it is simple to give
a heater a safety check. Is the glass broken? I have heard some people
say that they work best on their side for better water circulation to
that I say bull dust. If the water movement in your tank is that bad buy
a filter of some kind.
BTW Heater thermostates have a number of adjustments. If anyone doesn't
know how to adjust a heater and would like to please ask.
I agree that a power head or anything else that is fully bellow the
water could be the problem.
Please don't see as GFI or ELCB as a device that will make everything
else ok. That would be like saying that if you car has an air bag it
doesn't matter if the brakes don't work! ELCB's are a safety net and
that is all.
Well now I feal better!!
See ya
Tim Thornley