GFI tripping on well pump used in a lake.
GFI tripping on well pump used in a lake.
(OP)
So I've had a question posed to me about a well pump used in a recreational lake. It's a single phase pump with the typical start/run package on shore. The circuit will not run reliably on a GFI but of course runs just fine with a standard breaker. Clearly it has leakage of more than 6mA.
I was asked if an isolation transformer would work. Probably it would work for preventing the GFI from tripping but I don't think that would help the soon to be electrocuted swimmers. That strikes me in this particular case as a tool to isolate only the GFI from reality.
The motor leads show 2Mohms to ground, seems low to me, but I'm told Franklin techs only consider it actionable at 500kohms or less.
The wire run is several hundred feet.
I'm not sure if code would allow a GFI with a higher or adjustable trip point in this app in NEC land.
I was asked if an isolation transformer would work. Probably it would work for preventing the GFI from tripping but I don't think that would help the soon to be electrocuted swimmers. That strikes me in this particular case as a tool to isolate only the GFI from reality.
The motor leads show 2Mohms to ground, seems low to me, but I'm told Franklin techs only consider it actionable at 500kohms or less.
The wire run is several hundred feet.
I'm not sure if code would allow a GFI with a higher or adjustable trip point in this app in NEC land.
Keith Cress
kcress - http://www.flaminsystems.com





RE: GFI tripping on well pump used in a lake.
However, "The wire run is several hundred feet."
How about wire with thicker insulation?
Bill
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"Why not the best?"
Jimmy Carter
RE: GFI tripping on well pump used in a lake.
RE: GFI tripping on well pump used in a lake.
Interestingly, Sqare D Q0 GFI breakers don't nuisance trip. I had a heck of a time on my spa motor using a Siemens breaker, changed it to Sq D and it never nuisance tripped again. I thought it had once, turned out the insulation on the heater coil had failed. So it did its job when it needed to.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: GFI tripping on well pump used in a lake.
Keith Cress
kcress - http://www.flaminsystems.com
RE: GFI tripping on well pump used in a lake.
RE: GFI tripping on well pump used in a lake.
RE: GFI tripping on well pump used in a lake.
Keith Cress
kcress - http://www.flaminsystems.com
RE: GFI tripping on well pump used in a lake.
RE: GFI tripping on well pump used in a lake.
Due diligence may require a similar transformer for life safety.
Better to reduce the capacitive leakage if possible.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: GFI tripping on well pump used in a lake.
Keith Cress
kcress - http://www.flaminsystems.com
RE: GFI tripping on well pump used in a lake.
RE: GFI tripping on well pump used in a lake.
Yes, I see your point, Lionel and it is well made and I agree with it.
However, please consider the following points.
Thank you.
I would consider it due diligence to evaluate the possible implications of one line becoming grounded.
In the medical application that I mentioned, this possibility was addressed by a monitoring system. The medical systems must be small enough so that capacitive leakage to ground is within a very low acceptable range.
If one line becomes grounded, there will be a possible ground return path, and this path may pass twice as much current as before. The voltage to ground may be 240 Volts rather than the original 120 Volts.
With no ground reference at the transformer I doubt that a GFCI will see this possible ground fault path.
Now to the cost of the transformer we may need to add the cost of ground detection and tripping equipment. Also, for life safety, CYA may suggest a PE stamp on the drawings. This may or may not be a significant added cost.
I suggest a cost comparison between changing the cables and adding a transformer and detection and switching.
I would favour changing cables to reduce capacitive leakage.
As a reality check, it may be well to scope the circuit to verify that the leakage is, in fact, capacitive.
My first rule in trouble shooting is:
Make sure that you know what the source of the problem really is.
My third rule:
Re-check the first rule.
How many of us have seen this:
First find the problem and fix it.
Second, remove, repair or otherwise deal with the last three attempts by previous repairmen to "fix" the wrong problem.
Back to rule one.
Verify that we are seeing capacitive leakage.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: GFI tripping on well pump used in a lake.
RE: GFI tripping on well pump used in a lake.
The most likely cause is the pump has a small amount of moisture in the windings lowering it's resistance to ground. But, if you can't get the damn pump fixed then you have to start looking for other solutions.
I have no idea how the voltage and current of an isolation transformer could double...
RE: GFI tripping on well pump used in a lake.
Keith Cress
kcress - http://www.flaminsystems.com
RE: GFI tripping on well pump used in a lake.
However, there will be a capacitive current to ground from each of the ungrounded conductors.
Grounding either line will shunt the capacitance to ground and current will flow.
Further in the event of a second ground fault a ground fault current will flow. I will accept that this current may be low enough to be non-threatening on a small circuit but we can't assume that this circuit is small enough.Double?
Well with a grounded 120:240 Volt circuit the voltage driving a ground fault current will be 120 Volts.
However, if one line of a 240 Volt circuit goes to ground, then a second ground fault current will be driven by 240 Volts.
Isolation and safety is well addressed in the code for life safety isolated circuits in operating theatres. Not only must the circuit be isolated from ground but monitoring equipment must be installed to prove the absence of any leakage paths to ground.
The isolated circuit is great, but it must be isolated and there must be a system to prove that there is no inadvertent or unintended path to ground.
This is addressed here:
Excerpt from the Canadian Electrical Code; I am sure the NEC has a similar rule.
(2) Wiring systems supplied by an ungrounded supply shall be equipped with a suitable ground fault detection
device to indicate the presence of a ground fault.
(3) Ground fault indication activated by the ground fault detection device required by Subrule (2) shall be
clearly
(a) labelled as to its purpose; and
(b) visible to persons monitoring the status of the system.
And
10-112 Isolated circuits
Special circuits shall be permitted to be supplied from the ungrounded secondaries of transformers having the
primary and secondary windings separated by a grounded metal shield if
(a) installed under the provisions of other Sections of this Code; or
(b) this is required to recognize a particular accident or fire hazard.
A long cable will have capacitance to ground. If the cable is under water we must also consider the fairly high capacitive constant of water.
When I started out there were a lot of legacy ungrounded three phase systems in industrial plants.
The ground detection lights were primarily to avoid equipment damage in the event of a second ground fault on another phase.
The capacitive leakage current in many plants was well above lethal levels.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: GFI tripping on well pump used in a lake.
http://www.msnewsnow.com/story/31982936/parents-ra...
RE: GFI tripping on well pump used in a lake.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: GFI tripping on well pump used in a lake.
RE: GFI tripping on well pump used in a lake.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: GFI tripping on well pump used in a lake.
Mike Halloran
Pembroke Pines, FL, USA