GFI Outlet

Page 3 of 4  

wrote:

More accurately, if the Hot and Neutral currents are not equal within a tolerance range, a gfi will trip. It doesn't matter where the current leaks to; it can be to other than ground. It's just that usually it will be ground. So, it's "Only if it leaks current from one conductor more than another, regardless of whether it's to ground or not.". Ground is irrelevant to the operation of a GFCI.
HTH,
Twayne`

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You are quite right that the current can also leak to a conductor of another circuit. And GFCIs will work on an ungrounded circuit and increase safety. But I wouldn't go quite so far as to say the ground is irrelevant; grounding still improves safety. For example, if an ungrounded appliance on a GFCI circuit has a high resistance short from hot to the case, the GFCI won't trip until you complete the circuit from the case to ground or another circuit's conductor. While if the appliance is grounded, the GFCI will trip as soon as current through the short exceeds the 5ma threshhold.
Cheers, Wayne
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I only meant it's irrelevant to tripping the gfi; not that that a safety ground is irrelevant period. Could have been more precise I guess.
Twayne`
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I only mention this because too many people thing GFIs work on the ground lead:
It's strictly an imbalance between Hot and Neutral: whether the current goes to gound or anywhere else. GFCIs do not require the ground lead to operate and don't care about it. It's an assumption that a voltge difference will be to ground but it could be to any other place such as another line or short between adjoining cables by a nail, etc. etc..
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 11 Sep 2009 13:23:39 -0400, "Twayne"

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yup; that's the inductive/capacitive arguement for their tripping. But if you think about it, even surges/spikes from a motor may be latitudinal and not longitudinal. I know it's true that they don't false-trip nearly as much these days so I think I might have to see if there are any articles that explain how they do that. Maybe it's the dv/dt they've started to look at.
Twayne`
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I have a fridge outside that has always been on a GFCI and never tripped it. I guarantee you, if you put a 2-3 prong adapter on the plug of a fridge that trips a GFCI (floating the ground) and then measure the case to ground, you will see 120v. It may be spikes when it starts and stops or it may be solid. Be careful not to get killed. They develop shorts inside the compressor and that is why you have burnt smell when you open up the freon line of an old fridge.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

By measuring from the case (intended to be but not grounded and metal) to earth gnd is a measurement of two different references, one of which is floating. In a non-fault system, the green gnd wire only has a reference back to the service box and carries zero current. You are extremely unlikely to see 120Vac on that wire. If you do see a solid 120Vac, then there is another ground connection somewhere on the unit meaning a FAULT exists that needs attention. Depending on the length of that floating ground wire, one end open, the other connected at the service box, you will see, usually between 15Vac and 90Vac. You will specifically NOT see the identical voltage you see between Hot and Neutral. Depending on what other current carrying wires may be parallel to the floating ground, crossing it (little effect), or any other fields that may impact it, including the earth's magnetic field and some other rudimentary sources, along with the measuring instrument's input impedance, battery or line operated, and whether one lead is earth grounded (capacitively, usually), and the distance from the box, you will see differing "phantom" voltages appear on the measuring instrument. It's a very simple task to prove whether what you're seeing is a phantom voltage or an actual improper connection of some sort. Just lower the measureing instrument's input impedance with a bulb, resistor, even a wet finger and you'll see the voltage drop to 0.0x V quickly. You would have the same condition if you disconnected the wire at the service box and connected it to the unit, but you'd have to go measure at the Service Box to see it.
It may be spikes when it starts and

Phantom voltages are completely safe and have no potential behind them. With one end of a wire open, current can NOT flow! Removing earth ground creates an open ckt! NO current can flow in an open ckt. With no source behind the phantom voltage, as soon as it gets a path to anywhere, the voltage will disappear. As soon as you remove your measuring equipment, the voltage becomes unknown. You will not measure any current unless you have something capable of measureing micro-amps across a known resistor, or just using the meter's input Z for that figure. There is no need to fear a phantom voltage. There IS a reason to fear a voltage though, in the event it's NOT a phantom and is instead a fault situation where it is actually connected somehow to something with a connection outside the intended ckt. That has to be fixed and quickly! Else make sure the fire insurance is paid to date<g>.

What? If there ever WERE a burnt smell to it, you'd have a pretty special nose to pick it out from the intentionally added "perfume" they put into it. Freon is odorless and deadly; that bad smell is in all freon perfume; they don't make freon without it.
HTH,
Twayne`
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

insulation good for 50,000 volts on a 110 device and still get an inbalance on startup if the inductive OR capacitive reactance is too high.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

For sure. It's an "iffy" area.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@snyder.on.ca wrote:

How many feet of 12/2 with ground romex does it take to get 5mA of 'leakage' current?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Several hundred feet
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@aol.com wrote:

Sounds reasonable.
And sounds kinda unlikely you would get a trip from capacitive reactance.
--
bud--

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I have never had a problem and I have an extensive network of lights and receptacles in my 2600 square foot screen cage and out to a remote shed and boat lift. It is all wire in EMT or RNC and all on GFCIs. All told there is close to a half mile of THHN/THWN out there.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I'm curious--you said earlier that several hundred feet of NM cable might be enough to allow 5 ma of leakage current. But then you mention several thousand feet of THHN/THWN in conduit without any trouble. Is the upshot that the leakage current in NM cable is much greater (per unit length) because the outer sheath holds the hot and ground in close proximity?
Cheers, Wayne
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 14 Sep 2009 15:29:55 +0000 (UTC), Wayne Whitney

1000' of wire). I imagine the longest single run an a GFCI is about 250' of wire in EMT. The only time it has ever tripped was when I had water in a box. One tip. Point all wirenuts up and keep them towards the top of the box. They all collect water now and then. All outside wiring is a "wet location". That is particularly true underground
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

While this may be true it has frequently been mentioned here on these pages that any 115 volt motor equipped domestic appliance, fridge, freezer, washer etc. should NOT be plugged into a GFCI equipped circuit. Too much chance of a momentary unbalance! And they can't all have defective winding insualtion? Especially those all-enclosed fridge compressor units?
GFCI (So called Ground Fault ...... ) operate when there is a 'slight imbalance' of a few milliamps (thousandths of amps) between the live and neutral current flow.
During motor starting of any AC induction or other types of motors, due to capacitance of motor windings to the grounded appliance framework etc. there 'might' be a momentary slight current unbalance which is quite normal and OK.
GFCI are designed to protect humans against a fault such as a wire inside touching the metal frame of an appliance especially in damp/wet conditions; such as an operating but faulty electric lawn mower, or electric drill. (But they both have electric motors! So what gives?) The human touching the defective appliance can provide a path to ground and get a potentially lethal shock. The faulty path to ground (through the human) unbalances the current and 'trips' the GFCI for safety.
Can somebody make a reference to an electrical code that confirms the above?
Section 210.8 of the new code spells it out. As Wayne Whitney points out, many of the responses are out dated, the new code have very few exceptions for the GFCI outlets in required areas. If you stick your fridge, or washer in a garage or unfinished basement, for example, they must be GFCI protected
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Just for preciseness because too many people think gnd is neccessary for a GFI to work: It's not the current to ground that is detected; it is the difference in current between the Hot and Neutral wires that is detected. The ckt to ground is where the current went, but what's detected is the Hot/Neutral current difference > 5 mA.

That's good to know. I use GFCI's for those, even on my shop tools but I didn't know it was a requirement. It seems that as long as I keep one tool to one breaker, I don't have any problems nowadays. I did think once I had one that was nuisance tripping, until I realized it was one particular tool when I plugged it into my bench. Rewired the tool; all OK. Never did figure out the "problem" but it's gone now. And I've had one GFCI that just plain quit working; no test, no set, nothing; it's straight thru like it's not there anymore. Guess NOW, I'm planning to switch that one out this weekend<g>!
Cheers,
Twayne``
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 10 Sep 2009 10:47:49 -0700 (PDT), stan

210.52(A)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 10 Sep 2009 10:47:49 -0700 (PDT), stan

No, but the drill or lawn mower do not have INDUCTION motors. They are both universal (or in some cases straight DC) motors. Many lawn mowers are DC motors run through a bridge rectifier.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.