An electrical problem

IaLeo

Well-known Member
Facts:
Inside a metal "quonset" shed.
200Amp panel .
A stomg of 6 outlets each,both walls, prof. installed, first outlet in string is GFCI protected. 12GA all in conduit, no visible damaage. Mounted on wood board fastened to metal shed wall.
Worked flawlessly for 20 years. 120 volt.
Past winter unplugged everything on east wall, wasn't using it.
This spring replugged drill press&light, tripped GFCI & breaker.
Reset, same tripping regardless of what I plug in.
Examination: no evidence of water, corrosion, mud dauber wasps,and no construction changes, new screws, no outside bldg work.
Disconnected string after outlet #3 isolating some of the string, no change, disconnect after #2, no change.
Installed new GFCI, no change.
Installed new breaker, no change.
I understand how GFCI sense differences in current in hot vs return wire. So is there something gone bad on on common (white) or grounding circuit? How? The GFCI trips sometimes w/o breaker tripping. All energizing shows 120volt+. Testing does not trip anything, but plugging in any load (like 60 watt) non grounded lamp, triggers GFCI.

Any thoughts on what to look for? And thanks for listening to my problem. Leo
 
I would also disconnect after outlet #1 just for grins. Something in the string is causing problems. It may be a loose connection.

Larry
 
Start from the gfi ,unhook, it do your test. Go two or 5hree down 5he
line qnd repeat. If it stays on then the last couple have a bug. If it
pops then it is back towards the gfi. Takes a little time but you
should find it. Gfi circuts can be a huge pain in the butt.
 
(quoted from post at 16:31:08 05/23/17) Facts:
Inside a metal "quonset" shed.
200Amp panel .
A [b:2854fe6949]stomg [/b:2854fe6949]of 6 outlets each,both walls, prof. installed, first outlet in string is GFCI protected. 12GA all in conduit, no visible damaage. Mounted on wood board fastened to metal shed wall.
Worked flawlessly for 20 years. 120 volt.
Past winter unplugged everything on east wall, wasn't using it.
This spring replugged drill press&light, tripped GFCI & breaker.
Reset, same tripping regardless of what I plug in.
Examination: no evidence of water, corrosion, mud dauber wasps,and no construction changes, new screws, no outside bldg work.
Disconnected string after outlet #3 isolating some of the string, no change, disconnect after #2, no change.
Installed new GFCI, no change.
Installed new breaker, no change.
I understand how GFCI sense differences in current in hot vs return wire. So is there something gone bad on on common (white) or grounding circuit? How? The GFCI trips sometimes w/o breaker tripping. All energizing shows 120volt+. Testing does not trip anything, but plugging in any load (like 60 watt) non grounded lamp, triggers GFCI.

Any thoughts on what to look for? And thanks for listening to my problem. Leo

For anyone wondering what stomg means, the urban dictionary defines it as: "so totally oh my god". Hope this helps.
 
If you feel comfortable doing so, check at the panel and the outlets to see if the neutral for that circuit (Should be white if done by an electrician) has been interrupted. It could be loose at the neutral bonding bar in the panel, at the outlet, etc. The neutral bar has all of those circuits hit it at once, and occasionally as a guy is tightening them he gets distracted and misses a screw. It would cause every symptom you have.
 
Go to 1st device on circuit, unhook line side and
test. If a Good 120, split circuit in half from that point
and energize to see if you get 120 to that point. It's
time consuming and it's usually something little.
Like a bare ground wire touching.
 
I appreciate all the hints. I just unhook the "hot" to isolate the rest of the string.
I unhooked the string hot from the 1st (GFCI), isolating the rest of the string. No Change. I checked tightness of screws in the panel for the return and ground....all tight and no one has been messing with the still open panel this year. ?? So with all grounds and returns (commons?) still hooked up in the string, only GFCI hot, plugged in the two wire 60 watt flood light, and it tripped the GFCI instantly.
Don't have time to work on this further as the grass and garden are crowding me....but will let you know if I ever solve this. Leo
 
Suspect you have a weak neutral.

Turn off all power before starting. Go to the first receptical, temporary in a regular outlet.

Turn on the main breaker. Check the voltage before turning the load on, line to line, and line to neutral.

Plug in something that will apply a load, something heavy, like an electric heater. Recheck the voltage.

Likely you will find a substantial drop between the loaded line and neutral.

If the voltage across the lines is still good, there is a weak neutral.

If the voltage across the lines is low, there is a weak line.

Most likely it will be a bad neutral connection.

Be very careful doing this test! Avoid touching anything metal while doing the test, make sure no one else is around the outside of the building or touching anything. Be sure you are standing on something nonconductive!
 
When hooking up a new GFCI it's very easy to reverse the in and out wires. So give that a check.

Dusty
 
Pay attention to line and load on the GFI. Line is hot coming in load is out to the rest of circuit. GFIs work off neutral so check that.
 
If a neutral and ground become connected anywhere except in the main panel, the GFI will false trip. Reason is that part of the neutral
current flows through the ground path. Because it is now less than current from the hot side, the GFI trips.
 
I agree with Steve, have seen this issue when there is a bad neutral, can even be an incoming neutral into building.
 
> I just unhook the "hot" to isolate the rest of the string.

A GFCI will trip if EITHER the hot or neutral is grounded. (Ole George and I had a far too lengthy discussion on this a couple years ago.) So you are not "isolating" anything by only disconnecting the hot conductor. You must disconnect BOTH hot and neutral.

Start over by isolating different parts of the circuits until you find the culprit, remembering to disconnect both hot and cold conductors.
 
If everything on the load side of the GFCI receptacle is disconnected and it still trips. Test with something else other than the drill press and light you have been plugging in. you could have gotten another bad GFCI receptacle. The 20 amp breaker supplying the circuit should not enter into the picture at all. If the GFCI will hold as when the drill press is plugged in start reconnecting the line side wiring. Make sure you have line and load connected in the proper locations on the GFCI
 
Have you tried plugging the drill press and light into another GFI protected circuit? Could be the equipment an not the GFI.
 
Leo, sorry I got here late, here's my take:

With all the talk about a loose or bad Neutral below such as in the panel etc (which I agree can be a problem and needs inspected and fixed) FYI REALIZE a GFCI "RECEPTACLE" ONLY monitors CURRENT FLOW OUT the Hot versus that returned back IN by the Neutral DOWNSTREAM (if fed off LOAD side of GFCI) or loads connected directed into the GFCI outlet (it doesn't measure current paths or faults from or in panel out to the GFCI receptacle). Even if there was a panel or utility service problem that reduced voltage or allowed improper UPSTREAM current divider paths, still if a load connected to the GFCI has the same Hot and return Neutral current it will NOT trip. It trips ONLY when the Hot current it sends OUT THROUGH THE GFCI TORROID SENSING COIL is 0.005 to 0.006 amps different then the Neutral current being returned THROUGH THE SAME GFCI TORROID SENSING COIL because its returning elsewhere due to a short or leak or ground fault. Don't anyone have a calf now, SURE its ALWAYS good to check and tighten all Hot and Neutral and Grounds in the panel and at junctions and splices and the feeder circuit THERE COULD BE A PROBLEM THERE MIND YOU.

If any load trips a GFCI I would try the same load connected elsewhere into a different GFCI or different GFCI protected circuit to see if the appliance is the problem or your GFCI receptacle or circuit.

On a 120/240 volt panel a Loose Neutral could cause L1 to be different from L2, but if a load is connected to a GFCI receptacle (even if reduced to 100 volts) as long as current flowing OUT the HOT is same as that being returned back IN by the Neutral TO THE GFCI CONNECTED LOAD it will NOT trip. The GFCI's Torroid sensing coil is located in the GFCI receptacle, sensing downstream load current OUT and back IN, NOT in the panel or the feeder circuit. Even if there was a fault between the GFCI and panel or in the panel, that current divider there DOES NOT mean there still cant be equal current out the GFCI that gets returned through the GFCI's Torroid coil BUT THEN IS LATER IMPROPERLY (due to a fault) DIVIDED IN PANEL OR BETWEEN PANEL AND GFCI

FYI how a GFCI works is having the HOT going OUT and Neutral flowing back IN pass through a Torroid Coil. So long as they are equal they cancel out any induced voltage so she don't trip. HOWEVER if there's as little as 0.005 to 0.006 amps difference a voltage is induced which triggers the trip. It does NOT measure upstream current flow paths (like a short or ground fault or loose Neutral etc) ONLY that flowing out then back in (to loads downstream) through the GFCI's Torroid Coil.

Check all panel Neutral and Ground and Hot connections and for any minor shorts and then if a load trips a GFCI try the same appliance in a different GFCI and different circuit.

SURE there could be a panel or branch circuit feed problem (loose or bad connection or short) but likewise SURE there could also be a faulty (even if new) GFCI or a faulty appliance/load CHECK FOR BOTH

NOTE I'm talkin a GFCI receptacle NOT a GFCI breaker here

John T NO WARRANTY I'm too long retired and rusty from electrical engineering practice and things may have changed or my old memory cells lapsed grrrrrrrrrrrrrr lol
 
A BIG THANK YOU, ONE AND ALL! IT IS SOLVED. Apparently the GFCI went bad and when replacing it with a new one, I hooked the line to where the load should be. Corrected that and whole string works fine. Thanks again. IaLeo I owe you a drink if we ever meet!
 

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