If there is a gound fault at a receptical, What are the reasons the breaker will not trip. One of our offices had a bad receptial. When I had arived the breaker had arced and melted some of the metal box. The breaker did not trip. I know that breakers are designed to handle a high inrush current and that sometime the arc does not draw enough current to trip a breaker. Is it also possible that the ground path is not good.
Ground fault
- Thread starter JdoubleU
- Start date
- Status
- Location
- Logan, Utah
How old is the breaker and what brand is it?
This does sound like it could be a high impeadance ground fault current path.
Chris
This does sound like it could be a high impeadance ground fault current path.
Chris
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
I do, among other things, consulting for a national magazine. To illustrate this very thing, for a story editor, I hooked up a simple plug and cord 1500 Watt electric space heater to a photo set (mocked up) receptacle.
I supplied this photo set with a simple cord to a 120 V 20 A circuit.
I loosened one terminal screw to conductor connection on my photo set receptacle, just so, and turned on the heater.
The heater ran, the breaker did not trip, and this little tiny plasma arc shown at the loose terminal screw and slowly ate away at the copper and screw.
I kept it running that way for about 10 minutes until the receptacle was "photo ready".
The more common name for this type of connection is "glowing connection". Try googling it.
What would be the best way to measure the resistance of the EMT that is being use for the ground.
If you want the DC resistance you could use an ohm meter. However, the impedance of the conduit varies with the magnitude of fault current. In your case the arc has an impedance value and thats probably why the breaker did not trip. If you are interested in the calculations for the conduit, check here
tonight and in a short time you will sleep soundly.
http://www.steelconduit.org/pdf/groundingpart1.PDF
tonight and in a short time you will sleep soundly.
http://www.steelconduit.org/pdf/groundingpart1.PDF
In your opinion do you think that it was just the impedance of the ARC that the breaker didin't trip and not the impedance of the ground. It was a pretty nasty arc that left about a quarter inch hole in the metal box. My Boss said if was not a poor ground, but I have seen arcs in outlet boxes that would trip the breaker right away.
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
Can't you just continuity test between the neutral and the metal box? Or drag a ground wire from the panel and test from that to the metal box?
IMO You had an impedance in the ground fault path or a bad breaker.
kwired
Electron manager
- Location
- NE Nebraska
HotConductor
Senior Member
- Location
- Philadelphia
Does this originate from a main panel and is the main bonding jumper in place and properly connected with the correct machine screw or bolt/nut? This is critical for clearing ground faults.
I just opened up three panels two weeks ago after a 4kv line dropped across two 240v lines and sent 4kv into these panels and found a drywall screw holding the main bonding jumper to the can.
I just opened up three panels two weeks ago after a 4kv line dropped across two 240v lines and sent 4kv into these panels and found a drywall screw holding the main bonding jumper to the can.
- Status