How to test strength of ground.

[green2012]

Im not entirely sure what the problem is. Let me start by explaining the problem. A small fire broke out inside a residential panel. The 2pole 30 amp breaker for the A/C unit burnt itself out from the inside. It took the bus with it an finally the main tripped and thats when they noticed the problem. Whole panel needed changing out obviously. The A/C unit compressor grounded out and was replaced as well. The A/C seemed to start the issue but why didnt the breaker trip? After changing out the panel I decided to check other circuits. Apparently a few years back same thing happened to the kitchen circuit but didnt cause a fire. It just destroyed the breaker and the bus "tab" that it stabbed into. I checked the circuit and it draws 25 apms on a 15 amp circuit and doesnt pop the breaker. This is a brand new breaker. I changed it just to be sure but it wont pop regardless of how much aperage goes through it. I checked the grounding electrode and it looks fine. It terminates 6 feet from where the main water line comes through the ground. Seems to be solid. I did one final test to see if I can get a breaker to trip. I grounded out an outlet to the pipe feeding it and it sparked pretty good but did not pop the breaker. Im at a loss. Panel is bonded to the neutral. I get a reading of ground at the outlets I have plug tested and I get ground readings in the panel. Any thoughts????

 

[don_resqcapt19]

How long did you let the 25 amps flow through the 15 amp breaker? Looking at the time trip curve for one brand of breaker shows that it could take as long as 250 seconds before the 15 amp breaker trips with a 25 amp load. If you are actually measuring 25 amps on the hot conductor, that is what is flowing through the breaker and the grounding and bonding does not have anything to do with the breaker not tripping.

 

[green2012]

I didn't time it. I didn't let it go for 4 minutes though. I will look into the trip curve for cutler hammer ch style breakers. What about the intentional grounding test though. I put the hot wire directly onto conduit and it didn't trip. I plug tested the outlet before and after and it showed ground?

 

[kwired]

I didn't time it. I didn't let it go for 4 minutes though. I will look into the trip curve for cutler hammer ch style breakers. What about the intentional grounding test though. I put the hot wire directly onto conduit and it didn't trip. I plug tested the outlet before and after and it showed ground?

I was going to ask if it was a FPE panel but apparently is CH series - they are typically pretty good breakers. When you performed the intentional ground test did you get a pretty good fireworks show? If not you either don't have a good enough ground, at least at the point you touched to, or maybe have fairly high impedance in the circuit - possibly even including the source. Small POCO transformer along with long service conductors can significantly reduce how much current flows in a short circuit/ground fault. It should still trip eventually, and in much less time then the 25 amps on a 15 amp breaker situation, but maybe something else gives up first and interrupts the circuit in some cases. And you likely were not all that willing to see just how long it would take for it to trip in that situation either.

Any other poor installation method that adds impedance to the circuit will also reduce amount of current that flows during such a fault and will retard response time of the overcurrent device as compared to having low impedance. If steel raceway one example is not having all circuit conductors in the same raceway, you effectively are making a one turn core and coil (inductor) if you don't run all the circuit conductors in the same raceway, and is part of reason NEC requires them all to be in same raceway/cable.

 

[don_resqcapt19]

How did you do the intentional ground test? It is hard to hold the wire so as to get a solid contact and get enough current to flow to get into the instantaneous trip range of the breaker.
Also it is never a good idea to do that type of test. You really don't know what the current path may be or the impedance of the path. You can start a fire, or energize things and create a shock hazard.

 

[kwired]

How did you do the intentional ground test? It is hard to hold the wire so as to get a solid contact and get enough current to flow to get into the instantaneous trip range of the breaker.
Also it is never a good idea to do that type of test. You really don't know what the current path may be or the impedance of the path. You can start a fire, or energize things and create a shock hazard.

The more available fault current the easier this task becomes - but also becomes more dangerous to attempt as well.

 

[SG-1]

Keep in mind the grounding electrode system has nothing to do with the breaker tripping or not. The EGC being bonded in the panel to the neutral bar has everything to do with tripping the breaker on a ground fault. The breaker should trip for simple overload, too.

If you decide to do another short circuit test, measure the current.

 

[K8MHZ]

I was going to ask if it was a FPE panel but apparently is CH series - they are typically pretty good breakers. When you performed the intentional ground test did you get a pretty good fireworks show? If not you either don't have a good enough ground, at least at the point you touched to, or maybe have fairly high impedance in the circuit - possibly even including the source. Small POCO transformer along with long service conductors can significantly reduce how much current flows in a short circuit/ground fault. It should still trip eventually, and in much less time then the 25 amps on a 15 amp breaker situation, but maybe something else gives up first and interrupts the circuit in some cases. And you likely were not all that willing to see just how long it would take for it to trip in that situation either.

Any other poor installation method that adds impedance to the circuit will also reduce amount of current that flows during such a fault and will retard response time of the overcurrent device as compared to having low impedance. If steel raceway one example is not having all circuit conductors in the same raceway, you effectively are making a one turn core and coil (inductor) if you don't run all the circuit conductors in the same raceway, and is part of reason NEC requires them all to be in same raceway/cable.

Sorry, I don't agree with you on CH breakers. I have heard far too many issues of them not tripping and have seen it myself. I will not put CH panels in and know several contractors that will not, either. I saw one 15 amp CH breaker hold 115 amps and not trip.

Other people love them, I don't.

 

[green2012]

I did the intentional ground test by making contact between the hot and the conduit. This isn't Romex situation. I checked the bond to the panel. There are actually multiple points of attachment. The grounding electrode from cold water is landed right on neutral bar and there is a wire from grounding bushing to neutral as well as the main bonding jumper from panel to neutral. I've never heard of issues with ch breakers either. I won't use stab lock style breakers so my other option is square D but hard to get in my area. Any other ideas to check?

 

[K8MHZ]

2012,

What probably happened was that the breaker's connection to the bus started getting weaker and over time created enough resistance to start the heating process. Hastening the process is running the breaker close to it's max load so it's just on the verge of tripping, but not quite there yet.

I have seen this several times, burning up both the breaker and a small part of the bus bar. No brand is immune. It's just plain physics.

 

[Dennis Alwon]

2012,

I have seen this several times, burning up both the breaker and a small part of the bus bar. No brand is immune. It's just plain physics.

I agree with that. I always laugh when people complain that an FPE breaker didn't trip. We had a fast short the other day and a sq.d breaker did not trip. It might have if it is longer but it "blew clear " as we used to say. I have seen almost every brand not trip in certain situations.

 

[K8MHZ]

I did the intentional ground test by making contact between the hot and the conduit. This isn't Romex situation. I checked the bond to the panel. There are actually multiple points of attachment. The grounding electrode from cold water is landed right on neutral bar and there is a wire from grounding bushing to neutral as well as the main bonding jumper from panel to neutral. I've never heard of issues with ch breakers either. I won't use stab lock style breakers so my other option is square D but hard to get in my area. Any other ideas to check?

I am a bit confused.

Why are you trying to verify a low impedance grounding system when your issues were a burned out breaker and a 15 amp breaker not instantaneously tripping at 15 amps?

As for the 15 amp breaker, please tell us you did not use a breaker ampacity higher than the conductor it's protecting.

Your 'test' of intentionally grounding a live ungrounded conductor is very dangerous, could have caused a fire, could have damaged sensitive equipment and is NOT the way to test ground integrity.

Again, I stress, if the smallest conductor is a 14 AWG, the largest breaker can only be a 15 amp breaker. There are exceptions, but I don't see any here.

 

[SG-1]

I did the intentional ground test by making contact between the hot and the conduit. This isn't Romex situation. I checked the bond to the panel. There are actually multiple points of attachment. The grounding electrode from cold water is landed right on neutral bar and there is a wire from grounding bushing to neutral as well as the main bonding jumper from panel to neutral. I've never heard of issues with ch breakers either. I won't use stab lock style breakers so my other option is square D but hard to get in my area. Any other ideas to check?

If conduit is used as the EGC then one loose connection in the run could severely limit the amount of fault current available.

 

[GoldDigger]

Going back to the title of the thread, testing the "strength" of the ground, I would just like to point out that there really are two separate factors in play:

1. The resistance of the EGC back to the bond point. This will be in the low ohm or sub-ohm range and can be measured with a low ohm meter that uses either DC or pulses at low voltage and high current (compared to a regular ohmmeter.) The biggest problem will be finding a wire to complete the loop for the ohmmeter testing. You can use a cord or temp wire and measure its resistance separately since you will be able to bring both ends together.
2. The "strength" of the connection in terms of current carrying capacity and mechanical integrity. The first part can be tested with high current, but at the risk of creating an arc or hot spot somewhere out of sight. Low resistance by itself does not necessarily imply high current capacity. Look at a fuse for example!
The mechanical integrity, on the other hand, pretty much requires end to end inspection or at least sampling of the joints involved. Maybe jumping up and down real hard while watching the milli-ohmeter reading?

 

[green2012]

In response to marky the sparkys last post,

"I am a bit confused.

Why are you trying to verify a low impedance grounding system when your issues were a burned out breaker and a 15 amp breaker not instantaneously tripping at 15 amps?

As for the 15 amp breaker, please tell us you did not use a breaker ampacity higher than the conductor it's protecting.

Your 'test' of intentionally grounding a live ungrounded conductor is very dangerous, could have caused a fire, could have damaged sensitive equipment and is NOT the way to test ground integrity.

Again, I stress, if the smallest conductor is a 14 AWG, the largest breaker can only be a 15 amp breaker. There are exceptions, but I don't see any here."

I am using a 15 amp breaker with 14awg wire. The problem, is that the circuit when in full swing is pulling 25 amps and not tripping. I of course wouldn't just up the size of the breaker without upping the wire size. This wouldn't solve my concern anyway.

The test of intentional grounding, I chose a dedicated circuit that I unplugged sump pump from. Cant see how its dangerous considering that the grounded raceway under normal conditions should have caused the breaker to trip. I needed to create a ground fault to test the breaker. I wasn't testing ground integrity. There are easier and less violent ways of testing for that.

As I said in the beginning of this thread, Im not sure what the problem is and I decided to test the breaker in all ways I could think of because they didnt seam to trip under any condition. The entire house was off and I did these tests in a controlled setting. My concern is that the old panel had the exact issues that the new one is showing. Breakers are not tripping and burning themselves up. Panel is bonded and I just needed to know if there is anything Im missing.

 

[brian john]

1. IMO for residential no one manufacture is that much worse than the other, though I do prefer Square D.
2. If you want the breaker properly tested send it to me, I'll test it on a calibrated test set. IM me if you are serious.
3. The issue you described is a defective breaker or bad bus connection issue.
4. Earth could care less if this circuit breaker ever trips.

 

[PetrosA]

1. IMO for residential no one manufacture is that much worse than the other, though I do prefer Square D.
2. If you want the breaker properly tested send it to me, I'll test it on a calibrated test set. IM me if you are serious.
3. The issue you described is a defective breaker or bad bus connection issue.
4. Earth could care less if this circuit breaker ever trips.

Hey, I have a few milk crates full of old breakers. Could you test them out for me so I can reuse them? Just kidding

 

[kwired]

I agree with that. I always laugh when people complain that an FPE breaker didn't trip. We had a fast short the other day and a sq.d breaker did not trip. It might have if it is longer but it "blew clear " as we used to say. I have seen almost every brand not trip in certain situations.

A little surprising to me, usually the Square D breakers are going to trip faster then most others - especially the 15 and 20 amp standard single poles. They do make them in a "high magnetic" model - which has a different trip curve that comes in handy for some motor applications it is same model number with "HM" suffix. I don't know what the trip curve for that looks like compared to other brands, but have seen many standard QO120's that trip when trying to start some motors - usually some power saws, air compressors or other high inrush tools, yet other brands never have this problem unless maybe there is already other load on the circuit when you try to start those mentioned tools. Switch to the "high magnetic" unit and no more trips at starting.

 

[orion]

I have to laugh about this thread. First.......there are ground testers that actually measure the amount of ohms / resistance. I would highly suggest to purchase one from Fluke before any additional field bolted fault ground testing is applied to the homes wiring :thumbsup:. Second......there are also hipot testers available to test a circuit WITHOUT applying unnecessary current to a conductor that is not sized properly. Those 125A, 250A field test through a 15A breaker??..... You may now want to check the conductor to see how much insulation or conductor damage was done :ashamed:

 

[suemarkp]

Again, I stress, if the smallest conductor is a 14 AWG, the largest breaker can only be a 15 amp breaker. There are exceptions, but I don't see any here.

He said an HVAC unit. That would be probably the most common residential exception. If the HVAC unit is drawing 25A though, what is its MCA rating? If the MCA is 25A, then #14 wire would be too small. But it could have an MCA of 15A, #14 wire, and a 30A breaker and be compliant. The compressor could be failing though and when it gets bad enough should trip the 30A breaker.

How are the equipment grounds terminated in this panel? Are they on the same bar as the neutral? If so, then you know you have a good bond if all the lug screws are tight and you don't have ground and neutral in the same hole. If the grounds are on a separate bar, is the main bonding jumper installed and is that separate bar well bonded to either the panel chassis or the main bonding jumper?