200amp disconnect on side of house tripping

[hardworker]

House has 200amp service. The panel is installed on an interior wall of the house, so by local code it needed a 200amp breaker disconnect on the outside of the house by the meter.

The 200amp disconnect breaker keeps tripping.

The house had a new heatpump system with emergency heat installed this past summer. I found inside the air handler unit it had been installed using awg #6 - 3 conductor with grd and awg #10 - 3 conductor with grd on a 60amp 2 pole breaker and 30 amp 2 pole breaker respectly. This is correct, except the extra conductor. Neutral is not needed on these 2 pole applications. The installer had just clipped the white neutral on both the 30 and 60 and left copper exposed on both.

This HVAC installer did the same with the neutrals inside the panel.

Per the homeowner, a handiman was in the panel lately and told the home owner two of the neutrals were not hooked up, so he installed them onto the neutral bar. Of course he did not trace them.

Heating season came and the outside disconnect started tripping. Apparently the #6 neutral in the HVAC was shorting against the housing of the unit.

I cleaned up the mess, but my question is the following?

Why did not the 60amp breaker in the panel not trip. Why did it hold and the disconnect outside was the one to trip? Why did not the 200amp panel main not trip?

 

[Dennis Alwon]

Let's back up and explain to me how the neutral shorting to the housing can blow the circuit.

It is not unheard of to have a breaker ahead of the branch circuit blow. It has to do with the trip setting of the breakers but I have not had that happen in a residence-- I have heard of it.

 

[charlie b]

First of all, shorting a neutral wire to the housing of a component should not cause anything to trip. It could cause current to flow along paths that should not have current flowing, but it would not cause any more current to flow from the breaker than had been flowing before the short. So that part of your story does not make sense to me.

But when a large current flows through several breakers in series (i.e., the outside 200 amp breaker, the panel's main breaker, and the 60 amp unit breaker), it is a matter of guesswork as to which breaker will trip first. It will depend on the breaker models and the points to which any adjustable setpoints had been dialed in. Unless someone had done a "selective coordination study," and nobody does such calculations for single family homes, and unless the breakers had been chosen and adjusted in order to cause the breaker closest to a fault to trip first, then there is no reason to expect the breaker closest to the fault to trip first.

 

[hardworker]

Thanks for correcting me about the neutral short causing the breaker to trip. It sounds like which breaker goes first is not relevant.

That means the source of the problem still exists. It has not tripped since I cleaned this up, but most likely it will happen again.

What would you advise is the best way to find this intermittent problem?

 

[charlie b]

What would you advise is the best way to find this intermittent problem?

Be there when it happens next. :slaphead:

OK, back to the real world. Much depends on what you did when you "cleaned this up." It is not impossible that you corrected the problem, without having seen exactly what the problem had been.

I should also mention that the handyman's actions (i.e., connecting the neutrals within the panel), while not proper, may have been irrelevant. When something goes wrong, it is often caused by something that recently changed. So perhaps the handyman's wiring did bring about the tripping. But the other thing that recently changed is that winter has arrived. If the heating system, and in particular the "emergency heat" provided when it gets really cold, had not yet been used so far this year, then perhaps the problem was there all along, just waiting to manifest itself until the system was turned on.

But now the situation is different, in that the tripping no longer happens. Once again, when the symptoms change (in this case, by the trips no longer happening), then in order to find out why the symptoms change, start by looking for what has recently happened. The answer is that you did some wiring corrections. So I say again, you may have fixed the problem. Then again, is there something else that recently changed? Has the weather in that area gotten warmer, so that the emergency heat is no longer needed? Perhaps the problem will come back, the next time the emergency heat kicks in. I mention this possibility because it happened to me long ago. We had a heat pump that worked well by itself when the weather was not too cold. But every time we tried to use the emergency heat, something shorted out in the control system, taking the entire heat pump out of service. We never figured out what was wrong with the system. All the repair persons could do is replace a coil or something, without being able to prevent the problem from happening again. So we stopped trying to use the emergency heat.

 

[USMC1302]

Sir Charles, you beat me to it. Sounds like the HVAC installer needs to check his work, especially the "emergency heat". Additionally, what exactly was the "handyman" doing?

 

[hardworker]

The handyman added a circuit for crawl space lights. That circuit and lights seem to work fine.

The homeowner says the d/s has not tripped since I was there last week, but we will see as a few more days pass.

If it trips again, I will get a HVAC guy to look over the installation of that unit.

If you have any other ideas, please let me hear them.

 

[Cow]

Time to buy a megger....

 

[kwired]

Was a load calculation done when the electric heat was added? Maybe service is simply not large enough now that the heat is on it.

Maybe aux heat has not been needed since you "straightened things out", or some other significant load has not coincidentally been in operation.

 

[hardworker]

Load calculation is well within acceptable range with emergency heat active.

Emergency heat has been active since my work was done. You can demand emergency heat at any time by moving the switch over. I did this before I left the job.

 

[Little Bill]

Load calculation is well within acceptable range with emergency heat active.

Emergency heat has been active since my work was done. You can demand emergency heat at any time by moving the switch over. I did this before I left the job.

You said you looked in the air handler cabinet. Maybe something is loose in there and you touched/moved something that temporarily corrected the problem. I believe I would go back to the air handler and check for loose or near shorted conductors, then maybe retrace your steps.

 

[n1ist]

Could the stray end of the neutral in the air handler be shorting to a hot instead of the case? That would explain the breaker tripping.
/mike

 

[kwired]

Could the stray end of the neutral in the air handler be shorting to a hot instead of the case? That would explain the breaker tripping.
/mike

If the supply end is connected, or shorted to something yes. Otherwise it is just sitting there - open circuited.

 

[Little Bill]

If the supply end is connected, or shorted to something yes. Otherwise it is just sitting there - open circuited.

The OP did say the handyman connected the neutral in the panel but not in the air handler. That could have been the case until he corrected the panel.

 

[hardworker]

The point about the live neutral touching the hot inside the air handler is a very good point. That neutral was just hanging down very close to the hot, when I opened the air handler.

There is no way of knowing at this point.

 

[kwired]

The point about the live neutral touching the hot inside the air handler is a very good point. That neutral was just hanging down very close to the hot, when I opened the air handler.

There is no way of knowing at this point.

Burn spots are a pretty good indication that it touched:happyyes:

 

[mbednarik]

I would think that the inside breaker would be quicker to trip on overload due to a higher ambient temp. Is there a loose connection on the outside breaker, possibly a defective breaker.

 

[dana1028]

"but my question is the following? Why did not the 60amp breaker in the panel not trip. Why did it hold and the disconnect outside was the one to trip? Why did not the 200amp panel main not trip?

Because the fault current flows through the main breaker on the outside of the house first....then through the interior 200A disco.....then through the 60A breaker. When the bonding path back to the service "effectively creates a low-impedance circuit facilitating the operation of the OCPD" ....the [fault] current will be high enough to trip the first OCPD it comes to when returning [from the utility transformer].

The 60A breaker never gets a chance to 'see' the fault current. [The fault returns to the service equipment via an 'effect ground-fault current path (the bonding jumper, EGC - see 250.5(A)(5)....then it jumps to the utility neutral in the service equipment.....returns to the utility transformer....which supplies the current to the faulting line side conductor(s).....which returns to the service equipment....and attempts to move through the service OCPD. If the (faulting) current is high enough at this time the service OCPD will trip....if not....the current will pass through the service equipment to the next OCPD ...which may trip [in your case that would be the interior 200A disco]....if that does not trip then the current moves on to the final OCPD [your 60A disco].

I'm sure other may wish to clean up this explanation.....I got the impression the OP may not have been aware of the direction fault currents move.

 

[kwired]

Because the fault current flows through the main breaker on the outside of the house first....then through the interior 200A disco.....then through the 60A breaker. When the bonding path back to the service "effectively creates a low-impedance circuit facilitating the operation of the OCPD" ....the [fault] current will be high enough to trip the first OCPD it comes to when returning [from the utility transformer].

The 60A breaker never gets a chance to 'see' the fault current. [The fault returns to the service equipment via an 'effect ground-fault current path (the bonding jumper, EGC - see 250.5(A)(5)....then it jumps to the utility neutral in the service equipment.....returns to the utility transformer....which supplies the current to the faulting line side conductor(s).....which returns to the service equipment....and attempts to move through the service OCPD. If the (faulting) current is high enough at this time the service OCPD will trip....if not....the current will pass through the service equipment to the next OCPD ...which may trip [in your case that would be the interior 200A disco]....if that does not trip then the current moves on to the final OCPD [your 60A disco].

I'm sure other may wish to clean up this explanation.....I got the impression the OP may not have been aware of the direction fault currents move.

I'm not so sure you know either. If the fault is on the load side of a 60 amp breaker the current the fault current is the same at the transformer terminal as it is at the 200 amp main as well as at the 60 amp breaker and at the point of the fault. The only reason for the 200 to trip and not the 60 is either malfunctioning 60 or instantaneous trip level of the 200 is lower than that of the 60.

Current does not flow through any one component before another, it flows through all of the circuit at same time at the same level. I may get shot down with this comment but for a simple explanation of what is happening in this scenario that is accurate enough. Any time difference is in the millisecond or even less ranges.

It does not attempt to move through conductive items, there is either a path for current or there is not.

 

[K8MHZ]

I'm not so sure you know either. If the fault is on the load side of a 60 amp breaker the current the fault current is the same at the transformer terminal as it is at the 200 amp main as well as at the 60 amp breaker and at the point of the fault. The only reason for the 200 to trip and not the 60 is either malfunctioning 60 or instantaneous trip level of the 200 is lower than that of the 60.

Current does not flow through any one component before another, it flows through all of the circuit at same time at the same level. I may get shot down with this comment but for a simple explanation of what is happening in this scenario that is accurate enough. Any time difference is in the millisecond or even less ranges.

It does not attempt to move through conductive items, there is either a path for current or there is not.

We had an instance where a fault or a surge, we never did figure out what happened, took out two 400 amp fuses in a three phase panel, left downstream 50 - 100 amp breakers and fuses intact, and took out dozens of smaller fuses from 30 amp to 5 amp. I spent the rest of my shift changing fuses and re-setting breakers. When all the OCPDs were re-set, everything worked fine, like nothing happened.

None of the OCPD's were coordinated. The ones that tripped just had a faster reaction time than the ones that didn't.