Main breaker without sufficient ground?

[mdakxotaz]

Imagine there is a certain situation in a residential installation; where the panel was not sufficiently bonded to earth ground, however the home was nearly completely wired. While pulling in a 14-2 Romex, ground touched busbar, and touched panel enclosure.

The circuits which already had their grounding conductor connected to the grounding busbar within the panel, had their grounding conductor red hot, as was the grounding conductor that touched busbar and panel. This caused some damage.

The question is why wouldn't the main breaker trip? Breakers are designed to trip where there is excessive current, and it seems to me this would be excessive current.. is it possible that there was enough resistance to keep the current under 200A? Also, if this system had sufficient bonding to earth ground, would it have tripped the breaker?

 

[Mule]

Imagine there is a certain situation in a residential installation; where the panel was not sufficiently bonded to earth ground[/U], however the home was nearly completely wired. While pulling in a 14-2 Romex, ground touched busbar, and touched panel enclosure.

The circuits which already had their grounding conductor connected to the grounding busbar within the panel, had their grounding conductor red hot, as was the grounding conductor that touched busbar and panel. This caused some damage.

The question is why wouldn't the main breaker trip? Breakers are designed to trip where there is excessive current, and it seems to me this would be excessive current.. is it possible that there was enough resistance to keep the current under 200A? Also, if this system had sufficient bonding to earth ground, would it have tripped the breaker?

I'm lost here....are you saying the panel enclosure and ground bus was not bonded to the neutral bus? If so, there must have been another ground path? so where was it?

 

[George Stolz]

The earth is not for tripping overcurrent protection devices. Check out this thread.

 

[480sparky]

Why would making a path between the neutral and the tub cause any breaker to trip?

 

[boboelectric]

The #14 ground should of vaporized,not tripping the main.What was all damaged? Maybe electronics? You didn't get arc fault flash burns,did you? Working hot is always a gamble.

 

[mdakxotaz]

The ground which was missing is the (normally) 8 AWG with 240V services. It runs from the panel, out to the meter enclosure and then through 2-6 foot ground rods.

 

[celtic]

The ground which was missing is the (normally) 8 AWG with 240V services.

What size service is "normal" for you?

 

[boboelectric]

How did this service get power anyway,without a service inspection,anyway????? Sometimes,this site makes me feel like I'm on a jury .

 

[Mule]

The earth is not for tripping overcurrent protection devices. Check out this thread.

Bingo, my point exactly....

 

[George Stolz]

The earth is not for tripping overcurrent protection devices. Check out this thread.

Bingo, my point exactly....

I'm thinking mdakxotaz didn't look, so I'll suggest he look at it again.

 

[mdakxotaz]

Ok, so grounding with your two 6 foot rods will not help in tripping a main breaker in this situation.

Why then did the main breaker not trip, where this bare conductor made contact with the 120/240V busbar, and the electrical panel, which is oviously electrically bonded to the grounding busbar, and grounded busbar.

 

[Mule]

Ok, so grounding with your two 6 foot rods will not help in tripping a main breaker in this situation.

Why then did the main breaker not trip, where this bare conductor made contact with the 120/240V busbar, and the electrical panel, which is oviously electrically bonded to the grounding busbar, and grounded busbar.

So if Im reading your first post correctly, the fault path was from one of the phases, through the #14 bare ground, to the unbonded neutral. If this is what you mean, the #14 probably could not pass enough current to heat up the main quick enough...

Am I missing something?

 

[benaround]

Ok, so grounding with your two 6 foot rods will not help in tripping a main breaker in this situation.

I know you meant to say 8' ground rods.

 

[Rick Christopherson]

So if Im reading your first post correctly, the fault path was from one of the phases, through the #14 bare ground, to the unbonded neutral. If this is what you mean, the #14 probably could not pass enough current to heat up the main quick enough...

Am I missing something?

Apparently you have never had a loose strand from a 4/0 cable touch an adjacent bus?

If a 28 ga (or smaller) strand can trip the main on a 125 KVA generator, I am pretty sure 14 gauge would do the same with a 200 amp main. Not that I am admitting to making such a foolish mistake.

The OP said the grounds were cherry red. For 14 ga copper to glow cherry, I am pretty sure there would be more than 200 amps. I am assuming the OP didn't leave the short sitting there for an hour.

I would question the validity of the mains.

 

[mdakxotaz]

Hah, yea a foolish mistake indeed but hey things happen.

So if Im reading your first post correctly, the fault path was from one of the phases, through the #14 bare ground, to the unbonded neutral. If this is what you mean, the #14 probably could not pass enough current to heat up the main quick enough...

Am I missing something?

I would say so, but not sure where you got lost. The ground touched busbar, and touched panel enclosure. Imagine a 40 Slot 200A 120/240V panel enclosure, I'm sure you've installed one before Mule?

After reading the Powerpoint again this morning it seems to me that the only way this scenario did not trip the main is two reasons... and I'm not sure "heating up the main quick enough" would be one, I would think if there is this much current it would happen instantly.

1.) Bad main breaker
2.) Neutral bus not bonded to the panel enclosure

I would stray down bonding issues in the rest of the home, but where it happened in the panel enclosure itself, it seems that the panel enclosure should be bonded to the neutral busbar and therefor would trip the main. If you look at slides 52-61 it talks about how much resistance each wire has coming from transformer through to load. (there is a typo on slide 60, should be .057 Ohms panel to service).

Now, for simplicity and the fact that it was very close, assume we have the same service as the powerpoint, take away the load since this short happened right at the panel, and there would have been 120V/.057 Ohms = 2105A!! I'm guessing it must have been a bad panel to neutral bonding issue, or simply a bad breaker.

I'm thinking mdakxotaz didn't look, so I'll suggest he look at it again.

Yea, you thought correctly Stolz, thanks for the help on this one. The presentation is well written, I would say it most definitely cleared my original question. I would encourage anyone with questions similar to mine to take the time and read through it.