Arcing and Sparking from Objectionable Current VS Fault Current

[Cindysparky]

Okay, so I have one of Mike Holt’s video set. He said something that really got me wondering.

Let me set the scene.

In his 2017 video series on Understanding the Code (Art 502 in Hazardous location) he goes on this long winded talk about objectionable current. Objectionable current is an issue in hazardous locations because of arching and sparking. So, that’s why bonding bushings and bonding jumpers are required. It helps prevent possible issues with loose locknuts if there’s objectionable current. (Objectionable current comes about when the neutral and the equipment grounding conductor are tied together in a location other than the service or the secondary side of transformer)

Please help me sort out what you read below:

He said very casually that fault current is less of an issue with causing arching and sparking with loose locknuts. He said this was because of the amount of amperage at the time of the fault. Could be like 2000Amps.

But he said objectionable current was a bigger issue. A loose connection with less current is a bigger issue with arching.

What I gathered from this was that fault current would make a very strong connection back to the source regardless of the loose locknuts. Which would cause less of an arch and less spark. Whereas the objectionable current would be in normal current ranges (lets say 20 amps) and pose a bigger risk of igniting. I don’t really understand this. Any input on this topic would be greatly appreciated

 

[jeffelectric1992]

I would speculate that high fault currents will weld loose connections together extinguishing the arc quickly. Low amperage faults will arc over and over again, never developing sufficient surface temperatures to weld the loose steel parts together. Low amperage recurring faults can also lead to glowing contacts that could easily reach ignition temperatures.

 

[Cindysparky]

I would speculate that high fault currents will weld loose connections together extinguishing the arc quickly. Low amperage faults will arc over and over again, never developing sufficient surface temperatures to weld the loose steel parts together. Low amperage recurring faults can also lead to glowing contacts that could easily reach ignition temperatures.

Ok, this makes perfect sense to me. Thank you

 

[Hv&Lv]

When you tie the neutral and grounds together at some other point inside the building you now have an alternate path.
Electricity doesn’t take the path of least resistance. It takes ALL paths relative to resistance.
Let's say you have a disconnect mounted on a column holding a vibrating piece of equipment. With a loose locknut the vibration will cause the arcing and sparking, but it's not enough for the breaker to react to. When the resistance goes up on a loose locknut SOME of the current shifts to the Neutral.

All paths to neutral. Not just the least resistant. If you don't connect the neutral and ground together at any other point, then there is one and only one path-the neutral.

 

[tom baker]

I would speculate that high fault currents will weld loose connections together extinguishing the arc quickly. Low amperage faults will arc over and over again, never developing sufficient surface temperatures to weld the loose steel parts together. Low amperage recurring faults can also lead to glowing contacts that could easily reach ignition temperatures.

Yes that is my take as well. The fire at the Los Vegas MGM grand was caused by a loose fitting on an icemaker.