Please explain this ground fault

[teeger]

I was checking out a video on YouTube which showed finding an nac ground fault at the panel.

It was a silent knight 5496.

Can someone please explain this to me?

While checking the nac on the first circuit he got the following readings Vdc.

19.77 negative lead

0.445 positive lead

Went on to the next circuit...

-21.26 negative 0.005 positive

There’s the ground fault.

What I would like to know is how do you get to this conclusion?

Is it because one lead has next to no voltage on it?

Video just shows how to find it, but doesn’t explain anything. I know ground faults are common and often can be a pain at times.

If someone can explain this in a simple way I’d appreciate it.

Also - I assume a ground is different from a short and an open correct? I know if there’s a short often there would be a drop in voltage. If there’s an open, it’s usually pretty raised, yes?

Thanks!

[Manon_Chaboud · Accepted solution]

Hello @teeger !

The voltage readings you provided are indeed indicative of a ground fault. In the case of a ground fault, you may see a significant voltage reading between the negative lead and ground (close to the system voltage) and a much lower voltage reading between the positive lead and ground. This is because the ground fault provides a path to ground, causing a voltage drop.

As for your question about the difference between a ground, short, and open:

• A ground fault occurs when a live conductor makes contact with a ground or grounded surface.
• A short circuit happens when a live wire comes into contact with another live wire or a neutral wire, resulting in a sudden drop in voltage.
• An open circuit occurs when there's a break in the circuit, leading to a significant increase in voltage.

Understanding these differences is crucial for effective troubleshooting. I hope this helps clarify things for you!