Why we ground electrical systems (2015)

I&#x27;m actually the person who wrote this Reddit post. I&#x27;d never heard of Hacker News before, but someone messaged me on Reddit telling me this 4 year old post just surfaced over here.<p>Let me know if you have any questions about electrical theory or installation, or anything else!

I have been studying Grounding vs Bonding these past few weeks, great timing to see this HN discussion.<p>Some training videos for pro electricians and US National Electric Code compliance helped me.<p><a href="https:&#x2F;&#x2F;youtu.be&#x2F;qNZC782SzAQ" rel="nofollow">https:&#x2F;&#x2F;youtu.be&#x2F;qNZC782SzAQ</a><p>Basically, <i>bond</i> everything together if it can carry a charge. <i>Ground</i> that bond at <i>only one place</i> in an electrical service.<p>More than one &quot;ground&quot; sets up a situation where a potential difference can develop between the various &quot;grounds&quot;. Ground Fault detection may no longer work in that case. Which is not good.<p>(The presentation is weirdly sexist in offhand comments, which I often encounter in trade work of this kind, but I do believe that&#x27;s changing. Slowly. The USA needs more people who know how to build things.)

Beware as this explanation does not apply to every country in the world, in France for residential systems at least, the protection (green&#x2F;yellow) wire is never connected to the neutral (blue) wire, only to earth with a metal rod at the house. You would get a shock if it was somehow disconnected from the rod&#x2F;earth. Neutral is also not bounded to earth inside the house. Be safe!

&quot;Since the ground-fault current path has inherently much higher resistance than the neutral wire, the amount of current flowing through the circuit jumps enormously during a ground-fault.&quot;<p>This is incorrect (probably a typo) - the GFC ensures there is a very <i>low</i> resistance path to source, which ensures a current spike that is sufficient to blow the fuse.

The details of this also vary based on where you&#x27;re at. In the US, neutral is bonded to earth at every house I think. In Europe, neutral is only bonded to earth at a local power station.

This blew my mind. So the white wire (neutral) is actually what I thought the ground was (connected to earth) and the “ground” wire (usually bare or green) is a conductor for clearing ground faults and isn’t connected to earth.<p>Marvelous explanation.

See also &quot;Why Three Prongs (1996)&quot; discussed recently:<p><a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=20378852" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=20378852</a><p>Also, be aware of grounding requirements when using a generator:<p><a href="https:&#x2F;&#x2F;cpower.com&#x2F;PDF&#x2F;InfoSheets&#x2F;44.pdf" rel="nofollow">https:&#x2F;&#x2F;cpower.com&#x2F;PDF&#x2F;InfoSheets&#x2F;44.pdf</a>

Why are there three wires in new receptacles? From my understanding, new code has you have to have a 3+ground but why is that safer? Did they just add an extra wire so you can have a hot, lead, and neutral to ground all the receptacle? (Plus the green&#x2F;bare to bond the receptacle to switch&#x2F;outlet)<p>Also, for home owners, what’s the best resource to learn common sense basics of electrical work (besides reading the city&#x2F;states codes). Are there classes for such cases?

One of the few times I wish I had a reddit account, just so I could give an old post some $REDDIT_KARMA_POINTS (whatever currency they use). That is an outstanding explanation that cleared up some things for me that I do because electrical code, not because &quot;knows the &#x27;why&#x27; of what he&#x27;s doing&quot;.

This section is plain wrong:<p>&quot;The ONLY purpose for the EGC (or green wire) is to clear a ground-fault (clearing a ground-fault means tripping a breaker or blowing a fuse) in the &#x27;oh shit moments&#x27;. It has absolutely NOTHING to do with the ground or the Earth and will work exactly as it is intended to regardless of whether it is connected to the Earth or not.&quot;<p>If the EGC is floating, no current will flow in a ground fault and the breaker never trips.