Grounding the neutral

[Seven-Delta-FortyOne]

Grounding the system is intentionally creating the first ground fault. The first ground fault causes no problems. The second one can be deadly. So we intentionally create the first one, then bond everything together, and now we know when we get the second one and can remedy it.

Soares Book On Grounding and Bonding is an excellent textbook on the subject, sure to make your head spin, teach you more than you every knew existed about the subject, and leave you more confused than ever. I highly recommend it.

 

[electrofelon]

I am fairly well versed in fundamental theory, so we don't really need to discuss the minutia but, You say, " so when we say measure to "ground" " when was the last time you measured to ground? The OP is asking why we tie to earth, not why we bond everything together. What we measure to all the bonded metal parts has little to do with what we measure to earth.

I think I explained specifically in my post #3 what a measurement to "ground" means. IF everything is done correctly, all metal parts will be bonded and also connected to earth. I was just trying to say that "ground" would be any point on that system. I also said that if you did indeed stick one of the probes in the actual dirt, you would probably still measure something but it would be rather meaningless

Also, a ground fault to earth is often not strong enough to trip a circuit breaker, so while I get why we bond the neutral to unenergized metal that may become energized, I don't fully understand how advantageous it is to bond to the earth.

I also covered system grounding and the advantages and disadvantages of grounded and ungrounded systems in post #3

 

[electrofelon]

As to why a zero volt reference point is necessary or desirable, that is a question for someone else.

I would say that we dont really system ground to obtain a zero reference point. That is a result, but its not something we really need. System grounding effects insulation levels, Location of OCPD's, and what happens when there are faults. The other reason we system ground is to help clear a fault to a bare messenger that comes in contact with a MV line. The NEC gives some other reasons, but IMO they are hogwash.

 

[LarryFine]

In the micro sense, the earth sucks as a conductor, but in the macro sense, it’s a relatively good conductor.

By intentionally earthing (one conductor of) the electrical system, we at least have a predictable voltage between that system and earth.

A floating system could unpredictably (theoretically) develop voltages to earth as high as the primary system, or even higher.

Earth is certainly more than conducive enough to create hazards for humans and animals that accidentally contact energized parts.

At least with grounded systems, the voltages are predictable and we can design equipment and insulation adequate to handle those voltages.

 

[kwired]

I heard Mike Holt mention in the old days there were things like side flashing and over voltage problems. I'm not sure what a side flashing is. I know capacitance can be a problem on ungrounded systems and that's why high impedance systems evolved.

There was a post on here a while back about Norway going all ungrounded because it would be safer and it turned out to be a nightmare because there would be a fault that would go undetected and would become the default grounded conductor and then somewhere down the street there would be another fault and eventually there would be fuses blowing and nobody knew where to find the problem.

Good reason why when you do use an ungrounded system that it should supply limited items and definitely not multiple structures.