Re: about grounds… a New Discussion

[Philip Pedersen]

Grounding and bonding always engenders a lot of discussion, and even more so when you start talking about data centers and electronic equipment in general.  

As far as I know, the National Electrical Code says that there should be a ground rod at the service transformer bonded to the neutral leg of the feed going to the house.  At the house Service Entrance Panel (SEP), the neutral should be bonded to the panel which also is the grounding point for the house.  There is supposed to be a ground rod attached to the SEP as well as bonding of all metal pipes (water and gas, including well water pipes) to the SEP.  This is to limit transient overvoltages due to lightning.   

Where there is a separate building fed from the SEP with a feeder circuit, another ground rod should be driven for that non-service panel.  That's to limit the possibility of large currents and arcing caused by lightning.  

Non-service panels fed by a feeder circuit from the SEP should not have the neutral bonded to the sub-panel.  The reasons for this have always been explained to me as follows:

If you bond the neutral at locations other than the SEP, you then have multiple paths for the current to follow back to the SEP and you don't really know where the current is flowing.  If you remove a ground from some part of the system because you're repairing something and that ground is carrying some of the current, you would at least get an arc as you remove the conductor.  If you happen to have one hand on the box and the other on the conductor, you could be part of the path, which wouldn't be a good thing.

The other reason mainly applies to older houses or industrial settings.  If you're using conduit (older houses used BX cable, with two wires and the metal sheath used as ground) or raceway, the current caused by multiple paths  could cause heating in the conduit and raceway joints, which could lead to arcing, fires, etc as well as having the shock hazard.  In a modern house wired using Romex and non-metallic boxes, it's not as much of an issue, although the shock hazard is still there, but pretty small.  

Phil

On Oct 12, 2013, at 3:49 PM, Warren Whiteside <warrenwhiteside at verizon.net> wrote:

> George, one small correction. I didn't post about not taking the ground to a sub panel. I have done that here to my shed and also drove a ground rod at the shed sub panel which is terminated in the sub panel's grounding bar. I think someone else commented about that part. As to terminating your #6 solid copper to your panel ground bar: Yes, you must do this regardless of your utility having a ground at its transformer that should be bonded to their neutral/common wire of a 230VAC single phase service. I'm sure as far as grounding might go it is possible to get too much of a good thing but over the years I haven't seen this.
> 
> Warren
> 
> On 10/12/2013 3:16 PM, George Handley wrote:
>> Good afternoon Michael, and thanks for bringing the correct subject back to the front burner.
>> 
>> Yes, I am ONLY reflecting on this grounding question after KCP&L did their thing. I have nothing new… good or bad to necessarily report, (Except still no blinking lights) but this AM, Warren's post on grounds and not taking the ground to a sub panel doesn't make sense to me. Also James said: "THere is no ground carried from the panel out to the pedestal, at least not around here."
>> 
>> Also, the Lineman who opened the pedestal and hooked up my ground to their terminal commented that he'd seen this before, and didn't think it was going to make any difference because it was the same as the neutral. I told him I was the only one in the neighborhood that had virtually any form of electronics which included X10, many of whose devices have a separate ground wire that I maintain has to be used for the switch to operate correctly. It's also been explained to me over the years by many… both local and on this list, that there most certainly is a difference between ground and neutral, and that both were essential to expect an X10 system to consistently work.
>> 
>> Even you said: "When I first read your power engineer's discovery, I was rolling on the floor…  I could just imagine
>> how a garbage truck rumbling past that power stub would easily 'move' the problem … and the problems
>> you thought you fixed the previous evening were now 'different'…"
>> 
>> So, since getting KCP&L out here to find what they found, and then reporting it here on the list, there have been a few people that have advised that I shouldn't have my #6 ground wire from my service even hooked up to KCP&L. This smacks me in the face of common sense. Yes, I sure know the tightening of all the other wires was super critical as well, but how could there be such a question on this List?
>> 
>> Thanks,
>> 
>> George
>> 
>>  
>> On Oct 12, 2013, at 12:55 PM, Michael Ferguson <michael at shed.com> wrote:
>> 
>>> Hello George,
>>> 
>>> Are you describing things that you did before or after the discovery and correction
>>> of your power main connections ?
>>> 
>>> michael
>>> Sent from my iPad
>>> 
>>>> On Oct 12, 2013, at 11:49 AM, George Handley <ghandley at kc.rr.com> wrote:
>>>> 
>>>> It wasn't until I disconnected the ground wire to this unit, that sanity returned. So, I believe I know, first hand, that the grounding wire and X10 do have a meaningful electrical purpose.
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>> 
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