Panel Bonding

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shawn73

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I am an Industrial Electronic Technician in our automotive factory. The 6 of us (2 per shift) are responsible for all of the electrical work, plc programming, and machine electrical troubleshooting in our facility. I have been trying to find a good answer to this question with confident back-up information for some time. I would really appreciate some input.

We are responsible for our electrical system once it enters our facility, usually throuh 3-4,000 amp 480V, 3 phase panel. Typically from that point we run 400-800 amp, 480V, 3 phase to another panel for distribution smaller distribution such as to a 480V Delta, 208/120 Wye transformer providing 200 amps for typical recepticals, etc. This is where I start to have questions.

Lets say I just finished wiring the 200 amp 208/120V panel described above. I now need to install a 60 amp subpanel fed from the 200 amp panel. Should both the 200 amp and 60 amp 208/120V panels have bonded neutrals?? I have always had a difficult time with is issue because bonding a ground to a neutral creates a parallel neutral wire. I have been told by some people that your neutral should not carry any current, but I'm not confident of this because of all I have read about harmonics currents.


Another example:

We recently had an outside contractor add a 60 amp 208/120V service to a small building outside our main facility (No foundation, just a sitting 12X14 metal building). I was required to run conduit etc, in the building and found that the 60 amp panel was not bonded and there was not a ground rod driven for the equipment ground. (So, the metal building could have been electrified.) I understand that there should not be another ground rod driven because of potential between ground rods, but if I bond the neutral to ground in the 60 AMP panel I again create a parallel neutral.

These are both examples of issues I encounter from day to day. I want to do things correctly, but I cannot seem to get a confident answer form anyone I ask. Thank you all for your help.
 
Shawn, The 60 amp panel from the 200 amp panel is a sub panel and requires a seperate ground and neutral connection.

As far as the 200 amp panel/xfrmr goes, you need to decide if you will bond the neutral at the xfrmr or the panel. If you decide that the xfrmr is the best place, then thats where the GEC to building steel or water needs to go and then the grounds and neutrals at the panel will be seperated. If you decide to bond the neutral at the panel, then thats where the GEC goes and the grounds and neutrals will be seperated in the xfrmr.
 
grounding

grounding

Shawn, You pretty well ran the full gambit of the problems associated with bonding/grounding :)

The basic rule would be that there should be no connection between the grounded and grounding conductor except at service equipment.
--however--
as RUwired has pointed out, there is such a connection at a SepDervied System
--and-
In regard to your seperate building, the Code does require a grounding electrode, and since you elected to install a seperate equipment grounding conductor, the grounded and grounding shall be seperate at that building with the electrode(s) attached to the grouning conductor.
(There are circumstances where you could feed that building without pulling an equipment ground, but an electrode would still be required)
 
(Wow, two other responses while I typed, so please forgive any redundancies.)

shawn73 said:
Lets say I just finished wiring the 200 amp 208/120V panel described above. I now need to install a 60 amp subpanel fed from the 200 amp panel. Should both the 200 amp and 60 amp 208/120V panels have bonded neutrals??
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The 200a panel, yes; the 60a panel, no.

The transformer makes for the beginning of a separately-derived system, which is treated as a service, inlcuding grounding electrodes and neutral bonding; the latter anywhere between the transformer and the 200a panel.

Beyond that, neutrals and grounds must be kept separate, as in any sub-panel.

I have always had a difficult time with is issue because bonding a ground to a neutral creates a parallel neutral wire. I have been told by some people that your neutral should not carry any current, but I'm not confident of this because of all I have read about harmonics currents.
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On the contrary, it is the grounding conductor that should normally carry no current. Unless the three phases' loads happen to be perfectly balanced, the neutral will indeed carry current.


Another example:

We recently had an outside contractor add a 60 amp 208/120V service to a small building outside our main facility (No foundation, just a sitting 12X14 metal building). I was required to run conduit etc, in the building and found that the 60 amp panel was not bonded and there was not a ground rod driven for the equipment ground. (So, the metal building could have been electrified.) I understand that there should not be another ground rod driven because of potential between ground rods, but if I bond the neutral to ground in the 60 AMP panel I again create a parallel neutral.
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The answer to this depends on whether this is fed from the main building.

If it is, then the neutral should not be bonded, as long as there is a separate equipment grounding path run, either a conductor or a metallic conduit. However, there should be a ground rod driven at this small building.

If the small building has its own service, then it should be bonded and grounded as any main service should be.

In any case, the earth is not conductive enough to be considered a parallel path to a grounding conductor, but you're correct that a neutral and a grounding conductor should never be bonded at both ends.
 
I don't mind being redundant about things like this. :D

To put it as simply as possible, there should only be one path between the point where you connect the load to it's neutral, and the source.

If you connect neutrals and grounds (EGCs) together twice, then there are two paths. This violates 250.6 - Neutral current begins flowing on the EGC as well.

Personally, I've all but scrubbed panels out of the picture when thinking about when to bond. You bond an EGC to neutral once. Be it inside the transformer of a seperately derived system, or at the disconnect, or what have you. Once you get the once idea in your head, you can apply the other codes as they come into play.
 
I cant believe the responses

I cant believe the responses

This electronics technician Is neither qualified licenced or insured to do electrical work in a factory of this magnitude. You should all be discouraging a do it yourselfer with some more electrical knowledge to be performing these installs. What if he misinterprets one of your posts on bonding and accidentally electrocutes or maims someone?
 
shawn73 said:
The 6 of us (2 per shift) are responsible for all of the electrical work, plc programming, and machine electrical troubleshooting in our facility.
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This is all I need to see: Electricity is his profession.

In this case, it appears the apprenticeship is under way, and the questions are reasonable ones. When I first started I asked what the bare wire did in romex, and was told, "Nothing."

If we can offer better answers than that, we are in line with the interests of safety, and also in line with the forum rules.
 
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georgestolz said:
This is all I need to see: Electricity is his profession.

In this case, it appears the apprenticeship is under way, and the questions are reasonable ones. When I first started I asked what the bare wire did in romex, and was told, "Nothing."

If we can offer better answers than that, we are in line with the interests of safety, and also in line with the forum rules.
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Touche George!

The OP appears to be a company employee trying to learn and gather information that will allow him to better and more safely perform his job for the company that employs him.

If giving correct and pertinent information is wrong, what's the purpose of this forum?

Just a opinion
steve
 
Thanks

Thanks

Thank you for letting me post my question (For the record I am 3 classes from my Associates degress in Industrial electricity and less than one year from my Journeymans card.) and thanks to all who responded. I will feel more confident in my quality of work. I like this forum and I will continue to use it for quesions that I can't seem to get answered elsewhere.
 
georgestolz said:
it appears the apprenticeship is under way
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Who is the captain of this apprenticeship and where is supervision. If none of the 6 technicians can answer this question confidently then who takes responsibility when 6 untrained or undertrained electronics techs short something out or blows something up or worst case scenario electrocutes someone. Someone must take responsibility for all electrical work performed I believe it is the law. I hope that these guys learn all there is to learn and I dont mean to be negative but this isnt right or fair to all legitemate licenced and insured contractors
 
Why are you so convinced that the work isn't licensed or insured, much less unsupervised? :confused:

There have been more than a couple long-time electricians who've been through this forum and exposed deep-seated yet incorrect views about theory and especially grounding. There is absolutely no reason to assume that a license means perfection.

In my state, you must pass with a 70% to get a Residential Wireman or a Journeyman Wireman's license. I've seen a guy pass the RW with no knowledge that 210.52 exists, they always simply wired to plan and that lack of knowledge was only exposed when a house failed inspection.

Does that make the less-code-savvy RW a moron, or a hack, or so worthy of contempt that the knowledge is not passed onto him?

That is not what this place is about. If we all knew it all, there wouldn't be anything to talk about. :mad:
 
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