ECN Forum Forums Code Related Discussion NEC & other Code issues Grounding

Glenn,
Thanks for the info. The panel comment in the rejection of 5-32, is like many issued by the CMPs, that is if you don't have a "body count" the proposal gets rejected even if it has technical merit. From an electrical standpoint, the best system is a single point connection between the grounded and grounding conductors, and the most logical point for this connection is at the transformer.
Don(resqcapt19)

I am in favor of the having the services bring two neutrals of equal or greater ampacity than the two hots.

This would ensure a lower resistance return which would mean less current in the EGC.

I have a problem with not tying the EGC and neutral in the entrance panel since lightning will arc between the two when it arrives. I would prefer that lightning get from one to the other without arcing.

I will still drive those ground rods too.
If lightning strikes the transformer, I don't want it coming into the house looking for water pipes or the furnace on the basement floor to get to earth.

That said, once the EGC and neutral are bonded in the residence, a separate EGC back to the transformer would actually be just another grounded conductor anyway.

This is completely true when there are separate grounded and grounding conductors.
If one were the tie the neutral wire to the ground wire anywhere past the point of service, the ground wire would carry current in parallel with the neutral wire.

Thus if the utility company provided a separate EGC and you made a connection anywhere between the two, their EGC would become just another neutral.


However, I see no harm in bonding the grounded conductor to ground rods as often as anyone cares to *outside* of the residence on the line side for the simple reason that the grounded conductor is fully intended to be carrying current at all times. If that current is normal and intends to return to the transformer and wants to go via the earth, then it is simply a lower resistance path back (which is more efficient). It is not a diversion of current into a conductor that was supposed to be reserved for fault current.

So grounding the neutral at the meter, at the weatherhead, in the middle of your yard, at the pole, etc., will not energize your equipment grounds inside your house.

However, tying your neutral to your ground in your bathroom could be fatal even if that was the single point of connection in your entire system.

The best system, therefore, is not characterized strictly by a single point of connection between the two.

The best system is characterized by not making connections where it (illogically) energizes a conductor that is reserved for bonding and/or fault current.

Dspark,

Welcome to the group!!

What Don is getting at in his message is to have the Utility company's secondary point of ground bonding to the grounded conductor be the one and only point where the grounded conductor is bonded to the earth.

The equipment ground bonding conductor that would run parallel with the service feeders is bonded to the X0 terminal [center tap on 1 phase 3 wire, or common for 3 phase 4 wire, or 1 phase for 3 phase 3 wire], which is also the grounding point and output of the grounded conductor. From there, the EGC would be the conductor which would be bonded to each service / grounding electrode system per customer. Kind of like how a separately derived system would be grounded - except there's not multiple Grounding Electrode Systems and services. Same consept, though.

This method would create one grounding point, but not have the problem of carrying L-N currents [unless some joker hooks up a load to the ground bonded equipment or conductor].

As for Lightning, each discharge will have such a large electrostatic field built up in a somewhat circular fashion around the central point where the main discharge will occur. This field will be bringing in and pushing away charges from all around - at times upto 2 miles. During the discharge event, the stroke leaders that did not make a solid connection will still be active throughout the duration of pulses and build up / drain of the potential energy between the cloud mass and the earth at point of contact - plus field areas. The main stroke[s] are the few stroke leaders which make solid contact, then create the brightest / largest plasmas and have the largest current flows [1"-1.5" diameter area of charge flow].

All throughout the discharge field area, there's thousands of branch discharges - some barely visiable, most not. They flow on any possible conduction paths around.

These are the ones that range 1KA to 5KA, whereas the main stroke would have a level of 50KA or higher.

The main stroke when it [and the branches] begins to conduct, would have the highest voltage [pressure] between the cloud and earth. After the Plasma is created, the voltage drops to very low values [from 250KV per meter to less than 1KV per meter], while the current level rises rapidly [from 500 amps to 50KA].

Anyhow, eliminating numerous ground bonding points that are common to overhead power lines and to underground piping, would assist in lowering TVSS and Lightning potentials.

Having the equipment ground bonding conductor grounded at the transformer and at each service would drive the EGC to ground level at that point of service.


Feel free to throw flames!!!

I'm just mentioning the Lightning stuff for FYI and discussion reasons only. Feel free to debate any part that seems odd.


Scott SET

I've been suspicious that the #12 wired lightning arresters have a bunch of wax and a wirenut for each conductor attached... connected to absolutely nothing... Just a big scam to sell to unsuspecting customers.

Seriously, how can these devices do anything to shunt (or perhaps eliminate?) lightning strikes to the load centers they are attached to? I'd guess that they are some sort of capacitor, but how does it "attract" the lightning as the path of least resistance? How can these things possibly control these powerful plasma arcs that can jump a gap a mile long?

Pardon my ignorance once again...

much lightning vs. grounding here! the NEC is somewhat lame on this, i suppose they realize there is no sure thing for megavoltage spikes! as a matter of code 230-209 is 'permissive'! And only so on ungrounded conductors,as opposed to 280-21

one can't help Q this, as the center tap of the X-former is the only true common to the utility grid!

Having seen lightning strike earth ( or appearing to, as the nature of it is) and enter thru earth-grounding-GEC-EGC to fry any completed ciruit made me realize this is a no-win scenario.

of interest is 280-12, asking for short leads, no bends in the arrester, this being i take it due to heavy charges following straighter lines.

66' ,the gizmo is a coil, rated in joules no where near a direct strike. so if you have a customer in lightning alley, they need to call an air-spike installer.

the only thing we can provide is those straight lines for the GEC to drain off directly under a meter.

theortically a super-large coil under a meter would be a barrier for the MDP, maybe an X-former with the larger ( sec or prim) only hooked up across the hots???



blissfully ignorant also???

Around forty years ago, salesmen came around this area and used scare tactics to sell air spikes (lightning rods). My house has beautiful copper rods with glass ball "insulators" and even a weather vane on the center rod. They've never been used as far as I know. I still wonder how much hard earned money my grandfather paid for the installation. I guess it leaves a bad taste in my mouth (not the copper taste you get when getting shocked though!). There are no "modern" lightning rods in this area.


Back to the arrestor thing...
Anyone ever use a tesla coil to test an arrestor to see if they actually do anything?

I still like the placebo theory...

66,
come to think of it, how do we know the older arresters we see are ok?
maybe we need that Telsa coil afterall!

Thanks for the welcome, Scott.

That's how I understood it. And I see problems with that.

I'm not sure why you consider it a problem. The conductor is intended to be carrying current - unlike the grounding conductor found in branch circuits.


And the itty bitty wires from my service entrance back to the transformer are not going to haul much.

I would like to see your justification for this. I think you have it backward. The connections mean that lightning can just hit the utility pole without having to hit my house too.

Which is a terrific and necessary thing.

You asked for it!

I'm not sure that it has so much to do with the amperes as it does with the frequency. Lightning is no 60 Hz sinusiodal waveform.

Electrons traveling in higher frequencies like to jump off at bends. And keep in mind that with lightning, the currents are actually electrons making the trip (that is, a "static electric" discharge) unlike in 60 Hz in a conductor where electrons migrate very slowly.