600 amp service

[don_resqcapt19]

Re: 600 amp service

I don't think that there is any problem with the wording of 250.66(A). A grounding electrode conductor that ends at a ground rod is never required, by the code, to be larger than #6 no matter where that GEC originates. That is what the words in the section mean to me. Yes, the job specs will often call for much larger GECs, but the code does not.
Don

 

[hurk27]

Re: 600 amp service

Jim I think if you did the resistance calculation of the rod, you will understand the intent of the CMP. even at half the resistance of 12.5 ohms at 120 volts would only draw 9.6 amps if any hot conductor were to ever heat up the grounding some how and you had the full 120 volts at the rod this is what the current would be at half the resistance the NEC requires us to meet. at the 25 ohms it would only be 4.8 amps. this is why there is no need to ever install a EGC larger than a #6 and if you have a UFER it only increses to a #4

Remember the grounding electrode is not for fault current.

[ December 31, 2003, 10:08 PM: Message edited by: hurk27 ]

 

[hurk27]

Re: 600 amp service

Lets look at it another way The only thing the ground rod or any grounding electrode for that matter is installed for is to keep the voltages from a source of a higher system from energizing the grounding in the building. this is of course ether lightning or the primary of the service feeding the transformer. Now let's say the primary breaks and contacts the neutral flown to the building it burns the neutral apart and welds it self to the portion running to the building. this primary is 7.2kv line and is protected at about 15 amps yes the ground rod at 25 ohms would have the ability to pass about 288 amps at 7.2kv. which would give you about 480 amps on the secondary side of the transformer. but the ground rod would have the ability to open the primary fuse with no problem at 15 amps. now for lightning which is fast enough that it wouldn't have a chance to heat the wire. When it comes to lightning look at the article for cable drops it only requires a #10 to bond the ground rod for cable and this is for lightning.

 

[hurk27]

Re: 600 amp service

Just as I was thinking about this I thought of how much fuss that is made over any GE and GEC.

Now here is the problem we have sevral inspector's that are adament about installing all EGC's in metal conduit. It is like this is the most dangerous wire in a house! I know that the NEC says that it shall be protected if exposed to severe physical damage. But I ask why are there so many that are that scared of it being damaged? and now I think I know why. It is because of so many thinking that the purpose of it is for the clearing of fault current or was taught by somone that thought this way. This is why they try to protect it to the hilt!. When it is probley the safest wire in the house if it was damaged. SEC would be the worst as it has no OCP protection at all if it shorted out. Then the neutral.

 

[roger]

Re: 600 amp service

Wayne, with all the explaining you can type until your fingers are gone, the real shame is that many in our profession have the same misunderstanding of a ground rod that the laymen have.

Roger

 

[jim sutton]

Re: 600 amp service

1)I never said the ground rod is for clearing faults

2) what does "that portion of the conductor mean"

you guys are reading much more into this than humble electricians should, our job is to install by code, not interpret varying theories

if you back up your comments with anything other than the NEC you are missing the point

the code could be more clearer on this subject


the nec handbook is not a binding document, just the writers interpretation of the english language

happy new year

 

[websparky]

Re: 600 amp service

Jim,

The commentary and supplementary materials, therefore, solely reflect the personal opinions of the editor or other contributors and do not necessarily represent the official position of the NFPA or its technical committees.

Mark W. Earley, P.E.
Editor-in-Chief
Joseph V. Sheehan, P.E.
Senior Editor
Jeffrey S. Sargent
Editor
John M. Caloggero
Editor
Timothy M. Croushore, P.E.
Editor

I've read these guys work for quite sometime now. I'm affraid I don't share your "contractor's" opinion. Maybe you could drop them a note and tell them where they have missed the boat?

 

[iwire]

Re: 600 amp service

Originally posted by jim sutton:
what are they referring to when they say "that portion of the conductor"? The conductor is the same its entire length right?

I think it means exactly what it says "that portion of the conductor" not the entire length.

I know this is strange but thats what it says.

Hi Jim, can you explain what you mean in the above statement?

Are you saying I would run 2/0 to the rod and the last 1" of conductor can be 6 AWG or that I can shave down the 2/0 to fit in a 6 AWG lug?

250.66(A) Connections to Rod, Pipe, or Plate Electrodes. Where the grounding electrode conductor is connected to rod, pipe, or plate electrodes as permitted in 250.52(A)(5) or 250.52(A)(6), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.

I am sorry but that section is clear as day, no gray area.

 

[roger]

Re: 600 amp service

Bob, Bob, Bob,

Are you saying I would run 2/0 to the rod and the last 1" of conductor can be 6 AWG or that I can shave down the 2/0 to fit in a 6 AWG lug?

you know we would have to come back more than 1".

Roger

 

[iwire]

Re: 600 amp service

Originally posted by a.wayne3@verizon.net:
I go by the incoming feeder sizing table.That`s the max needed by any articles. Yeah you can pick the nec apart and find other articles that say otherwise

That is correct Table 250.66, but directly under the table is 250.66(A) Ground Rods only need a 6 AWG, I do not see how this is picking the NEC apart.

Originally posted by a.wayne3@verizon.net:
I forgot about the footer bonding....Duhhhh
If the ufer was not done and/or inspected the NEC says a ditch 30 inches deep and 20 ft long with the ground wire in it.

If the footing was done before the electrician started then as far as the NEC is concerned it is not available and you do not need it. (some local amendments change this)

There is no NEC requirement for "a ditch 30 inches deep and 20 ft long with the ground wire in it"

You may be thinking or a ground ring, which would have to encircle the entire building minimum length of 20'.

250.52(A)(4) Ground Ring. A ground ring encircling the building or structure, in direct contact with the earth, consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 2 AWG.

Again this is not required in place of any of the other electrodes.

Originally posted by a.wayne3@verizon.net:
Here the AHJ wants ground rods with it but for a 200 amp service the NEC requires a # 2 wire so do you double the sizing acoordingly to the the amperage of the service???

Huh?

If you are again talking about a ground ring the conductor size is 2 AWG no matter what the service size.

Read this section carefully and you can see the NEC has given us options in the grounding electrode requirements, in no way do they expect all listed electrodes to be available.

250.50 Grounding Electrode System.

If available on the premises at each building or structure served, each item in 250.52(A)(1) through (A)(6) shall be bonded together to form the grounding electrode system.

Where none of these electrodes are available, one or more of the electrodes specified in 250.52(A)(4) through (A)(7) shall be installed and used.

To keep this short.

250.66(A) Connections to Rod, Pipe, or Plate Electrodes.

6 AWG Copper max required


250.66(B) Connections to Concrete-Encased Electrodes.

4 AWG copper max required


250.66(C) Connections to Ground Rings.

Not required to be larger than the conductor used for the ground ring itself.

 

[roger]

Re: 600 amp service

Here is Mike Holts interpretation,

) if I should not post these images here please remove it and let me know. I will not do it any more.

Thanks

Roger

 

[jim sutton]

Re: 600 amp service

Morning Bob,

to answer your question:
"Are you saying I would run 2/0 to the rod and the last 1" of conductor can be 6 AWG or that I can shave down the 2/0 to fit in a 6 AWG lug?"

Thats exactly what it says, thats why the section needs to be changed.

A portion of a conductor is a part of a conductor,if you consider the "conductor" in 250.66(A)to be one wire.

Or if you consider it to be a current path in which several wires may be interconnected then the portion connecting to the rod only could be no.6

Thats how I read it

 

[russ]

Re: 600 amp service

Bob:

See if I understand what your saying.

250.66(A) "that portion of the conductor that is the sole connection to the grounding electrode shall not be required to larger than 6AWG copper....".

That portion of the conductor, could be the piece of #6 that goes from the ground rod to the water pipe, or that goes to a GEC going to the water pipe, or it could be going all the way to the service equipment, if that's the only place to land it.

Makes sense to me.

Russ

[ January 01, 2004, 10:53 AM: Message edited by: russ ]

 

[websparky]

Re: 600 amp service

Here is an example from the 2002 NEC Handbook

As illustrated in Exhibit 250.29, if a grounding electrode conductor is run from the service equipment or separately derived system to a water pipe or structural metal building member and from that point to one of the electrodes mentioned in 250.66(A), that portion of the grounding electrode between the service equipment or separately derived system and the water pipe or structural metal building member must be a full-size conductor, per Table 250.66. If the grounding electrode conductor from the service equipment was run, for example, to the ground rod first and then to the water pipe, the conductor to the ground rod would also have to be full size, per Table 250.66. Note that Exhibit 250.29 is not intended to show the physical routing and connection of the bonding jumpers.

 

[iwire]

Re: 600 amp service

Thank you Websparky

 

[bennie]

Re: 600 amp service

Here in Oregon, the ufer is hit first then the other electrodes. The water pipe may go away.

Many electricians feed to each electrode separately. I say this is wrong.

Bonding is performed similar to the drawing, except each ground electrode should be daisy chained. One ground electrode conductor should leave the loadcenter.

 

[dana1028]

Re: 600 amp service

Originally posted by bennie:
Many electricians feed to each electrode separately. I say this is wrong.

Bonding is performed similar to the drawing, except each ground electrode should be daisy chained. One ground electrode conductor should leave the loadcenter.

Why do you say that Bennie? Why does more than one GEC leaving the panel make a 'wrong' installation?

In your 'daisy chain' installation, if you lost the original GEC leaving the panel, then all the other GE would be lost (i.e. not connected back to panel). With multiple GECs leaving the panel, losing one (damage, etc.) would not endanger the GES.

Generally speaking I do install the 'daisy chain' you suggest only because this is usually an easier installation; however there are times when having 2 GECs leaving the panel is an easier installation (i.e. easier to make the connections to GEs in different locations).

 

[iwire]

Re: 600 amp service

Either way is NEC compliant and I wish Bennie would say so.

 

[bennie]

Re: 600 amp service

Bonding means shorting, feeding the electrodes separately is not shorting, it constitutes an inductor.

A short circuit has little potential difference from one end to another. An inductor has a measurable difference in potential from one end to another.

Therefore multiple feeds to the earth is not single point grounding. It is multi-point creating voltage gradients during a lightning strike, or high voltage line contact.

 

[bennie]

Re: 600 amp service

250.64 Grounding Electrode Conductor Installation.
(F) This section is addressing the fact that the ground electrode conductor can run to any electrode in the ground system, or to more than one individually. This does not imply that two ground electrode conductors can run to separate electrodes, as many think.

Notice that the name of "ground electrode conductor" is always in the singular form of grammar. There is no mention of ground electrode "conductors".

Both procedures are not code compliant.