waterline and cee

[eds]

never questioned this before, why am i required to size my gec to the water line based on my service entrance conductors and my cee is only required to be a # 4.

 

[Pierre C Belarge]

250.66 is the reference for sizing the GEC.

250.66(B) provides a different size than the table to permit the difference in size you have posted.

Also check out .66(A) & (C) for other different sizes other than the table that are permitted.

 

[eds]

I understand the tables but what I want to know is why am I required to use a larger wire to the water line , 500 kcmil reqires a 1/0 to a waterline and a #4 to cee if that water line is plastic it is still a #4 to cee

 

[infinity]

I understand the tables but what I want to know is why am I required to use a larger wire to the water line , 500 kcmil reqires a 1/0 to a waterline and a #4 to cee if that water line is plastic it is still a #4 to cee

I would assume that it's for the same reason that you only need a #6 to a ground rod. Any size larger conductor will provide no better protection.

 

[tom baker]

It may be based on the amount of lightning energy a given electrode can absorb. Those rules have been in the NEC for a very long time, based perhaps on research done in the first part of 1900.
In lightning there is very little difference between the current on a 4 AWG and 4/0 conductor, as its high frequency current.

 

[bkludecke]

It has been my understanding that the reason for the max required size GEC for CEE & rods is because the electrodes can only disperse a limited amount of energy because of their size. A water line could be miles long and can disperse alot more energy.

 

[petersonra]

I think it is something left over from the dark ages the code panels are afraid to take out, probably because no one is sure at this date why it was done that way in the first place.

 

[winnie]

Bob is probably right on the money, however I can think of a couple of factors that make the connection to the water line different from the connection to the CEE or to a ground rod.

1) The connection to the water line serves as both the grounding electrode conductor to the underground portion of the pipe _and_ as the bonding conductor (thing EGC) for the interior portion of the piping.

2) In an urban area with metal underground water pipe, and with multiple services that share the same service transformer, the metal water pipe becomes a metallic path between multiple neutral-ground bonds. This means that the water pipe and its 'GEC' may function to carry full neutral current if the proper neutral is lost.

IMHO if 1) is the reason, then the code could reasonably permit running a small conductor to within 5 feet of the water pipe entrance, and a larger conductor to a closer location, rather than simply requiring the large conductor only. If 2) is the reason, then this really shouldn't apply to large installations where a transformer feeds a single customer.

But I don't know the real reason. I'm just guessing.

-Jon

 

[tom baker]

I think it is something left over from the dark ages the code panels are afraid to take out, probably because no one is sure at this date why it was done that way in the first place.

I agree 100%. The reasons and panels members are long gone. I do know that water pipe was the #1 electrode of choice as:
Electrically continuous
Water makes it conductive
Available at most buildings
And
Did not want to use gas piping

 

[cpal]

never questioned this before, why am i required to size my gec to the water line based on my service entrance conductors and my cee is only required to be a # 4.

I was once informed (mfg I think) that a 1/2" clad rod would burn off before a No 6 Cu GEC???

if my memory is accurate then there may be a like cause for the No 4 to a 1/2 Re Bar??

just a thought

 

[haskindm]

The reason for the increased conductor size to a waterline is simple and completely logical, but it has to do more with bonding than grounding. If the waterline becomes energized for any reason such as a fault from an ungrounded conductor the waterline and the grounding/bonding conductor will need to carry enough fault current to open an overcurrent device. Because of the high impedence of a ground rod or other grounding electrode, it will never carry more than a few amps, even in the event of a direct fault. If we achieved the suggested 25-ohm resistance and have a 120-volt circuit connected directly to the grounding electrode the maximum amperage the conductor would carry would be 4.8-amps (120/25=4.8). In the event of a 120-volt short to a waterline, the waterline and the conductor that connects the waterline to the panel and ultimately to the grounded (neutral) service entrance conductor may carry several hundred amps until the overcurrent device clears the fault. These are two different conductors with two very different jobs and, in this case, the code making panels got it right!

 

[LarryFine]

The connection to the water line serves as . . . the grounding electrode conductor to the underground portion of the pipe . . .

Keep in mind that both the connection within 5' of the pipe's entrance and at least 10' continuous pipe in contact with the earth must be met for this to qualify as an electrode; the latter can be tough to prove for existing work, making two rods relatively economical.