2017 NEC 250.52, 250.53, 250.66 - Sizing GEC

Joe.B

Member
Location
Arcata Ca
Occupation
Building Inspector
Hello, I am just looking to make sure I'm understanding things right.

250.52 (A)(3) CEE allows either 1/2 inch minimum conductive steel reinforcement at the bottom of the footing (20 ft min) or 20 ft of #4 bare copper. (If a new foundation is being built we require the use of the CEE.)
250.52 (A)(5) defines acceptable rod and pipe electrodes. (In remodels where a CEE does not exist and no foundation work is being done we accept rods.)
250.53 (A) defines GES requirements. (A)(2) defines supplemental electrode requirements. (E) states that the supplemental electrode bonding connection does not need to be larger than 6 AWG copper.
250.66 (A) states that connections to Rod that does not extend to other types of electrodes shall not be required to be larger than 6 AWG copper. (B) States that that if the CEE does not extend... then it is not required to be larger than 4 AWG copper.

So if I am understanding all of this correct, and all of those conditions are met, then the grounding electrode conductor does not need to be larger than 6 AWG copper for rods and 4 AWG copper for CEE regardless of the requirements in table 250.66.

I'm digging into Table 250.102(C)(1) next and it appears that there are not similar "exceptions" for bonding jumpers, correct?

Am I on track? Thanks very much.

P.S. I'm headed out for the weekend so I won't be able to see replies till Monday morning.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
So if I am understanding all of this correct, and all of those conditions are met, then the grounding electrode conductor does not need to be larger than 6 AWG copper for rods and 4 AWG copper for CEE regardless of the requirements in table 250.66.
Correct. I adjusted you thread title to reflect that you meant GEC not EGC.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector
Depending on how deep you wish to dig, you might note 250.102 is actually for:
Grounded Conductor, Bonding Conductors, and,Jumpers.
 

Joe.B

Member
Location
Arcata Ca
Occupation
Building Inspector
Depending on how deep you wish to dig, you might note 250.102 is actually for:
Grounded Conductor, Bonding Conductors, and,Jumpers.
Thank you. I'm digging deep. Why is "grounded conductor" in the title of this section? (Besides the confusion of terminology, that's another debate entirely...) All the subsections talk about bonding jumpers, supply-side bonding jumpers, and equipment bonding jumpers. When would the grounded conductor (neutral?) be smaller than the ungrounded conductors? 240V or 3 phase? MWBC?

I started digging into these two sections because I got schooled by a very experienced electrician here. He knows I am not an experienced electrician and like many electricians he (rightfully so) doesn't like being inspected by inexperienced inspectors like me. Nevermind that I have to inspect everything, but that's ok. I take it as an opportunity to learn, and not be "that guy". So I ask questions and read the book. He appreciates that I'm trying but he won't hesitate to send me away with my tail between my legs. So here's the story.

Residential remodel, #6 AWG copper going to two ground rods over 6 feet apart. #4 AWG copper running to the water heater to catch water and gas pipes. I asked why they were different sizes. He told me to go study Article 250... So that's what I'm doing. Jobs not finaled yet so I want to make sure I understand this before I get called back. If the largest ungrounded conductor is 2/0 or 3/0 copper then he's using the #4 to satisfy table 250.102(C)(1) but only using #6 for the ground rods based on the "exceptions" in 250.53 and 250.66?

Thanks again!
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
Thank you. I'm digging deep. Why is "grounded conductor" in the title of this section? (Besides the confusion of terminology, that's another debate entirely...) All the subsections talk about bonding jumpers, supply-side bonding jumpers, and equipment bonding jumpers.
The terminology is the biggest part of the problem. Hang in there. Don't expect to get this all at once, and most of all don't expect to figure this out all alone. Come back here and ask more questions.

It's called the grounded conductor because we take one of our circuit conductors and physically connect it to the earth. All of the bonding jumpers are ways to connect that grounded conductor to other parts of the electrical system that we want "grounded".

Check out this old post from one of our best members. Depending on your level of electrical education it may or may not be helpful to you but it is an excellent explanation of the grounded conductor.
https://forums.mikeholt.com/threads/understanding-the-neutral-conductor.140537/

When would the grounded conductor (neutral?) be smaller than the ungrounded conductors? 240V or 3 phase? MWBC?
Rules for sizing circuit conductors and more specifically sizing of the neutral conductor are different and are in different parts of the code. That is another discussion for another time.

In the context of art 250 the general rule of thumb was anything to do with sizing the grounded conductor or grounding electrode conductor or any of the bonding jumpers was based off 250.66. For some reason 250.102 was added and made things more confusing. The two tables are almost identical.

If you make it up to art. 250 Part IV come back and ask questions again.
Residential remodel, #6 AWG copper going to two ground rods over 6 feet apart. #4 AWG copper running to the water heater to catch water and gas pipes. ...... Jobs not finaled yet so I want to make sure I understand this before I get called back. If the largest ungrounded conductor is 2/0 or 3/0 copper then he's using the #4 to satisfy table 250.102(C)(1) but only using #6 for the ground rods based on the "exceptions" in 250.53 and 250.66?
Correct.
 
. #4 AWG copper running to the water heater to catch water and gas pipes. I asked why they were different sizes. He told me to go study Article 250... So that's what I'm doing. Jobs not finaled yet so I want to make sure I understand this before I get called back. If the largest ungrounded conductor is 2/0 or 3/0 copper then he's using the #4 to satisfy table 250.102(C)(1) but only using #6 for the ground rods based on the "exceptions" in 250.53 and 250.66?

Thanks again!
Also it's good to note that bonding interior piping systems and using an underground pipe as a grounding electrode are not the same thing. One conductor often does both, but if the pipe does qualify as a GE, then you need to hit it within 5 feet of where it enters the building.
 

Joe.B

Member
Location
Arcata Ca
Occupation
Building Inspector
Also it's good to note that bonding interior piping systems and using an underground pipe as a grounding electrode are not the same thing. One conductor often does both, but if the pipe does qualify as a GE, then you need to hit it within 5 feet of where it enters the building.
Thank you. The water supply for this house has been replaced with plastic.

In the context of art 250 the general rule of thumb was anything to do with sizing the grounded conductor or grounding electrode conductor or any of the bonding jumpers was based off 250.66. For some reason 250.102 was added and made things more confusing. The two tables are almost identical.

If you make it up to art. 250 Part IV come back and ask questions again.

Correct.
Will do. Thanks!
 

Joe.B

Member
Location
Arcata Ca
Occupation
Building Inspector
Check out this old post from one of our best members. Depending on your level of electrical education it may or may not be helpful to you but it is an excellent explanation of the grounded conductor.
https://forums.mikeholt.com/threads/understanding-the-neutral-conductor.140537/
Totally with you there, the term commonly used as "neutral" isn't appropriate in many situation and I follow the logic behind why it's called a "grounded" conductor. That's a rabbit hole I've been down a few times. I've also read through many of the discussions regarding grounded vs. grounding, oh boy oh boy.... All good there though. What caught me off guard here was the idea that your "grounded conductor" could be sized smaller than the ungrounded conductor. But it sounds like the term "grounded conductor" used in this section is not referring to what is commonly called the neutral in circuits, it's referring to the fact that in section 250 we are talking about conductors that are grounded?

Part IV. Enclosure, Raceway, and service connections. Part V. Bonding. Part VI. Equipment Grounding and Equipment Grounding Conductors. I've read all of this before, several times, and now I'm doing it again. Seems like every time I do something jumps out at me. Last time I dug through this was in regards to gas fired water heaters in new construction with PEX water lines. Huge debate locally, some electricians (in conjunction with GC's) emphatically say it's required to bond the water lines (and gas) at the water heater regardless of pipe type and fuel type. Others argue that there's no electricity supplying the water heater, and the water pipes are plastic so bonding there isn't necessary (assuming gas is bonded elsewhere.) I've heard the lightning argument, surge voltage from POCO, water is conductive, etc... ugh...
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
What caught me off guard here was the idea that your "grounded conductor" could be sized smaller than the ungrounded conductor. But it sounds like the term "grounded conductor" used in this section is not referring to what is commonly called the neutral in circuits, it's referring to the fact that in section 250 we are talking about conductors that are grounded?
It's referring to the neutral in services and feeders, not individual circuits. Line-to-line-only loads do not contribute to neutral current.

When there is a neutral, it's almost always the conductor that is required to be grounded. In fact, no neutral need be run to a panel with only line-to-line loads.

Last time I dug through this was in regards to gas fired water heaters in new construction with PEX water lines. Huge debate locally, some electricians (in conjunction with GC's) emphatically say it's required to bond the water lines (and gas) at the water heater regardless of pipe type and fuel type. Others argue that there's no electricity supplying the water heater, and the water pipes are plastic so bonding there isn't necessary (assuming gas is bonded elsewhere.) I've heard the lightning argument, surge voltage from POCO, water is conductive, etc... ugh...
If the water service is metallic, the bond must be made within five feet. If the water service pipe is not metallic, but there is a metallic interior system, it must be bonded somewhere.

Gas piping should be bonded on the service side of any CSST in the system, to avoid lightning-induced voltages between it and any gas appliances, effectively bypassing the CSST.

Gas appliances with power are considered bonded by the EGC of the circuit supplying it. A gas-only appliance does not need bonding. Plastic pipe certainly never does.
 

Joe.B

Member
Location
Arcata Ca
Occupation
Building Inspector
It's referring to the neutral in services and feeders, not individual circuits. Line-to-line-only loads do not contribute to neutral current.

When there is a neutral, it's almost always the conductor that is required to be grounded. In fact, no neutral need be run to a panel with only line-to-line loads.

If the water service is metallic, the bond must be made within five feet. If the water service pipe is not metallic, but there is a metallic interior system, it must be bonded somewhere.

Gas piping should be bonded on the service side of any CSST in the system, to avoid lightning-induced voltages between it and any gas appliances, effectively bypassing the CSST.

Gas appliances with power are considered bonded by the EGC of the circuit supplying it. A gas-only appliance does not need bonding. Plastic pipe certainly never does.
Thank you and mostly understood.

Line-to-line load would typically be 240V, correct? And/or 3 phase?

Gas-only water heater in new construction with PEX piping system needs no bonding, that is how I am reading code as well. Interestingly that view seems to be in the minority in my area, by contractors, builders, and other inspectors. I'm certainly not going to complain about extra bonding even if it's unnecessary. The only semi-convincing argument I've heard for bonding water lines (at the gas only water heater) in new construction with PEX was the "lightning-induced voltages" caused by the metal body of the water heater then traveling through the water itself. Seems like a one-in-a-billion but I guess I'd hate to be taking a shower when lightning struck nearby... If they're already bonding the gas supply at the water heater then it's two more clamps and a foot or so of extra copper, in their mind it's probably worth it so they don't have to worry about passing their inspection? I hear that some of the other inspectors around here are set in their ways, so to speak...

Haven't seen it in person, but I've seen pictures posted here of plastic pipes bonded, cracks me up.
 
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