art 250 Q

romex jockey

Senior Member
Location
Vermont
I'm confused (easy to do) :confused: between the use of #6 cu and #8 cu in art 250

in my case, I'm 'bonding' metallic systems back to the panel area , and the groundING bar

which meets code?

~RJ~
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
What exactly are you bonding? Metallic systems encompass many things. If it's pool equipment then #8 (minimum) is specified. Also this is for equipotential bonding not system grounding/bonding. Most other bonding is done via the EGC of the circuit.
 

romex jockey

Senior Member
Location
Vermont
What exactly are you bonding? Metallic systems encompass many things. If it's pool equipment then #8 (minimum) is specified. Also this is for equipotential bonding not system grounding/bonding. Most other bonding is done via the EGC of the circuit.
gas lines, water lines & duct work Bill

~RJ~
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
gas lines, water lines & duct work Bill

~RJ~
Unfortunately I don't think your question is a simple this or that. Too many variables are made within Article 250 that affect the size, and these variables need to be addressed to get the correct size. (Like so many other code sections. Do this, but if you do this or that you must now do this other thing.)
First off, Are you bonding for GEC or EGC? Makes a difference.
Gas line, and most duct work would be sized as a EGC and subject to 250.122 and not as GEC. Waterline could be either GEC or EGC, and if used as grounding electrode or meeting language of 250.53, 250.64 and it would be sized by 250.66. Or if EGC only sized according to the requirements of 250.122 as an EGC. All of these methods or reasoning for bonding use the associated system or circuit amperages, or ungrounded conductor sizes.
Duct work would seem to me to be associated only to the HVAC and amperage related to it and sized accordingly.
Any of these are are also affected by the ungrounded sizing and any increase in size that could push a normally #8 to need to be a #6.
 

romex jockey

Senior Member
Location
Vermont
First off, Are you bonding for GEC or EGC? Makes a difference.
Thx Fred
methinks maybe you've hit on the fundamental difference , so now i'm wondering how the whole 250. 122/66 difference applies
how many places is this in the code comes to mind as well

~RJ~
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
When you are bonding gas lines, duct work, etc you are reducing the potential voltage to a safe point and, in the event of a fault, the current the bonding conductor might carry is limited by an overcurrent device hence it is sized by 250.122 based on OCP size. When the conductor is used to connect to a grounding electrode (building steel, underground water line) the current is not limited by an OCP device and a larger condcutor is required.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Thx Fred
methinks maybe you've hit on the fundamental difference , so now i'm wondering how the whole 250. 122/66 difference applies
how many places is this in the code comes to mind as well

~RJ~
This might be one of the most confused aspects, the difference GEC and EGC. Although seems should be easy enough to identify, GEC is run to anything on the list in 250.52 and 53 for use as a Grounding Electrode creating a grounding electrode system, anything else is a bonding to EGC and covered by 250.122, to clear a fault if incedently the item becomes energized. But it doesn't seem to most persons, to be that clear, I guess, with exceptions and exeption to the exceptions throughout 250. And I might be wrong but it might be the largest single code article, that adds to the confusion.
 

romex jockey

Senior Member
Location
Vermont
When you are bonding gas lines, duct work, etc you are reducing the potential voltage to a safe point and, in the event of a fault, the current the bonding conductor might carry is limited by an overcurrent device hence it is sized by 250.122 based on OCP size.
This might be one of the most confused aspects, the difference GEC and EGC.
methinks you tow are getting into the meat it, which i appreciate .

~RJ~
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
But there is one inconsistency in the code and that is bonding of water pipes. Even when just bonding them, they are sized per 250.102 (which is pretty much like 250.66) and not 250.122. All other pipes and metal use 250.122 when bonding. Just not water system pipes. If the water system pipes happen to qualify as a ground electrode, all that changes is where the wire must attach to the pipe, not its size.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
But there is one inconsistency in the code and that is bonding of water pipes. Even when just bonding them, they are sized per 250.102 (which is pretty much like 250.66) and not 250.122. All other pipes and metal use 250.122 when bonding. Just not water system pipes. If the water system pipes happen to qualify as a ground electrode, all that changes is where the wire must attach to the pipe, not its size.
I agree that the bonding of interior water pipes is inconsistent with the other bonding rules. It really should be based on the rating of the largest OCPD that could possibly energize the water pipe and Table 250.122.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
But there is one inconsistency in the code and that is bonding of water pipes. Even when just bonding them, they are sized per 250.102 (which is pretty much like 250.66) and not 250.122. All other pipes and metal use 250.122 when bonding. Just not water system pipes. If the water system pipes happen to qualify as a ground electrode, all that changes is where the wire must attach to the pipe, not its size.
I believe if you look also at the other items listed in in 250.104 that references the sizing table 250.102, these items all have potential fo contact across multiple systems and even as in the case of structural metal, lightning strike; so to size more in line with GEC makes sense as opposed to items more likely to be only covered under 250.122 for EGC that may have limited exposure to a singular circuit and known amperages.
 

romex jockey

Senior Member
Location
Vermont
I believe if you look also at the other items listed in in 250.104 that references the sizing table 250.102, these items all have potential fo contact across multiple systems and even as in the case of structural metal, lightning strike; so to size more in line with GEC makes sense as opposed to items more likely to be only covered under 250.122 for EGC that may have limited exposure to a singular circuit and known amperages.
Reading & reading Fred.....so it appears the only distinction is GEC vs EGC (250.102 vs 250.122) , one being sized via service conductors, the other from OCPD size.

So let's say i end up in T250.122, i'm bonding a gas line serving multiple gas appliances (for ex) , all are powered by no more than a 20A OCPD

Does one reference the 20A ocpd >>>#12 CU.......or does one reference the main breaker, 100A>>>#8 CU ?

~RJ~
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Reading & reading Fred.....so it appears the only distinction is GEC vs EGC (250.102 vs 250.122) , one being sized via service conductors, the other from OCPD size.

So let's say i end up in T250.122, i'm bonding a gas line serving multiple gas appliances (for ex) , all are powered by no more than a 20A OCPD

Does one reference the 20A ocpd >>>#12 CU.......or does one reference the main breaker, 100A>>>#8 CU ?

~RJ~
I would think for 250.122(C) it states the highest load appliance determines the size so I would say sizing base on the common single load value of 20A. If any of these fail and energize the gas line it will trip the breaker of the offending appliance. If gas line was to run to both a 20 amp and a 30 amp appliance then protect to the 30Amp level
 

romex jockey

Senior Member
Location
Vermont
I would think for 250.122(C) it states the highest load appliance determines the size so I would say sizing base on the common single load value of 20A. If any of these fail and energize the gas line it will trip the breaker of the offending appliance. If gas line was to run to both a 20 amp and a 30 amp appliance then protect to the 30Amp level
agreed & found a paragraph that actually states it Fred>>>

The bonding conductor(s) or jumper(s) shall be sized in
accordance with Table 250.122, and equipment grounding
conductors shall be sized in accordance with Table 250.122
using the rating of the circuit that is likely to energize the
piping system(s)
. The points of attachment of the bonding
jumper(s) shall be accessible.


i guess i'm just having a hard time imagining 6000 amps of appliances

~RJ~
 

norcal

Senior Member
Just for grins and giggles, what if the gas appliances do not require electricity? These days that is not very common but is possible.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
agreed & found a paragraph that actually states it Fred>>>

The bonding conductor(s) or jumper(s) shall be sized in
accordance with Table 250.122, and equipment grounding
conductors shall be sized in accordance with Table 250.122
using the rating of the circuit that is likely to energize the
piping system(s)
. The points of attachment of the bonding
jumper(s) shall be accessible.


i guess i'm just having a hard time imagining 6000 amps of appliances

~RJ~
Thanks for finding that reference, I knew it said it somewhere.
Yeah 6000A and gas, what would that look like?
 
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