Max Size for Paralleled EGCs?

Status
Not open for further replies.

AQC

Member
I understand the theory regarding normal size equipment grounding conductors when paralleling. For example, a 1200A service requires 4 sets of conduits, and the appropriate size EGC is #3/0, and a #3/0 is needed in EACH of the 4 conduits.

My question is this. Is there a maximum size conductor I can get to before I need to break that down even further??? For example, for argument's sake, let's say I need a #1500 KCMIL EGC for EACH conduit. Can I instead use two #750 KCMIL EGC for EACH conduit?
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
For example, for argument's sake, let's say I need a #1500 KCMIL EGC for EACH conduit. Can I instead use two #750 KCMIL EGC for EACH conduit?
Nope. There are no provisions for using two smaller wires as an equivalent to a larger size EGC. Welcome to the forum.

 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I understand the theory regarding normal size equipment grounding conductors when paralleling. For example, a 1200A service requires 4 sets of conduits, and the appropriate size EGC is #3/0, and a #3/0 is needed in EACH of the 4 conduits.

Not sure I understand the question. For one thing a service would not have any ECG's run in with the service entrance conductors.

My question is this. Is there a maximum size conductor I can get to before I need to break that down even further??? For example, for argument's sake, let's say I need a #1500 KCMIL EGC for EACH conduit. Can I instead use two #750 KCMIL EGC for EACH conduit?

Secondly, table 250.122 goes up to 6000 amps and no further. Is it possible that there's a load greater than 6000 amps that would require an EGC larger than 800 kcmil?
 

AQC

Member
The moderator Charlie B seems to have most closely understood my question. So to be clear, I am NOT allowed to use two smaller EGC wires as an equivalence to one larger EGC wire, correct. So basically, this is the opposite theory of using ungrounded phase conductors, where you CAN use two smaller phase size wires as an equivalence to one larger phase size wire, correct?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I don't see why you could not parallel an EGC in each of the conduits. The problem would be that the EGC must be 1/0 or larger. Of course you would have to follow 310.4(B).

Charlie is there somewhere in the code that will not allow this or are you just saying there are no provisions. No provisions does not necessarily mean non compliant.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
That appears to be the case. I can find no Code reference on paralleling equipment grounds to match an equivalent size of that required by 250.122 and I could located nothing in the books I have on grounding.
(Dennis, your post came in as I was typing..I agree that I see nothing specifically prohibiting it except 250.122 says use conductors sized by Table 250.122 which seems to limit you to that requirement)
 
Last edited:

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
That appears to be the case. I can find no Code reference on paralleling equipment grounds to match an equivalent size of that required by 250.122 and I could located nothing in the books I have on grounding.
So, does that mean it can't be done.-- I posted at the same time you did. Read my response - what say you.
 

iwire

Moderator
Staff member
Location
Massachusetts
Dennis each EGC in each conduit is required to be 'full size'

If you needed a 500 Kcmil EGC you could not run two 250 Kcmils instead, either in the same conduit or separate conduits.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Dennis each EGC in each conduit is required to be 'full size'

If you needed a 500 Kcmil EGC you could not run two 250 Kcmils instead, either in the same conduit or separate conduits.
I guess I am asking what article states the EGC must be full sized
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
IMO the closest you're going to get is 250.122(F) which directs you to Table 250.122. In that section and that table I see no provisions for parallel EGC's.

My point exactly-- there are no provisions against it. If we meet the definition of parallel conductors in 310.4 then I don't see this as a violation. I could be, and usually am, wrong......;)
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
My point exactly-- there are no provisions against it. If we meet the definition of parallel conductors in 310.4 then I don't see this as a violation. I could be, and usually am, wrong......;)

IMO the sizes in the table are singular and make no provisions for paralleling. If could parallel them how would you size the EGC's? If you needed a 500 kcmil would you use 2-250's or 2-#3/0? Would you size it according to ampacity?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
IMO the sizes in the table are singular and make no provisions for paralleling. If could parallel them how would you size the EGC's? If you needed a 500 kcmil would you use 2-250's or 2-#3/0? Would you size it according to ampacity?

Good point. I would think that you must size it based on ampacity.
 

AQC

Member
Typically, most electrical contractors will say that 500KCMIL is the largest conductor they prefer to pull, and after that it becomes very difficult to pull anything larger. So if the service is 6000 amps and table 250.122 states to use a 800KCMIL, the contractors must deal with pulling 800KCMIL, even if it's harder?

Also, what would you do if you needed an EGC for something larger than 6000 amps?
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
I would think that you must size it based on ampacity.
That would not make any sense. Ampacity tables are based on limiting the amount of current that can flow for long enough time to cause overheating and failure of the insulation system. EGCs don't have to have insulation system, and the current that flows in them does not flow for very long.


The code article that prohibits (yes, I did use that word on purpose) paralleling EGCs is 250.122. Its very first sentence states, in no uncertain terms, that the EGC shall not be smaller than the values shown in the table. What would make anyone think they could start there, and find an equivalent value based on cross sectional area, on ampacity, or on any other parameter? You can't go smaller than the table. As a previous boss was fond of saying, "Chapter closed."
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
So if the service is 6000 amps and table 250.122 states to use a 800KCMIL, the contractors must deal with pulling 800KCMIL, even if it's harder?
That is correct. There is one alternative, however, and that is to use the raceway as the EGC.
Also, what would you do if you needed an EGC for something larger than 6000 amps?
What I would do is to separate the distribution system into smaller sub-groups, so that no single feeder is that large.

 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Typically, most electrical contractors will say that 500KCMIL is the largest conductor they prefer to pull, and after that it becomes very difficult to pull anything larger. So if the service is 6000 amps and table 250.122 states to use a 800KCMIL, the contractors must deal with pulling 800KCMIL, even if it's harder?

Also, what would you do if you needed an EGC for something larger than 6000 amps?

For a service there would be no EGC. Are there singular systems with larger than 6000 amp OCPD's?
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
For a service there would be no EGC.
Good catch, Rob. But to answer once again the intended question, if there is a feeder of 6000 amps, you would have to pull the 800 MCM EGC.

Are there singular systems with larger than 6000 amp OCPD's?
I can't imagine one. I recently completed design of Phase 1 of a facility. It included provisions for providing 4000 amps of 480/277 volts power to a future Phase 2. I plan to split that into two 2000 amp feeders.

 
Status
Not open for further replies.
Top