250.66

Status
Not open for further replies.
To answer your question, see note 1 to Table 250.66, and you'll need to use Table 8.

But, there is table 250.66 and section 250.66 for sizing GEC. The size of the GEC depends on what the GE is.
 
3/0 copper = 167800 cir. mil from Chapter 9 Table 8

167800 x 2 = 335,600

Closest equivalent is 350,00 cir. mil

Table 250.66 for 350 kcm states a #2 copper for the grounding electrode conductor.
 
wirenut48 said:
Can you show me the calculation.
Click to expand...
Go to table 8 as mentioned and look up how many circular mils a 3/0 conductor is. Since you have two 3/0 in parallel you need to double that figure to get total circular mils of the "overall conductor". I didn't look it up, that is for you to do, but say you had two parallel 250 kcmil - you would size the GEC same as if you had a single 500 kcmil conductor (that one is easy because you already know the circular mils of conductors larger then 4/0 without going to the table)
 
So if I had 3 500 kcmil conductors the answer would be 3/0 according to 250.66 unless I was dealing with 250 .102 (c) 1 then I would need to take 12.5 percent.
 
wirenut48 said:
So if I had 3 500 kcmil conductors the answer would be 3/0 according to 250.66 unless I was dealing with 250 .102 (c) 1 then I would need to take 12.5 percent.
Click to expand...

The GEC is never required to be larger than #3/0 copper. The 12.5% rule is for system or main bonding jumpers.
 
infinity said:
The GEC is never required to be larger than #3/0 copper. The 12.5% rule is for system or main bonding jumpers.
Click to expand...
But if the conductor is both a GEC and the bonding conductor for structural steel or metal water piping the 12.5% does apply.
 
Jim1959 said:
The structural steel bonding jumper is not a system or main bonding jumper.
The 12.5% does not apply.
Click to expand...

I agree, the 12.5% is to ensure that the jumper carrying the fault current back to the neutral is large enough.
 
Jim1959 said:
The structural steel bonding jumper is not a system or main bonding jumper.
The 12.5% does not apply.
Click to expand...
Specifically covered by the following. Supersedes all other interpretations.
250.104 Bonding of Piping Systems and Exposed Struc-
turalMetal.
...

(C) Structural Metal. Exposed structural metal that is in-
terconnected to form a metal building frame and is not
intentionally grounded or bonded and is likely to become
energized shall be bonded to the service equipment enclosure;
the grounded conductor at the service; the disconnecting
means for buildings or structures supplied by a feeder
or branch circuit; the grounding electrode conductor, if of
sufficient size; or to one or more grounding electrodes used.
The bonding jumper(s) shall be sized in accordance with
Table 250.66 and installed in accordance with 250.64(A),
(B), and (E). The points of attachment of the bonding jump-
er(s) shall be accessible unless installed in compliance with
250.68(A), Exception No. 2.
Click to expand...

See 250.104(A) for metal water piping... but I can tell you sizing is to Table 250.66 or 250.122.
 
Last edited:
Smart $ said:
Specifically covered by the following. Supersedes all other interpretations.


See 250.104(A) for metal water piping... but I can tell you sizing is to Table 250.66 or 250.122.
Click to expand...
The problem is the 2017 says differently

(C) Structural Metal. Exposed structural metal that is interconnected
to form a metal building frame and is not intentionally
grounded or bonded and is likely to become energized
shall be bonded to any of the following:
(1) Service equipment enclosure
(2) Grounded conductor at the service
(3) Disconnecting means for buildings or structures supplied
by a feeder or branch circuit
(4) Grounding electrode conductor, if of sufficient size
(5) One or more grounding electrodes used, if the grounding
electrode conductor or bonding jumper to the
grounding electrode is of sufficient size
The bonding conductor(s) or jumper(s) shall be sized in
accordance with Table 250.102(C)(1) and installed in accordance
with 250.64(A), 250.64(B), and 250.64(E). The points of
attachment of the bonding jumper(s) shall be accessible unless
installed in compliance with 250.68(A) Exception No. 2.
Click to expand...
 
Tables 250.66 and 250.104 are identical till you get to the end of the table. This is partly why they made a different Table for bonding
 
Status
Not open for further replies.
Top