250.24 (C)(2) vs. 310.4 (C)

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TJjr

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I currently was given a new class on Service Entry. I have been trying to build a new curriculum on proper bonding and grounding for the class. I have been using a residential book for over-head and lateral services and Soars book on Grounding for commercial and industrial services. I have come across some irregularities in sizing of parallel feeds. If taken the information on 250.24 you are referenced to the cir-mil calculations and Table 8 Chapter 9 for total area and then T 250.66 for size of gec in each race-way. however if referring to 310.4 you are instructed that you only have to size the gec in accordance to the feeders per raceway not the total of the cir-mil of the combined raceways. I have to teach this information and can in no way be compliant in teaching this incorrectly. Any feed back on this subject matter would be appreciated. I am a set in stone kind of person and feel I have to absolutely know the answer or else I can not rest. Thank you for your help and considerations.
 
Welcome to the Forum. Where does 310.4 address the GEC???

310.4 Conductors in Parallel.

(A) General. Aluminum, copper-clad aluminum, or copper conductors of size 1/0 AWG and larger, comprising each phase, polarity, neutral, or grounded circuit conductor shall be permitted to be connected in parallel (electrically joined at both ends).

(B) Conductor Characteristics. The paralleled conductors in each phase, polarity, neutral, grounded circuit conductor, or equipment grounding conductor shall comply with all of the following:
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TJjr said:
I currently was given a new class on Service Entry. I have been trying to build a new curriculum on proper bonding and grounding for the class. I have been using a residential book for over-head and lateral services and Soars book on Grounding for commercial and industrial services.
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What residential book are you using? Just curious. rbj
 
GEC conductors are not typically installed in parallel. I think you may be confusing this with the EGC.

Table 250.66 doe not require a GEC to be larger than 3/0 copper, which is hardly a reason it would need to be installed paralleled.
 
Thank You premature freak-out

Thank You premature freak-out

Sorry for the fuss. I was on code O.L. I think?
I was making a power point at the same time I was finalizing my student packets and got turned around on the GEC and the EGC. While going through my power point I remembered 250.122 and clarified what I was confusing myself over. I apologize for the misleading question and truly am thankful for all the responses. This forum seems great already and am sure I will be asking many more questions. Thank you again TJ
 
TJjr said:
Sorry for the fuss. I was on code O.L. I think?
I was making a power point at the same time I was finalizing my student packets and got turned around on the GEC and the EGC. While going through my power point I remembered 250.122 and clarified what I was confusing myself over. I apologize for the misleading question and truly am thankful for all the responses. This forum seems great already and am sure I will be asking many more questions. Thank you again TJ
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A response by a gentlemen..thanks for letting us know what happened.
 
TJjr said:
I have come across some irregularities in sizing of parallel feeds. If taken the information on 250.24 you are referenced to the cir-mil calculations and Table 8 Chapter 9 for total area and then T 250.66 for size of gec in each race-way. however if referring to 310.4 you are instructed that you only have to size the gec in accordance to the feeders per raceway not the total of the cir-mil of the combined raceways.
Click to expand...


If you look at 250.122(F)(1) you will see that you are required to size the EGC from table 250.122 at the size of the breaker/fuses protecting the circuit conductors, so yes you will have to run a full size EGC with each of the parallel runs.

This is because if there was a fault to the EGC lets say, in one of the conduits of a parallel run, it would have to carry the full load of the fault which would be determined by the OCPD of the whole circuit,
 
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