Parallel EGC Question

P

prattz99

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Location
Long Island NY
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Electrician
Hi, I'm getting a little confused with table 250.122 and 250.66. My application is I'm running parallel 350 kcmil wiring for a generator automatic transfer switch. The ATS is service rated and I will move the load side of the meter over to it. When I then run the wiring for the 600 amp island main distribution breakers can I use #1 from table 250.122 or should it be 1/0 as in 250.66? I'm thinking #1 but I get confused because it's service equipment? Also I'm thinking the 100kw generator would fall under table 250.122? 600 amp ATS and generator = #1 EGC? Am I understanding this correctly or am I missing something?
 
infinity

infinity

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New Jersey
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On the line side of the service disconnect if required to bond the raceways each service raceway has a SSBJ based on the size of the ungrounded conductors in each raceway and T250.102(C). As masterinbama stated once you get to the load side of the service disconnect then the EGC in each raceway is sized for the OCPD ahead of the feeder.
 
augie47

augie47

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This seems to help in my class:::: IF the conductors associated with the "ground" are protected on tye supply side by an OCP device, it's 250.122.
 
P

prattz99

Member
Location
Long Island NY
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Electrician
All I know is I'm confused by it all. I ran two sets of 1/0 Cu with the sets of 350kcmil from the ATS to the main distribution panel. The main bonding jumper provided by the manufacturer of the 600 amp ATS cabinet is 2/0 finely braided (Cu I think) And the existing main bonding jumper in the island is 2/0 Cu I don't understand why? I'm thinking #1 would have been sufficient from the ATS to the main distribution panel but I didn't want to have to do it twice....

My next question is from the ATS to the generator. I understand that the wires need to be sized according to the breaker in the ATS (600 amps) two sets of 350 kcmil and I'm thinking two sets of #1 would be code compliant via table 250.122 Am I correct in my understanding?
 
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P

prattz99

Member
Location
Long Island NY
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Electrician
Great, thank you so much! Now when it comes to the grounding electrode for the generator, I'd use a #2 correct? As per Table 250.66
Or would a #6 suffice?
 
S

Strathead

Senior Member
Location
Ocala, Florida, USA
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Electrician/Estimator/Project Manager/Superintendent
prattz99 said:
Thankfully, no it doesn't.
Click to expand...
So, code wise, your generator doesn't need a grounding electrode conductor. If you run one, it is more of a lightning and surge protection. That said, for your future reference keep this in mind. Regarding grounds. Table 250.66 (and 2501.02 for bonding jumpers) use the line conductor SIZE to size the needed conductor. Table 250.122 uses the overcurrent protection upstream to size the needed conductor. Any time you have a breaker upstream of the feeder, you use 250.122. Anytime you don't you use one of the other tables. Use this hint as a guide, not a code.
 
Fred B

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Tulsa Electrician said:
So your generator is a an SDS?
Your ATS switches the neutral
( grounded conductor). Is that correct.
Click to expand...
prattz99 said:
Thankfully, no it doesn't.
Click to expand...
In this case you would be required to have an EGC not a GEC. Sizing thus would the same criteria as any EGC, and if use of parallel conductors then both EGC in the parallel sets must be capable of carrying the full current available not just the single pairing set of current carrying conductors.
250.122(F)(1)(b)
Multiple Raceways. If conductors are installed in multiple raceways and are connected in parallel, a wire-type equipment grounding conductor, if used, shall be installed in each raceway and shall be connected in parallel. The equipment grounding conductor installed in each raceway shall be sized in accordance with 250.122 based on the rating of the overcurrent protective device for the feeder or branch circuit.
 
P

prattz99

Member
Location
Long Island NY
Occupation
Electrician
Strathead said:
So, code wise, your generator doesn't need a grounding electrode conductor. If you run one, it is more of a lightning and surge protection. That said, for your future reference keep this in mind. Regarding grounds. Table 250.66 (and 2501.02 for bonding jumpers) use the line conductor SIZE to size the needed conductor. Table 250.122 uses the overcurrent protection upstream to size the needed conductor. Any time you have a breaker upstream of the feeder, you use 250.122. Anytime you don't you use one of the other tables. Use this hint as a guide, not a code.
Click to expand...
Is that right? I haven't completed the job, I can still not drop one in. I thought I didn't need one but I asked my buddy who does more generator work than me and said I needed one.
 
augie47

augie47

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Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
You might refer to the generator manufacturer guidelines. Since your generator is not an SDS (as the neutral is not switched) as noted by others there is no NEC reason for a grounding electrode conductor. On occasion I have seen the generator manufacturer calling for a ground rod in which case the NEC would only require a #6.
 
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