Grounding electrode size

[MiamiValleyelec]

I have a 300 amp service upgrade with a double lug meter. I’m planning on coming off the meter to the existing 150 amp main breaker panel then setting a nema 3 main breaker 150 amp panel outside for an EV and a hot tub. Do I size my grounding electrode for 300 amp or for 150 amp?

 

[Dsg319]

Size your common grounding electrode conductor to your 300ampere ungrounded conductors, than size your taps off that to each 150amp service disconnect conductor sizes.

I believe this is correct. If not someone feel free to put your input.

 

[infinity]

Where is the existing main breaker panel? The two service disconnects will need to be grouped. You can size the GEC according to the SEC's feeding the meter and tap off to each service disconnect with a split bolt.

 

[Strathead]

I have a 300 amp service upgrade with a double lug meter. I’m planning on coming off the meter to the existing 150 amp main breaker panel then setting a nema 3 main breaker 150 amp panel outside for an EV and a hot tub. Do I size my grounding electrode for 300 amp or for 150 amp?

Look at table 250.66. Grounding electrode conductor is sized to the incoming conductor size, not the amperage, so technically the answer is neither.

 

[MiamiValleyelec]

Look at table 250.66. Grounding electrode conductor is sized to the incoming conductor size, not the amperage, so technically the answer is neither.

Yes, I should have said wire size but in my head I’m thinking service size and over current

 

[MiamiValleyelec]

Where is the existing main breaker panel? The two service disconnects will need to be grouped. You can size the GEC according to the SEC's feeding the meter and tap off to each service disconnect with a split bolt.

Both service disconnects will be outside

 

[infinity]

Yes, I should have said wire size but in my head I’m thinking service size and over current

What are your wire sizes?

 

[MiamiValleyelec]

350 aluminum to line side of meter, 2/0 aluminum to each of the 150 mains

 

[Strathead]

350 aluminum to line side of meter, 2/0 aluminum to each of the 150 mains

So it must be sized to the 350 AL

 

[MiamiValleyelec]

So it must be sized to the 350 AL

Dang, I was hoping to not have to pull a #2 through conduit. A #6 would be a lot easier.

 

[MiamiValleyelec]

Thanks to all for their replies

 

[LarryFine]

Dang, I was hoping to not have to pull a #2 through conduit. A #6 would be a lot easier.

Why not use two #6s then?

 

[Strathead]

Why not use two #6s then?

Oops, still not enough information. 250 states the maximum size required GEC for a ground rod is #6, for the Concrete encased electrodes is #4

 

[MiamiValleyelec]

Why not use two #6s then?

That’s what I’m trying to figure out if I can do. I would like to pull #6 gec ,which is the size required for 2/0, since I’ll have 2-150 amp main breakers or if I have to size the gec based on the 350’s. It sounds like you believe I can run a #6 gec to each main?

 

[infinity]

That’s what I’m trying to figure out if I can do. I would like to pull #6 gec ,which is the size required for 2/0, since I’ll have 2-150 amp main breakers or if I have to size the gec based on the 350’s. It sounds like you believe I can run a #6 gec to each main?

Yes, you can run a single GEC based on the 350 kcmil SEC's and tap off to the service disconnects or you can run a separate GEC to each service disconnect based off of the #2/0 SEC's.

 

[MiamiValleyelec]

Yes, you can run a single GEC based on the 350 kcmil SEC's and tap off to the service disconnects or you can run a separate GEC to each service disconnect based off of the #2/0 SEC's.

Cool, thank you