Residential Feeder Calc

[david luchini]

the primary GRC is going to be 2 local ground rods at the main panels. The #6 is just to satisfy the ‘GRC within a pathway.’

If I understand your layout correctly, the meters/disconnects are located at a separate structure. The main bonding jumper connection would be made at the disconnects. A grounding electrode conductor should also be connected there.

There would need to be a grounding electrode system at each dwelling unit as well, connected to the equipment grounding at each panel, but not to the grounded (neutral) conductor.)

 

[kwired]

If I understand your layout correctly, the meters/disconnects are located at a separate structure. The main bonding jumper connection would be made at the disconnects. A grounding electrode conductor should also be connected there.

There would need to be a grounding electrode system at each dwelling unit as well, connected to the equipment grounding at each panel, but not to the grounded (neutral) conductor.)

His use of word "pathway" instead of "raceway" might be adding some misunderstanding. Probably a good chance meter(s) not on a separate structure, but "pathway" kind of makes one think it might be.

 

[honestjoe]

If I understand your layout correctly, the meters/disconnects are located at a separate structure. The main bonding jumper connection would be made at the disconnects. A grounding electrode conductor should also be connected there.

There would need to be a grounding electrode system at each dwelling unit as well, connected to the equipment grounding at each panel, but not to the grounded (neutral) conductor.)

Correct I will have a total of 2 ground rods at each structure. Two at the meter locations and two at the panel locations at the rear building.

4 total

 

[honestjoe]

OK but you used it to describe two different conductor applications

You’re probably right, sorry for the confusion

 

[honestjoe]

His use of word "pathway" instead of "raceway" might be adding some misunderstanding. Probably a good chance meter(s) not on a separate structure, but "pathway" kind of makes one think it might be.

Meters are on building #1, with two ground rods. Panels are on building #2, with two ground rods.
#6 wire within the conduit is not the ‘primary’ ground source, on both structures the primary ground source is the two ground rods. Hope this clarifies things.

grounding aside, do my fill/ampacity numbers look to meet relevant code for 2x dwellings in this scenario? It seems as though the design meets code requirements.

 

[kwired]

Correct I will have a total of 2 ground rods at each structure. Two at the meter locations and two at the panel locations at the rear building.

4 total

So is there more than one building (other than possibly considering each dwelling as a separate building even though they might be connected to one another)? Depending on what you do have could possibly change what you may or may not be able to do here. For one thing 225.30 pretty much only allows one feeder to a separate structure.

 

[Dennis Alwon]

Meters are on building #1, with two ground rods. Panels are on building #2, with two ground rods.
#6 wire within the conduit is not the ‘primary’ ground source, on both structures the primary ground source is the two ground rods. Hope this clarifies things.

grounding aside, do my fill/ampacity numbers look to meet relevant code for 2x dwellings in this scenario? It seems as though the design meets code requirements.

What do you mean grounding aside. You need to calculate the fill based on at least one equipment grounding conductor as that is all that is required.

 

[honestjoe]

In review of 225.30, it appears to work because of (B) Special Occupancies, A single building sufficiently large enough to make 2 or more supplies necessary.

the structure is two stories, with a residence above another residence, both 600 sqf each

Being a multi unit structure, I don’t fully understand the exemption for (A)

 

[honestjoe]

What do you mean grounding aside. You need to calculate the fill based on at least one equipment grounding conductor as that is all that is required.

Yes I understand this.

 

[ptonsparky]

Ok, then I’m still under fill at 1x #6 sized off the highest ampacity conductor in the raceway

It is not sized off the highest ampacity of the conductor in the raceway.
It is sized per the OC protection ahead of those wires. In this case,125 Amp if that is indeed what you have below the meters.

I don't like the idea of them being in the same raceway, conduit, but if they were in a 4x4 wireway I wouldn't have an issue. Go figure.

 

[honestjoe]

Yes, I don’t like it either, which is why I’m scrutinizing it so heavily and fielding feedback such as this.

thank you everyone for the feedback!!

 

[retirede]

GRC is a ground rod connector or acorn

My acronym decoder ring has GRC = Galvanized Rigid Conduit.

 

[honestjoe]

Hahahahaha so many acronyms

 

[retirede]

Hahahahaha so many acronyms

That’s why I bought the decoder ring!

 

[kwired]

In review of 225.30, it appears to work because of (B) Special Occupancies, A single building sufficiently large enough to make 2 or more supplies necessary.

the structure is two stories, with a residence above another residence, both 600 sqf each

Being a multi unit structure, I don’t fully understand the exemption for (A)

That mostly comes into to play when you need more than say a 2000 amp feeder, or when the POCO can not/will not supply you with over certain size individual transformer - which can be lower for single phase supply than for three phase supply. That cut off point for single phase sort of kicks in if needing more than a 167 kVA transformer, about 700 amps @ 240 volts.