To avoid these ads, REGISTER NOW!

Service entrance --> sub-panel on same structure --> 2nd sub-panel detached structure

L

luvtheheat

Well-known member
Joined
Jan 28, 2017
Messages
489
Location
Tucson AZ
Hi,

I have an existing main service entrance (200 amp) with a 100 amp 2 pole breaker serving sub-panel, (as well as a bunch of others for the house) and from that breaker I ran aluminum 1/0 X 3 + ground about 80 feet to sub panel attached to same structure. Currently all that first sub-panel serves is air conditioning compressor. Sub-panel 1 has no jumper between ground and neutral which from what I can tell of the pics on the 'sticky thread' is correct since this sub-panel is on main structure.

So far so good, I believe.

See pic of sub-panel 1.

I'm planning on building a new detached garage on same end of house where sub-panel 1 is. I want to run 80 amps / 240v to a new sub-panel 2. My plan is to add an 80 amp breaker in SP1, run 4/4/4/4 all CU from SP1 to SP2, about a 30 foot distance, underground in 2" electrical conduit, to SP2 on inside/outside? of new detached building.

(I know 50 amp to AC and 80 amp to shop is more than 100 amp which is breaker size on main panel, but there is no way I'll ever pull 80 amps in the garage at same time AC is running. I happen to have wire I bought 10 years ago that will handle 80 amps, so I figure I ought to use its capacity.)

So, my question(s) are related to ground to neutral bonding at SP2. Again, based on pics in the sticky thread, my understanding is the only difference between SP1 and SP2, is that SP2 must have a grounding rod 6 ft into earth, or be tied into rebar in new foundation (UFER).

Am I missing anything?

My area (Pima county AZ) requires adherence to 2017 NEC.

Thanks so much for your feedback.

Steve
 

Attachments

  • Panels - South interior.jpeg
    Panels - South interior.jpeg
    277.6 KB · Views: 19
To avoid these ads, REGISTER NOW!
A

alfredeneuman

Well-known member
Joined
Mar 3, 2011
Messages
4,590
Location
Fullerton, CA
luvtheheat said:
So, my question(s) are related to ground to neutral bonding at SP2. Again, based on pics in the sticky thread, my understanding is the only difference between SP1 and SP2, is that SP2 must have a grounding rod 6 ft into earth, or be tied into rebar in new foundation (UFER).
Click to expand...
If it's in the same structure you don't need a separate ground rod.
If it had the rod would have to be driven 8' not 6'
 
M

mike93lx

ALLIANCE MEMBER
Joined
Dec 9, 2013
Messages
37,847
Location
Richmond, VA
2 rods, or the ufer.

Neutral /ground bonding isn't tied to where the panels are. Every panel after the first means of disconnect needs to have isolated neutrals. Same structure or detached is the same.

What the breakers add up to doesn't matter. It's about how much you are drawing. If you won't draw 80a out at the detached shop, you can breaker it lower. There can be significant differences in price and availability between breakers, so don't be tied to an 80a
 
W

wyliesdiesels

Well-known member
Joined
Aug 14, 2012
Messages
20,067
Location
Modesto, CA
luvtheheat said:
Hi,

I have an existing main service entrance (200 amp) with a 100 amp 2 pole breaker serving sub-panel, (as well as a bunch of others for the house) and from that breaker I ran aluminum 1/0 X 3 + ground about 80 feet to sub panel attached to same structure. Currently all that first sub-panel serves is air conditioning compressor. Sub-panel 1 has no jumper between ground and neutral which from what I can tell of the pics on the 'sticky thread' is correct since this sub-panel is on main structure.

So far so good, I believe.

See pic of sub-panel 1.

I'm planning on building a new detached garage on same end of house where sub-panel 1 is. I want to run 80 amps / 240v to a new sub-panel 2. My plan is to add an 80 amp breaker in SP1, run 4/4/4/4 all CU from SP1 to SP2, about a 30 foot distance, underground in 2" electrical conduit, to SP2 on inside/outside? of new detached building.

(I know 50 amp to AC and 80 amp to shop is more than 100 amp which is breaker size on main panel, but there is no way I'll ever pull 80 amps in the garage at same time AC is running. I happen to have wire I bought 10 years ago that will handle 80 amps, so I figure I ought to use its capacity.)

So, my question(s) are related to ground to neutral bonding at SP2. Again, based on pics in the sticky thread, my understanding is the only difference between SP1 and SP2, is that SP2 must have a grounding rod 6 ft into earth, or be tied into rebar in new foundation (UFER).

Am I missing anything?

My area (Pima county AZ) requires adherence to 2017 NEC.

Thanks so much for your feedback.

Steve
Click to expand...
You dont need #4 for the EGC for the 80a feeder. Use #8 instead.

You need 2 rods not 1...

Neutral bus needs to be isolated as you stated.
 
To avoid these ads, REGISTER NOW!
You must log in or register to reply here.
To avoid these ads, REGISTER NOW!
Top Bottom