Question on a residential detached building???

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jango

jango

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We have a small guest house which is detached from the main residence and is approximately 10-15 feet away from the main house. We are putting a sub panel on the exterior of the detached guest house. Now I know this sub panel must have a main disconnect in lieu of the terminal lugs for the 125A sub feed. Do I also need to have a separate ground rod? Can anyone refer me to the section in the NEC that should steer me in the right direction? Also, there is an A/C condenser right below and to the right of the sub panel. Can the circuit breaker in the sub panel act as the means of disconnect for the A/C, or do I need a separate disconnect box outside of the sub panel? Any help and/or reference to the NEC would be helpful. Thanks!
 
Jim W in Tampa

Jim W in Tampa

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Location
Tampa Florida
jango said:
We have a small guest house which is detached from the main residence and is approximately 10-15 feet away from the main house. We are putting a sub panel on the exterior of the detached guest house. Now I know this sub panel must have a main disconnect in lieu of the terminal lugs for the 125A sub feed. Do I also need to have a separate ground rod? Can anyone refer me to the section in the NEC that should steer me in the right direction? Also, there is an A/C condenser right below and to the right of the sub panel. Can the circuit breaker in the sub panel act as the means of disconnect for the A/C, or do I need a separate disconnect box outside of the sub panel? Any help and/or reference to the NEC would be helpful. Thanks!
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Yes you need ground rod and yes can be disc for the AC, dont forget you need receptacle for that AC and that can be off the panel too
 
Dennis Alwon

Dennis Alwon

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Chapel Hill, NC
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Retired Electrical Contractor
Jim W in Tampa said:
Yes you need ground rod and yes can be disc for the AC, dont forget you need receptacle for that AC and that can be off the panel too
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I agree with Jim. If you want you can use the ground rods from the existing dwelling but you would have to run your GEC underground to the house. You probably will need to install 2 rods anyway.
 
jango

jango

Senior Member
Dennis Alwon said:
I agree with Jim. If you want you can use the ground rods from the existing dwelling but you would have to run your GEC underground to the house. You probably will need to install 2 rods anyway.
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If I drive a ground rod right at the ground where my new sub panel is at the detached structure, does the GEC just need to link the ground rod (with an acorn nut or J-clamp) to the ground bus in the new panel on the detached structure, and that's it?
 
Dennis Alwon

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
jango said:
If I drive a ground rod right at the ground where my new sub panel is at the detached structure, does the GEC just need to link the ground rod (with an acorn nut or J-clamp) to the ground bus in the new panel on the detached structure, and that's it?
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Yes, you do not have to tie the ground rod from the house to the guest house rod. Are you sure one will be enough. Code requires 25 ohms or drive a second rod. Also, make sure you run 4 wires to the guest house
 
jango

jango

Senior Member
Dennis Alwon said:
Yes, you do not have to tie the ground rod from the house to the guest house rod. Are you sure one will be enough. Code requires 25 ohms or drive a second rod. Also, make sure you run 4 wires to the guest house
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10-4, four wires to the guest obviously meaning hot, hot, neutral, equipment ground? Also, can someone explain this phrase from the NEC: "Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).???
 
raider1

raider1

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Location
Logan, Utah
jango said:
Also, can someone explain this phrase from the NEC: "Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).???
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This means that you must keep the grounded (Neutral) conductor isolated at the panel at the separate structure.

Chris
 
TOOL_5150

TOOL_5150

Senior Member
Location
bay area, ca
You will need a ground rod on a detatched structure, no matter what. You dont necessarly need a main breaker in the sub IF you have 6 or less throws. You can hook the A/C to the panel as long as your A/C does not require more than 50% load of what the panel can provide.Ex. If your AC needs 30A and you have a 70A sub - youre good to go.

~Matt
 
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