I need some help understanding the requirements for a feeder from a detached garage to a house for a major interior remodel of the house originally built in 1959.
Some background:
- Service entrance is an overhead drop to the garage with an exterior meter
- Existing main service panel is a 150 amp panel inside the garage behind the meter
- Existing feed to the house is by means of three 2 AWG CU wires (no ground) with a 100 amp OCPD in a 1 1/2" PVC underground conduit to a main lug subpanel in the house
- Existing panel in the house has no proper grounding either back to the main panel or a ground rod and is only bonded to the copper plumbing waste line
- Conduit length from the garage to the house is around 50'
- All walls are open down to the studs
- AHJ is Boulder County, Colorado. 2020 NEC
The plan:
- Completely remove the existing subpanel in the house and rewire the entire house.
- The load calculation for the house after the remodel comes out to 138 amps so I need at least 150 amps to a new panel.
- The new panel location is in the center of the house on an interior pantry wall. A conduit from the exterior ground level to the new panel through the attic is around 30' for a total conduit length of around 80'.
- The voltage drop calculators tell me that I need 2/0 CU (or 3/0 AL) for 150 amps at 80 feet or 3/0 CU (or 4/0 AL) for 200 amps in at least a 2" conduit (preferably 2 1/2").
- Install a new 200 amp service panel on the exterior of the garage next to the meter
- Feed the existing garage panel from the new exterior service panel.
- Install a new 2 1/2" PVC conduit between the new garage service panel and house.
- Install a new subpanel in the house that is rated as service equipment for 200 amps with a main disconnect (lHOM4080M200PCVP)
- Feed the new panel in the house from the new 200 amp service panel at the garage with three 3/0 CU THHN and one 6 AWG CU THHN ground.
- Install new grounding rod where the conduit rises out of the ground connected to the ground bar of the subpanel with 6 AWG bare CU (and of course do not bond the neutral and ground in the subpanel)
- Bond the hot, cold, and gas lines to the ground bar in the house subpanel with 6 AWG bare CU.
Questions:
1. Is 2/0 CU (or 3/0 AL) for 150 amps at 80 feet or 3/0 CU (or 4/0 AL) with a 6 AWG ground correct for a 200 amp sub panel?
2. It does not seem to be much difference in cost and labor to go with 200 amps in the house rather than 150. Is it overkill to go with 200 amps?
3. What wire type is preferred? CU vs AL? THHN vs SER (or MHF or other)?
4. Is a building disconnect means required on the exterior of the house where the conduit enters or does the disconnect in the subpanel qualify? If an exterior disconnect is required, how is this typically accomplished?
5. Is it preferred that the feeder to the house from the new garage service panel be connected to a 200 amp OCPD or feedthrough lugs in the new service panel?
6. Is it permitted for the conduit to enter the house just above grade (into the crawl space)? It would save about 10' in length vs going up the the attic.
7. What brand/model is recommended for the new exterior 200 amp service panel on the garage?
Is this a reasonable plan overall?
Thanks in advance.
Some background:
- Service entrance is an overhead drop to the garage with an exterior meter
- Existing main service panel is a 150 amp panel inside the garage behind the meter
- Existing feed to the house is by means of three 2 AWG CU wires (no ground) with a 100 amp OCPD in a 1 1/2" PVC underground conduit to a main lug subpanel in the house
- Existing panel in the house has no proper grounding either back to the main panel or a ground rod and is only bonded to the copper plumbing waste line
- Conduit length from the garage to the house is around 50'
- All walls are open down to the studs
- AHJ is Boulder County, Colorado. 2020 NEC
The plan:
- Completely remove the existing subpanel in the house and rewire the entire house.
- The load calculation for the house after the remodel comes out to 138 amps so I need at least 150 amps to a new panel.
- The new panel location is in the center of the house on an interior pantry wall. A conduit from the exterior ground level to the new panel through the attic is around 30' for a total conduit length of around 80'.
- The voltage drop calculators tell me that I need 2/0 CU (or 3/0 AL) for 150 amps at 80 feet or 3/0 CU (or 4/0 AL) for 200 amps in at least a 2" conduit (preferably 2 1/2").
- Install a new 200 amp service panel on the exterior of the garage next to the meter
- Feed the existing garage panel from the new exterior service panel.
- Install a new 2 1/2" PVC conduit between the new garage service panel and house.
- Install a new subpanel in the house that is rated as service equipment for 200 amps with a main disconnect (lHOM4080M200PCVP)
- Feed the new panel in the house from the new 200 amp service panel at the garage with three 3/0 CU THHN and one 6 AWG CU THHN ground.
- Install new grounding rod where the conduit rises out of the ground connected to the ground bar of the subpanel with 6 AWG bare CU (and of course do not bond the neutral and ground in the subpanel)
- Bond the hot, cold, and gas lines to the ground bar in the house subpanel with 6 AWG bare CU.
Questions:
1. Is 2/0 CU (or 3/0 AL) for 150 amps at 80 feet or 3/0 CU (or 4/0 AL) with a 6 AWG ground correct for a 200 amp sub panel?
2. It does not seem to be much difference in cost and labor to go with 200 amps in the house rather than 150. Is it overkill to go with 200 amps?
3. What wire type is preferred? CU vs AL? THHN vs SER (or MHF or other)?
4. Is a building disconnect means required on the exterior of the house where the conduit enters or does the disconnect in the subpanel qualify? If an exterior disconnect is required, how is this typically accomplished?
5. Is it preferred that the feeder to the house from the new garage service panel be connected to a 200 amp OCPD or feedthrough lugs in the new service panel?
6. Is it permitted for the conduit to enter the house just above grade (into the crawl space)? It would save about 10' in length vs going up the the attic.
7. What brand/model is recommended for the new exterior 200 amp service panel on the garage?
Is this a reasonable plan overall?
Thanks in advance.
