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ADDING A SUB-PANEL IN MY HIGH TUNNEL GREENHOUSE

I need to add electricity to my new greenhouse that will be powering my exhaust fan and shutters, the automated roll-up sides, a couple of small water pumps and a circuit of outlets.

Below are some of the specifications that I’ve gathered from the components in the greenhouse:

  • 36” Queitaire GDD Box Fan, .5-.75 HP, 6.6/3.5-3.3 Amps, 11,410 CFM at .10 static pressure, wired for 115/208-230 volt operation
  • Two (2) each 39” Motorized Quietaire shutters, 0.33 Amps
  • Two (2) each E-Z Roll Up Curtain Gear Motors, 24 Volt
  • Penn 2 Stage Thermostat Control 30-110 degrees F, 16 Amp rating @120volts
  • Bartlett RWL 11x2 Curtain Controller & Vent Boss panel, controls the two 24V DC curtain motors, 2 heating outputs and one timer output for irrigation or lighting.
  • 60 CFM Blower Motor, 120V, 60Hz,0.15 Amp, 1/60 HP
  • A GFCI protected electrical outlet circuit (Number of Outlets undetermined at this time.

CURRENTLY Main House breaker box is located in the garage with a Tesla (Solar) PowerWall 2. My house runs on 32 LG 355 Watt solar panels tied to the grid. I also have one other 8 slot sub-panel connected to the main panel (see photo 1&2). There are a couple open slots on the main panel but I plan to add Tandem breakers to some to free up space, if possible.

END GOAL My plan was to run wire up from the main panel up through the attic to the opposite corner of the house, come out and down the exterior wall to the ground (in conduit), run underground about 15 feet (18” deep, conduit), and come up the interior wall of the greenhouse A distance of approximately 110-130 feet max (see photo 3). The greenhouse Sub-panel will be “outdoor” rated and all wiring inside the greenhouse will be direct bury or ran in conduit as it can be a wet/moist environment with a lot of equipment running through it.

My Questions are:

  1. Will a 125 Amp, 8 Spaces, 16-Ciruit Convertible “Outdoor” panel from Lowes/HD be sufficient for the components and their specs listed above? Or will I need bigger?
  2. What size, rating type, and number of wires should I run up through the attic and down through the conduit into the greenhouse?
  3. Will I need to found this panel and with 1 or 2 copper rods?
  4. How many and what amperage of breakers will each of the components listed above need?
  5. Can my main panel handle the additional subpanel based on its specifications show in Photo 2? My solar array produces between 9-10 kWh on a nice sunny day.

Also any other advice regarding this project will be greatly appreciated.

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Ryan Moore
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    Welcome to [diy.se]! While very thorough, your 5 questions makes this bordering on too broad. The answer to #3 can be found in dozens of other questions here about grounding sub-panels in out-buildings. The answer to #1 is _always_ "go big or go home!" spaces are cheap if you add them today, they're much more expensive in the future if you need to expand (for something you can't even conceive of today). – FreeMan May 19 '21 at 14:22
  • I agree on the larger panel as every receptacle will need to be GFCI protected so 1/2 size slots are not as useful. You can use GFCI receptacles but if you find the 120v 16 amp heat not sufficient going to 240v becomes more efficient add a breaker position I did not see any lighting in the list what about grow lights many high end lights are 240v think about a 20 full sized breaker box. – Ed Beal May 19 '21 at 14:47
  • You can't use tandems in that panel. It's a BR panel in the Cutler Hammer era, meaning it is a CTL panel. More than 42 circuits per panel is not allowed, and the bus bars will not have the gating required to accept a tandem. Somebody was really trying to pinch pennies on those panels... and it's time for you to learn from their mistake lol. – Harper - Reinstate Monica May 19 '21 at 21:31
  • How many kitchen receptacle branch circuits do you have in your panel, how many square feet is your house, and are your heavy appliances (range, water heater, dryer) gas or electric? Also, can you post the nameplate info for your A/C please? – ThreePhaseEel May 20 '21 at 01:46
  • My house is 2900 sq. ft. I have two kitchens in my house as I have an attached in-law suite apartment. I have 4 breakers for 2 ovens, 2 breakers for kitchen receptacles, 1 breaker for apartment kitchen receptacles, 1 break for vent hood in apartment, 1 breaker for main refrigerator, 1 breaker for kitchen lights. I have two dual fuel HVACs, 2 washers, 2 dryers. All appliances are electric. HVAC is dual fuel (propane/electric), propane is used as supplemental heat. – Ryan Moore May 20 '21 at 02:39
  • @RyanMoore -- can you post the nameplate Minimum Circuit Amps ratings for both your heat pumps? – ThreePhaseEel May 22 '21 at 01:22

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