Hi,
I’ve been a carpenter/contractor most of my 50 years, but I’m working in a new realm right now and need the advice of an electrician or someone in the know.
I’m overseeing the construction of an indoor horticultural room for a friend who needs to grow med marijuana for health reasons. They are licensed w/ the state, so this is completely legal, the job is/will be permited, inspected, etc, etc.
I have looked at 4 bids for the elec subcontracting and the is a portion of the elec that two of the four electricians disagree on.
Elec is a major portion of this project because of the high wattage of the high pressure sodium (HPS) lights, the metal halide (MH) lights and the ventilation system. The design for ventalating/cooling the extremely hot lights is to bring cool air from beneath the house, filter it, use the it to cool the lights & exhaust it back into the heating system of the house to capture some of the heat generated by the lights.
The contractors all agree that a sub-panel service should be installed. The disagreement comes on the subject of a installing or not installing a grounding rod.
Two of the electricians say to bring a ground wire from the main service, while the other two electricians recommend also adding a new ground rod under the house, through one of air intake sources for the ventilation system which will be cut in the floor.
One of the two electricians recommending this new grounding rod suggest that it be installed in addition to a ground wire from the sub-panel to the main service. The other electrician says the ground wire back to the main service panel would be un-needed if the new ground rod is installed.
I’m looking for opinions whether the new grounding rod should be installed, and if it is, does the ground wire back to the main service panel become unneeded?
Thanks, in advance, for your advice.
GeoD
Replies
Its four wire to main on subpanels, always. if the bldg is not touching main building with a metal path, then adding a ground rod is needed, but still 4 wires to main box
If this is attached/within the main building then it is 4 wire system (ground back to the main pannel). No extra ground is needed.
If this is a detached outbuilding with NO OTHER METALIC paths to the main building then it can be treated the same as a entrance service pannel; 3 wires and local grounding.
Otherwise it uses a 4 wire system, but still requires a local ground.
I agree that another ground rod is not required.
That said another grounding electrode conductor off the subpanel, #6 solid, and another ground rod wouldn't hurt, might potentially help save any electronics being used to control this grow room and is a relatively inexpensive proposition. I can't see it running more than $20 in parts, assuming a health mark up and another $10 to $20 in labor. Prices may vary depending on where they are and what the cost of living is.
I would go ahead and install it. Most of these, I assume a reasonably short and direct path, can be put in in under 15 minutes while the help cleans up. If it gets too involved, time and material wise, the balance might swing the other way and cause me to go with the code minimum.
What Bill says is the truth. If either electrician doesn't understand these rules then don't use him.
If the job is going to be inspected, ask the inspector what he wants to see.
To paraphrase; "What grounds lie in the hearts of buildings? The Inspector knows."
SamT
Ground rods have too much resistance. Run a solid #8 wire and clamp it to the 20' piece of rebar in the bottom of your footing (if you didn't pour the footings yet).