Cruzan80
Well-known member
After much research, I think I have figured out what I need to do for running a subpanel into my garage. But, since I am not as experienced as some on here, figured I would turn to the group for final confirmation and suggestions. Tried to bold what I think is the most relevant information. The garage is a detached structure, located about 75ft away from the house in Colorado. I am looking to add a 100a subpanel, and my main box is 200a. The main feeder is located on the exterior of my house, and I will be putting EMT conduit down from there, buried 24” in the ground from the house to the garage, and then back up the exterior of the garage, and finally thru the wall to an interior mounted subpanel. I had the main panel replaced by a licensed electrician when we moved in under a year ago, and it only has a single grounding rod.
I am going to be having the following circuits installed:
30A 240V for an electric heater (hardwired), 30A 240V for an air compressor motor (hardwired), 20A 240V for an EV charger (mine is a hybrid with an extended battery pack, can’t take advantage of higher amp chargers)(plug-in), 20A 240V for machinery (plug-in), two 20A 120V for machinery (plug-in), a 15A 120V for garage lighting and the garage opener (mix of hardwire and plug-in). At the end, I am also asking for advice on a three way circuit and how to handle it in this situation.
Questions:
Type of Cable (THWN/XHHV): I am trying to figure out if it would be better to run THHN/THWN or XHHV between the main panel and the subpanel. Looking around, I have found a place where the difference between THWN and XHHV is under 5 cents more for the same gauge. From reading about the differences, I think XHHV would pull easier, and be more resistant long term. However, at the gauge I am using, XHHV only comes in black and green sheathing. Can someone confirm I can tape each end of the second hot red and neutral white to designate which is which? From my reading, it seems like if the wires are over #6ga, you are allowed to re-mark the ends for hots and neutrals (but not grounds).
Wire Gauge: Looking at ampacity charts, I see that I can go with #3 copper (never worked with AL) for the hot wires. I have read that I can downsize the neutral to a #4, since I have at least half of the circuits as 240V without using a neutral (I don’t need 120/240 on any of those circuits). I also understand that I can use #8 as a ground up to 100A service. So therefore I am thinking 3-3-4-8 (B-R-W-G) is correct. Suggestions?
Conduit Size: If I am going to be going with 3-3-4-8, I think I will need to be using at least 1.25” EMT, as 1” EMT is rated for no more than 3x #3ga wires. Since a #4 and a #8 added together (diameter-wise) exceed a #3, it would not allow 1” correct? Is it worth it to go up to 1.5” EMT? There will be two 90deg sweeps and a hard 90deg elbow to go inside the building, right into the panel.
Grounding Rod: Since the main panel was swapped out last year by certified electricians (former panel was a Zinsco, and we swapped it out within a week of moving in), and there is only one grounding rod (due to only seeing one copper wire coming down to a clamp, and one small pole sticking up), am I then ok following this for the grounding rod at the subpanel? Or do I need to add two rods? I have also read it is better to err on the side of caution and get a 10ft ground rod if I am going to leave a bit exposed to clamp onto, rather than an 8ft, as NEC calls for <=8ft of rod to be touching the dirt.
Load Calculation: Rather than do a traditional load calculation, I figured with me being a one-man shop, I added up the potential draws I could have at one time max (heater, compressor, car charging, 240V tool and lights) to decide on a 100A subpanel. As none of these actually draw full capacity of the breaker (heater is actually 23A, most of my 240V tools are <10A, etc), I do not think I will be exceeding the overall capacity by accident.
GFCI: Because I know a garage is a wet location, where/when do I need GFCI protection? Do I simply use a GFCI breaker at the main board, protecting everything downstream, use GFCI breakers in the subpanel or some other solution? I know I can get GFCI outlets easily for the 120V lines, but not sure for any 240V line (especially when it is hardwired).
Two circuits on duplex outlets: I am planning on running two 120V lines to all of the outlets I am putting in, having the top outlets be on one circuit and the bottoms on another. My plan is to pull 12/2 NM-b to each, and then break off the connecting hot tabs. Do I just wirenut the neutral for the top together and same for the bottom? Is it better to pigtail the ground and have three #12 into a wire nut, rather than 2 #12 under a grounding nut on the outlet?
Circuit/Spaces: Adding up what I currently see myself wiring, I come up with 11 or 12 spaces (see below for the 12th) occupied. I do want to leave a few empty spaces in case I need to add anything later. Looking around, I see that most boxes are offered in either a 12 or 20 space configuration. Is this standard, or are their sizes in between (16 space, for example)?
Bonus Extra Credit Question: WTF do I do here?
Exterior Light: Here is where it gets interesting. Right now, there is an exterior light mounted on the garage, facing the house and driveway. Currently, it is on a three way switch, with a switch inside the house and one inside the garage. From my understanding, I would need to move the circuit this is on to the subpanel, as otherwise there is a possibility of a live wire inside the detached building, even when turning off the subpanel (the exterior light is currently supplied by the main). My wife still wants this light to be able to be controlled by a switch inside the house, but doesn’t care if there is a switch inside the garage. Currently, it is powered by a direct-buried line from the house to the garage. I see myself having a couple of options. One option is to remove all wire from this circuit from the garage, and run conduit up the outside of the garage to the light. Therefore, by having it exit the ground outside the detached structure, and never enter the detached structure, it would not be subject to the subpanel. Or do circuits in conduits attached to a building still need to be supplied by the panel in that building? Second option, I move the circuit to the subpanel, route the interior garage wiring to the relevant switch and light (easy) but how do I get the access back to the house? Do I use the existing buried cable, and follow the wiring back to the switch, disconnecting it from the main feeder? Or do I need to pull a second set of cables through a second conduit back to the house? From my understanding, I can’t have the cables feeding a subpanel in the same conduit as a subpanel circuit running to a switch, correct? If I use a second conduit, I still would not be able to access that conduit for any other low-voltage circuits such as telephone or Ethernet, correct? That would require a third conduit.
I am going to be having the following circuits installed:
30A 240V for an electric heater (hardwired), 30A 240V for an air compressor motor (hardwired), 20A 240V for an EV charger (mine is a hybrid with an extended battery pack, can’t take advantage of higher amp chargers)(plug-in), 20A 240V for machinery (plug-in), two 20A 120V for machinery (plug-in), a 15A 120V for garage lighting and the garage opener (mix of hardwire and plug-in). At the end, I am also asking for advice on a three way circuit and how to handle it in this situation.
Questions:
Type of Cable (THWN/XHHV): I am trying to figure out if it would be better to run THHN/THWN or XHHV between the main panel and the subpanel. Looking around, I have found a place where the difference between THWN and XHHV is under 5 cents more for the same gauge. From reading about the differences, I think XHHV would pull easier, and be more resistant long term. However, at the gauge I am using, XHHV only comes in black and green sheathing. Can someone confirm I can tape each end of the second hot red and neutral white to designate which is which? From my reading, it seems like if the wires are over #6ga, you are allowed to re-mark the ends for hots and neutrals (but not grounds).
Wire Gauge: Looking at ampacity charts, I see that I can go with #3 copper (never worked with AL) for the hot wires. I have read that I can downsize the neutral to a #4, since I have at least half of the circuits as 240V without using a neutral (I don’t need 120/240 on any of those circuits). I also understand that I can use #8 as a ground up to 100A service. So therefore I am thinking 3-3-4-8 (B-R-W-G) is correct. Suggestions?
Conduit Size: If I am going to be going with 3-3-4-8, I think I will need to be using at least 1.25” EMT, as 1” EMT is rated for no more than 3x #3ga wires. Since a #4 and a #8 added together (diameter-wise) exceed a #3, it would not allow 1” correct? Is it worth it to go up to 1.5” EMT? There will be two 90deg sweeps and a hard 90deg elbow to go inside the building, right into the panel.
Grounding Rod: Since the main panel was swapped out last year by certified electricians (former panel was a Zinsco, and we swapped it out within a week of moving in), and there is only one grounding rod (due to only seeing one copper wire coming down to a clamp, and one small pole sticking up), am I then ok following this for the grounding rod at the subpanel? Or do I need to add two rods? I have also read it is better to err on the side of caution and get a 10ft ground rod if I am going to leave a bit exposed to clamp onto, rather than an 8ft, as NEC calls for <=8ft of rod to be touching the dirt.
Load Calculation: Rather than do a traditional load calculation, I figured with me being a one-man shop, I added up the potential draws I could have at one time max (heater, compressor, car charging, 240V tool and lights) to decide on a 100A subpanel. As none of these actually draw full capacity of the breaker (heater is actually 23A, most of my 240V tools are <10A, etc), I do not think I will be exceeding the overall capacity by accident.
GFCI: Because I know a garage is a wet location, where/when do I need GFCI protection? Do I simply use a GFCI breaker at the main board, protecting everything downstream, use GFCI breakers in the subpanel or some other solution? I know I can get GFCI outlets easily for the 120V lines, but not sure for any 240V line (especially when it is hardwired).
Two circuits on duplex outlets: I am planning on running two 120V lines to all of the outlets I am putting in, having the top outlets be on one circuit and the bottoms on another. My plan is to pull 12/2 NM-b to each, and then break off the connecting hot tabs. Do I just wirenut the neutral for the top together and same for the bottom? Is it better to pigtail the ground and have three #12 into a wire nut, rather than 2 #12 under a grounding nut on the outlet?
Circuit/Spaces: Adding up what I currently see myself wiring, I come up with 11 or 12 spaces (see below for the 12th) occupied. I do want to leave a few empty spaces in case I need to add anything later. Looking around, I see that most boxes are offered in either a 12 or 20 space configuration. Is this standard, or are their sizes in between (16 space, for example)?
Bonus Extra Credit Question: WTF do I do here?
Exterior Light: Here is where it gets interesting. Right now, there is an exterior light mounted on the garage, facing the house and driveway. Currently, it is on a three way switch, with a switch inside the house and one inside the garage. From my understanding, I would need to move the circuit this is on to the subpanel, as otherwise there is a possibility of a live wire inside the detached building, even when turning off the subpanel (the exterior light is currently supplied by the main). My wife still wants this light to be able to be controlled by a switch inside the house, but doesn’t care if there is a switch inside the garage. Currently, it is powered by a direct-buried line from the house to the garage. I see myself having a couple of options. One option is to remove all wire from this circuit from the garage, and run conduit up the outside of the garage to the light. Therefore, by having it exit the ground outside the detached structure, and never enter the detached structure, it would not be subject to the subpanel. Or do circuits in conduits attached to a building still need to be supplied by the panel in that building? Second option, I move the circuit to the subpanel, route the interior garage wiring to the relevant switch and light (easy) but how do I get the access back to the house? Do I use the existing buried cable, and follow the wiring back to the switch, disconnecting it from the main feeder? Or do I need to pull a second set of cables through a second conduit back to the house? From my understanding, I can’t have the cables feeding a subpanel in the same conduit as a subpanel circuit running to a switch, correct? If I use a second conduit, I still would not be able to access that conduit for any other low-voltage circuits such as telephone or Ethernet, correct? That would require a third conduit.