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Electrician Help: Direct burial wire size from house panel to feed shed 60A sub panel
Posted on 5/14/24 at 1:26 pm
Posted on 5/14/24 at 1:26 pm
I want to run power to my shed from my house. The run is approx. 75' through my attic then down the wall and another 125' underground to the shed panel. Lets say 225' total LF to be safe. I have conduit run in my foundation up my exterior wall and into the attic to route the wire in.
I can do the work but i can't get a good grasp on what wire size, material, and type I need. Reading some stuff, i think 2-2-2-4 Aluminum MFH (Mobile Home Feeder) is what i need but can't confirm. I've also read that both it needs to be in a conduit indoors and it doesn't.
Any assistance or insight would be appreciated.
I can do the work but i can't get a good grasp on what wire size, material, and type I need. Reading some stuff, i think 2-2-2-4 Aluminum MFH (Mobile Home Feeder) is what i need but can't confirm. I've also read that both it needs to be in a conduit indoors and it doesn't.
Any assistance or insight would be appreciated.
6
Posted on 5/14/24 at 1:56 pm to poochie
Southwire Voltage Drop Calculator
This was by far the most confusing part of when I ran power to my shop. When you start mixing indoor, outdoor, and conduit it gets very confusing.
Fortunately, mine was all conduit underground and outside. So I used THHN wire in the conduit and put a junction box to transition to NM-B inside the house. You may need to do something similar when going from inside to outside and UG.
This was by far the most confusing part of when I ran power to my shop. When you start mixing indoor, outdoor, and conduit it gets very confusing.
Fortunately, mine was all conduit underground and outside. So I used THHN wire in the conduit and put a junction box to transition to NM-B inside the house. You may need to do something similar when going from inside to outside and UG.
Posted on 5/14/24 at 2:07 pm to poochie
You can run direct burial cable the whole way. If its suitable for direct bury it will be suitable indoors as well. You don't have to run in conduit but you can if you like. #2 / 3C with ground should suffice whether aluminum or copper. I would use a UF cable.
Posted on 5/14/24 at 2:08 pm to poochie
good luck. I had even different answers from different electricians to a similar deal a few years ago.
I think we ended up burying 4wire 4ga aluminum. May've been mobile home feeder. This was for a 60a panel nearly 100 yards away. The charts said this was too small wire but its what at least one of the electricians said would work.
fyi, its been working fine but also hasn't been tested with a large load like a welder so that might not mean much.
It terminated to a box outside the the home so I can't help on the attic stuff.
I think we ended up burying 4wire 4ga aluminum. May've been mobile home feeder. This was for a 60a panel nearly 100 yards away. The charts said this was too small wire but its what at least one of the electricians said would work.
fyi, its been working fine but also hasn't been tested with a large load like a welder so that might not mean much.
It terminated to a box outside the the home so I can't help on the attic stuff.
Posted on 5/14/24 at 2:38 pm to LSUtigerME
Thanks for the response. I want to run direct burial because, conduit would be cost prohibitive. I assume i can run up the wall in a conduit all the way to a large junction box and transition from the direct burial wire to a wire that can run exposed in my attic to above my panel then drop down through the top plate into the panel.
Posted on 5/14/24 at 8:37 pm to poochie
what size is the breaker that will feed the run to the shed? Are you going to use copper or aluminum? Feeds under 100A will need to be sized according to the NEC 60C rating. It needs to be buried at least 24" deep.
This post was edited on 5/14/24 at 8:42 pm
Posted on 5/14/24 at 9:07 pm to poochie
2224 should be enough for a 100A subpanel, but I’m not an electrician. Don’t forget a ground rod at the subpanel, separate the neutrals and grounds, and a disconnect if it’s a detached building.
Posted on 5/15/24 at 9:17 am to AyyyBaw
quote:
2224 should be enough for a 100A subpanel, but I’m not an electrician. Don’t forget a ground rod at the subpanel, separate the neutrals and grounds, and a disconnect if it’s a detached building.
Installing a ground rod at the subpanel could be more complicated. If that is done, you typically dont want to run a ground from the main panel. you'd just run 2 hots and a neutral. Then you'd need to do a neutral-ground bond at the sub-panel and have that ground-rod bonded to the ground bus in the sub panel.
If you run the ground from the main panel to the sub-panel, you dont need the ground rod and you dont do another neutral-ground bond. Both ways are acceptable.
This post was edited on 5/15/24 at 9:18 am
Posted on 5/15/24 at 9:23 am to notsince98
quote:thats what i did
If you run the ground from the main panel to the sub-panel, you dont need the ground rod and you dont do another neutral-ground bond
Posted on 5/15/24 at 9:30 am to notsince98
quote:
what size is the breaker that will feed the run to the shed? Are you going to use copper or aluminum? Feeds under 100A will need to be sized according to the NEC 60C rating. It needs to be buried at least 24" deep.
I will use whatever size breaker is adequate. I do plan on running the cable at least that deep and also plan on using aluminum.
Posted on 5/15/24 at 10:27 am to poochie
Ok, so using the following:
- 60A breaker at main panel
- 225' conductor length
- AL conductors
- Direct Buried
You now have to try and guess how much current will actually be drawn by equipment on the subpanel. Here are some limits based on a starting allowable conductor size of #6 AWG and allowing a 3% voltage drop from the main panel to the sub panel:
- #6 AWG & 11A load = 2.95% voltage drop
- #4 AWG & 18A load = 3.09% voltage drop
- #3 AWG & 22A load = 3.06% voltage drop
- #1 AWG & 33A load = 3% voltage drop
- #1/0 AWG & 38A load = 2.97% voltage drop
- #2/0 AWG & 50A load = 3.05% voltage drop
You probably wouldn't want load a 60A breaker more than 48A. If you get an idea of your largest equipment loads and you know you wont run them all at the same time, you can probably get by with smaller conductors. I dont know what kind of equipment you'll have but at the very least I'd probably go with #3 AWG if you only have 20A breakers in the sub-panel. If you end up with something like a 40A breaker in the sub-panel, i'd probably go with #1/0 to be safe.
The NEC recommends no more than a 5% voltage drop. By assuming 3% for this calculation, you have 2% voltage drop available from your sub panel to the end devices. There will be voltage drop in the branch circuit wiring and extension cords.
- 60A breaker at main panel
- 225' conductor length
- AL conductors
- Direct Buried
You now have to try and guess how much current will actually be drawn by equipment on the subpanel. Here are some limits based on a starting allowable conductor size of #6 AWG and allowing a 3% voltage drop from the main panel to the sub panel:
- #6 AWG & 11A load = 2.95% voltage drop
- #4 AWG & 18A load = 3.09% voltage drop
- #3 AWG & 22A load = 3.06% voltage drop
- #1 AWG & 33A load = 3% voltage drop
- #1/0 AWG & 38A load = 2.97% voltage drop
- #2/0 AWG & 50A load = 3.05% voltage drop
You probably wouldn't want load a 60A breaker more than 48A. If you get an idea of your largest equipment loads and you know you wont run them all at the same time, you can probably get by with smaller conductors. I dont know what kind of equipment you'll have but at the very least I'd probably go with #3 AWG if you only have 20A breakers in the sub-panel. If you end up with something like a 40A breaker in the sub-panel, i'd probably go with #1/0 to be safe.
The NEC recommends no more than a 5% voltage drop. By assuming 3% for this calculation, you have 2% voltage drop available from your sub panel to the end devices. There will be voltage drop in the branch circuit wiring and extension cords.
Posted on 5/15/24 at 10:52 am to notsince98
this is a small garden shed. the max equipment I'd be using would be a 10" table saw, a well pump, or a small welder for misc. home welding. All 120v. I also have a small pancake air compressor in there. I can't see anything more than that in this area. So assume one of those things with general lighting, maybe some battery chargers plugged in at all times.
Posted on 5/15/24 at 10:59 am to poochie
i assume everything just plugs in to a standard receptacle?
If so, then none of that would have more than about 12A full load. You'd just need to consider what "could" be running at the same time. I'd guess the pump/saw/compressor/lights or pump/welder/compressor/lights would be worst case.
If so, then none of that would have more than about 12A full load. You'd just need to consider what "could" be running at the same time. I'd guess the pump/saw/compressor/lights or pump/welder/compressor/lights would be worst case.
This post was edited on 5/15/24 at 11:00 am
Posted on 5/15/24 at 11:00 am to notsince98
You can separate those three. The pump is just to fill so not constant running.
Yes, all are 120v.
Yes, all are 120v.
This post was edited on 5/15/24 at 11:01 am
Posted on 5/16/24 at 3:16 am to poochie
I'm no electrical expert, but one thing I know is pulling UF cable through conduit is a BITCH
Posted on 5/16/24 at 8:57 am to indytiger
quote:
I'm no electrical expert, but one thing I know is pulling UF cable through conduit is a BITCH
Makes sense. I think UF is designed primarily for direct bury. If you do conduit, you would want to use a standard wet rated conductor like XHHW-2 or THWN-2.
Posted on 5/16/24 at 5:13 pm to poochie
The conduit will be the least cost prohibitive part of this project. You will wish you had a conduit. Next time you are poking around the backyard with a shovel.
Posted on 5/16/24 at 5:43 pm to whatshisface
quote:
he conduit will be the least cost prohibitive part of this project.
someone hasn't bought pvc products since covid
But I do get your point. I would bury atleast 24". 30" is better. Not many holes dug that deep even with a posthole digger.
Posted on 5/16/24 at 6:49 pm to notsince98
quote:
Makes sense. I think UF is designed primarily for direct bury. If you do conduit, you would want to use a standard wet rated conductor like XHHW-2 or THWN-2.
The OP said he'd be running UF underground, but then running it up his walls in conduit, which I was trying to warn him wouldn't be very easy.
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