Garage is built-need advice on electrical solution

[BRAVOZULU9]

Good evening all,

Apologies if this topic has been discussed many many times but I'm new to the forum and have very little experience with electrical.

My detached garage/guest house structure is now built. It is a new 20x24 wood frame Amish built garage that I intend to split down the middle. 1/2 will be a single-car garage and the other half (long-axis) will eventually serve as a single bedroom and bathroom.

It's located about 160 feet (including turns, bends, etc) from the main panel in the cellar of the primary house.

As I'll be doing the groundwork myself for the sewer and water supply plumbing, I'd like to also bury the electrical cable in the same trench. My intent is to bury the cable/conduit and have an electrician come out later as funds are available to make the connections at both ends with the appropriate sub-panels, etc.

My question is this: what size/type wire and conduit does the forum recommend?

Some considerations for power consumption:

1) the 'guest house' side of the structure will be about 220 sf and will include the standard light fixtures, power receptacles, etc together with a bathroom. I may have a small fridge in there as well. The largest power draw I can think of will be a mini-split type HVAC system. I'm sure some guests will occasionally use a hair dryer but again, nothing major.

2) the 'garage' side will include the standard light fixtures, receptacles, etc but the main power draw will be the occasional use of a 220v air compressor that'll support a blast cabinet that I'll use for small car parts. I don't see the need to runt the HVAC and compressor at the same time as when guests are staying over, I'll likely not be out there bead blasting car parts.

I understand copper to be better than aluminum but beyond that, I'm clueless.

I live in Northern VA and understand the cable must be buried 18" deep. I believe I can run it in the same trench as the sewer line and water supply line so long as it's encased in schedule 40 or better conduit but I'm not absolutely certain on this.

Any suggestions are appreciated!

 

[wyliesdiesels]

well first I gotta ask why you didnt trench in and set the electrical conduit before it was built

but regardless, will there be any dryers, or heating in the garage side?

What is the HP rating on the compressor?

Aluminum feeder wire is fine to use

you will need 4 wires, a subpanel with isolated neutral bus and 2 ground rods.

 

[BRAVOZULU9]

Thanks Wylie. Garage was built about 130 feet behind main home and foundation was dug by hand/shovel so no trencher was rented.


The compressor will be about 5 HP/15 AMP and no, there will be no heaters or dryers installed in the garage. Just the compressor and eventually a small mini-split type HVAC.

well first I gotta ask why you didnt trench in and set the electrical conduit before it was built

but regardless, will there be any dryers, or heating in the garage side?

What is the HP rating on the compressor?

Aluminum feeder wire is fine to use

you will need 4 wires, a subpanel with isolated neutral bus and 2 ground rods.

 

[p_mori7]

#1 Copper to go that distance @ 100A.

You can run it in pipe, or get direct burial Teck Wire (often used in mines).

Dig right up to the exterior foundation or slab, Run it into an elbow then pipe up the side of the building, then enter the building using an LB Box, then right into the panel.

It's not gonna be cheap.

 

[SGKent]

I smell code, and possibly zoning violations if one is not careful here.

 

[ard]

I live in Northern VA and understand the cable must be buried 18" deep. I believe I can run it in the same trench as the sewer line and water supply line so long as it's encased in schedule 40 or better conduit but I'm not absolutely certain on this.

Sewer?
That needs to slope.... what and how are you tying into?

Will this project be inspected? permitted and all?

What code does it need to meet?

Any concerns when you go to sell if it isnt permitted?

I smell code, and possibly zoning violations if one is not careful here.

I smell it too.

 

[tyme2par4]

I would say go with 2-2-2-4 Aluminum MHF wire.
Make sure when you trench you take good photos of the conduit with a tape measure to show the inspector (if you don't get it inspected before hand) as conduit has a minimum burial depth. If you can't prove it's the right depth, they will make you dig it all up.

 

[BRAVOZULU9]

Ard,

Yes, the sewer (3") needs 1/8 run per 12 inches. It'll go from the new structure to the main house, punch through the cellar/foundation wall (with sleeve), and tie-into the main sewer line leave the house toward the street.

Yes, I've already pulled a permit and it will be inspected.

Needs to meet the county code here in Northern VA (Fairfax County), which is the 2015 Virginia Plumbing code.

Sewer?
That needs to slope.... what and how are you tying into?

Will this project be inspected? permitted and all?

What code does it need to meet?

Any concerns when you go to sell if it isnt permitted?





I smell it too.

 

[Norcal]

#1 Copper to go that distance @ 100A.

You can run it in pipe, or get direct burial Teck Wire (often used in mines).

Dig right up to the exterior foundation or slab, Run it into an elbow then pipe up the side of the building, then enter the building using an LB Box, then right into the panel.

It's not gonna be cheap.

Teck is more of a Canadian thing, not common here so would be expensive.

 

[theoldwizard1]

Aluminum cable is much less expensive compared to copper.

MHF cable is rated for direct burial and is very cost effective.

 

[Innovate1]

#1 Copper to go that distance @ 100A.

You can run it in pipe, or get direct burial Teck Wire (often used in mines).

Dig right up to the exterior foundation or slab, Run it into an elbow then pipe up the side of the building, then enter the building using an LB Box, then right into the panel.

It's not gonna be cheap.

In the US (Location of OP)you could do 100A with #3 copper and still be under 3% drop at 240V. Or go to #1 aluminum - much cheaper. At least that's the way I read the tables and what I did with aluminum and AHJ said it was good.

XHHW works well if you are putting it in conduit.

As far as what can be close to what you need to check with AHJ. That seems to vary a lot. Here I think they only are worried about gas and that needs to be at least 2' from electric. They didn't want to see the trenches here which kind of surprised me.

 

[Innovate1]

Sewer?
That needs to slope.... what and how are you tying into?

Will this project be inspected? permitted and all?

What code does it need to meet?

Any concerns when you go to sell if it isnt permitted?





I smell it too.

I noticed both people smelling possible code issues are in California and the OP is in Virginia. Beyond national codes there are likely quite different rules for zoning and other things. I am guessing having a second building on the property with living quarters may be what they noticed... Would help to know what sort of things are thought to be an issue.

 

[Norcal]

3” needs a 1/4” per foot slope, 4” can be 1/8” per foot for drain lines 4” is a better choice anyway, even if it costs more. I mention this despite this being the GJ electrical forum since it was written in another post.

 

[u2slow]

Garage was built about 130 feet behind main home and foundation was dug by hand/shovel so no trencher was rented.


The compressor will be about 5 HP/15 AMP and no, there will be no heaters or dryers installed in the garage. Just the compressor and eventually a small mini-split type HVAC.

5HP would need about 30amp @ 240V. 15A compressors are in the 1-3HP range depending if 120V or 240V.

I agree that copper Teck cable is expensive. An alternative for USA folks may be MC w/PVC jacket (aluminum conductors). I would say this type of cable accounts for 80% of power distribution around here for anything 60amps and greater. Its also real easy to roll out, install, and power up long before you get around to burying things.

 

[wyliesdiesels]

Thanks Wylie. Garage was built about 130 feet behind main home and foundation was dug by hand/shovel so no trencher was rented.


The compressor will be about 5 HP/15 AMP and no, there will be no heaters or dryers installed in the garage. Just the compressor and eventually a small mini-split type HVAC.

5Hp would be over 20a.

15a is about 3HP....

#1 Copper to go that distance @ 100A.

You can run it in pipe, or get direct burial Teck Wire (often used in mines).

Dig right up to the exterior foundation or slab, Run it into an elbow then pipe up the side of the building, then enter the building using an LB Box, then right into the panel.

It's not gonna be cheap.

Thats way overkill, as #3 cu is good for 100a at that distance and yeah wouldnt be cheap at all.

Did you do the VD calcs? #1 cu would give 2.1% VD.

Using #1 AL would give 7.68v @ 100a (would never hit that), which is 3.2% VD.

Try calcing the VD next time instead of just throwing out a number thats "not gonna be cheap."

5HP would need about 30amp @ 240V. 15A compressors are in the 1-3HP range depending if 120V or 240V.

I agree that copper Teck cable is expensive. An alternative for USA folks may be MC w/PVC jacket (aluminum conductors). I would say this type of cable accounts for 80% of power distribution around here for anything 60amps and greater. Its also real easy to roll out, install, and power up long before you get around to burying things.

5HP would actually be closer to 20a. Most 5HP motors I see have an FLA of 21-22a....

 

[BRAVOZULU9]

This is a screenshot from the county site...unless I'm reading it incorrectly, shows 1/8 per foot if I use 3" pipe for sewer drainage.

3” needs a 1/4” per foot slope, 4” can be 1/8” per foot for drain lines 4” is a better choice anyway, even if it costs more. I mention this despite this being the GJ electrical forum since it was written in another post.

 

[BRAVOZULU9]

I'm hoping this comes out more clearly than the other image. In case it doesn't, I'm referencing the county code located here (Table 704.1):

https://codes.iccsafe.org/content/VPC2015/chapter-7-sanitary-drainage#VPC2015_Ch07_Sec703.1

3” needs a 1/4” per foot slope, 4” can be 1/8” per foot for drain lines 4” is a better choice anyway, even if it costs more. I mention this despite this being the GJ electrical forum since it was written in another post.

 

[Roundhouse]

Call and talk to the county inspector that will be inspecting it

I assume you have pulled a homeowners building permit ?

Most building inspectors are nice and are not secretive about what they want to see and what will fail the inspection. They don’t want to be coming back multiple times for re inspections any more than you do.

Make a list of questions before hand and leave room on your list to write down their answers

And just ask em
“Can I put electrical and plumbing in the same trench?”

Etc

 

[Zeke]

W/o getting into code and interpretation thereof, just plan for a 100 amp sub panel on the garage. The best way for you to proceed is to get your sewer and water in place and before you cover up, get the inspector to look at your trench and have what will pass code AFA electrical conduit loosely laid in the trench and let he or she tell you what they will pass. Or direct burial cable.

You say that you will have a qualified electrician do the actual hook up so why not get some bids and tell them as well what your plans are. If you use conduit, leave it empty with a pull string and let the electrical pull the wire. Small part of the job.

Do not ask an inspector for advice. They are a go, no go type of person. If they see a potential code issue, 99% of them will bring it up. Go big on your electrical conduit if you do use it. Put another conduit for data in the trench away from the electrical. 1/2 should handle some Cat5 easy as well as a coax if you want.

This is typical of a trench fill but IDK about your county.
24 inches between gas and electric lines
12 inches between water and electric lines
24 inches between sewer and electric lines
12 inches between communications and electric lines

And usually deeper than 18" but YMMV.

 

[Zeke]

This is a screenshot from the county site...unless I'm reading it incorrectly, shows 1/8 per foot if I use 3" pipe for sewer drainage.

With a bathroom involved and 160' of run, you'll be happier with 4" especially if there are any "bends" as you say. Not that much more expensive. Do you guys use PVC underground or ABS? We use ABS everywhere for DW&V except exposed outdoors. And when is that?

I know this is an electrical forum, but as Norcal says...

If you do have anything like a 45º in that sewer line, put a cleanout wye at the bend. Just bury the plug and mark it.

 

[u2slow]

5Hp would be over 20a.

5HP would actually be closer to 20a. Most 5HP motors I see have an FLA of 21-22a....

I was referring to circuit sizing, but yes.

 

[wyliesdiesels]

I was referring to circuit sizing, but yes.

well that wouldnt be accurate either. A 5HP motor needs 35a rated wire NOT 30a rated wire, like you claimed.

 

[u2slow]

well that wouldnt be accurate either. A 5HP motor needs 35a rated wire NOT 30a rated wire, like you claimed.

My bad... I always forget the NEC wants larger wire than needed.

 

[wyliesdiesels]

My bad... I always forget the NEC wants larger wire than needed.

because of the continuous circuit rules.

Does the NEC oversize wire for continuous load circuits?

 

[yatg]

I am guessing having a second building on the property with living quarters may be what they noticed...

What's wrong with you people? That's an office with a bathroom.

 

[BRAVOZULU9]

What's wrong with you people? That's an office with a bathroom.

hahha...that's precisely how I had to 'word it' to obtain the permit!

 

[ard]

What's wrong with you people? That's an office with a bathroom.

hahha...that's precisely how I had to 'word it' to obtain the permit!

Add a closet to that office and it becomes a bedroom... (with some AHJs)