Underground Conduit Rules

[John McKissick]

Shortest path for new conduit is through the wall in front of the house to get to a distribution panel in the garage. Is there a way, per code, to come through the poured concrete underground then maybe 60 feet to garage? I have access inside the basement to drill hole right next to main panel on basement front wall.

Trying to avoid the visible conduit on the front of the house.

Option 2 is maybe 2x or more total the distance coming out the back of the house traditionally (about 30 feet) then a longer run underground.

In planning stages. Thinking 100 amp for now.

[Rod Sheridan]

Sure you can go through the foundation and underground to the garage.

You’ll have to follow local regulations for depth of burial...Rod

[Bruce Wrenn]

Water coming in around conduit? This could be a problem. Be sure to grout hole with hydraulic cement, not mortar mix. Grout from outside,not inside. If foundation is poured concrete, you could pack hole with lead wood and a use caulking iron to compress it.

[Charlie Velasquez]

Mmmm... Don’t have my code book with me.
But...
Because of its corrosive nature, any conduit in contact with concrete must be rated for concrete. PVC qualifies, but not all metal conduit does.
Article 300.5(something) talks about protection from earth movement. Coming directly from the foundation wall to the soil means any frost heave from the soil in Massachusetts would be a shear force wrt to your conduit and your conductors. Don’t know what your frost line is there. Coming out above grade, then going down allows for an expansion fitting to accommodate that.

Any underground conduit is a wet location. Temperature differences between the endpoints and length of the conduits will set up convection currents throughout the run. Moisture from the air outside the conduit will constantly migrate through the conduit. Anytime the temperature of the conduit 18” underground is lower than the dew point of the air outside the conduit that moisture will condense and slowly fill the conduit. If the conduit in your basement is the lowest spot...

How does your service entrance enter your house?

[Jim Becker]

Yes, you can do what you want to do. It has to be at code compliant depth as has been noted and you'll want/need to seal the penetration through the foundation with hydraulic cement, also as noted. You'll want to trench to proper depth, use appropriate sized PVC conduit for the intended pull and make sure there is a trace wire in the trench above the conduit so it can be located in the future. If you can get your pull tape in the conduit while you are assembling it, it will save time and effort when you do the pull of the actual conductors and ground.

[Ian Lerew]

PVC conduit needs to be buried 18”. You could come through just above grade and use an LB to turn the pipe down. You won’t have to worry about water this way and there won’t be much visible. Or you can come through below grade but like Bruce said make sure you seal it well. Hydraulic cement will work or closed cell spray foam.

[John McKissick]

Thanks all for your input and advice. Sounding a bit more complex and an error could have me mopping up water.

Plan B might be a strategically placed bush or just go the longer way.

[Robert Engel]

Is there such a thing as conduitaphobia?

[John McKissick]

Is there such a thing as conduitaphobia?

Technically hydrophobia, fear of water...lol

[Jim Becker]

Thanks all for your input and advice. Sounding a bit more complex and an error could have me mopping up water.

Plan B might be a strategically placed bush or just go the longer way.

It's not difficult to do what you want to do. You just need to follow the steps carefully at the house end of the connection when it's below grade. Hydraulic cement is simple and easy to use and it cures fast, too. But coming up above grade and going through the foundation with a pull box on the wall is "less risky" for water penetration for sure. And you can paint the exposed conduite to match the foundation. It will be barely visible by itself and probably would disappear entirely with some landscaping planning. The requirements for the trench remain the same either way.

[Julie Moriarty]

Shortest path for new conduit is through the wall in front of the house to get to a distribution panel in the garage. Is there a way, per code, to come through the poured concrete underground then maybe 60 feet to garage? I have access inside the basement to drill hole right next to main panel on basement front wall.

Trying to avoid the visible conduit on the front of the house.

Option 2 is maybe 2x or more total the distance coming out the back of the house traditionally (about 30 feet) then a longer run underground.

In planning stages. Thinking 100 amp for now.

Every installation I've ever done, that runs conduit from the house down into the ground, exits the house above the foundation wall. I've been on service calls where someone drilled through the foundation below grade and the called us to stop the water leaks.

One homeowner didn't want an exposed electrical fitting so I suggested he use Waterplug to see if that stops the leak. I was back a few weeks later changing the conduit run to exit the house above the foundation.

On commercial jobs I've worked, where they had to go through the foundation, there's always some feature there to channel the leaks when they happen. Or they just rely on maintenance crews to monitor it.

[John McKissick]

Thanks for your real world experience. The others have suitable "askeered" me away from underground penetration but I am so glad I asked and for the advice here

[Charlie Velasquez]

You didn’t mention how your service enters the house. If it is through a meter pedestal check the model # and look up the specs. Some allow for a secondary feeder to share the space. Most don’t but it is worth checking. If so, you may be able to exit above grade into the space of the pedestal, then branch off into its own trench after going down.

[John McKissick]

You didn’t mention how your service enters the house. If it is through a meter pedestal check the model # and look up the specs. Some allow for a secondary feeder to share the space. Most don’t but it is worth checking. If so, you may be able to exit above grade into the space of the pedestal, then branch off into its own trench after going down.

The service is a bit untraditional. Technically a condo with meter/mains on front of house on neighbors side. Transformer 200 feet away with underground cable feeding both meters above grade. My line comes in through wall into their basement and routes into mine inside to my panel with no main breaker in it. Breaker is outside with meter.

Wife is warming up to exposed conduit coming through the wood/siding with a pullbox then going gopher-mode underground to garage/shop.

[Wayne Cannon]

I don't know the scope of the requirement, but here the contractor poured several inches of gravel in the trench atop the PVC conduit plus a colored ribbon so future backhoe operator gets some warning before cutting into the conduit.

[Bill Dufour]

While the tench is open...back fill 6" or so then throw in two or more 3/4 conduit runs, another 6" of back fill then the marker tape or old iron pipe etc, then fill to the top. The extra conduit can just be capped at both ends underground and left unconnected for future use.
Bill D

[Bruce King]

You need an underground rated cable even though it’s in conduit.
3 conductor plus ground. Be sure to run large conduit, looks like 1.5 inch will work if you are going with 100 amp. This cable is about one inch diameter.
https://www.wireandcableyourway.com/2-2-2-4-dyke-underground-secondary-distribution-cable.html?utm_source=google-shopping&utm_medium=organic&gclid=CjwKCAiA_Kz-BRAJEiwAhJNY70Wvxj5OCI3_CigEnmskmAzSXVGhTJHsZE3GIf YtbN1NiIwBiSUOnBoCtTgQAvD_BwE

[Bill Dufour]

I do not think the cable has to be rated for underground just for water?
Bill D.

[Jim Becker]

I do not think the cable has to be rated for underground just for water?
Bill D.

The cable through the underground conduit must be rated for outdoor/underground/direct-burial. The conduit provides a level of physical protection but is considered a "wet" environment. I could be wrong, but I don't believe there's a multiple cable types for this application.

[Charlie Velasquez]

The cable through the underground conduit must be rated for outdoor/underground/direct-burial. The conduit provides a level of physical protection but is considered a "wet" environment. I could be wrong, but I don't believe there's a multiple cable types for this application.

Mobile Home Feeder is considered an assembly. I used mhf 2-2-2-4 aluminum to run my panel. If used as a service to run your dwelling it is rated at 100 amps. If used as a feeder it is rated at only 90 amps. Check with your local AHJ ahead of time. Many will sign off on its use as a 100amp feeder, mine did.

Clarification: #2 aluminum is always rated at 90 amps. It is allowed for 100 amp service if it is a dwelling service.
If you decide to go this route instead of copper thwn, get the AHJ to sign off, or ask via email and print the approval, keeping it with your permit.
If not, in a residential shop, probably not much difference between 90 and 100 amps. You may need to special order the 90 amp breaker.

[Doug Dawson]

While the tench is open...back fill 6" or so then throw in two or more 3/4 conduit runs, another 6" of back fill then the marker tape or old iron pipe etc, then fill to the top. The extra conduit can just be capped at both ends underground and left unconnected for future use.
Bill D

Or to give the trench digger a good harmless scare. :^)

[Charlie Velasquez]

While the tench is open...back fill 6" or so then throw in two or more 3/4 conduit runs, another 6" of back fill then the marker tape or old iron pipe etc, then fill to the top. The extra conduit can just be capped at both ends underground and left unconnected for future use.
Bill D
I would suggest a 3/4” spare and a 1” or larger.
The most likely upgrades are a/v, internet which can be handled by the 3/4” conduit; and 4 #6awg for a generator inlet to feed your main panel which can be handled by the 1” (assuming a 9600 watt to 12000 watt portable generator). The communication conduit does not need to be at the 18” depth, but the possible generator inlet does.

While 1 1/4” conduit meets code for a 100 amp pull, I would upsize it. Not sure how many turns you have, but it’s a lot easier with oversized conduit.
Even if you go with 1 1/4” conduit, if you have a number of turns consider upsizing your LB or pulling elbows. NEC says you cannot use a conduit body smaller than the size of your conduit, but you can use one bigger to help with the pull.
Plan your pull. Make sure all the bells are going in the direction of the pull.

[james manutes]

Years ago , I was in a condo . Soon as you added that , alarms went off in my mind . Do you have an HOA , or a "board" to answer to ? It can be worse than local code and building hoops to jump thru . Condo's suck !

[Bill Dufour]

I believe in conduit you can have only four turns before you have to add a box for a pull point. That would be one at each underground end and maybe one at each end into the wall or side of a external panel.

[Charlie Velasquez]

I believe in conduit you can have only four urns before you ahve to add a box for a pull point. That would be one at each underground end and maybe one at each end into the wall or side of a external panel.

Kinda, no more than 360° of bends.
So LB’s at the entry points, short stub, expansion fitting, stub to trench depth, then no more than 360° of bends underground. You need 90° at each end to make the vertical/horizontal change, so you’re limited to 180° in your run before you would have to add another conduit body.

The cable Bruce linked to is commonly called URD. It is rated for direct burial. If you have a number of underground turns you could forego the underground conduit and just lay it in the trench after stubbing it to your trench. (edit: you may have to go deeper than 18” if direct burial. If you’re paying someone to do the trenching, probably not an issue.). But URD is not rated for indoors and must transition to indoor rated conductors immediately, usually to SER (some ahj’s interpret that to mean “immediately” others allow a few feet; check with your local ahj). transitioning to SER allows you to run the cable following the rules for regular nm-b (romex)

I used MHF. Like URD, it is also rated for direct burial, but it is allowed indoors if enclosed in conduit. It saves on large junction boxes and connectors, probably split-bolt or morris; but you have to run conduit to your panels.