Schedule 40 vs. Schedule 80 PVC conduit underground 6

[bdn2004]

I'm upgrading the service to my house. I intend to put it in underground. The Utility requires schedule 80 PVC pipe that is exposed near the meter base and at the service pole.

There is about a 75 feet from the pole to the house where the new service entrance will run. The Utility told me to run a conduit underground. This section where I intend to put it screams for some landscaping that either I or the next owner will surely put in. I can see rototillers, spade shovels, etc directly over this conduit and cable.

I just wonder for safety's sake would it be better to install Schedule 80 the whole way, encase schedule 40 in concrete, and if I did encase it, or dig it down deeper...is schedule 40 good enough?

 

[dpc]

Using Schedule 80 for a residential service seems like serious overkill. We use Schedule 80 for exposed indoor and outdoor industrial application where we can't use rigid steel.

If you encase it, then Sched 40 is surely good enough.

Also, when using Sched 80, make sure you use the correct conduit fill calculation, since the ID is reduced compared with Schedule 40.





David Castor

http://www.cvoes.com

 

[IRstuff]

Another problem for residential service, I think, is moisture intrusion. This requires adequate sealing from the above ground access points, and a sufficiently robust conduit that can tolerate earth movement without breaking, and can tolerate plant root movement/penetration.

I don't know whether schedule 40 is adequate, but I would think the extra thickness from schedule 80 would be worth the investment.

TTFN

FAQ731-376

 

[davidbeach]

Moisture intrusion is a moot point. Everything below grade is assumed by code to be full of water, and the water won't cause any harm. I'm surprised it wouldn't just be direct bury between the elbow at the bottom of the pole and the elbow at the bottom of the meter riser. Put a warning tape in the trench about 12" above the cable and another one about 6" below finish grade.

 

[TurbineGen]

Most installations I have seen are just direct bury cable and not fully encased in conduit. Do you really forsee equipment penetrating 24" into the ground? If so, do you think it will be significant enought to do damage? A rototiller isn't likely going to destroy sch40 buried in the ground. A spade shovel will certainly not penetrate it unless you are driving it in with a sledge hammer.

There is certainly nothing wrong with the schedule 80 if you take dpc's suggestion and account for the reduced internal diameter, but I'd probably run sch40. I never liked the idea of direct bury cable when placing it in conduit isn't difficult.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[stevenal]

You can always go deeper than the utility requires. And possibly your landscaping might decrease the final depth. Anyone doing any type of excavation is typically responsible for the damage they do, and utilities will generally respond fairly quickly to requests for locating their facilities.

PVC is brittle, and can and will be damaged by rototillers and spades. That's why the sch 80 is required at the risers; a little better for fending off lawn mowers and trimmers that might contact it.

 

[bdn2004]

Since we are digging our own trench the Utility asked me to put it in conduit. They said they would hook it up for nothing if we did it...so whatever they say goes.

There is no problem going from Sched 80 to Sched 40 right?
This is a 200A service. The extra fill requirements for the Sched 80 must be why they asked it to be 2-1/2" instead of 2".

 

[TurbineGen]

The external diameter is constant and therefore you can connect a schedule 80 and a schedule 40 together. I would absolutely use schedule 80 at the risers. I would also recommend having a little extra room inside the conduit for future use incase you wanted to increase the ampacity of the panel or add a shed or garage later on. That's a great reason to use conduit. You can always pull wires without digging the yard back up.

One last thing; be mindful of your jam ratio if you are pulling 3 wires at once.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[IRstuff]

The main thing is to protect against roots and other burrowing things. Once you have the conduit in place, the street access opening needs to be well sealed, particularly if your house access is at a lower elevation; you could be looking at nice water source running into your garage or whatever in the next rain storm.

While others may pooh-pooh this, my coworker had that exact thing happen to him, and this is a million-dollar home, to boot.

TTFN

FAQ731-376

 

[davidbeach]

While others may pooh-pooh this, my coworker had that exact thing happen to him, and this is a million-dollar home, to boot.

There is no limit on the cost of bad design.

 

[IRstuff]

Part of that is also unintended consequences, a confluence of several bad things happening:
> bad sealing on the conduit
> citywide storm drain debris prevention
> big rainstorm that overflowed the storm drains

The second one is the most annoying. Why bother having storm drains if you're going to prevent rainwater from getting to them?

TTFN

FAQ731-376

 

[davidbeach]

I think my point was missed. It needs to be part of the design that water in conduits can not flow to somewhere that it can do harm. The water is a given. The damage is optional.

 

[bdn2004]

IRstuff,

Are you saying that water seeps into the conduit and into the meter base even if the meter base is 5' above grade?

 

[IRstuff]

No, it was just an unfortunate happenstance of geometry that the inlet to the conduit was at a higher elevation than the outlet in the house. When the sealing on the inlet was compromised AND there happened to be issues with stormwater drainage on the street, the water went into the conduit into the garage of the house and flooded it. In a perfect world, that sort of thing wouldn't happen, of course.

Likewise, there wouldn't be burrowing animals and tree roots that do other sorts of damage...

TTFN

FAQ731-376

 

[Electic]

It is standard in many jurisdictions to install Schedule 40 below grade and Schedule 80 for the accessible lower part of the riser. The Schedule 80 is to protect the installation from vehicles or equipment.

Water can enter the conduit albeit very minor amount of water unless the conduit is connected to a vault that happens to collect water from a parking lot or something like that. If there is a chance that water will enter this conduit from a vault or utility connection to a vault than the standard installion would include a 30" x 30" handhole with drain near the service entrance riser, with conduit broken (not continuous) at the handhole. The handhole will prevent hydrostatic pressure build up.

This sounds unlikely but I have witnesses a large hotel service entrance that was flowing water like a waterfall down the finished interior walls because the CT enclosure was well below the utility vault several hundred feet, away that was collecting water. As a utility concerned with liability, we dug down to the LV conduit and chopped a hole into the conduit while the service remained energized. Water 'geysered' up about 10' from the conduit: it is possible to build up substantial flow and head in a large interconnected conduit system.

 

[BigInch]

If you had no objection to direct bury UG cable, is there any reason for not using direct bury cable w/o conduit and with a thin red concrete slop in the backfill about 1 foot above the cable?

**********************
"Being GREEN isn't easy" ..Kermit

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[bdn2004]

Electic,

When you say a vault are you talking like a manhole? And how does water get it to them if they are all sealed PVC conduits coming into them? Matter of fact I don't really understand get how water is getting into any of the conduits underground. It certainly doesn't get into the plumbing system does it?...so why the electrical?

BigInch, the Utility came out and told us to put it in conduit and run it to their service pole and they would do the job freebie....so actually I don't have a lot of choice. And as others have described here, there are some additional benefits to running conduit - easy replacement, added protection. And when conduit is less than $100 for the whole job, I think its worth it.

 

[TurbineGen]

A plumbing system is a closed and pressurized system. Unless you have an external pressure greater than the internal pressure and a broken point, then the outside water will not enter the pipe.

Electrical conduit is a completely different animal. It has no internal pressure and it is open on both ends. Water will therefore find its way in. Sometimes it happens quickly, other times it takes years. It all depends on the design and installation.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[stevenal]

A manhole is the entrance on the top of the vault, and is one location the water can enter.

 

[jghrist]

You could drill a hole in the conduit at the low point and surround it in crushed rock to allow water out of the conduit. If not, as water eventually gets in the top of the pole riser from rainfall, it could rise to the top of the conduit at the other end inside our house unless that point is higher than the pole riser end.