Confirming Wire and Conduit size

[beowulf]

I need to run wire in underground conduit for a run of 140 feet from a meter/panel (on pole) to a 200-amp subpanel on a house daughter is building. We are doing some of the work - the project is 'permitted'.

My calculations are that we can use 3/0 copper wire in 2" conduit - given the distance and amps. Three wires in the conduit - appropriately tape-tagged.

The meter and the subpanel are in, appropriately grounded, and the County inspector has signed off on both. The trench is being dug on Tuesday. I will be ordering schedule 40 2" conduit and two 2" x 36" sweeps (for each end) and will use schedule 80 coming out of the ground.

I am posting to confirm that the wire size (3/0) and conduit size (2") that I intend to use are correct - out of an abundance of caution - before I order everything. And seeking any other advice that may be helpful, e.g., re pulling the wire in consecutive 10' conduit sections, and laying in the trench. I have done this before but suggestions welcome.

I am not an electrician but also not a novice and am very aware of the need to be accurate and careful. I ran underground service to our home when I changed out the overhead service and have run underground service to sub panels on other buildings on the property and have - over the years - managed a number of electrical projects, always mindful of a need to be accurate and careful.

As always - this is my go-to resource. Appreciate any input.

 

[dstig1]

You are pulling a ground wire also, I assume, since you said subpanel. The ground won't need to be as big but I don't know the charts for sizing that. That is going to be a brutal pull with copper. Hopefully one of the electricians will chime in @grsthegreat

 

[grsthegreat]

For a 200 amp subfeed you can use either 4/0 4/0 4/0 1/0 Aluminum wires ( some locals allow 4/0 4/0 2/0 2 aluminum for primary feeders) usually xhhw rated in 2 inch conduit or you can use 3/0 copper. If you choose copper, youll need a loan.

Aluminum4/0 is currently $1.22 per foot
3/0 copper $4.85 per foot.

At 140 feet if it was me, id upsize the aluminum to 250 mcm to account for voltage drop. But then youll also have to increase pipe size to 2.5” you might be able to squeeze it into 2” if you install pipe and wire at same time, but it would be tight. But 140’ wont make much of a voltage drop issue on the 4/0. Probably not worth the added expense.

Absolutely no issue running aluminum feeders to subpanel. All utility wires are aluminum. Todays aluminum feeder wires arnt like your grandfathers wires.

Ive been an electrical contractor for 35 years, and have never run copper subpanel feeders. Ihave for things like hottubs and such, just not for subpanels.

Even on my own house. Everything feeding house and sub panels in outbuildings is aluminum. It is all aluminum in pvc conduit. I HATE direct bury.
My own house is 29 years old no issues ever.

You do have to run a ground with the hots and neutrals for all subpanels.

 

[grsthegreat]

Also, if possible lay out the wires on ground and slip the conduit onto it one stick at a time and run it down wires. Youll hate trying to pull 140’ by hand.

I have a Greenlee wire puller myself, but i doubt anyone rents one of those.
Mine uses a cordless drill to exert 1,000# + pulling strength.

 

[grsthegreat]

The only time we arnt required to run a ground with the feeder wires is if the meter was posted away from the house AND there is no panel or shut off device at the meter. This would allow 3 wires run to the house with the house hosting the first disconnecting device. This is only allowed in certain circumstances in my local, as fire departments want a disconnect at meter now days.

 

[beowulf]

Thanks to everyone. Very useful information!

There will be shut offs at the meter panel - one main shutoff to shut off the power coming in from overhead to the breaker bar, and another to shut off the lines running from the meter panel breaker bar to the house subpanel.

The comments about needing a ground were valuable as I was not certain about that aspect and had not given that full attention.

I was concerned about using aluminum wire (based on older horror stories) so it is good to know that today that will work. Thanks for that. Clearly save a lot of money. I will check code to make sure that is okay - assume so. I will rethink this given this information.

BTW - the way that I ran wires through conduit to go in a trench before was 1) have extra help, 2) run the wire through the conduit one stick at a time (sliding the next stick all the way down and gluing - taking care to have cardboard or tarps laid out to prevent debris etc.) and leaving the initial pieces on top next to the trench 3) after I have done that - stick by stick - for the length of the run, I add the sweeps at each end (having calculated how much wire I need to leave out at each end for the requisite connections - and being generous) and matching their vertical rise so the sweeps are vertically parallel, 4) then attach the schedule 80 vertical pieces, 5) slip all into the trench with help and rope, and then - topside - size it all up and wriggle it into the panels. For smaller conduit I have laid it into the trenches leaving the last piece out with the end on a board running across the trench and then moving on down the line. I'll have to think about which way to do this.

I think the punch out at the meter panel is 2 inches max.

Again, Thank you all so very much.

 

[dstig1]

Also, if possible lay out the wires on ground and slip the conduit onto it one stick at a time and run it down wires. Youll hate trying to pull 140’ by hand.

That was how I did it, but I was also going 400' and as a result had huge conductors (alum, 500 mcm IIRC...hmmm it might have been even bigger than that...). I also used 20' sticks of 4" conduit. 20' for fewer joints.

You can use bigger conduit and then just step it down at the meter or panel with a fitting or two if you need to. Makes life easier.

One trick I used was to take one of those wobble-style deburring tools and run it around the inside of the conduit to knock off the sharp edge so it didn't gouge the insulation. I noticed it shaving the insulation on the first stick as it slid along, so on the next one I used the tool to chamfer the inside of the end of the tube on the end I was feeding through. Takes 2 seconds to run a quick zip around the tube. Worked like a charm.

Don't forget the antioxidant paste on alum connections.

 

[grsthegreat]

Also, check your local power company. Here, we have to install expansion fittings between the ground and the power box. This allows for expansion and contraction of the pipe in summer or winter. May not be necessary in your neck of the woods.

I also deburr all pvc pipe. Sharp edge will damage wire coatings if pulling 1 stick at a time.

 

[ultrarunner]

My only experiences with underground have been problematic due to water intrusion.

In Washington the direct burial PSE cable has been repaired several times but the conduit from the transformer vault to the basement panel became Niagara Falls during a heavy week of rain… vault is at higher elevation and filled with water and the conduit became the overflow.

In Oakland utility pole work damaged my conduit at ground level and rain water puddled and had a straight shot to my panel… at least panel was outside…

Having your panel or meter base flooded is never a good thing!

I used closed cell foam to seal in both cases and so far so good.

 

[kenmac]

I'm no electrician. but have read about placing electrical wires underground/ in conduit, and consider heat dissipation and how it related to wire size

 

[grsthegreat]

Thats true, but 2” pvc conduit is rated to carry 4 runs of 4/0 wire without issues.

 

[caver]

Do you recall what section of code that is in? I knew about sub panels but wasn't aware of the 1st breaker turning my cabin into a sub. I have this (picture) getting ready to happen by the end of summer. I do have a Coop breaker right before the pole month meter that i think is 400amp. A bit overkill. I plan to meet with a Coop guy soon next time I'm over there. Ideally I would like for them to run about 100+ of triplex and set another pole. If I have them put a 2nd service right by my cabin that's another $500+ a year for at least one meter mostly at idle. into a sub panel.

 

[BackRoad]

Two years ago, we had about 150 feet of buried from the last pole with the transformer to the meter base on the house.

The Co-Op provided the aluminum feeder wire, all wound and wrapped together, but before providing the wire, they required the meter base to be mounted and the conduit to be buried and inspected. So the actual wire install was a tough pull with 4 guys, two pushing and two pulling when we put it in.

The other thing they required (by code I was told) was we had to bury a red 4 inch plastic warning tape along the length of the run, 12 inches above the conduit, so anyone digging would "hopefully" stop upon digging up the tape!

 

[DarkBlack]

Maybe the code has changed lately, or there’s some regional variations on the NEC standard being mentioned here. This installation sounds like a pole meter loop to me. That panel on the pole, probably feeds only the new house. It’s effectively acting as a disconnect with one downstream load.
I disagree with calling and treating the new house main service panel, a sub-panel.
I also disagree with the need or desire , to run a grounding conductor from the pole to the new house.
The first panel in the house is the main service panel. There should be a grounding rod at the house, same as every other house. This is where your main panel will bond the neutral with ground . You certainly don’t want to not physically earth ground at the house entrance, and rely on a little ground wire running 150 feet to a pole meter setup

 

[ponytug]

Maybe the code has changed lately, or there’s some regional variations on the NEC standard being mentioned here. This installation sounds like a pole meter loop to me. That panel on the pole, probably feeds only the new house. It’s effectively acting as a disconnect with one downstream load.
I disagree with calling and treating the new house main service panel, a sub-panel.
I also disagree with the need or desire , to run a grounding conductor from the pole to the new house.
The first panel in the house is the main service panel. There should be a grounding rod at the house, same as every other house. This is where your main panel will bond the neutral with ground . If you ran a ground wire from the pole, your ground and neutral would be connected at both ends, and that defeats the purpose, and you certainly don’t want to not physically ground at the house entrance, and rely on a little ground wire running 150 to a pole meter

I'm not, repeat not, an electrician.

Isn't the underlying issue where the neutral to ground bonding occurs? A panel with a meter and a breaker at the pole needs a ground. A panel at a separate building (sub panel or not) needs a ground rod grounding the building wiring.

If the ground to neutral bonding is at the meter, then wouldn't a ground be required? If there is no bonding at the meter, then the ground there is local to the meter and panel, with no further need for a ground to be continued to the house, right? What am I missing? (Think of the meter panel to the house from the perspective of a service drop that has a neutral, grounded at the pole in the center of the transformer, and the neutral grounded (bonded) at the main panel. What is different?)

I would readily admit that the logic of the NEC escapes me sometimes, but I recognize that their hearts are trying to do the right thing for safety.

All the best,

Peter

 

[grsthegreat]

Ok, here goes.

The FIRST panel which includes the meter AND a breaker HAS to have a ground rod or 2 and the ground wire AND the neutral have to be bound together within the panel. In other words the ground and neutral can be located on the same buss, or the neutral buss will have a green screw that attaches to the metal can.


Years and years ago, only 2 hots and a neutral had to go to any other subpanel and at the subpanels the additional ground rods and wires were again bonded together. This went away a long time ago.

Currently, EVERY OTHER subpanel HAS to have 4 wires run for single phase, 240v power. 2 hots, a neutral and a ground. Every subpanel has to have a isolated neutral buss (cant be mechanically grounded in any way) AND a grounded buss bar. The neutral and ground cannot connect together in any fashion in a subpanel.

 

[grsthegreat]

Do you recall what section of code that is in? I knew about sub panels but wasn't aware of the 1st breaker turning my cabin into a sub. I have this (picture) getting ready to happen by the end of summer. I do have a Coop breaker right before the pole month meter that i think is 400amp. A bit overkill. I plan to meet with a Coop guy soon next time I'm over there. Ideally I would like for them to run about 100+ of triplex and set another pole. If I have them put a 2nd service right by my cabin that's another $500+ a year for at least one meter mostly at idle. into a sub panel.
View attachment 3519356

For that long of a run, you will need to upsize the wire that you run due to voltage drop. If it were me, id run a longer primary utility run towards the house instead of a huge secondary wire required for a 260’ run.

At 260’ to maintain a 3% voltage drop you would need to run

400kcml aluminum @ $2.30/ft x 3 plus smaller ground

250kcml copper @ $ 6.49/ft x 3 plus smaller ground


When planning a new service, we try and keep transformer within 100’ of the residence to keep from having to upsize the wire size to account for voltage drop.

 

[grsthegreat]

For the code, its very complicated. Covered under article 230. Grounding requirements under article 250.

But basically, back in 2008, they eliminated the ability to feed a subpanel with 3 wires and reestablish a new grounding system. But it grandfathered in old installations (like my house) where this was allowed in the past.

 

[DarkBlack]

Utility company’s pole meter loop requirements take priority over NEC code. If they require your neutral bonded to earth ground at the pole, in addition to simply earth grounding metal parts, then you have no choice.
But, it doesn’t change the fact that it’s in direct opposition to NEC code stating, never bond more than one point, for good reasons.
This means it you ground at the service entrance at the house, you now have 2 neutral-ground bonds separated by 150’. Not good. The pole to house ground and neutral are now parallel current paths.
If you choose to not, earth ground at the house, your house ground wires are relying on 150’ of a ground wire in a pvc pipe to the pole earth location. Far from ideal….
That’s why normal pole transformer to house meter installations don’t run a ground wire.

 

[ultrarunner]

It’s fascinating to me to see the evolution of residential service starting around 1910 to now…

I almost bought a Victorian with original gas lighting that was refit for electric often reusing the gas pipe as conduit for wire and the gas fixtures electrified.

Many prewar nothing more than one hot and a neutral with a single 30 amp Edison fuse main.

At todays cost of material running new underground service could very well require a mortgage…

No wonder so many shopping centers are hit by copper thieves stealing wire running to parking lot lights.

12 years ago my brother wanted lights in the tractor shed some distance from the home…

I penciled it all out and he decided to wait until copper prices dropped and is still waiting.

What about a step up transformer at the source and step down at the shop so as to be able to reduce conductor size?

I did wire the shed but went with 12 volt solar battery system and RV bulbs.