When I run an entrance conductor underground in conduit, should I come directly up out of the ground on either end or is there supposed to be some kind of "loop" to allow for settling of the ground? I have a meter on the transformer pole and I run from there underground 180 feet to the house breaker box.
Underground Electrical Service Question
- Thread starter Believer
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s78wingrider
Gold Member
Just a 90 on each end
captaincrab55
Silver Member
Believer, It would be nice to know where this is being done??? Rules/Codes can change from State to State & County to County.... The NEC allows the AHJ a lot of lead way as the Power to Be..... Sometimes the Power Co has a Spec when your wiring a meter....
shinnlinger
Silver Member
They also make slip couplings to allow about 4" of movement up or downs as the ground settles/heaves. They are code in NH.
eepete
Platinum Member
The captaincrab is right, and while he's looking at it from a code and the Authority Having Jurisdiction point of view, you'll also want to ask around to see what is done locally. New Hampshire needs the slip couplings, they are not used here in North Carolina (as an example). Definitely talk to your power company.
No matter where you are, I'd be sure the soil that the conduit lies on near the ends of the run (about 10' or so) is undisturbed or compacted or has pea gravel fill so that the pipe won't move.
Pete
No matter where you are, I'd be sure the soil that the conduit lies on near the ends of the run (about 10' or so) is undisturbed or compacted or has pea gravel fill so that the pipe won't move.
Pete
WVBill
Veteran Member
Same here in Jefferson County, WV
Obed
Elite Member
Here's how our underground electrical wire runs from the transformer to the house. We will have a service panel mounted to the 6x6 posts that will have disconnects so that I can shut off all power to the house from the outside without having to remove the electric meter. The service panel will contain a 400A meter and 2 200A breakers. There are 2 200A breakers and two conduits because we are running 2 200A lines to the house, one for the basement and the other for the rest of the house.
There are more pictures at this link.
Obed
There are more pictures at this link.
Obed
RedOak
New member
Here in the Berkshires, the service conduit are specified with two 90 degree bends on each end...and speaking of specifications, they should be in written form from the local power utility/provider.
For our house project, we received drawings and engineered spec's from the power company. Obviously, the drawings detailed both ends of the run -- the pole end and the transformer end. This specifically addresses getting power from your nearest pole to an underground transformer, however.
The service entrance run -- from the underground transformer to the house itself -- should be handled the same way. The ends of the conduit should have some form of arced bend in them.
By the way, if the source end of either run is exposed -- pole to transformer or pole to house (I'm not really sure about your situation) -- you have to consider the possibility of water entering the conduit and freezing. Needless to say, this can cause breakage due to heaving. I'm not sure where you are, but you may want to ask your electrician about this.
Have a good one,
Red 
For our house project, we received drawings and engineered spec's from the power company. Obviously, the drawings detailed both ends of the run -- the pole end and the transformer end. This specifically addresses getting power from your nearest pole to an underground transformer, however.
The service entrance run -- from the underground transformer to the house itself -- should be handled the same way. The ends of the conduit should have some form of arced bend in them.
By the way, if the source end of either run is exposed -- pole to transformer or pole to house (I'm not really sure about your situation) -- you have to consider the possibility of water entering the conduit and freezing. Needless to say, this can cause breakage due to heaving. I'm not sure where you are, but you may want to ask your electrician about this.
Have a good one,
Red
brokenknee
Platinum Member
My brother in law (who is an electrician) put in my electrical service, with me getting in the way. In MN a frost loop is required, but he said nothing about the slip joint others are referring to, but that may have changed by code since he put mine in.
Raspy
Veteran Member
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My service entrance conduit had to be "below" 5 feet, or "over" 5 feet deep. It had to have a pull box every 100' and mine was 220 feet to the pole so I had two. The 90s at the ends are long radius sweeps. All above ground service entrance conduit must be either schedule 80 PVC or rigid metal conduit. No EMT thinwall metal conduit. No EMT below grade in the ground. So, the main runs can be sch 40 but must switch to heavier grade where they turn up. My utility wanted a pull rope installed and some even want the official thing (can't remember the name) pulled through to prove the conduit is clear. At approximately one foot above the conduit an official 6" wide red caution tape must be run to warm of the conduits location. If the ditch is to be used for other lines, like water for instance, they should or must be at least one foot apart.
All this is for the main service conduits. The secondary conduits that run to sub panels or from the meter to the house, can be at 24 inches. But mine are deeper because they run with water lines and I needed at least three feet for those to prevent freezing.
Always run a big enough size! Larger means a much easier pull, less chance for wire damage and the chance to get another wire through if needed. Bigger is better!
I was concerned about settling and stress on the box so I just filled it slowly and washed it in with water to compact it without downward pressure. No other special design was used. We don't get heaving here and the initial settling was handled by washing it in for compaction. The conduit comes up to a male thread coupling and a nut in the box.
You also can't have more than 270 degrees of bends in each run of conduit. But the casual bending in the ditch doesn't count.
All this is for the main service conduits. The secondary conduits that run to sub panels or from the meter to the house, can be at 24 inches. But mine are deeper because they run with water lines and I needed at least three feet for those to prevent freezing.
Always run a big enough size! Larger means a much easier pull, less chance for wire damage and the chance to get another wire through if needed. Bigger is better!
I was concerned about settling and stress on the box so I just filled it slowly and washed it in with water to compact it without downward pressure. No other special design was used. We don't get heaving here and the initial settling was handled by washing it in for compaction. The conduit comes up to a male thread coupling and a nut in the box.
You also can't have more than 270 degrees of bends in each run of conduit. But the casual bending in the ditch doesn't count.
horse7
Gold Member
Many years ago when I put in my meter, there was no specification on having a slip joint or other means for ameliorating the effects of heave. So I mounted the meter (which comes up by itself between the ground mounted transformer and the house) on a plate with machined vertical slots, having lags going through the slots to the mounting wood. Basically I figured I needed something and rolled my own. Now they have codes to cover the potential problem.
The slots are only 2-3" long, and I've had to remount the lags a couple of times between heave and settling of the 5' deep trench.
If I had to do the underground over again, the one thing I'd do is check different secondary conductors, one brand of 4/0 was way stiffer than the other brand, causing a lot of extra effort for installation. I had figured they'd all be about the same... one brand worked reasonably easily in 2" LBs, other one was a PITA (with a mallet) [used sweeps outside, but inside needed LBs to drop to the distribution panels.].
The slots are only 2-3" long, and I've had to remount the lags a couple of times between heave and settling of the 5' deep trench.
If I had to do the underground over again, the one thing I'd do is check different secondary conductors, one brand of 4/0 was way stiffer than the other brand, causing a lot of extra effort for installation. I had figured they'd all be about the same... one brand worked reasonably easily in 2" LBs, other one was a PITA (with a mallet) [used sweeps outside, but inside needed LBs to drop to the distribution panels.].
captaincrab55
Silver Member
Mandrel is the word for today, that is if I spelled it right....
Raspy
Veteran Member
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Captain,
Yeah, I think that's it. Thanks.
A short cable with eyes on each end and a few very thick flat washers in the middle.
Sheesh, brain fade.
John
Yeah, I think that's it. Thanks.
A short cable with eyes on each end and a few very thick flat washers in the middle.
Sheesh, brain fade.
John
captaincrab55
Silver Member
John, Your quite welcome... I can't get the word "Mandrel" out of my mind, after running a job installing a several new underground services for a Hospital in Annapolis, Maryland... Power Co. required a mandrel to be pulled in all PVC conduit.. Installed about 15,000' of 6" PVC conduit and pulled a 6" mandrel in all the conduit...
crazyal
Super Member
Wow things are different from state to state. I had to run 1400' of service line to the meter then another 350' from the meter to the house. In Vermont (or maybe it was a power company requirement) the service line had to have a vault every 600'. I could do the trenching and install the 2 1/2" conduit but they provided and installed the cable. they also installed a transformer on top of the last vault and ran the wire to the meter.
From the meter the power company no longer cared. In VT there is no inspection so you can do what you want from the meter on but when you go to sell the house if it's not to code good luck. I figured it out on my own but a good friend is an electrician so before I did anything. For me, 200 amp service and a run of over 300' 4/0 alum is not thick enough so I had to go with mcm350 (it's been a few years so I could be off a little). But I think code was the outside diameter of cable could only be 40% of the inside diameter of the conduit so I had to use 3". I also had to use slip joints everywhere the conduit penetrated the ground where it could freeze. Since the conduit comes into the house through my cellar slab I didn't need one there but everywhere else I did. I think my buddy said the 40% rule was to allow the wire to move inside the conduit to compensate for the frost movement.
The service line to the meter had to be 3' down and if anything else was to be buried in the same trench it had to be at least 1 foot apart. It was either 1' or 2' down there needed to be a red "warning powerline" tape buried into the hole. On the house side it only had to be 2' down.
I would go to a local electrical supply shop (not Lowes) and ask. They may be able to help you or know of an electrician who will give you answers for a reasonable price (I doubt you'll find free unless you know one).
From the meter the power company no longer cared. In VT there is no inspection so you can do what you want from the meter on but when you go to sell the house if it's not to code good luck. I figured it out on my own but a good friend is an electrician so before I did anything. For me, 200 amp service and a run of over 300' 4/0 alum is not thick enough so I had to go with mcm350 (it's been a few years so I could be off a little). But I think code was the outside diameter of cable could only be 40% of the inside diameter of the conduit so I had to use 3". I also had to use slip joints everywhere the conduit penetrated the ground where it could freeze. Since the conduit comes into the house through my cellar slab I didn't need one there but everywhere else I did. I think my buddy said the 40% rule was to allow the wire to move inside the conduit to compensate for the frost movement.
The service line to the meter had to be 3' down and if anything else was to be buried in the same trench it had to be at least 1 foot apart. It was either 1' or 2' down there needed to be a red "warning powerline" tape buried into the hole. On the house side it only had to be 2' down.
I would go to a local electrical supply shop (not Lowes) and ask. They may be able to help you or know of an electrician who will give you answers for a reasonable price (I doubt you'll find free unless you know one).
crazyal
Super Member
I would also note the 90s, or sweeps come in two styles. There are tight or sharp bends and then a more gradual style. If I remember correctly I couldn't use the sharp bends, something about pulling cable through them.
Again I did my house and just recently my garage myself but would recommend you talk to a pro. There are rules of thumb as to what size wire you need for the service load you are installing all over the internet but the correct way is to figure it out with max current vs distance. Doing it wrong, even if no inspection is required, could prove very costly even if it's able to handle the load you put on it without a problem.
Again I did my house and just recently my garage myself but would recommend you talk to a pro. There are rules of thumb as to what size wire you need for the service load you are installing all over the internet but the correct way is to figure it out with max current vs distance. Doing it wrong, even if no inspection is required, could prove very costly even if it's able to handle the load you put on it without a problem.
captaincrab55
Silver Member
crazyal, I left out the 2 piece (1600 lb each) vaults and the Power Co. pulled in their high voltage wire.. Vaults were no more then 600' apart...
