Just to be on the safe side

[mshields]

Ordinarily we specify concrete encased PVC for incoming services to a building.

I've got a client who would like to utilize directional boring to install a 1600A, 480Y/277V service from the service pad mounted transformer to the new service switchboard. I had no knowledge of this technology previously but have learned that this equipment bores a whole large enough for 4 - 4 inch conduits.

I told him I wanted 6 (to provide 2 spare) so he'll bore those two in a second hole immediately adjacent to the first. I think they need to be something like 18 inches apart. Once the holes are bored this guy will pull back through the hole 4 Schedule 40 HDPE conduits in the one whole and 2 sched 40 HDPE in the second hole.

The directional boring guy has told me that he does a lot of work for NStar and that this is the technique that they use. I don't have any immediate concern with it. But as I've never done it before and as I know full well the NStar can do what ever it wants and I can'ts, I wanted to take the temperature of this approach with this erudite group.

What do you think? Obviously we need to adhere to the depths in Chapter 3. Other than that, I don't see any code issues. Do you?

Thanks,

Mike

 

[charlie b]

For starters, how are you going to put 1600 amps worth of wire into four parallel conduits? You would need 600 MCM conductors, and 5 of them (A, B, C, N, G) would fit into a 4" schedule 40 PVC. But it would be a tight fit. Secondly, if you do wind up using one of the conduits in the second hole, how are you going to match the total conductor lengths, as required by 310.10(H)(2)(1)? Finally, if you are concerned about getting a concrete encasement, I think that is still possible. Others who have done this install will have to verify this. But I think both sides of the hole can be blocked, and concrete can be poured into the internal space.

 

[mshields]

what's wrong with 4 sets of 600's

what's wrong with 4 sets of 600's

I plan to run 4 sets of 600kcmil and a 600kcmil grounded service conductor; so 4 conductors per conduit, not 5. Furthermore, I'm told that pulling in HDPE conduit is actually easier than PVC. Don't know if that's true. But regardless, it strikes me as do-able.

I wondered about the disparity of length; that's a good point.

Thanks,

Mike

 

[Cow]

Our inspector over here would shoot us down in an instant for not maintaining spacing between the conduits using that method. It may be different elsewhere, but it's something he specifically looks for when we run multiple conduits together.

 

[gadfly56]

Our inspector over here would shoot us down in an instant for not maintaining spacing between the conduits using that method. It may be different elsewhere, but it's something he specifically looks for when we run multiple conduits together.

I was wondering about that.

 

[GoldDigger]

I was wondering about that.

Fit the pipes into spacer disks and pull the whole assembly?

 

[charlie b]

Our inspector over here would shoot us down in an instant for not maintaining spacing between the conduits using that method.

And exactly what requires the conduits to be evenly spaced? :?

 

[GoldDigger]

And exactly what requires the conduits to be evenly spaced? :?

The duct bank thermal calculations require controlled spacing. Not sure what other spacing requirements might apply at these voltages.

 

[petersonra]

why does it even need to be in conduit?

 

[GoldDigger]

why does it even need to be in conduit?

Either conduit or sleeving seems appropriate if you are going to pull more wire/cable after the bored hole has been filled in.
If you are looking at unsleeved cable, it becomes even more important to maintain spacing for thermal purposes.

 

[Cow]

And exactly what requires the conduits to be evenly spaced? :?

I wouldn't say they necessarily need to be evenly spaced the entire distance, they just need some sort of space even if it varies. Sometimes I'll use short stakes made of 1/2" emt driven between multiple conduits as an example.

 

[Fulthrotl]

Ordinarily we specify concrete encased PVC for incoming services to a building.

I've got a client who would like to utilize directional boring to install a 1600A, 480Y/277V service from the service pad mounted transformer to the new service switchboard. I had no knowledge of this technology previously but have learned that this equipment bores a whole large enough for 4 - 4 inch conduits.

I told him I wanted 6 (to provide 2 spare) so he'll bore those two in a second hole immediately adjacent to the first. I think they need to be something like 18 inches apart. Once the holes are bored this guy will pull back through the hole 4 Schedule 40 HDPE conduits in the one whole and 2 sched 40 HDPE in the second hole.

The directional boring guy has told me that he does a lot of work for NStar and that this is the technique that they use. I don't have any immediate concern with it. But as I've never done it before and as I know full well the NStar can do what ever it wants and I can'ts, I wanted to take the temperature of this approach with this erudite group.

What do you think? Obviously we need to adhere to the depths in Chapter 3. Other than that, I don't see any code issues. Do you?

Thanks,

Mike

well, call the inspector who is going to have to sign your ticket, and ask HIM. he's gotta sign off on it.

i'd look at the second group with an eye towards the length of the run, and the percentage deviation.
if it's a 300' run, and there is a 3' deviation, you have a 1% disparity, nothing worth getting in a bunch over.
i wouldn't sweat that.

as for heat dissipation, you have four pipes in a cloverleaf. none of the pipes are surrounded by other conduits.
they all have ample cold dirt around them. you could grout them, but there isn't any advantage. the pipes are
gonna be laying on the bottom of the bore hole, and if you grout them, they will be floating on the top of the
bore hole, with minimal grout coverage for protection.

of much higher entertainment value, is jacking all this a long way... the data guys do it a lot around here,
going under streets and such.... and one time i watched the pipe jacker punch right thru a 8" fire main.
it flooded the entire parking lot, UNDER the asphalt, with water squirting up all the way around the parking
lot, between the asphalt, and the curb... 100' x 300' parking lot..... then the asphalt started failing in a couple
weeks, being laid over mud..... big fun.

 

[kwired]

I had no knowledge of this technology previously but have learned that this equipment bores a whole large enough for 4 - 4 inch conduits.

The proposed Keystone XL pipeline that is to go through areas near where I live is supposed to be a 30" pipeline and will be directional bore installed where it crosses rivers/streams and many existing public roads, apparently your boring :lol: contractor can't go that large of a hole.