ductbank vs concrete encased conduits

[anbm]

What is the difference between concreted encased conduits and ductbank? I guess ductbank is a big concrete block holding conduits while concrete encased conduit, the conduit can covered by only 2" concrete as minimum?

 

[don_resqcapt19]

I don't think that there is any actual definition of a duct bank. It is simply conduits run together in an underground installation. The choice of concrete encasement is most often a design issue and not a code issue.

 

[JoeStillman]

I consider a duct bank to be any group of underground conduits more than one. The duct bank may be concrete encased or direct buried. I wouldn't call a single, concrete encased conduit a "duct bank".

There are some ad-hoc definitions out there on the inter-webs. The family of duct bank figures under B.310.(B)(2) are all drawn like concrete, but if you look carefully at the legend, it says Backfill (earth or concrete).

 

[petersonra]

I don't think that there is any actual definition of a duct bank. It is simply conduits run together in an underground installation. The choice of concrete encasement is most often a design issue and not a code issue.

You do get the advantage of being able to not have to dig real deep if you cover the UG conduit in concrete.

 

[infinity]

I consider a duct bank to be any group of underground conduits more than one. The duct bank may be concrete encased or direct buried. I wouldn't call a single, concrete encased conduit a "duct bank".

There are some ad-hoc definitions out there on the inter-webs. The family of duct bank figures under B.310.(B)(2) are all drawn like concrete, but if you look carefully at the legend, it says Backfill (earth or concrete).

I agree. I've always understood it to mean concrete or back-fill, it's still a duct bank if it's buried in the ground.

 

[Julius Right]

The National Electric Safety Code presents different definition of embedded conduit and duct bank.
NESC 2007 Section 32. Underground conduit systemsNOTE 1: While it is often the practice to use duct and conduit interchangeably, duct, as used herein, is a single enclosed raceway for conductors or cable; conduit is a structure containing one or more ducts; and conduit system is the combination of conduit, conduits, manholes, handholes, and/or vaults joined to form an integrated whole.
NESC presents also requirements for duct bank construction in 322. Ducts and joints
NEC 310.2 Definitions.
Electrical Ducts. Electrical conduits, or other raceways round in cross section, that are suitable for use underground or embedded in concrete.
There are underground electric distribution standards for direct buried duct bank as of JEA [Florida], for instance, in order to comply with NESC.

 

[Julius Right]

See also NSTAR standard

 

[anbm]

The National Electric Safety Code presents different definition of embedded conduit and duct bank.
NESC 2007 Section 32. Underground conduit systemsNOTE 1: While it is often the practice to use duct and conduit interchangeably, duct, as used herein, is a single enclosed raceway for conductors or cable; conduit is a structure containing one or more ducts; and conduit system is the combination of conduit, conduits, manholes, handholes, and/or vaults joined to form an integrated whole.
NESC presents also requirements for duct bank construction in 322. Ducts and joints
NEC 310.2 Definitions.
Electrical Ducts. Electrical conduits, or other raceways round in cross section, that are suitable for use underground or embedded in concrete.
There are underground electric distribution standards for direct buried duct bank as of JEA [Florida], for instance, in order to comply with NESC.

Thank You!

 

[don_resqcapt19]

You do get the advantage of being able to not have to dig real deep if you cover the UG conduit in concrete.

It really doesn't matter to me, it is still a design issue, and if I have concrete encased raceways, I will still specify a depth, typically of at least 3' feet to help minimize the crushing damage to the conductor insulation from the freeze thaw cycles we have here in Illinois.
Yes that is not below the frost depth, but it is still much better than 12" where there will be a number of freeze thaw cycles over the winter.

 

[chrisplusian]

@Julius Right does NESC apply to premises wiring that does not belong to the utility? I was always under the impression that was utility side of the service point. I would think it would be in the best interest of both industries to have terminology defined similarly, but that is not always the case.