Schedule 40 PVC

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mshields

mshields

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Boston, MA
Can I safely assume that sched 40 (as opposed to 80) is appropriate/adequate for any concrete encased duct bank application. i.e. including 35kV applications.
 
mshields said:
Can I safely assume that sched 40 (as opposed to 80) is appropriate/adequate for any concrete encased duct bank application. i.e. including 35kV applications.
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Wouldn't the 75 degree C limitation on the conductor be an issue

352.12 (E)
 
Gregg Harris said:
Wouldn't the 75 degree C limitation on the conductor be an issue

352.12 (E)
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FWIW 2008 NEC 352.12(E) was deleted from NEC 2011...

...but I fail to see how it makes any difference in a use comparison between PVC Schedule 40 and PVC Schedule 80...???
 
Smart $ said:
FWIW 2008 NEC 352.12(E) was deleted from NEC 2011...

...but I fail to see how it makes any difference in a use comparison between PVC Schedule 40 and PVC Schedule 80...???
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Maybe the thicker walls of the Schedule 80 are thought to be required to keep the weight of the concrete from collapsing the pipe?
 
mshields said:
Can I safely assume that sched 40 (as opposed to 80) is appropriate/adequate for any concrete encased duct bank application. i.e. including 35kV applications.
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....

310.60 Conductors Rated 2001 to 35,000 Volts.

(A) Definitions.

Electrical Ducts. As used in Article 310, electrical ducts
shall include any of the electrical conduits recognized in
Chapter 3 as suitable for use underground; other raceways
round in cross section, listed for underground use, and embedded
in earth or concrete.

...
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GoldDigger said:
Maybe the thicker walls of the Schedule 80 are thought to be required to keep the weight of the concrete from collapsing the pipe?
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That's a structural consideration... not an NEC requirement.

However, I was trying to point out the OP was asking about sch-40 vs. sch-80 PVC, so 352.12(E) [2008] would be irrelevant.
 
90C conduit, 105C cable

90C conduit, 105C cable

We use 90C Schedule 40 PVC in concrete encasement quite often. The Sch 40 PVC is overkill because DB or EB can be used. Sch 80 is only used where physical damage is likely (exposed walls, pole risers, etc.)

BTW, if you use 105C-rated conductors you cannot use the 105C ampacity when installed in 90C-rated conduit.
 
I don't see how its irrelevant. Sch 40 and Sch 80 PVC conduits have temp. ratings. You have to follow the product listing below unless the conduit is marked for a higher temp:

RIGID NONMETALLIC SCHEDULE 40 AND SCHEDULE 80 PVC CONDUIT (DZYR)
USE AND INSTALLATION
...
Unless marked for higher temperature, rigid nonmetallic conduit is intended for use with wire rated 75?C or less including where it is encased in concrete within buildings and where ambient temperature is 50?C or less. Where encased in concrete in trenches outside of buildings it is suitable for use with wires rated 90?C or less.
...
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Even under the 2011 NEC, I would assume the product listing would still apply even though the NEC doesn't directly reference it.
 
steve66 said:
I don't see how its irrelevant. Sch 40 and Sch 80 PVC conduits have temp. ratings. You have to follow the product listing below unless the conduit is marked for a higher temp:

RIGID NONMETALLIC SCHEDULE 40 AND SCHEDULE 80 PVC CONDUIT (DZYR) USE AND INSTALLATION
...
Unless marked for higher temperature, rigid nonmetallic conduit is intended for use with wire rated 75?C or less including where it is encased in concrete within buildings and where ambient temperature is 50?C or less. Where encased in concrete in trenches outside of buildings it is suitable for use with wires rated 90?C or less.
...
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Even under the 2011 NEC, I would assume the product listing would still apply even though the NEC doesn't directly reference it.
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I'm not saying it don't apply. I'm assuming since the OP didn't question S40 rated differently than the S80, that is not at issue regarding the question as posed.
 
steve66 said:
I don't see how its irrelevant. Sch 40 and Sch 80 PVC conduits have temp. ratings. You have to follow the product listing below unless the conduit is marked for a higher temp:



Even under the 2011 NEC, I would assume the product listing would still apply even though the NEC doesn't directly reference it.
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That was my contention UL 651 states

[FONT=arial,helvetica][h=3]1.3 Type EB and A conduit and fittings[/h] 1.3.1 The Type EB and Type A rigid PVC conduit and fittings mentioned in 1.1.1 are intended for use at 50?C (122?F) and lower ambient temperatures. Type A rigid PVC conduit and fittings are intended for use with 75?C (167?F) wiring. Type A and Type EB rigid PVC conduit and fittings, where encased in concrete in trenches outside of buildings, may be used with 90?C (194?F) wiring.

1.3.2 Type EB (encased burial) rigid PVC conduit is intended for encasement in concrete in trenches outside of buildings. Type A rigid PVC conduit is intended for encasement in concrete in any location.

[/FONT]
 
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