Anyone see a logical reason

[ohmhead]

Well Roger heres one with 75# - 4 inch conduits straight thur pulling mostly 750 mcm .http://i611.photobucket.com/albums/tt195/stringking/P1010093_02.jpg
Our two piece box we have the pvc cups installed with bells flush on inside so there sealed you just glue & push in the pvc conduit .

We pull straight thur no need for rigid !


Or the engineer is thinking its like when we poke thur a deck or under a slab we change from pvc to rigid for stress and a good seal between the the barriers of earth and above slab so the pvc does not crack from the movement of slab expanding and contracting .

Or maybe its just his way of writing the specs or copying the specs from 1954 we see the same over and over 1600 spec never change much its about time to write some new stuff.

 

[quogueelectric]

A duct bank consisting of 66 concrete encased 4" PVC conduits and 18 manholes. Each manhole has 11 conduits entering and leaving, and the concrete encasement is all the way to each manhole. The last 5' straight section of each concrete encased conduit is specked to be RMC and they are installed per the specs

My question is, does anyone see a reason for this spec besides added expense for the RMC, labor for threading the RMC, bond bushings, copper EGC, and introducing half of a lethal circuit into the equation? Remember this is a complete concrete encasement for physical protection


Roger

Very often in the north on a small scale pvc in a deck gets snapped off at the couplings so many people use emt for the last 5 ft to a box to eliminate this problem in the cold. I have seen some bank deck jobs lose 80% of thier pipes de to pvc being snapped off in the pour with concrete buggys running over the pipes. I can see an engineer who has run into/frost heaves or shifting causing pvc conns to snap off at the manholes. Very few contractors tamp properly. This would also help ridgidly connect the duct bankto the manhole in my opinion. Bonding is a small price to pay as opposed to losing a feeder. An experienced man on a collins machine can pump out 5 foot 4" nipples in short order when set up right. Lots of NYs moving down south check the architect.

 

[ohmhead]

Well on a duck bank with rows of conduits stacked thats poured in concrete you tamp the bottom only.
If its a clean fill non poured duck bank its not tamped with a plate compactor its washed in with a water hose thats the only way to fill it in you dont compact between conduits that are 3 inches apart kinda hard to do .

There is expanding and contracting but the rigid pipe 5 foot extensions to the box are not going to make one bit of difference.
Install pvc expansion couplings thats what there for .

I see no use for the rigid 5 foot conduit electrically or mechanically its just a waste of time and money ! Grounding, bushings, threading ,and sealing up holes in manhole and how about bitimus painting the rigid !


RFI this to the engineer ask him ?
Say - The connection between manhole of rigid conduit to pvc conduit underground there being a concerned with the relation to metal and plastic thermodynamics and the expansion of each over time metal expands faster then plastic we see a solution to this problem a continous pvc conduit run please advise us to you final resolution in this matter .

Most of the time they agree if they think it sounds good because they dont have clue to actual doing electrical work .

 

[iwire]

Well on a duck bank

I think Roger is installing a duct bank, but who knows, maybe it is for ducks.:grin:

 

[Article 90.1]

I have found that PVC female adaptors are weak and brittle. I had a foreman who had us just glue up end bells of 6" PVC and slide them over the ends of 6" GRC. I fought him tooth and nail, but after the glue set you could not budge the connection, and it was mechanically stronger than the adaptors were, and cheaper (UL listed, maybe not).

The GRC, as specced, is for settling, or expansion and contraction. And I, for one, am glad to see a spec that is to a higher standard than simply using PVC all the way. Our industry is in a downward spiral of, "Jam it, Ram it, Hide it"! The quality of our materials is deteriorating, and the installation practices are becoming more sickening.

PS. The bushings would be bonding bushings, not grounding bushings.

Did the spec. call for wrapping the bundles of conductors with flame retardant tape before racking them in the manhole?

 

[Rockyd]

Roger,

Maybe a copy of this whole thread should be taken along to defend your position to the engineer, and perhaps, invite the engineer to the forum thread here, and we could offer the most effeient, effect solution, or learn something new as to how he, or she, see's the engineering problem.

I'm working in Alaska, on a national defense project where money is no object, and we have nothing such as Roger addresses in the Spec call out. And we have various ducts (2" to 6") ran all over the facility, some PVC coated GRC, some PVC, but no mixture such as you discuss.

Perhaps the engineer is not familiar with caging the PVC with rebar where the duct bank is subject to vehicular traffic?

 

[ohmhead]

I think Roger is installing a duct bank, but who knows, maybe it is for ducks.:grin:

Well iwire its a spelling problem yes duct bank sorry .

We joke about it down here in Florida because when we dig we always have a water problem and we are standing in mud and water while were running pipe so we have a name by habit its duck bank in Florida.

Most jobs on a large scale have to have some kind of De-Watering System installed during construction underground work mostly the construction managers do it for us .

Our company rents mud hogs and we do the old 5 gallon bucket with the sump inside . Our state is the worst for underground it rains every day in summer months or its so dry you have to add water to compact the sand .

 

[roger]

Roger,

Maybe a copy of this whole thread should be taken along to defend your position to the engineer, and perhaps, invite the engineer to the forum thread here, and we could offer the most effeient, effect solution, or learn something new as to how he, or she, see's the engineering problem.

Rocky, it really doesn't matter to me, we quoted the job as specked, so we are covered. It would have probably been a deductive CO and I would rather not bother with that, I don't want to give anything back. I was just curious as to whether anyone could give me a logical reason for doing it, I can't see one.


Roger

 

[mivey]

This message has been deleted by iwire. Reason: This forum is not ET.

What does that mean?

 

[Rockyd]

Roger,

Pick up the money!

 

[roger]

Roger,

Pick up the money!

:grin:


Roger

 

[iwire]

What does that mean?

Only that different forums have different practices.

Dennis posted a joke photo that while IMO funny did not fit here at the MH forum.

 

[mivey]

Only that different forums have different practices.

Dennis posted a joke photo that while IMO funny did not fit here at the MH forum.

I was trying to figure out some acronym like Electrical Training, Excessive Teasing, Euro Trash, but couldn't come up with anything.

I wasn't even thinking of another forum. It's been a while, but I guess I should drop in to see what's new.