duct bank

[elect36]

We've got 4 runs of 3" for a 1200 amp service that is 20' from switch gear to utility pad trans. Is it code somewhere that the duct bank be concrete encased or could we get by backfilling with just dirt and no concrete

 

[charlie tuna]

Re: duct bank

check with your local utilities but in south florida we normally do not encase with concrete..

 

[elect36]

Re: duct bank

What kind of depth is typical for a service like that? Or would that be utility comp also

 

[redfish]

Re: duct bank

If you don't encase it with concrete, then you should use premium fill (sand) in order to fill all of the voids between the ducts.

 

[mdshunk]

Re: duct bank

If money and time were not an object, and you asked a guy what the best method is, it would have to be concrete encasement. About half of the duct banks I've done are concrete encased, and half are not. It seems that the half that were concreted were run in areas where digging might very likely be done in future. Anybody using the red tinted concrete? I did a job a few years ago where the specs called for the concrete encasement to be tinted red. That's a little different.

 

[coulter]

Re: duct bank

Originally posted by mdshunk:
...Anybody using the red tinted concrete? I did a job a few years ago where the specs called for the concrete encasement to be tinted red. That's a little different.

A red tint concrete cap is a pretty normal industrial spec. More often than not what you get is normal color concrete with the red dye powder shovel-spread on top.

Having had to dig up a few, I would recommend putting a couple inches of sand over the conduits and then pour the lowest strength concrete available - unless, of course the spec says otherwise.

carl

 

[iwire]

Re: duct bank

Originally posted by coulter:

Originally posted by mdshunk:
...Anybody using the red tinted concrete? I did a job a few years ago where the specs called for the concrete encasement to be tinted red. That's a little different.

A red tint concrete cap is a pretty normal industrial spec. More often than not what you get is normal color concrete with the red dye powder shovel-spread on top.

I agree with Carl, do not order red concrete $$$, go to a masonry supply store and by the red die.

Let the cement get poured then spread the die on top of the cement, I find a stiff broom spreads and sticks it down just fine.

Of course read the job specs carefully but I bet all they really want is the top marked.

 

[luckyshadow]

Re: duct bank

poured in concrete vs direct buried is a spec issue. Read the specs and go over the drawing details, thats where we find it. I have done both direct bury and concrete encased. As for Red dye - never done that.... yet. Sounds like a good idea. What we do is use a 6" wide metallic ribbon buried half way between top of ductbank / pipe and finish grade. Use metallic this way it can be located ( so they say )Last job it was located with a track hoe

 

[benaround]

Re: duct bank

Somewhat on the subject,Compaction Rate. Some spec's will call for 100% compaction,we usually fill the entire area,trench,whatever with slurry mix.It's a lot less expensive than concrete and gives 100% compaction every time.

frank