Dnkldorf

Anyone care to share a supplier of pipe spacers? I found one supplier on the web, but have no experience in building them.

Any info you can share would be appreciated.

Do you vibrate the concrete when pouring, if racks exceed one row high?

william1978

You can vibrate the concrete, but you will need to be carefull so that the conduit doesn't float up to the top of the concrete.

The spacers just snap together, but I wrap some tie wire around the spacers so the don't pop apart.

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JayH

http://www.wescodirect.com/direct/im...019_Elec08.pdf

Here are a few options. You should be able to order these through your wholesale house.

We do vibrate our concrete when pouring. Just drop the vibrator in every five feet or so and pull it right back out.

I've been on a few military jobs that the concrete hardness and slump was specified. If it's not specified then just pour enough for the concrete to not flow away and be wet enough for easy working of the concrete.

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Dnkldorf

Is that a 4' deep trench?
Who makes the spacers?

Don't you rebar it down, before pouring, to avoid conduit float?

JayH

That's going to be some awfully wet concrete if your duct bank is floating in it.

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william1978

The ditch was about 3' deep.

I don't remember who makes those spacers it has been about 3 years ago.

Yes, we stake them down to help with the conduits floating to the top.

Dnkldorf

I see....I think....

You nail the bottom row into the dirt with rebar, and then the rest of the spacers tie to the bottom row?

william1978

I find some rebar that is left over that has a 90 bent on it and stake the whole rack down.

varmit

Spacers: If memory serves me correctly, most of the PVC manufacturers also sell spacers.

If you don't stake the PVC down, it will float like a balloon. My method for staking was to drive a piece of rebar into each side of the ditch, near the top of the duct bank, then tie a piece of rebar across the top. If you have more than 3 tiers of pipe, you probably need to install more than one rebar "strap". If you want the pipe to be strait, so it is easier to pull the wire, stake it down every 6 to 8 feet depending on the number of conduit in the cross section.

Another consideration is thermal expansion. Four inch PVC will expand in length about 1" to 1 1/2" per 100 feet with a 30 degree temperature change.
Say you install the conduit on a day when it is 50 deg. F and sunny, you plan on pouring the next morning, over night the temperature drops to 20 degrees, if the run length is 300 feet, the pipe will now be 3 to 6 inches shorter than when it was installed.

A job that I worked MANY years ago had huge duct banks with 30 to 80 conduit from 1 1/2 to 6 inch. There, to avoid the expansion / contraction problem, the concrete crew would start pouring when the conduit was installed out to about 80 feet from the starting manhole. The concrete would almost be splashing on us when the run was finished at the next man hole. A lot of these runs would take several days to install, but the concrete was always poured to within 20 feet of the end of that days installation. It was stupid hard work, but I was young and poor then. ( I am still poor, just older.)

manchestersparky

Something I always did when doing duct banks.
I ordered my concrete with pea gravels instead of the standard # 6 stone.
There was no difference in cost and it flowed better between the racked conduits.

LawnGuyLandSparky

Yes, April 7, 2007 If I recall...

MDShunk

I always order concrete that way, no matter what I'm pouring. It works and finishes so much easier, with a lot less air pockets. Flows so much better. Generator pads, housekeeping pads, concrete encasement, whatever. You're absolutely right. No difference in price.... just gotta tell the batch plant when you call to order it.

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nitro71

Carlon makes spacers. Tie wire your pipe to the spacers. Set a stake every now and then and tie wire off to it so your pipe doesn't float. I recommend vibrating as you don't want gaps in your concrete. Be careful if you are using EB as it's very thin and could get punctured by the vibrator.

jw0445

EB has a tendency to egg also.

william1978

What is a EB?

Dnkldorf

What he said.

nitro71

EB is a thin PVC that you can use for concrete encasement. Doesn't hot box and cracks easily.

http://www.carlon.com/Master%20Catal...t_Brochure.pdf

william1978

Ok. Around here we call that schedule 20.

Sparky480

Ive used those same spacers. I always tye wire them all together and than to a peice of re bar. Id love to work in trenches like that we get nothing but roots/ rocks up here in NY

adh11676

Here's an interesting product that may be useful in this application. I think the width of the trench would have to be consistently the same size to be effective.

www.sta-down.com