distance between boxes

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jimmy3214

Member
Location
Indiana
I have been in the trade for 13 years now.. ever since i started I have been told that there has to be no more than 100 feet between boxes on a conduit run. Where does it state this in th code book?

[ March 03, 2003, 04:10 PM: Message edited by: jimmy3214 ]
 

amptech

Senior Member
Location
Indiana
Re: distance between boxes

As long as you don't exceed 360? worth of bends, the length of a run of conduit without a j-box is limited only by the length of wire you can buy. I have several 600'+ runs of pipe in factory slab floors with no boxes, just 90? sweeps on both ends. I also have quite a few as long or longer overhead. The rolls of line on the Mighty Mouse are 2000'long. Greenlee sells poly line in 6500' pails.
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: distance between boxes

We have 1000' pull ropes for our Greenlee tuggers and they get used often. More often then not on such long runs we are likely to use some sort of tractor to pull them in.
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: distance between boxes

Hurk27, you are absolutely right, if we were running 4, 600kcmils the max pulling force would work out like this.

Area of the wire is 600,000cmil

Allowable stress on soft drawn copper is .008 pounds per cmil

Number of conductors is 4

A constant for more then 3 conductors is .8

600,000 x .008 x 4 x .8 = 15,360 lbs of pulling force allowed, however southwire recommends not to exceed 10,000lbs and 90% of our sheaves are rated 10,000lbs so we try not to exceed this.

Our largest Greenlee tugers are rated 8000lbs continuous or 10,000lbs intermittent, it is faster and easer to use a large all terrain scissor lift, it has the power and steady slow speed you want.

Here is a link to more info on this.

Southwire Technical Paper
 

luke warmwater

Senior Member
Re: distance between boxes

Bob, do you have the latest Greenlee tugger?? The one on a wheeled cart that doesn't require anchoring it to the floor. I personally haven't used one yet. My buddy used one last week where the floor had been tiled, so the GC was glad not to see a new tiled floor looking like swiss cheeze.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: distance between boxes

When looking at the pull and the forces required you must remember that in many cases it is not the pulling force itself that is the limiting factor. In many cases it is the "sidewall" pressure. This is the crushing force that is applied to the conductor insulation when pulling around bends. The amount of sidewall pressure is a function of the pulling force and the bend radius. The Southwire Power Cable Handbook has the calculation in it. I'm not sure if it is on the website.
Don
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: distance between boxes

Yes we have a few of the "Ultra Tuggers" they are much better then the "Super Tuggers" for most things.

If you use it as the directions show you will not bend, break, pull off walls or otherwise destroy your work. :cool:

You can replace the 2 boom sections with 3" RMC, you get the machine 20' from the raceway so you can pull plenty of slack or reach overhead

Bad side, very heavy to transport, a lot of potentially amputate your finger "pinch points" and it is slower speed then the older ones, Greenlee will sell you a speed booster, we do not have that.

The newest thing we got was 2 "Ultra Feeders", I have not used them but I am told they work great.

When I went to the Greenlee site I saw that I was mistaken with the capacity of the tugger it is 8500 Max 6000 Cont.

Greenlee Ultra Tugger & Feeder

[ March 04, 2003, 11:22 PM: Message edited by: iwire ]
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: distance between boxes

Don, I can only say I know of sidewall pressure I do not know how to calculate it and to be honest it has not come up when we have been pulling.

I can tell you we have a very successful record, proper use of steel,(even in the middle of a PVC run) large radius sweeps is essential. And the feeding end must be set up for minimal drag so hopefully we do not have to reach those numbers.

A pull I remember was 4 500kcmils in 3" EMT 325' -350' and 5 90s (we pulled right thru a braced can) the strain gauge stayed around 5000-6000lbs with some higher peaks.

I only know of one failure and that turned out to be poor backfill (*&#% rock). The excavation contractor paid the bill.

[ March 04, 2003, 11:51 PM: Message edited by: iwire ]
 

Nick

Senior Member
Re: distance between boxes

Here is a link to Polywater. They have some great software we use for this purpose. The Demo is not working right now but check back.

Also, here is some good info and a calculator for sidewall pressure.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: distance between boxes

I think that the maximum permitted sidewall pressure shown in the examples in the Newton calculator is off by a factor of 10!! The Southwire Power Cable Manual shows the maximum permitted sidewall pressure in the 300 to 500 pound per foot range.
Don
 
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