VFD Drive Cable Tension

[iMuse97]

On the Belden Cable site, the maximum pulling tension on a cable we will be pulling is shown as 3088 lbs. See http://www.belden.com/pdfs/catalogs/VFD_Brochure.pdf This shielded drive cable (three #2AWGs) is going to be pulled through 8 ninety degree bends of 2 1/2" RMC. We have two soaping points along the way, and we will soap it as it goes in.

Any comments as to whether we will exceed the max. allowable tension?

 

[iMuse97]

Why did I put this on contracting/estimating? Only because I didn't post it on calculations which was the page I thought I was on. Sorry. Anyway, your comments would still be appreciated. Thanks.

 

[Cow]

Why would you try to pull through 8 nineties?

 

[iMuse97]

It was not my choice. Set up by others. :happysad: There are a couple kicks in there, too. Thankfully, there are also two C's where soap can be added.:roll: One after the third ninety, and one after the sixth.

The job is going to be done (or attempted) as is. It's not my call. As I looked at the plan, I thought that someone here might have an idea as to how to estimate such pulling forces. Just thought I'd ask.

And I'll report back as to what transpires with the pull and subsequent start-up.

 

[don_resqcapt19]

There is an online pulling calculator here. It is somewhat difficult to use. You also need to know the maximum permitted sidwall pressure (crushing force as the wire is pulled around a bend) as that is more often the limiting factor. You will often exceed the sidewall pressure limit before you reach the pulling tension limit. You will need to know the radius of the bends to do the sidewall pressure calculation.

 

[controlled]

Can you pull it out of the "C" fittings? This would cut down the amount of 90's between pull points

 

[iMuse97]

The problem with pulling it out of the C fittings is getting it out (and back in) without overdoing the minimum bending radius.

 

[iMuse97]

PULL UPDATE

PULL UPDATE

And here's the results:

1. the max pull tension was 4200 lbs, not 3088 (size was 2/0, not 2 AWG).
2. we dumped the soap in at the start, and at the two Cs along the way.
3. we never went over 3200 lbs. on the supertugger.
4. Didn't get nearly as much overtime out of it as we had hoped!

 

[John120/240]

Good job getting it done. In the future remind the indivual who ran the

conduit that four nineties is perferred.

 

[mivey]

And here's the results:

1. the max pull tension was 4200 lbs, not 3088 (size was 2/0, not 2 AWG).
2. we dumped the soap in at the start, and at the two Cs along the way.
3. we never went over 3200 lbs. on the supertugger.
4. Didn't get nearly as much overtime out of it as we had hoped!

What about Don's note?

You also need to know the maximum permitted sidwall pressure (crushing force as the wire is pulled around a bend) as that is more often the limiting factor. You will often exceed the sidewall pressure limit before you reach the pulling tension limit. You will need to know the radius of the bends to do the sidewall pressure calculation.

 

[iMuse97]

Good job getting it done. In the future remind the indivual who ran the

conduit that four nineties is perferred.

Thanks. I am under the impression (just walked into the job two weeks ago) that in this plant we electricians just do what the plant and contract engineers say to do.

I'm not sure when it became SOP for engineers to specify where and how to run conduit, but that's the size of it. I actually ran 90s #s 6, 7, and 8. The equipment in the plant was moved, and I guess nobody wanted to pay for, and/or provide the real estate for, a 36x36x8 stainless pull box.

 

[iMuse97]

There is an online pulling calculator here. It is somewhat difficult to use. You also need to know the maximum permitted sidwall pressure (crushing force as the wire is pulled around a bend) as that is more often the limiting factor. You will often exceed the sidewall pressure limit before you reach the pulling tension limit. You will need to know the radius of the bends to do the sidewall pressure calculation.

Thanks Don. I'm sure I'll use this in the future.

 

[iMuse97]

What about Don's note?

Yes, sidewall pressure had to be quite intense as the head was rounding the last 90. I'll see if I can do some figures on that.

 

[don_resqcapt19]

... The equipment in the plant was moved, and I guess nobody wanted to pay for, and/or provide the real estate for, a 36x36x8 stainless pull box.

You could use a conduit pulling sleeve. Does not require the space that a pull box requires, but probably costs about as much.