MV Pulls

[mstrlucky74]

We are going to talk about this internally but I’d like to have some talking points to bring up regarding pulling and setup. Not expected but it would be nice if I could. This is not usual bid work I come across but I think there should be some serious thought given to the pulls etc.. Most of the duct banks consist of EXISTING 4” PVC. There on average (9) conduits in each duct bank. Average run is about 800’ and going through We are pulling 3 #500 5kv cables plus 600v ground in each conduit. I’m thinking:

Setup- I guess the wire will be delivered and staged somewhere on site. How are we getting it from staged area to where the pull will take place?
What is the most efficient way to do these pulls?
What will our pull points be?
Setup and Breakdown times?

Thanks guys.

 

[sameguy]

Temperatures on pulling days.

 

[jumper]

What is a 600V ground?

If insulation, why can the ground/EGC have a lesser value given 300.3(B)?

 

[ron]

When was a mandrel pulled through last?
What if it doesn't pull through?
How many elbows are there?
Who is doing the pull calculations?
Are there conductors in there currently?
Is there a need to verify the ductbank configuration / depth to reconfirm Neher McGrath calculations?

 

[MyCleveland]

What is a 600V ground?

If insulation, why can the ground/EGC have a lesser value given 300.3(B)?

See 250.184 A 1

 

[mstrlucky74]

When was a mandrel pulled through last? We have to mandrel.
What if it doesn't pull through? Will mandrel? If mandrel doesnt go through I don;t know what happens.
How many elbows are there? About 3 in each run with manhole that 90's the run.
Who is doing the pull calculations? OUr engineer after we get job.
Are there conductors in there currently? No
Is there a need to verify the ductbank configuration / depth to reconfirm Neher McGrath calculations?

.

When was a mandrel pulled through last? We have to mandrel.
What if it doesn't pull through? Will mandrel? If mandrel doesnt go through I don;t know what happens.
How many elbows are there? About 3 in each run with manhole that 90's the run.
Are there conductors in there currently? No
Is there a need to verify the ductbank configuration / depth to reconfirm Neher McGrath calculations. Not sure what you mean.
Thanks!!!

 

[mstrlucky74]

What is a 600V ground?

If insulation, why can the ground/EGC have a lesser value given 300.3(B)?

Yes if we are pulling 5kv #500 there is a 600v #2/0 ground.

 

[mstrlucky74]

Temperatures on pulling days.

And how does cold( i'd imagine cold would negatively affect pull) affect pull?

 

[don_resqcapt19]

And how does cold( i'd imagine cold would negatively affect pull) affect pull?

As it gets below 40°F the wire is much stiffer and harder to handle. Most conductor types cannot be handled below 14°F without risk of damage to the insulation.

Someone will have to do the pulling calculations. With 3 90s in an 800 foot run, there is risk of exceeding the maximum permitted sidewall pressure. To find the sidewall pressure you need to find the pulling tension coming out of each 90, and also know the radius of the 90. The sidewall pressure and not the actual pulling tension, is most often the limiting factor in a pull.

As far as pulling, for the above reason, it is always best to have the bends closer to the feed end, than to the pulling end. However you are limited by the installed configuration.

 

[jumper]

See 250.184 A 1

Thank you.

 

[LarryFine]

As far as pulling, for the above reason, it is always best to have the bends closer to the feed end, than to the pulling end. However you are limited by the installed configuration.

Seems like the opposite would be true.

 

[mstrlucky74]

As it gets below 40°F the wire is much stiffer and harder to handle. Most conductor types cannot be handled below 14°F without risk of damage to the insulation.

Someone will have to do the pulling calculations. With 3 90s in an 800 foot run, there is risk of exceeding the maximum permitted sidewall pressure. To find the sidewall pressure you need to find the pulling tension coming out of each 90, and also know the radius of the 90. The sidewall pressure and not the actual pulling tension, is most often the limiting factor in a pull.

As far as pulling, for the above reason, it is always best to have the bends closer to the feed end, than to the pulling end. However you are limited by the installed configuration.

So what happens if you do exceed sidewall pressure? Have to still make pulls.

Sent from my SM-N960U using Tapatalk

 

[jumper]

So what happens if you do exceed sidewall pressure? Have to still make pulls.

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Bad things happen. Usually conductor insulation damage.

Google it.

 

[don_resqcapt19]

So what happens if you do exceed sidewall pressure? Have to still make pulls.

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Excessive sidewall pressure damages the insulation and can result in complete cable failure. Ever without a complete failure, there may be enough damage that the cable will not pass the acceptance testing.

 

[don_resqcapt19]

Seems like the opposite would be true.

The tension on the conductor itself increases along the pull. You want the bends in the locations with the least pulling tension. If you have a 90 and the pulling end of the run, the cable will have almost 100% of the total pulling tension. As I recall the sidewall pressure is the pulling tension divided by the radius of the 90 in feet. Typical maximum sidewall pressure is 500 to 600.

 

[mstrlucky74]

The tension on the conductor itself increases along the pull. You want the bends in the locations with the least pulling tension. If you have a 90 and the pulling end of the run, the cable will have almost 100% of the total pulling tension. As I recall the sidewall pressure is the pulling tension divided by the radius of the 90 in feet. Typical maximum sidewall pressure is 500 to 600.

So if you have a 90 near where you are pulling that will be a to of pressure on that 90 because it's close to the pull point? Thanks.

 

[GoldDigger]

So if you have a 90 near where you are pulling that will be a to of pressure on that 90 because it's close to the pull point? Thanks.

Yes, because the tension in the wire is the friction around the 90 multiplied by the downstream tension of the long straight section.
If you feed at the 90 the overall pulling tension will be lower, the tension at the 90 will be much lower, but the remainder of the pull, from 90 to pull point will be under the full pulling tension. Usually there is no downside to that, unless there is a chance of multiple wires wedging.

 

[mstrlucky74]

So how does one determine where splicing/pull points would take place in a pull. FOr instance on the attached it's a 900' run with three manholes and bends. THe routing is in bluee.

 

[GoldDigger]

Calculate pulling tension for segments individually, then in various combinations. Analyze whether you can lay wire out at a given manhole to pull in and repull out. Is the dark area in/near substation 10 vault, duct bank, tunnel? Lots of bends there.

 

[mstrlucky74]

Calculate pulling tension for segments individually, then in various combinations. Analyze whether you can lay wire out at a given manhole to pull in and repull out. Is the dark area in/near substation 10 vault, duct bank, tunnel? Lots of bends there.

The dark part of the ductbank are the new conduits connecting to the existing conduit duck bank. THey go to substation 10,11 & 12.