roped conductors

[mikesimpson5]

Is anyone familiar with roped conductors and how they can increase the short circuit/withstand rating of equipment? I have a tap box rated 10k but if the conductors are "roped", the rating increases to 65k.

 

[jim dungar]

Conductors move during short circuits which can cause them to pull out of the lugs. Roping the conductors minimizes their movement.

 

[Mike01]

Roping

Roping

Like this (see attached)? This is definately not my handywork but I knew this photo would come in handy some day....

 

[mikesimpson5]

I saw this picture before, but I still don't understand how this would increase the withstand rating of the equipment from 10k to 65k.

 

[squaredan]

Like this (see attached)? This is definately not my handywork but I knew this photo would come in handy some day....

Nice Rope Job..Is there a special way that they must be tied, where can you find this INfo? Also wanted to add that during a short circuit there is Major Magnetic forces, Expand and Collapsing, at work and those wires would just pull right out of lugs whip all around, thats why they use rope to tie them down...

 

[jim dungar]

I saw this picture before, but I still don't understand how this would increase the withstand rating of the equipment from 10k to 65k.

Roping restrains the conductors movement, raising the amount of magnetic forces required before the conductors pull out of the lugs.

 

[zbang]

FWIW, some people say "roping" when they mean laying some number of conductors or cables into a rope form (like a flex. cord w/o the jacket). I've only seen this done in low voltage. Not real common, but there it is.

 

[jrannis]

Long ago, I think we had a debate about the type of material used for the rope in the pic.

 

[Mike01]

Roping Mfgr. Requirements

Roping Mfgr. Requirements

You usually have to approach high levels of fault current before manufacturers require roping (around 85Ka for load cables and 130Ka for service cables) Typically (in my parts) we do not see fault currents of this magnitude (typically but I have in some locations) but when parallel generators or even large enough single gen sets start getting involved with closed transitions transfers, and main tie-main with closed transition transfers anything is possible. I have attached two images from a Square D catalog about roping see the table at the right for Ka requirements. It appears it does not "increase" the "withstand" rating of the equipment it is just a manufacturers requirement to help with movement and stresses created during a short circuit. So it does not increase the rating just helps deal with the conditions. Like a K rated transformer it does not mitigate harmonics just helps remove the excess heat created by the harmonics by utilizing more copper (or aluminum).

 

[squaredan]

You usually have to approach high levels of fault current before manufacturers require roping (around 85Ka for load cables and 130Ka for service cables) Typically (in my parts) we do not see fault currents of this magnitude (typically but I have in some locations) but when parallel generators or even large enough single gen sets start getting involved with closed transitions transfers, and main tie-main with closed transition transfers anything is possible. I have attached two images from a Square D catalog about roping see the table at the right for Ka requirements. It appears it does not "increase" the "withstand" rating of the equipment it is just a manufacturers requirement to help with movement and stresses created during a short circuit. So it does not increase the rating just helps deal with the conditions. Like a K rated transformer it does not mitigate harmonics just helps remove the excess heat created by the harmonics by utilizing more copper (or aluminum).

thanks Mike for the rope links!

 

[MBaker1.33]

HVAC zip ties

HVAC zip ties

Nice Rope Job..Is there a special way that they must be tied, where can you find this INfo? Also wanted to add that during a short circuit there is Major Magnetic forces, Expand and Collapsing, at work and those wires would just pull right out of lugs whip all around, thats why they use rope to tie them down...

The zip tie on that size wire will last 15 years or more I've used them and seen after that time they may become loss but the integrity is in tack. Never use rope.

 

[Cow]

The CT cans we buy require roping.

 

[tish53]

thanks all for the great information. I have learned something today

 

[iwire]

The CT cans we buy require roping.

In all cases or only when the fault current exceeds a certain level?

 

[stew]

I have installed 4 ct cans in the last few years and all of them have instructions included with the can/service bussing that detail the size of rope (3/8) and number of wraps required regardless of loading.

 

[iwire]

regardless of loading.

The loading is irrelevant, it is the available fault current that would (or could) matter.

For instance you could have a section of switchgear with a 40,000 amp fault rating without roping but with roping it might increase to 65,000.

 

[stew]

I meant to say fault current. The instructions with the service bussing never specified a fault current only that roping was required.

 

[Cow]

I meant to say fault current. The instructions with the service bussing never specified a fault current only that roping was required.

Yep. Just like Stew said, the diagram tells you to rope and how to do it. No mention of fault currents on the diagram.

 

[George Stolz]

Got a link, or product name, or something to go on?

 

[stew]

Got a link, or product name, or something to go on?

trying to figure out how to upload a milbank pdf for you. I am electronically challenged and cant figure out how to do it on here.