360 degree maximum

[gene6]

Construction is routing 6, 1/C control cables #14AWG in a FOUR inch PVC underground conduit - they have approximately 500 degrees of bends - there is no way they’ll damage the cable with such a small conduit full

Im not the AHJ but it seems this should be allowed - opinions?


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Your asking for opinions, but avoiding the question of the engineers specifications and bid documents.
A "duct bank" install is a huge project, were not talking about a 2" PVC to a barn on a farm.
Someone had to get paid to engineer this thing, then it went out to bid, and I suspect the bid documents do not allow more than 270 degrees of bend.

 

[paulengr]

And this relates to pulling 14 AWG conductors in a four inch conduit? Did you ever do that calculation?

I just put the numbers in. Came up with roughly 150 pounds as an estimate without knowing the specific details. I was curious if 500-600 degrees was enough to make a pull impossible with such an obviously easy pull. When you reach pull limits it’s amazing how much even a single elbow adds on. The last elbow in this case increased the pull force 40%. Total bends increase the pull friction exponentially. Changing conduit diameter barely moved the needle.

 

[winnie]

I’d have to disagree with your take on ‘similar effects’ on sidewalk pressure if you mean they’re essentially the same. A factory 90 degree elbow is far less friendly than a 90 sweep.

I should clarify.

Current code is based upon an approximate theory, and does not make any allowances for conduit fill nor bend radius.

Under this approximation, the radius of a bend has no effect on pulling tension. A larger radius will reduce sidewall pressure, which is a separate requirement that needs to be met.

So if the inspector is working to the code as written, they should count elbows and sweeps the same because the code as written considers them the same.

If you (or your client) wishes to violate code as written, that is a decision you (they) can make. As many others here have noted in this case the pull is likely perfectly safe, and that even if a code required pull point were present it would likely not be used.

Jon

 

[Fred B]

Got a kind of sideways question. Count or don't count. Scenerio, 200 + ft of conduit, run in ditch that simply gradually curves giving overall bend of 90 deg. Do you count the 90 toward the total bends, if it can be acheived with no actual heat bending or sweeps installed? It could be lateral or incline related.

 

[ActionDave]

In a ditch I don't count anything that is not a factory elbow or a heat made bend.

 

[electrofelon]

Inspector’s review of duct bank prior to pull


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I am confused here. So this is an underground duct Bank. Was it inspected prior to backfill? If so did the inspector notice and take note of the more than 360° of bends (and say nice underground duct bank that you can never use)? If not, I don't understand how he would evaluate an existing duct Bank prior to a pull. FWIW I don't ever recall, in 20 years, an inspector following a conduit run and counting Bends.....

 

[infinity]

In a ditch I don't count anything that is not a factory elbow or a heat made bend.

I agree, there is no reason to split hairs since the 360° limit is to protect the conductors during installation and waves in the run won't change anything. If I have a conduit run that is all straight pipe but goes around the earth would I need a pull point?

 

[electrofelon]

If I have a conduit run that is all straight pipe but goes around the earth would I need a pull point?

Supply house have a master reel that can do that in one length without a splice?

 

[wwhitney]

Got a kind of sideways question. Count or don't count. Scenario, 200 + ft of conduit, run in ditch that simply gradually curves giving overall bend of 90 deg. Do you count the 90 toward the total bends, if it can be achieved with no actual heat bending or sweeps installed? It could be lateral or incline related.

Yes, you are supposed to count the gradual 90 degrees of bend.

Cheers, Wayne

 

[electrofelon]

Recent job had an approx 140' 3X 3/4 EMT pipe run, 540 of bends. Pull box in the middle. Didn't use it, pulled right through it.

 

[infinity]

Yes, you are supposed to count the gradual 90 degrees of bend.

Cheers, Wayne

Exactly how would one do that?

 

[SSDriver]

I don't buy into any of these pull calculations 100%. Pulling #14s through a 4" conduit with ONLY 540* of bends will not be a hard pull and will not damage wire. I personally would limit it to 360* but this is where adding up multipliers don't always work.

This is where I think doing something in the field and something on paper does not Coincide with each other. I never count the gradual bends even though I know I should. In real life those long gradual swoops don't seem to affect my pulling by much. They definitely affect it but not the same as a factory 90. This is where a multipliers for 90* is definitely not accurate.

I'm sure the radius of the bend plays a big role and is not factored in on most of these calculations other than factory bends.

 

[wwhitney]

Exactly how would one do that?

Take compass bearings on the direction of each end of the trench, and subtract. I.e. if I enter the trench walking S and then exit it walking ESE, that's 67.5 degrees of bend (minimum).

Cheers, Wayne

 

[Hv&Lv]

Yes, you are supposed to count the gradual 90 degrees of bend.

Cheers, Wayne

Disagree.
So you have to count bends in HDD pipe?
Roll pipe?

 

[electrofelon]

My opinion is the 360 limit should just go away. Speaking from years of experience, damaging conductors from too much pulling tension or sidewall pressure is one of the least likely ways to damage conductors.
There are nearly infinite many ways people who don't know what they are doing can damage conductors: pulling loops in and out of pull boxes or c-condeletes, having a mess of tangled wire all over, conductors coming out of the head and having to redo the pull.... Besides, I'm inappropriate pipe run will often let you know by having trouble getting a snake through, rope breaking etc. I can design a code compliant pull that is a thousand times harder than any number of non-code compliant pulls. Just let electricians do their thing.

 

[wwhitney]

So you have to count bends in HDD pipe?
Roll pipe?

Not familiar with those products, what are the applicable NEC article numbers?

I assume we were discussing PVC conduit. In which case (2017) 352.26 says "Bends — Number in One Run. There shall not be more than the equivalent of four quarter bends (360 degrees total) between pull points, for example, conduit bodies and boxes."

Seems clear to me if you connect together (15) 10' sticks of PVC conduit, and make 6 degrees of bend at each stick, that's the equivalent of a quarter bend.

Cheers, Wayne

 

[tortuga]

Speaking from years of experience, damaging conductors from too much pulling tension or sidewall pressure is one of the least likely ways to damage conductors.

I had a service call one time troubleshooting the power to a drying barn, I think it was a pretty long conduit run don't remember the bends but right at 360 if not over. It was an intermittent fault underground, we went able to pull the conductors out and they would not budge.
Then the framer offered the use of his tractor, he was like 'thats how we pulled em in'.
We ended up putting in at least one pull vault.

A few weeks ago I was practicing acrobatics in an attic to reach a troublesome contactor panel, I followed a run of 3/4 flex (FMC) on my way across the attic that was run like MC, it must have had a zillion 360 bends in it, there is no way they ever pulled those conductors in, they had to have pre-pulled the flex. It was to a PV array.

 

[winnie]

Besides, I'm inappropriate pipe run will often let you know by having trouble getting a snake through, rope breaking etc. I can design a code compliant pull that is a thousand times harder than any number of non-code compliant pulls. Just let electricians do their thing.

I could see the above as the basis for an exception to the 360 rule. Basically allow measured pull resistance on the pull rope.

Jon

 

[jim dungar]

If I have a conduit run that is all straight pipe but goes around the earth would I need a pull point?

No problem, it only takes 360 degrees to complete a circle.

 

[kwired]

I had to google that, interesting read:

https://en.wikipedia.org/wiki/Capstan_equation

I have found when running conduit for low voltage / control wires / data / fiber the IT people are waaaay waaay more picky about the number of bends and size of conduit, than we are for standard XHHW McM wire.
The IT crowd usually require a section of conduit be no longer than 100ft or contain more than two 90 degree bends between pull points or pull boxes. And they usually dont want more than 3 cables in any conduit.
Thats not enforceable of course other than in the contract specs and getting paid.

I have seen some that are picky and some that could care less about how they run cables. Most the latter ones though are more of the IT guy that knows where to plug things in at the equipment and how to set up software but can't fish a cable down a wall to save their *** if needed.