Parallel Feeder Conduits

[jap]

Show them this and tell them it's break time.

I agree. Maybe they'd look at the overbent factory 90's and it'd take their mind off of the conductors being exactly the same length.
And the couplings not being lined up at a symmetrical angle on the 90's (that is if the spacing between the pipes going into the J-Box are exactly the same, perfectly plum, and the 90's are supposed to be all the same) just goes to show that even when you try hard, the runs tend to not turn out exactly the same.

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[ron]

You all originally said the conductors had to be the same length.
Now your talking percentages.>

Ideally it needs to be exact. We have to be reasonable ......

 

[don_resqcapt19]

Ideally it needs to be exact. We have to be reasonable ......

Actually the code says the same length, so really the code says you can't install parallel conductors as the "same length" is an impossible standard to meet.

 

[electricalist]

I agree. Maybe they'd look at the overbent factory 90's and it'd take their mind off of the conductors being exactly the same length.
And the couplings not being lined up at a symmetrical angle on the 90's (that is if the spacing between the pipes going into the J-Box are exactly the same, perfectly plum, and the 90's are supposed to be all the same) just goes to show that even when you try hard, the runs tend to not turn out exactly the same.

JAP>

Ouch. If you're mad just say so.

 

[ActionDave]

You all originally said the conductors had to be the same length.
Now your talking percentages.
At those margins you could terminate, be code compliant, and not look like crap.
Good deal.

JAP>

So you'll pick apart irrelevant details that have nothing to do with code or safety in some pipe runs but you don't think twice about an actual code violation?

 

[jap]

So you'll pick apart irrelevant details that have nothing to do with code or safety in some pipe runs but you don't think twice about an actual code violation?

I'm not picking it apart. The picture looks good. I just used it as an example that its an imperfect world and you have to be reasonable with the allowances on parallel conductors and not get hung up on the exact wording of the code. Don hit the nail on the head with his response above. without some leiniency parallel conductors would not be allowed.

JAP>

 

[jap]

Actually the code says the same length, so really the code says you can't install parallel conductors as the "same length" is an impossible standard to meet.

This is exactly right.

JAP>

 

[jap]

So you'll pick apart irrelevant details that have nothing to do with code or safety in some pipe runs but you don't think twice about an actual code violation?

If the pipe runs are not exactly the same length, which in turn could make the conductors not be exactly the same length when installed, then it is relavant and has everything to do with code violation if you are following exactly what the code rule reads.

I agree some common sense needs to be used on the inspectors part when determining just how stringent to be on conductors installed in parallel that's all.


JAP>

 

[jap]

Ouch. If you're mad just say so.

Not mad at all. Installled several runs of pipe exactly like whats shown in the picture with all of the same issues.
But, the hard work and all the labor envolved in making the conduit look good doesn't waive the requirements or the rule for the parallel conductors.

 

[kwired]

No matter what code says, the idea here is to get each individual conductor of the set to have the same overall impedance so that current will be balanced among all conductors of the set. If the conductors are same material, same size, same length, and run through same environments they should have same impedance.

Reality is that you will have a difficult time achieving exact same conditions for each conductor though it is not too difficult to come pretty close. But NEC does not give us any acceptable tolerances either.

I also think this may have some to do with why they don't want us to use conductors smaller then 1/0 for parallel conductor applications. Might be easier to have different enough conditions on a pair of 12AWG to have too much imbalance then it is for a pair of 1/0.

 

[jap]

My question would be regardless of whether the conductors of parallel runs are exactly the same length or not, most parallel conductors are sized where theres a little lee way in the amperage anyway. If the current is divided between the conductors, even if it is 5% give or take, and its still below the ampacity of the single conductor rating, what's the issue?

JAP>

 

[Carultch]

My question would be regardless of whether the conductors of parallel runs are exactly the same length or not, most parallel conductors are sized where theres a little lee way in the amperage anyway. If the current is divided between the conductors, even if it is 5% give or take, and its still below the ampacity of the single conductor rating, what's the issue?

JAP>

I would agree. If one can use Ohm's law to prove that the conductors still operate at or below their ampacity, there is no issue.

However, if nominally the conductors operate at exactly their ampacity, that could be an issue. It would be of interest to know just how much of a safety factor is already in 310.15(B)(16). One example would be a 400A feed built from parallel 3/0 in two conduits.

 

[jap]

I would agree. If one can use Ohm's law to prove that the conductors still operate at or below their ampacity, there is no issue.

However, if nominally the conductors operate at exactly their ampacity, that could be an issue. It would be of interest to know just how much of a safety factor is already in 310.15(B)(16). One example would be a 400A feed built from parallel 3/0 in two conduits.

That was the exact scenario I was thinking about at the time also.

JAP>