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Concentric Neutral Bend Radius per NEC

Concentric Neutral Bend Radius per NEC

Concentric Neutral Bend Radius per NEC

(OP)
What would the bend radius be for a concentric neutral cable?  Does the NEC consider the concentric neutral to be a shield and requires 12x the diameter or would it just be 8x the diameter?

There is no tape shield or anything like that on the cable being used.  (15kV, 1000MCM copper, Single Conductor, Type UD)

Thanks.
 

RE: Concentric Neutral Bend Radius per NEC

NEC art 300.34 Conductor Bending Radius does not refer specifically to the kind of shielding but consider all of kinds. Apparently the tape shield or at least the flatten wire shield could damage the insulation strata beneath the shield. I think the tensioned round wire could damage the insulation also.
Let's do an approximation as follows:
The insulation could resist to a compressive stress of 2900 psi [before total crash] at 20 degree C.   
If we'll take a cable of 2" diameter under the shield and we bend it at 16"[8*dia] the upper side of the shield wire will be stretched to (16+2/2)/16=1.0625. A shield wire of 0.1145" diameter [cross section =0.010238 sqr.inch] wirelength= (16+1)*pi ()/2=26.7" will press the insulation with a force=0.0625*0.010238*16*10^6=10238 lbs [Force= (length1-length2)/length1*area*E [Young Modulus] considering the middle of the cable as unchanged [lenght2].
The compressive stress on insulation will be Force/ (wirelength*wiredia=10238/ (0.1144*26.7) =3351.8 psi.
For a bending radius of 12*cable dia the stress will be only 1585.7 psi.
 

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