Practical limit conductors in motor J Box

[RayPloeger]

Does any one know of a table listing the practical limit on conductor sizes in various 480 volt 3 ph motor Junction Boxes. Above 250 HP I will go to medium voltage with fabricated J Boxes.
Ray Ploeger P.E.

 

[don_resqcapt19]

In theory the supplied motor junction box is suitable for conductors sized per the rules in Article 430.

 

[jdsmith]

For NEMA 1 to NEMA 3 starters we often pull conductors that are suitable for the largest motor that could be connected to the starter, aiming for a maximum voltage drop of 3% on the motor feeder. Typical distance from an MCC to a motor are on the order of 400-800 feet in the refinery so cables are usually upsized one or two sizes beyond the minimum for a given motor. We use all IEEE 841 motors with oversized motor makeup boxes and have not had a problem fitting the terminations in the box.

This doesn't exactly answer your question, but you could compare the junction box sizes in IEEE 841 with the sizes in NEMA MG-1 and then look at feeder cable sizes to get some idea. We have a project to refeed 200 or so motors over the next year and a half so I'll try to take notes as we move along - this would be a good table to have for reference.

 

[cadpoint]

Using Image on Google, this page lists alot and this page gives a white paper covering the history and aspects that cover IEEE 841.