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Based on NEC The installed equipment may have different temperature limitations, so be sure to check the actual ratings. Certain cable types may also have a specified maximum temperature limit. This app assumes installation in conduit or direct burial when individual insulated wire types are chosen. If there are more than three current- carrying conductors, the ampacity from the table must be adjusted based on the values found in NEC Table Do not include equipment grounding conductors, and do not include neutral conductors that meet the exception conditions in NEC If there are multiple sets of conductors in a wiring method that supply electrical components that cannot be simultaneously energized, only the number of conductors that will be energized at any one time must be counted.

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Sign in. P Add Comment. Exception No. Click to Enlarge. In the NEC, parallel conductors inside an auxiliary gutter must be grouped together to prevent current imbalance in the paralleled conductors due to inductive reactance. In order to install conductors in parallel, the paralleled conductors in each phase, polarity, neutral, grounded circuit conductor, equipment grounding conductor, or equipment bonding jumper must comply with all of the following: 1 Be the same length.

Where single conductor cables comprising each phase, neutral, or grounded conductor of an alternating-current circuit are connected in parallel as permitted in My money would be on a bad connection at one or more of the terminations on Phase C. I don’t think a spacing problem would show up as a lower current on one phase in each of the three conductors associated with that phase. That statenent presumes that the cables were not intentionally laid with all Phase A conductors together, all Phase B conductors together, and all Phase C conductors together.

Charlie, My money would be on a bad connection at one or more of the terminations on Phase C. Click to expand Don, these are very large cables, with very low resistance. This might cause overheating without the release of smoke.

The Phase C cables all terminate at the same point. My first step in troubleshooting would be to look for a bad connection at that point. My next step would be to try to learn the exact manner in which the cables were laid. I would seek out the persons who installed the cables, and ask them what they remember about the installation. If that cannot be done e. I would not apply “Occam’s Razor” on this one.

You don’t have to look first at the simplest of possible causes. Rather, you should first attempt to verify or disprove the causes that are the simplest ones to investigate.

A thermal gun is all you need to test the connections. Checking the layout of the conductors in the trench is less easy. Charlie, The Phase C cables all terminate at the same point. Location Illinois Occupation Engineer.

A thermal photo or even a cheap infrared temp. It would be whole lot cheaper than replacing a overheated cable, also.


3 phase parallel feeders free.Conductors Connected in Parallel: Each Set Must Have the Same Electrical Characteristics

It consists of installing one current transformer around one of the parallel conductors (for each phase). It is appealing, because you can use one CT per phase. Parallel conductor installations are covered in NEC (H) and are permitted for each phase, polarity, neutral, or grounded conductor in sizes 1/0 AWG and. Paralleled conductors are permitted if sized at 1/0 AWG or larger. The number of parallel runs is the number of separate conductors installed within each phase.


Current Unbalance in parallel feeders | Mike Holt’s Forum


Parallel conductors are often installed where large ampacity feeders or services are used. Total understanding of the paralleling requirements permitted in the National Electrical Code is necessary before attempting to design a large electrical system or install these conductors.

Section Where used as parallel conductors, the circular-mil areas of these conductors are added together to provide the total cross-sectional area for the overall size of the parallel conductors. These parallel conductors can be used as phase conductors, neutral conductors or grounded conductors. Be careful though, since one of the primary concerns when installing parallel conductors is ensuring that each conductor in the paralleled set has the same electrical characteristics as the others in the same set.

All of the paralleled conductors in each phase, neutral or grounded set must be the same length and be made from the same conductor material. They must be the same circular mil area and have the same type of insulation. Finally, all parallel conductors must be terminated in the same manner. This ensures that each conductor in the parallel set will carry the same amount of current.

However, one-phase, neutral or grounded circuit conductors are not required to have the same physical characteristics as those of another phase, neutral or grounded conductor. Any taps made to the paralleled sets of conductors must be made to all the conductors in the set, not just one.

Tapping only one of the conductors in the set could result in an imbalance with one of the conductors carrying more current than the other, resulting in heating of that one conductor and possible insulation damage or failure. For example, if three kcmil conductors are run per phase, a tap from that particular phase must be a tap from all of the kcmil conductors, not just one of the set.

This would require a common terminal point for all three parallel conductors with a tap conductor connection to the common terminal. Where paralleled conductors are run in separate raceways or cables, the raceways or cables must have the same physical characteristics.

For example, if there are four kcmil conductors in a paralleled set of phase conductors, the four separate raceways enclosing the conductors must be all rigid steel, all IMC, or all PVC, etc. If the raceways were of different characteristics, such as three rigid ferrous metal conduits with one rigid nonmetallic conduit, the conductor in the PVC raceway would carry more current than the conductors in each of the metal raceways.

This would result in more impedance in the conductors within the ferrous metal raceways than in the PVC raceway. The higher current in the conductor in the PVC raceway would result in possible overheating of the conductor and insulation damage.

Each phase and each neutral or grounded conductor must be present within each separate raceway, auxiliary gutter, cable tray, cable bus assembly, cable or cord. There is an exception to this general rule located in Care must also be taken for compliance with Section Mark C.

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