Parallel Power Cables

By what percentage are they different?

What arrangements are you using to equalise the current flow?

What type of cables are they?

Give us more information!

Generally, if the cables are of the same size (gauge), same construction (stranding), same length, same type of termination, run in parallel path, and are properly physically connected properly (clean terminals, anti-oxide compound, bolt torque, etc.), then there should be minor differences in the current carried by the individual cables, maybe a few percent at most. Otherwise it would not be possible to use this construction because some cables would be over their rated capacity and burn up while others sit there. They are essentially parallel resistors, and will share the current in proportion to their (usually very close) resistances.

If you mix dissimilar cables or lengths, you should be able to use the cable resistance charts (from the maufacturer) to calculate the different resistances, voltage drops, and probably an estimate of your variation in current, but I have not seen this done anywhere.

See NEC article 310.4 for detail of the Conductors in Parallel. Article 310.4 (B) specifies the conditions of the parallel conductors as follows:

"The paralleled conductors in each phase, polarity, neutral, grounded circuit conductor, or equipment grounding conductor shall comply with all of the following:

(1) Be the same length

(2) Have the same conductor material

(3) Be the same size in circular mil area

(4) Have the same insulation type

(5) Be terminated in the same manner"

- MS

Hi,

We have another situation here, we followed NEC article 310.4 (conditions 1 to 5) for our parallel cables (cable #1 & #2), however, our cable # 2 (with Phase A, B & C) had some portion which is not on the same route with cable # 1 (with Phase A, B & C) due to space limitation.

Situation #1: From the switchgear inside the substation, cable #1 entered the substation from the bottom (thru ductbank) and cable # 2 from the top (thru cable tray) and terminates in the switchgear termination point. Outside the substation, they both ran underground.

Situation #2: Same cables in situation #1, due to space limitation along the way to the load, around 60 meters before the termination point @ load side, cable #1 & #2 was separated again (around 30 meters apart) and come together at the load side. They are both underground.

With the situations mentioned above, would there be any problem? As per NEC article 310.4, "same route" was never mentioned. We are talking about 480V system and 750MCM power cables.

Thanks,

-EW

Dear Sirs

All of conditions you mentioned are performed correctly.cable arrangement is as follows : 6 single core cable for phase R (L1) - 6 single cor cable for Phase S(L2) - 6 single core cable for phase T(L3). The difference in one of cables in phase r is abou four times of another.This is so for phases S & T. This unequality is due to mutual inductance. But the question is : How can we arrange the cables so they have the same current. This problem is not discussed in power distribution books. But a brief article is found in the internet.If anybody wants please send me an email to send him.

Best Regards

How are your cables fed? Conduit? Cable tray? You should have the cables arranged so that you have 1 of each phase R-S-T together, so that the E-M fields cancel out. Don't put all the R in one conduit or next to each other, all the S together, etc. Each conduit should have one of each phase.

Guys,

Can anyone here give their thoughts about the below situation please?

Thanks,

-electricwalt

Hi,

We have another situation here, we followed NEC article 310.4 (conditions 1 to 5) for our parallel cables (cable #1 & #2), however, our cable # 2 (with Phase A, B & C) had some portion which is not on the same route with cable # 1 (with Phase A, B & C) due to space limitation.

Situation #1: From the switchgear inside the substation, cable #1 entered the substation from the bottom (thru ductbank) and cable # 2 from the top (thru cable tray) and terminates in the switchgear termination point. Outside the substation, they both ran underground.

Situation #2: Same cables in situation #1, due to space limitation along the way to the load, around 60 meters before the termination point @ load side, cable #1 & #2 was separated again (around 30 meters apart) and come together at the load side. They are both underground.

With the situations mentioned above, would there be any problem? As per NEC article 310.4, "same route" was never mentioned. We are talking about 480V system and 750MCM power cables.

Thanks,

-EW