Parallel Power Cabling

K

Thread Starter

KRA

Dear All,

Is there any disadvantage in using parallel cabling? For example, I need to use 2x300sq.mm 4core cable for a motor. Since the motor terminal box is not large enough to terminate 300sq.mm cable, I have selected 4x95sq.mm cable.

Any IEC or IEEE standards explained about this situation?

Please advice.

Thanks in advance.
KRA.
 
Dear Mr. Phil,

Thank you very much for your quick answer.
Can you please explain little more if possible?

Regards,
KRA.
 
KRA... following is a list, copied from thread #1026236772, that lists at least 15 factors that should have been considered:

o Allowable voltage-drop for normal operating load.

o Allowable voltage-drop for future operating load as determined by motor's Service Factor.

o Allowable voltage-drop for starting condition.

o Allowable voltage-drop for reacceleration requirement (if any.)

o Conventional starting, i.e., full-voltage, reduced-voltage, part-winding, wye-delta.

o Electronic starting, i.e., soft-start, VFD.

o Short-circuit withstand capability for an in-close fault (e.g., motor starter.)

o Ground or earth-fault capability for a far-end fault (e.g., motor terminal.)

o Plastic or rubber sheath resistance to chemical attack.

o Metallic screen or shield material withstand capability for excessive heating.

o Derating factor(s) covering installation, i.e., free-air, direct-burial (dry, wet) in conduit (duct bank, clay, Al, steel, plastic.)

o Derating factor(s) covering conductor material (Cu, Al.)

o Derating factor(s) covering round or sector shaped wire, 3x1/c, 1x3/c, 3½/c, or 4-core, overall sheath and/or shield.

o Derating factor(s) covering insulation type and voltage level.

o Derating factor(s) covering termination type (bolt, lug, clamp, brazed, soldered.)

o If direct-burial, then address subsidence concerns.

Your plan to substitute 4x3c/95mmq cables for 2x3c/300mmq, could fall far short of being an adequate solution if voltage-drop alone was considered, was ignored.

A easy and more economoc solution to your dilema is available, but you must provide addtional detail.

Contact me off-list for a solution!

Phil Corso (cepsicon[at]aol[dot]com)
 
Dear KRA,

You can meet the voltage drop criteria using parallel cables. However you also need to check whether the 95mm2 cable you are going to use will withstand the short time fault current as in case of 300mm2 cable used earlier. This is the deciding factor. This is applicable in case of motors fed through breaker controlled feeders. However for fuse protected feeders, you can go for 95mm2 as minimum cable size required will be much lesser from a short time fault carrying capacity perspective
 
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