Power Cable and Components Selection for an Induction Motor (Star-Delta)

select the switchgear using the manufacturer's type2 coordination chart with careful consideration for ambient temperature and starting duty . . .

These are the kinds of services performed by a professional engineer under contract, one who can see the issues in person (hopefully) and understands your local requirements. This forum is NOT a substitute for this kind of process.

1) http://cr4.globalspec.com/thread/56416#comment586920

2) a) http://www.global-download.schneider-electric.com/85257578007E5C8A /All/5B43AD51E5E505608825757800770704/$File/24543-en%20%28web%29.pdf

b)http://cr4.globalspec.com/thread/59853#newcomments

3)http://www.electriciancalculators.com/

2) a)http://www.global-download.schneider-electric.com/85257578007E5C8A/All/5B43AD51E5E505608825757800770704/$File/24543-en%20%28web%29.pdf

you can hire an experienced consulting engineer for the requirements.

1. NEMA rated magnetic motor starters are for HP. For a 60 HP motor, NEMA size would be NEMA 4 starter. The Equivelent IEC starter AC-3 for squirrel cage motor sized to current. In your case, 85 amps. If continuous duty motor, meaning it on for longer than 3 hours, rate it 25 percent higher. NEMA 4 is satisfactory. NOTE THAT FOR MOTOR PROTECTION, AN OVERLOAD DEVICE IS BEST AND SHOULD BE REQUIRED. This is sized against nameplate FLA.

2. The NEMA rated CB for your motor should be 150 amps. Your IEC rating should be on or about the same. You can increase these depending on the CB holding the start of the motor, but, highly recommend that you consult a qualified electrician or engineer if this occurs before increasing the above sizes.

3. Cables are assessed against the current carrying ability of the cable. For performance issues where you want to insure that a percent voltage drop is accounted for, you can apply the formula "1.73*lenths of cable*current of load*the constant for copper wire,12.9" and divide this by the 3 percent voltage drop of your supply. Again, this is for performance issue but is good practice. The AWG for a continous rated 60 hp motor with NEC applicaiton is 77amp current carrying and the size cable for this is AWG 3 or AWG 4. Again, if continous duty, you rate current higher by 25 percent and resize. The cm (circular mils) size equivelent for AWG 3-4 is 41 -53 thousandth.

For USA sizing and assessment, the process of selection is the National Electric Code and NEMA standard rating.

All else is IEC.

I agree that with the others when they indicate that you should seek and consult with higher professionals (electrician-Engineers) if this process is not completely (and it is not) understood by you, however, this process should be understood by technicians and electricians working with motors and once understood, not deferred to engineers for application each and every time. It should be an already UNDERSTOOD process as part of thier every day job.

Good luck. I encourage you to always go to a forum EVEN IF YOU GET SPANKED and always encourage you to not be offended when spanked but to understand that you are treading in deep water. You can get or get someone hurt or more if you do not truly understand the issues here.

I really thank to you (Mr. Cyoung) for his concern to my issue posted on the forum, I really appreciate for this deed, hope we can be get connected in future as well.

One thing , which is confusing to me , in my case, what would be the size of thermal overload relay (perfect current range) against my requirement of 60 HP (44.67 KW)motor having FLA = 85 Amps, with the system voltage of 380 Vac.

Thanks once again.

Kind regards to you. God bless you.

http://sea.siemens.com/step/pdfs/cc_2.pdf should help you . . .
select the range of the overload relay such that the nameplate flc at rated voltage falls within that range . . . manufacturers give co-ordination charts to select the relay to match and work with fuses or mccbs or mpcbs in the circuit . . . .
more important is setting the relay . . . what we do is set the relay at flc and run the motor on actual load . . . then measure the current of the loaded motor . . . expect the actual current to be less than the flc . . . set the relay between the actual current and the flc . . . this requires involving the process person with the electrician and there is no had and fast rule . . .

for sizing contactors/switchgear/OL/cable, refer manufacturer's cataloque once you decide which brand is going to be used. For cable size as well as contactor/CB size the duty cycle AC1,or 2 or 3 also to be considered.

since you actually need to ask this question . . . please do not even consider using AC1 or AC2 duty ratings . . .

When sizing contactors various considerations/criteria are adopted by different consultants/engineers/manufacturers. One says main contactor to be rated 100%,delta contactor 58% and star contactor 1/3 of rated current. Another says main and delta contactors to be 58% rated current. Yet another says all three should be rated 58% FLA. Using same size for all the three is very convenient for stocking spares.

I really thank to you (Mr. Pnaban) for your concern to my issue posted on the forum, I really appreciate for this deed, hope we can be get connected in future as well.

One thing , which is confusing to me , in my case, what would be the size of thermal overload relay (perfect current range) against my requirement of 60 HP (44.67 KW)motor having FLA = 85 Amps, with the system voltage of 380 Vac. would it also be 60% of the rated full load current (FLA) of the motor or else.

Thanks once again.

Kind regards to you. God bless you.

As per british practice we use OL in phase rated at 58% FLA. As per NEC some say 25% to be added for continuous duty(>3hrs). For periodic and fluctuating loads like elevators and pressure switch operated water boosting pumps if trips often setting may be increased.