IEC NEC BS Breaker Overload Fuses for Motors

Your question is confusing. The title of your post is "fuses", but the text has "motor trip setting". Your list numbers, which I guess are clause numbers from NEC. I do not have NEC, being in UK. In principle, there can be no difference between NEC and BS - in a well designed system the fuses protect the isolators and contactor of the motor starter and the cables from damage (or at least from fire) but the motor starter overload device protects the motor from overloading. Setting the motor overload is done by moving its adjuster to the equivalent of motor full-load current. The isolator maker specifies a maximum fuse size. Please clarify where your problem lies.

Thanks for the reply I will try to rephrase it .

we have motor FLA or FLC then for Overload short circuit and backup protection we use different %ages like 175% 300% 250% and 800% of FLA for different protection .as per NEC

My question is how can we do it as per BS is there any BS standard dealing with it .

1. BS 7671 "Requirements for electrical installations IEE Wiring Regulations" is the equivalent of NEC. It does not go into as much detail on motor starters as you appear to be suggesting is given by NEC.
2. BS7671 refers to BS EN 60947 which is a European standard, technically identical with IEC, for Low Voltage Switchgear and Control Gear.
3. BS EN 60947-4-1 is the part dealing with electromechanical starters.
4. I am not sure how deep you need to go. BS7671 is about $100 equivalent here, but the parts of 60947 cost about $300 each.
5. Are you designing new equipment, covering conformance of an existing equipment or what? Are you just concerned with motor starter?
6. Are you dealing with 50Hz/ 60Hz or both (dual frequency)?

The percentages you give look like starting currents as % FLC, which depend on a motors speed (no of poles) and whether it is high start torque [175% being lots of poles and 800% high start torque]. BS7671 has about 1/3 page about "Rotating Machines".

To BS7671, Short Circuit protection for a fixed stationary equipment must operate in less than 5 seconds. The cables must not overheat in that time. In some cases the distance of the motor and volt drop on start decide the cable amp rating to be well above FLC.

Have a look at following :-

http://www.schneider-electric.co.uk/sites/uk/en/products-services/automation-control/products-offer/motor-control/motor-protection-and-control-circuit-breakers/tesys-gv2.page#

Please download document 1672546 (an example motor circuit breaker overload, complying with IEC 60947) on that page and advise if it gives the info you need.

I saw the document from Schneider Electric GV2 breaker as per IEC . This is based again on similar to NEC They comply with IEC as well but NEC is more elaborate .What I am doing is the selection of overload circuit breaker short circuit breaker instantaneous as per BS standard I am unable to find any FLA % ages like we have in NEC so I have to select all these FLA as per BS . I was also looking it in detail for selection of MCC Cable selection like we have in NEC . I have BS 7671 but I am unable to find I will read it again :)

The requirements are that voltage drop does not exceed 4% rated voltage at normal load BS7671 525 and that motors should have adequate voltage for starting at starting currents. Usually, the starting of the motor with highest starting current is necessary with all other loads running. If that is not adequate you must look at the actual sequence of start. Have a look at :-

http://www.brookcrompton.com/pdf-files/2104e_wp_v2.2e.pdf

motor data, see if it helps. The standards do not dictate a code for starting current, always ask the maker, if possible.