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Motor circuit calculator

Cable, breaker, contactor at overload para sa isang motor.

AS/NZS 3000AS/NZS 3008.1.2AS/NZS 3008.1.1

Reads AS/NZS 3008.1.2:2017 (NZ), AS/NZS 3000:2018 and AS/NZS 3008.1.1:2025 (AU). Tables checked 1 Oct 2026.

Subukan ang isang job 4

Nilalagyan ng halimbawang value ang bawat job. Palitan ang mga ito ng sarili mong value.

Mga input

Worked example gamit ang mga default na input.

Shaft power
15 kW
Mga phase
Three phase
Voltage
400 V
Power factor
0.85
Efficiency
0.9
Locked-rotor current
0 × FLC
Starter
Direct on line
Uri ng circuit-breaker
Curve D
Rating ng circuit-breaker
0 A
Standard
NZ · AS/NZS 3008.1.2
Haba ng ruta
30 m
Installation method
Enclosed sa hangin
Conductor
Tanso
Insulation
PVC 75 °C
Ambient na temperatura
30 °C
Mga circuit na pinagsama-sama
1
Ze sa board
0.35 Ω
Tumatakbo nang walang bantay
Hindi
Serbisyo ng fire protection
Hindi

Cable at circuit-breaker

16 mm² sa 32 A type D

Full load current
28.3A
Starting current
226.4A
Main contactor, AC-3
32A
Setting ng overload relay
28.3A
Saklaw ng overload relay
23 hanggang 32 A
Isolating switch, AC-23, hindi bababa sa
28.3A

Design aid lang ang resultang ito. I-verify ito laban sa kasalukuyang standard.

Mga hakbang ng kalkulasyon

  1. Full load current28.3A
  2. Locked-rotor current226.4A

    AS/NZS 3000:2018 Cl 4.13.1.2(i)

  3. Starting current, direct on line226.4A
  4. Circuit-breaker, uri D32A
  5. Mababang dulo ng instantaneous band (generic)320A
  6. Main contactor, AC-3, hindi bababa sa28.3A
  7. Setting ng overload relay28.3A
  8. Rating ng isolating switch, hindi bababa sa28.3A

    AS/NZS 3000:2018 Cl 4.13.1.2

  9. Proteksyon sa overloadKinakailangan

    AS/NZS 3000:2018 Cl 4.13.2

  10. Proteksyon sa overtemperatureKinakailangan

    AS/NZS 3000:2018 Cl 4.13.3.1(b)

  11. Ambient derating factor×1.00

    AS/NZS 3008.1.2:2017 Tables 27(1), 27(2) p.88

  12. Grouping derating factor×1.00

    One circuit, no grouping factor

  13. Soil derating factor×1.00

    AS/NZS 3008.1.2:2017 Table 29 p.90

  14. Derating factor ng lalim ng paglilibing×1.00

    AS/NZS 3008.1.2:2017 Tables 28(1), 28(2) p.89

  15. Total derating factor×1.00
  16. Kinakailangang tabulated current28.3A

    AS/NZS 3000:2018 Cl 3.4

  17. Napiling laki ng conductor16mm²

    AS/NZS 3008.1.2:2017 Table 13 p.62–64

  18. Derated na current capacity66A

    AS/NZS 3000:2018 Cl 3.4

  19. Voltage drop0.45%
  20. Device rating In32A

    AS/NZS 3000:2018 Cl 2.5.3.1

  21. Laki ng earth conductor6mm²

    AS/NZS 3000:2018 Table 5.1

  22. Earth fault loop impedance sa 230 V phase sa earth0.5Ω

    AS/NZS 3000:2018 Table 8.1

Tungkol sa calculator na ito

How this is calculated

The tool sizes the circuit for one motor: the cable, the circuit-breaker, the contactor, the overload relay and the isolating switch. It reads AS/NZS 3000:2018 Cl 4.13 and sizes the cable with the cable size tool.

  1. Full load current. It divides the shaft power by the supply factor, the power factor and the efficiency. This is the same figure as the motor tool.
  2. Locked-rotor current. It takes the maker's multiple of full load current. With none, it takes 8 times full load current (Cl 4.13.1.2(i)).
  3. Starting current. Direct on line, the start equals the locked-rotor current. Star-delta gives a third of it. A soft starter gives the limit you enter. A drive gives about 1.5 times full load current (generic).
  4. Circuit-breaker. It picks the smallest standard rating at or above full load current. The low end of its instantaneous band must clear the start. The bands are generic: type B 3, type C 5 and type D 10 times the rating.
  5. Cable. The cable size tool sizes it with that breaker. The cable current capacity must be at least the breaker rating. It also checks the voltage drop and the earth loop with the Ze you type.
  6. Contactor and overload relay. It picks an AC-3 frame and a relay range from generic lists. Direct on line and soft start use full load current. Star-delta uses full load current divided by √3 for the main contactor, the delta contactor and the relay. The star contactor uses full load current divided by 3.
  7. Isolating switch. It must carry full load current and break the locked-rotor current. An AC-23 switch at or above full load current does both (Cl 4.13.1.2).
  8. Motor protection. Overload protection applies above 370 W (Cl 4.13.2). Overtemperature protection applies above 2250 W, or above 240 VA for a motor that runs unattended (Cl 4.13.3.1). A motor on a fire-protection service has neither (Cl 4.13.3.2).
StepClause or sourceWhat it decides
Full load currentMotor toolThe running current
Locked-rotor currentCl 4.13.1.2(i)The current at standstill
Starting currentStarter type, genericThe current the device must ride through
Circuit-breakerGeneric bandsThe rating and the type
CableCable size toolThe conductor size
Contactor and relayGeneric frames and rangesThe AC-3 frames and the relay setting
Isolating switchCl 4.13.1.2The AC-23 rating
Motor protectionCl 4.13.2 and Cl 4.13.3Overload and overtemperature protection

Worked example

  • 15 kW, 400 V, three‑phase pump, direct on line, 30 m, type D. The tool gives a full load current of 28.3 A and a locked-rotor current of 226.4 A. The result is a 16 mm² cable on a 32 A type D circuit-breaker. The contactor frame is 32 A. The relay setting is 28.3 A in the 23 to 32 A range. The isolating switch must be 28.3 A or more at AC-23.

Limits

  • The contactor frames, relay ranges, breaker bands and the soft starter and drive starting currents are generic. They are not from a standard. Check the maker's catalogue and coordination tables.
  • The locked-rotor figure of 8 times full load current is a default. Use the maker's figure when you have it.
  • The cable is sized to the breaker rating. Where the overload relay protects the cable, a smaller cable can be allowed.
  • Star-delta needs six cables to the motor. Each carries full load current divided by √3.
  • A drive can draw a different input current. Size the supply from the drive data sheet.
  • The tool does not check the prospective fault current or the breaker breaking capacity.

See also: Motor circuit for a 15 kW pump: DOL or star-delta, Motor starters, contactors and overload relays, Motor circuits and starting, the motor calculator and the cable size calculator.

Mga tanong

Design aid ang resulta. I-verify ito laban sa kasalukuyang standard.

Ano ang ibinibigay sa akin ng Motor Circuit tool?

Isang resulta para sa isang motor: ang full load at locked-rotor current, ang starting current, ang cable, ang circuit-breaker, ang contactors, ang setting at range ng overload relay, at ang rating ng isolating switch.

Bakit type D circuit-breaker ang pinipili nito?

Humihila ang direct-on-line start ng ilang beses ng full load sa loob ng ilang segundo. Ang type D breaker ay nagti-trip agad lang kapag lampas na lampas sa rating nito, kaya nalalampasan nito ang start. Itinataas ng tool ang rating ng C type hanggang malampasan nito ang start.

Paano sina-size ang star-delta starter?

Dinadala ng main at delta contactor at ng overload relay ang phase current, na full load na hinati sa √3. Ang star contactor ay nagdadala ng isang katlo ng full load. Ang anim na cable papunta sa motor ay pareho ring nagdadala ng phase current.

Saan galing ang locked-rotor current?

I-enter ito mula sa maker o sa code letter. Kung wala ito, kukunin ng tool ang walong beses ng full load, ang figure na ibinibigay ng AS/NZS 3000 Cl 4.13.1.2 para sa a.c. motor. Dapat kayang putulin ito ng isolating switch.

Galing ba sa standard ang laki ng contactor at relay?

Hindi. Ang frame size, relay range at breaker band ay generic na figure. Ipinapakita nila ang klase ng part na hahanapin. Tingnan ang catalogue ng maker at ang coordination table nito bago ka bumili.

Mga worked example

Background

Mga clause at table na binabasa ng tool na ito

Bawat clause at table, kasama kung paano ito na-verify

Huling na-check ang mga table noong 1 Oct 2026.

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