06 — Calculators
Current-carrying capacity as installed
The tabulated value applies to a single cable at 30 °C. In the plant it sits in a filled duct beside eleven others, with a machine standing over it. The correction factors are the part people skip in a quick estimate — and the part that overturns the design.
Result
- Current-carrying capacity as installed
- —A
- Combined factor
- —
- Utilisation by the design current
- —%
- Assessment of the coordination
- —
Please fill all fields with valid numbers.
- Opens the print dialog. Choose “Save as PDF” as the destination.
- Opens your email program with the values from this calculation. Nothing is sent to us until you send it yourself.
A guide, not a design to standard. We give no warranty for the correctness of the results, the applicable standards and case-by-case verification govern.
Worked example
The default case the calculator starts with, worked through once. Change the values above and it recalculates immediately.
Inputs
- Base current-carrying capacity
- 41 A
- Ambient temperature factor
- 0.87
- Grouping factor
- 0.7
- Further factors
- 1
- Design current I_B
- 20 A
- Rated current of the protective device I_n
- 25 A
- Conventional tripping current factor I₂ / I_n
- 1.45
Result
- Current-carrying capacity as installed
- 25 A
- Combined factor
- 0.609
- Utilisation by the design current
- 80.1 %
- Assessment of the coordination
- The protective device is too large for the cable: I_n exceeds the capacity.
Formula
- I_z = I_z0 · f_temperature · f_grouping · f_other
- First condition: I_B ≤ I_n ≤ I_z
- Second condition: I₂ ≤ 1.45 · I_z
- with I₂ = k₂ · I_n
Assumptions and standards
- The base value and the correction factors come from the standard you apply and are entered here, not looked up. We deliberately do not reproduce normative tables: a wrong tabulated value inside a calculator is more dangerous than no calculator at all.
- The two conditions are the usual coordination of cable and overload protection.
- Short-circuit protection, the disconnection condition and voltage drop are separate proofs and not covered here.
Frequently asked
Where do I get the base value?
From the current-carrying capacity table for your case: conductor material, insulation, number of loaded cores and installation method determine it. The same cable carries considerably more in free air than in a wall under thermal insulation.
What does the second condition mean?
It ensures the protective device still disconnects in time under a small, sustained overload. The conventional tripping current is the current at which the device reliably operates. For miniature circuit breakers it is typically 1.45 times the rated current, in which case the condition is met automatically once the first is. For fuses at 1.6 times it is the stricter one.
May I simply multiply several factors?
For temperature and grouping that is the usual approach. For buried installation further influences arise that cannot always be expressed cleanly as a separate factor. Check the notes to your table in that case.
Calculating is the easy part.
A formula gives you a number. Designing a plant also demands installation method, grouping, discrimination, the standards in force and a look at the installed base. That is what we take on.
More tools
- 01Cable cross-section
- 02Voltage drop
- 03Cable resistance
- 04Cable losses
- 05Maximum cable length
- 07Parallel cables
- 08Conductor temperature
- 09Cable capacitance
- 10Short-circuit current
- 11Cable impedance
- 12Network impedance
- 13Short-circuit current at the far end
- 14Thermal short-circuit withstand
- 15Length and disconnection
- 16Motor current
- 17Torque
- 18Starting current
- 19Star-delta starting
- 20Soft starting
- 21Motor efficiency
- 22Speed control instead of throttling
- 23Speed and slip
- 24Setting the motor protection
- 25Single-phase motor
- 26Motor feeder
- 27Required motor rating
- 28PFD and SIL
- 29PFH and SIL
- 30Protective conductor size
- 31Earth rod
- 32Touch voltage
- 33Residual current protection
- 34Check discrimination
- 35Connecting a surge arrester
- 36Enclosure cooling
- 37Reference designation
- 38Reactive power compensation
Contact
Tell us what it is about.
A phone call or three lines is enough. From the very start you talk to the people who will later work on your project, not to a distribution list.
Direct
- Phone+49 (0) 5247 4070-66
- Emailinfo@fisekon.com
- AvailabilityMon – Fri, 8:00 – 17:00 CET
Locations
33428 Marienfeld (Harsewinkel)Gütersloh officeWagenfeldstr. 2
33332 Gütersloh
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