Cable Sizing for Building Services
Aim
To perform a basic cable sizing calculation for Building Services by a simple and presentable worksheet for internal checking and submission.
Functions
- Check current carrying capacity of supply cable
- Check voltage drop
- Confirm supply and earthing cable are protected by the protective device in normal and fault conditions
- Check whether earth fault protection can be achieved for 0.4s or 5s disconnection
- Calculate maximum fault level at downstream
Instructions
- Activate the functions for complex numbers in Excel. (Activate Analysis ToolPak under Tools -> Add-Ins)
- In the worksheet, you shall enter
- Source Fault Level (MVA)
- Voltage drop limit (%)
- Connected Load (A)
- No. of Phase ( 1 or 3 )
- Cable Type ( A ¡K. M )
- No. of Cable per phase ( 1 as initial trial )
- Length of Cable (m)
- Rating of Protective Device ( The rating shall be larger than the Connected Load )
- Type of Protective Device ( B / 3 / Fuse )
- Type of Earthing ( Cable / Armour / Tape )
- Size of Earthing ( ie. Size of Cable / N/A for Armour / Size of Tape (25x3 / 25x6 / 50x6 )
- Then, you shall increase the size of cable until all cells under Remark are blank. If this cannot be achieved with the largest cable size, enter a higher value in No. of Cable per phase.
Limitation
Performance of overall distribution (i.e. from LVSB to sub-panels to final circuits) cannot be evaluated in a single worksheet.
Comment and Recommendation
Comment and recommendation are most welcome. If you have install mailing program to send e-mail through the internet, please click here or copy this e-mail address: yeunghofan@yahoo.com to send your advice.
References
- Low voltage electrical installation handbook by Johnny C.F. Wong
- Code of Practice for the Electricity (Wiring) Regulations 1997 Edition by EMSD
Declaration
- The worksheet shall not be used for any commercial purposes.
- We shall not hold any liabilities on the accuracy of the worksheet.
Special Thanks to Roger who tackles all the I.T. issues
