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Cable Calcs
- Thread starter ems
- Start date
Four steps to happiness...
1. Apply diversity (App 1 & 8 in OSG) and specify circuit design current (Ib)
2. Select Nominal setting of protective device (In) such that In >= Ib
3. The tricky(ish) bit; Find the Tabulated current carrying capacity (It). This is the capacity you require: It >= In/CaCiCgCr (See Appendix 6 of OSG and apply the correction factors to In as shown on page 115.)
Now you should have: It >= In(corrected) >= Ib
4. Use the value of It in the relevant table (Table 6F, p. 126 for twin&earth) to select a suitable cable, then calculate the voltage drop for that cable using Ib x length of circuit x voltage-drop-per-ampere-per-metre from the same table. (It's given in millivolts, so divide by 1000 to get it into volts!)
You should then calculate Zs to determineif your disconnection times will be met and then check that your CPC will carry the prospective fault current for long enough to operate the protective device, but these steps are probably beyond what you need for Part One.
Hope that helps... if you haven't got a copy of the On Site Guide... get one
[/b]
1. Apply diversity (App 1 & 8 in OSG) and specify circuit design current (Ib)
2. Select Nominal setting of protective device (In) such that In >= Ib
3. The tricky(ish) bit; Find the Tabulated current carrying capacity (It). This is the capacity you require: It >= In/CaCiCgCr (See Appendix 6 of OSG and apply the correction factors to In as shown on page 115.)
Now you should have: It >= In(corrected) >= Ib
4. Use the value of It in the relevant table (Table 6F, p. 126 for twin&earth) to select a suitable cable, then calculate the voltage drop for that cable using Ib x length of circuit x voltage-drop-per-ampere-per-metre from the same table. (It's given in millivolts, so divide by 1000 to get it into volts!)
You should then calculate Zs to determineif your disconnection times will be met and then check that your CPC will carry the prospective fault current for long enough to operate the protective device, but these steps are probably beyond what you need for Part One.
Hope that helps... if you haven't got a copy of the On Site Guide... get one
[/b]
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