To do Cable calculation it has to meet the requirements from BS 7671.
Design Current
First thing to do is calculate the design current. (Ib) I=Watts/Volts. You do this so you can find out the total current.
Apply Diversity Factors (where applicable)
Diversity is described in the onsite guide Appendix A as a way to determine the maximum demand for an installation and includes the current demand for commonly used equipment. For example if in a domestic household there were 8 lights on a circuit, not all the lights would be on at the same time therefore the expected load will not reach the maximum amperes. The On Site Guide states in Table A2 that when completing a lighting circuit in small hotels, boarding houses or guest houses the diversity …show more content…
All the correction factors can be found appendix 4 table 4D5. A healthy circuit will always produce a certain amount of heat. When the heat builds up and can’t escape, the resistance will increase and will cause the PVC to melt and could catch fire. If the tabulated current is more than (Ib) you will need to increase the conductor size, instead of a 10mm conductor you might need to use a 16mm, it will create less heat as the cable will be larger so the current is below its capabilities. You can find the rating factors (Ca) for ambient air temperatures other than 30 degrees in table 4B1.The formula for tabulating current is It= In/ca so the protective device divided by the correct correction factor.
Select Cable
The cable (Iz) has to be greater or equal to than (It) Tabulated current. Now you would go to appendix 4 table 4D5. There is 6 different methods to choose. Example it could be reference method C, clipped direct or method 102 in a stud wall in thermal insulation with cables touching the inner wall. You would go down the list and pick the conductor that is capable of carrying the current. If the conductor is greater than 16mm you will need to go to table 4D2A.
Confirm Voltage Drop Meets
Design Current
First thing to do is calculate the design current. (Ib) I=Watts/Volts. You do this so you can find out the total current.
Apply Diversity Factors (where applicable)
Diversity is described in the onsite guide Appendix A as a way to determine the maximum demand for an installation and includes the current demand for commonly used equipment. For example if in a domestic household there were 8 lights on a circuit, not all the lights would be on at the same time therefore the expected load will not reach the maximum amperes. The On Site Guide states in Table A2 that when completing a lighting circuit in small hotels, boarding houses or guest houses the diversity …show more content…
All the correction factors can be found appendix 4 table 4D5. A healthy circuit will always produce a certain amount of heat. When the heat builds up and can’t escape, the resistance will increase and will cause the PVC to melt and could catch fire. If the tabulated current is more than (Ib) you will need to increase the conductor size, instead of a 10mm conductor you might need to use a 16mm, it will create less heat as the cable will be larger so the current is below its capabilities. You can find the rating factors (Ca) for ambient air temperatures other than 30 degrees in table 4B1.The formula for tabulating current is It= In/ca so the protective device divided by the correct correction factor.
Select Cable
The cable (Iz) has to be greater or equal to than (It) Tabulated current. Now you would go to appendix 4 table 4D5. There is 6 different methods to choose. Example it could be reference method C, clipped direct or method 102 in a stud wall in thermal insulation with cables touching the inner wall. You would go down the list and pick the conductor that is capable of carrying the current. If the conductor is greater than 16mm you will need to go to table 4D2A.
Confirm Voltage Drop Meets