| Interactive Tool |
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This simulator has sliders which allow you to alter the the supply voltage, cable length, wattage, cable CSA and whether the circuit is lighting or power (which determines the max allowable voltage drop).
Supply Voltage can be altered from 0 to 240V in 1V increments.
Wattage can be altered from 0 to 15kW.
Cable CSA can be altered between 1A and 16A at 0.5A increments. Note Not all of these values are valid cable sizes and some of the values may differ slightly from those in the look up tables in the Regs as they are calculated based on a single value and extrapolated for others.
Lighting & Power can be changed by way of the slider which toggles between calculating the max allowable volt drop from beteween 3% and 5% which in turn changes the calculated Volt Drop from green to red.
On changing these sliders the other elements of the circuit alter automatically.
Individual characteristics and or steps can be hidden or displayed by ticking/unticking various checkboxes.
When cables carry current to the load of a circuit there will be voltage drop in those cables and across the load that they are feeding. It is beneficial to limit the voltage drop in the cables as this allows the load to work optimally. If you have too high a voltage drop in the cables, less current is available where it is intended, so for example a water heater would take longer to heat a tank of water.
The Regs state that the drop in voltage from the supply to the fixed current using equipment must not exceed 3% for lighting circuits and 5% for other uses of the mains voltage. This means a maximum of 6.9V for lighting and 11.5V for other uses for a 230V installation.
The voltage drop of a circuit may be found from;
Working through the example given in Linsley pg 159.
An 18m long circuit feeding 6kw worth of lighting has already been calculated as having a Design Current (Ib) of 26.09A and needs a 10mm cable once derating factors have been taken into account.
As 2.06V is less than the max permissible value for a lighting circuit (6.9V) then the 10mm cable selected to meet current carrying capacity also satisfies the voltage drop requirements.
Had it not met the voltage drop requirement then the next larger cable of that type should be selected until one is found that does.
As current carrying capacities increase with cable CSA selecting a larger CSA cable to meet volt drop requirements will not result in failing to meet the previously passed current carrying capacity requirement.
The following questions should be answered and filled in in the answer sheet which is downloadable via the Download link below. The completed answers sheet should then be emailed as an attachment to Robert.Eyre@Hull-College.ac.uk
Find the Voltage drop in the following scenarios and state whether or not they meet the voltage drop requirements, recording the calculated voltage drop and max allowable volt drop for each question. All are based on 230V and should use tabulated values (NOT the tools which may use slightly different mV/A/m values for some sizes. These questions take no account of whether or not the cables chosen passed the current carrying capacity requirements,
Find the max allowable length in the following scenarios to meet the voltage drop requirements, recording the length, calculated voltage drop and max allowable volt drop for each question. All are based on 230V and should use tabulated values (NOT the tools which may use slightly different mV/A/m values for some sizes. These questions take no account of whether or not the cables chosen passed the current carrying capacity requirements.
Find the minimum cable size that meets the voltage drop requirements for the following scenarios, recording the cable size, calculated voltage drop and max allowable volt drop for each question. All are based on 230V and should use tabulated values (NOT the tools which may use slightly different mV/A/m values for some sizes. These questions take no account of whether or not the cables chosen passed the current carrying capacity requirements.
| Conductor cross-sectional area | Reference method 100 (above a plasterboard ceiling covered by thermal insulation not exceeding 100mm in thickness) | Reference method 101 (above a plasterboard ceiling covered by thermal insulation exceeding 100mm in thickness) | Reference method 102 (in a stud wall with thermal insulation with cable touching the inner wall surface) | Reference method 103 (in a stud wall with thermal insulation with cable not touching the inner wall surface) | Reference method C (clipped direct) | Reference method A (enclosed conduit in an insulated wall) | Voltage drop |
|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| mm² | A | A | A | A | A | A | mV/A/m |
| 1.0 | 13 | 10.5 | 13 | 8 | 16 | 11.5 | 44 |
| 1.5 | 16 | 13 | 16 | 10 | 20 | 14.5 | 29 |
| 2.5 | 21 | 17 | 21 | 13.5 | 27 | 20 | 18 |
| 4.0 | 27 | 22 | 27 | 17.5 | 37 | 26 | 11 |
| 6.0 | 34 | 27 | 35 | 23.5 | 47 | 32 | 7.3 |
| 10 | 45 | 36 | 47 | 32 | 64 | 44 | 4.4 |
| 16 | 57 | 46 | 63 | 42.5 | 85 | 57 | 2.8 |