The familiar 3% and 5% figures are design recommendations used to help ensure equipment receives a suitable voltage at its point of use. They apply between the origin of the installation and the load for installations supplied directly from a public low-voltage system.
Use 3% for lighting circuits
Lighting is more visibly affected by reduced voltage. Excessive drop can cause dim output, colour changes, flicker or unreliable operation of electronic drivers. At 230 V, 3% is equivalent to 6.9 V.
Use 5% for other circuits
For many non-lighting loads, the common recommended maximum is 5%. At 230 V, that represents 11.5 V from the origin to the load.
When a lower target makes sense
The maximum percentage is not automatically the best design value. Long cable runs, motor starting, EV charging equipment, sensitive electronics and manufacturer requirements may justify a tighter limit.
This article provides general information only. Electrical installation design and verification should be completed by a competent person using the current regulations and manufacturer data.