Voltage Drop Limitations in Low-Voltage Electrical Installations
Standards Governing Voltage Drop Calculations
The following provisions are derived from the regulatory framework and operational conditions specified within Australian and New Zealand standards.
Voltage Drop Limits for Low Voltage Installations
Regulatory requirements for voltage drop in low voltage (LV) installations are stipulated in Section 3.6 of AS/NZS 3000:2018. The standard prescribes the following maximum permissible voltage drop values:
- General Installations: The voltage drop between the point of supply for a low-voltage electrical installation and any point within that installation must not exceed 5% of the nominal voltage at the point of supply.
- Installations with a Dedicated On-Premises Substation: Where the point of supply is defined as the low voltage terminals of a substation located on the premises and dedicated solely to the installation, the permissible voltage drop may be increased to a maximum of 7%.
- Stand-Alone Power Systems: For stand-alone systems, the design must ensure that the combined effect of the source output voltage and the internal installation voltage drop does not cause the utilization voltage at any LV equipment to fall by more than 11% of the nominal supply voltage under standard operating conditions.
These limits are summarized as follows:
- Any low-voltage electrical installation: ≤ 5% voltage drop.
- Installation with an on-premises substation: ≤ 7% voltage drop.
Design Guidance and Heuristic Allowances
The following voltage drop allocations may be employed as preliminary design guidelines to apportion the total permissible drop across installation segments:
- Consumers’ Mains: Allocate approximately 0.5%.
- Sub-Mains: Allocate between 1.5% and 2%.
- Final Subcircuits: Allocate up to 2.5%, or a value that ensures the cumulative drop from upstream circuits remains within the prescribed overall limit.
Voltage Rise Limitations for Grid-Connected Photovoltaic (PV) Systems
For photovoltaic installations, separate limits apply to voltage rise on the AC side and voltage drop on the DC side:
- AC Voltage Rise: As per AS/NZS 4777.1:2016, the voltage rise from the inverter output to the point of grid connection must not exceed 2%.
- DC Voltage Drop: AS/NZS 5033:2014 specifies that the maximum voltage drop within the DC cabling of a PV array must not exceed 3%.
In summary:
- Voltage Rise (AC): Must not exceed 2%.
- Voltage Drop (DC): Must not exceed 3%.
