Voltage drop limits for Low Voltage installations

Standards for voltage drop calculations

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The following rules are based on Australian and New Zealand rules and the conditions.

The Rules

Section 3.6 in AS/NZS 3000:2018 covers the rules for Voltage Drop requirements.

The voltage drop between the point of supply for the low voltage electrical installation and any point in that electrical installation must not exceed 5 % of the nominal voltage of the point of supply.

Where the point of supply is the low voltage terminals of a substation located on the premises containing the electrical installation and dedicated to the installation, the permissible voltage drop may be increased to 7 %.

For stand-alone systems that are designed such that the combination of the oputput voltage from the source, together with the voltage drop within the installation, does not result in the utilisation voltage of the low voltage equipment to fall more than a total of 11 % of the nominal supply voltage under normal conditions.

The limit for voltage rise is 2 % from the inverter to the connection point as per Standard AS/NZS 4777.1:2016.

Rules of thumb

The following voltage drop limits can be used as a guide to assist with design.

Consumers mains – allow 0.5 % voltage drop
Sub-mains – allow 1.5-2 % voltage drop
Final subcircuits – allow 2.5 % or up to the prescribed limit considering the upstream circuits.

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