Extra-low voltage

The International Electrotechnical Commission (IEC) and the UK IET (BS 7671:2008) define an ELV device or circuit as one in which the electrical potential between two conductors or between an electrical conductor and Earth (ground) does not exceed 120 volts (V) for ripple-free direct current (DC) or 50 VRMS (root mean square volts) for alternating current (AC).

These can be supplied using sources including motor / fossil fuel generator sets, transformers, switched PSU's or rechargeable battery.

SELV, PELV, FELV, are distinguished by various safety properties, supply characteristics and design voltages.

Lower voltage can apply in wet or conductive conditions where there is even greater potential for electric shock.

A PELV circuit, just as with SELV, requires a design that guarantees a low risk of accidental contact with a higher voltage.

A typical example for a PELV circuit is a metal cased computer with a Class I power supply.

Examples for FELV circuits include those that generate an extra low voltage through a semiconductor device or a potentiometer or an autotransformer.

This system voltage is slightly above the ELV limit, but is still very commonly used for cord-powered hand tools and temporary lighting in hazardous areas.

Instead, high rupturing capacity fuses and appropriately rated circuit breakers are the recommended type for RAPS.

IEC 61140:2016, Basic safety publication defines ELV as ≤ 50 VRMS AC and ≤ 120 V DC ripple-free.

In Brazil, ELV (Extra-baixa tensão or EBT in Portuguese) is officially defined in Regulatory Standard no.