Instrument transformers are used to step-down current or voltage to measurable values. They provide standardized, useable levels of current or voltage in a variety of power monitoring and measurement applications. Instrument transformers consist of both voltage transformers and current transformers. A current transformer is a type of instrument transformer that is designed to provide a current in its secondary, which is accurately proportional to the current flowing in its primary. Current transformers are commonly used in metering and protective relaying in the electrical power industry where they facilitate the safe measurement of large currents, often in the presence of high voltages. The current transformer safely isolates measurement and control circuitry from the high voltages typically present on the circuit being measured. Voltage transformers are another type of instrument transformer, used for metering and protection in high-voltage circuits. They are designed to present negligible load to the supply being measured and to have a precise voltage ratio to accurately step down high voltages so that metering and protective relay equipment can be operated at a lower potential. Typically the secondary of a voltage transformer is rated for 69 or 120 volts at rated primary voltage, to match the input ratings of protection relays.