DC-DC converters can be implemented to provide isolation in a system. This electrical separation creates a barrier which can be used for safety protection or noise isolation. Two isolation factors are generally specified: isolation resistance and isolation voltage. The isolation resistance is a function of the material and spacing employed in the DC-DC converter. The isolation voltage is defined as the maximum voltage across the isolation barrier that a device can withstand for a fixed time period. The actual breakdown voltage is typically in excess of 1000 V higher than the rated isolation voltage. The reason for rating a conservative isolation voltage is to ensure that the isolation testing of a supply does not degrade the isolation barrier in any way. The required isolation voltage will depend on the market the device is being used in. Industrial applications will typically accept 1 kV isolation, whereas medical applications may require up to 6 kV of isolation. The higher isolation required in medical applications is implemented in order to comply with restrictive standards mandated by agencies like UL and TUV.