In electronic and wiring systems technology, there is a huge variety of installation testing devices to choose from. Often used in the field by installation operatives, testers can include anything from earth testing devices to insulation testers. Other types of device include machine and production testers, as well as solar energy measuring instrumentation. A wide variety of electrical manufacturers, such as Fluke, Gossen Metrawatt, Megger and PeakTech, produce installation testing equipment. Usually designed to be lightweight, testing equipment can either be battery or mains powered. Devices are often supplied with carry bags that protect them and make them easier to transport from one test location to the next. Many devices are used to measure the voltage being produced within an electrical installation, but can also provide data on insulation testing, if required. Earth testing instruments are made that can detect short circuit currents from fewer than 50 mA to 250 mA. Portable photovoltaic instrument testers are available, which have the ability to measure the irradiance of solar arrays that vary in power from anything between 100 and 2,000 watts per metre squared. Many testers also hold data they have recorded on board, and this can be downloaded later to a secondary device, such as a PC. Common interface types for installation testing devices include RS232, Bluetooth and USB.