One or more techniques and/or systems are provided for detecting reverse polarity of a photovoltaic system. A fuse holder may comprise a fuse holder body configured to receive a fuse used to protect against excessive current from a photovoltaic string of the photovoltaic system, such as current from a short circuit due to the photovoltaic string being installed backwards and having a reverse polarity. Because installation of the fuse while the photovoltaic string has reverse polarity may result in substantial damage and harm, a reverse polarity detection component may be configured to identify the reverse polarity and provide a warning of the reverse polarity before the fuse is installed (e.g., an audible alert, a blinking light, a locking of the fuse holder to prohibit installation of the fuse, etc.).