The contact voltage of 250V refers to the voltage value that can meet the nominal life of the relay at 250V. The insulation withstand voltage of 1000V is the non breakdown voltage that can be withstood by the gap between contacts measured under static conditions of the relay.
If you use a regular electromagnetic relay with a nominal voltage of 250V and a voltage of 500V, it is more dangerous because it can cause the arc to be difficult to extinguish when the contact acts, which will affect the service life of the contact. It is recommended not to use it this way. If you need such a relay, some dry reed relays can meet your usage requirements.
The withstand voltage of a relay can include two aspects: the FR4 insulation board is the voltage that the coil can withstand, and the second is the breakdown voltage between the relay contact and the body. The insulation withstand voltage of FR4 insulation board refers to the "impact voltage between contacts". The so-called "impact voltage between contacts" of FR4 insulation board refers to the breakdown voltage that can be withstood between adjacent multiple contacts, mainly considering the impact caused by contact spacing, arc pulling, environmental temperature and humidity. The working voltage refers to the voltage level at which the relay operates stably, that is, the coil voltage of the relay. Select the corresponding FR4 insulation board according to the different relay models and operating voltages.