There are two components which will need to be considered for input damage threshold.

In the 0.4v, 4.0v, and 40.0v ranges there is an input voltage divider made up of Vishay TOMC-1603-5002A. This component has a power rating for indibvudual resistors of 0.085W. Each input line contains four of these resistors in series, resulting in 200K Ohms to Ground.

At 85mW across 200K Ohms, the input can withstand up to ~130v before exceeding the specified power rating. This is a damage threshold for the resistances to ground, and WOULD allow for up to 260v between the + and - inputs, but the input amplifier damage threshold must also be considered. Since the voltage is divided by four, the result on each input pinof the amplifier with a 130v input would be ~32.5v. The damage threshold for the input amp that follows the divider network is +/-40v ()see following section for details), the input difference must be limited to a maximum 130v to ground, or a maximum of 160v between the two input pins.

In the 0.1v, 1.0v, and 10.0v ranges, the input divider is removed from the circuit, and the input signal is routed directly into an instrumentation amplifier. The input amp is a Texas Instruments/Burr-Brown PG204. The maximum safe input voltage to the PG204 is +/-40v.

Summary:

Max Input Voltage
0.4v, 4.0v, 40v ranges: Max 130v to ground (either pin), max 160v differential.
0.1v, 1.0v, 10.0v ranges: +/-40v to ground (either pin), max +/-40v differential.