I was wondering if it is safe to measure high AC voltages ( e.g. 4000 VAC ) from an energy limited source ( e.g. a 4000 V no CT plate transformer, max output 50mA ) using a Simpson 260 series 3 having the 5000 VAC input terminal, and neither side of the circuit is grounded. The meter's common terminal is not connected to ground either. The manual for the Simpson 260 series 3 gives no advice on this, nor the maximum common mode voltage with respect to ground. As we know in this measurement, the meter is floating. Each transformer lead has 2000 VAC on it. One lead of the transformer goes to the meter's 5000 VAC input, through the usual voltage attenuator network, then is at a low potential for the meter rectifier. However, the transformer's other lead goes to the common terminal, which doesn't have an attenuator stage similar to the other input. Wouldn't this kind of measurement damage the VOM, and if so, how? If not, why not? If damage would result, how are special meters that can make this measurement type designed with respect to the common terminal? The later Simpson 260s give the maximum common mode voltage as 1000 V either AC or DC, but their circuits haven't changed all that much, except that the 5000 V AC\DC jacks are no longer present.
By the way, this combination of voltage and current is highly dangerous, so all electrical safety precautions must be taken, which I am thoroughly familiar with.