[SonsOfCollins_Wallace]

It matter NOTHING if a building or whatever is connected to the power grid. If it is then the items connected are cooked.
However your metal building being disconnected is good IF it is fully metalized AND grounded AND has the windows covered in metal “ mesh” to absorbed the atmospheric electric charge generated by the EMP.
It is the atmospheric charge generated by the EMP that cooks whatever is sensitive (not able to handle excessive current) to currents beyond their designed capacity.
Any electronic device - ANY today-built/solid-state devices will be cooked dead if they are exposed to such currents. If said devices are in a Faraday cage/structure they would survive if not connected/on an insulated structure.

It bears reading the recent book “One Second After” to get a well defined picture of how any modern society will fair in such an event regardless of the source of the EMP event.

1986 Ontario/Quebec power grid failure and US 1858?? events where fence wire was hot-to-touch/burned the posts and large sections of telegraph system was destroyed illustrates what happens from a “small” scale EMP.

If the area the event effects is multi-country/continent then the recovery time will be long and filled with many dead people - whole sections of a society are venerable to the effects. Cars built after 1972 (Chrysler introduced electronic ignition in 1973, Ford & GMC later) will be dead and not coming back to life without a complete system replacement. Some automotive batteries and deepcycle batteries with photovoltaic units (they will be toast) will cook-off and land line telephones will go down.
Planet-wide societies today are so dependent on electrical/electronic devices that ANY replacement equipment will not be available for 9+months or years.
Therein is the main reason to have a society-wide effort to build in some safety-factors now.

[ChocChipCookie]

I was surprised to learn that even solar panels will be affected by an EMP or coronal mass ejection. They contain electronic panels and are just as vulnerable as anything else electronic.

[ChocChipCookie]

I was surprised to learn that even solar panels will be affected by an EMP or coronal mass ejection. They contain electronic panels and are just as vulnerable as anything else electronic.