[taxcontrol]

I agree, though most switching centers are fairly large blocks of concrete, at least some of the old ones are. While not as effective as a Faraday cage, concrete does help to mitigate the strength of the pulse and might be enough to prevent damage if the center has a bit of distance from ground zero

[Alas Babylon!]

When The solar storm of 1859, also known as the Carrington Event occurred, miles of telegraph wire became so charged that telegraph operators could send messages without a power source, and in some cases were badly shocked and fires were started.

Depending on how the overall wiring plan and grounding is arranged, some devices in a building could be terminal ends for the EMP. Bang!