My experience has been that SELV (safety extra low voltage, less than 60V peak and less than 240VA) is considered safe and anything exceeding that needs certain levels of protection.

But bus bars generally should be protected regardless of voltage as they carry currents from high current capacity sources so even a lower voltage can be a safety concern.

Many server power supplies can take AC or DC input, with the DC input in the 300-500V range as this is comparable to the boost voltage for the AC power factor correction circuit. I just assumed most data centers using DC would be distributing around 400V within each rack.