If equipment is designed with 3 prong plug (Class I Equipment) case is grounded protecting user from dangerous voltages. Grounding the case thru interconnect to another case is not only unsafe because of the limited current interconnect can carry, but also for the simple fact that interconnect can be disconnected making device unsafe. Two prong plug devices (Class II Equipment) offer user protection by double insulation. This insulation has to withstand 3000VAC. Wood alone is likely not suitable insulation since it can absorb moisture.
