Your comment provoked me to research this a bit. I was trying to find out if commercial transfer switches switch neutral. Apparently they don't. Found a good thread about this http://www.practicalmachinist.com/vb/general/question-about-generator-transfer-switches-166275/

If you disconnect it from the panel you are disconnecting it from ground, so any stray current that finds its way to neutral will not be grounded and you will have a potentially dangerous situation. If you disconnect neutral at the panel you should instead drive a ground rod and connect the neutral to that. The gound connection is what protects current from feeding back to the utility company transformer.

Unless neutral is grounded at the service entrance there is danger that a person touching equipment or a conductor enclosure will receive a shock. Metal conduit, BX cable, and boxes may be in contact with metal parts of a building or appliances at several points. Grounding the neutral keeps the electrical potential at or near zero (ground reference). Without grounding the neutral a GFCI will not operate properly either.