Electrical systems based on the 2011 nec book read reviews from worlds largest community for readers. Electrical systems based on the 2011 nec is a comprehensive reference and instructional tool for journeyman and master electricians inspectors contractors electrical designers and others in the electrical trade this authoritative textbook is recognized in the industry for providing a comprehensive overview of the national electrical coder. Electrical systems based on the 2011 nec answer key atp staff on amazoncom free shipping on qualifying offers electrical systems based on the 2011 nec answer key. That an ungrounded system exists but a sure method of identification is necessary a change in the 2011 nec requires that ungrounded systems be legibly marked ungrounded system at the source of a separately derived system or at the first disconnecting means of a service the marking is not required on downstream distribution equipment