Sample Course
Question 8 of 9
NEC 700- Emergency Systems- Transfer Switches
Section 700.6(C) is intended to ensure that relay contacts are mechanically held in the event of coil failure. This section was revised in the 2008 Code to require transfer switches rated 600 volts ac and below to be listed for emergency systems use.
When emergency systems are tested, both the normal and the emergency system are energized. If the two sources are not synchronized, as much as twice the rated voltage may exist across the transfer switch contacts. Some listed transfer switches are designed and tested to be suitable for switching between out-of phase power sources. Other protection methods may be employed, such as a mechanical interlock that prevents inadvertent interconnection, or an electronic method that prevents both systems from being interconnected.
x