Power and Grounding Requirements 5-7
scheme if the system input power is less than 50V thus not requiring any ground (see CEC par
CEC par 10-102
Two wire
The interpretation of "objectionable current" is to be aligned with the leakage current limits as defined in CSA 950 (maximum 5% current rating) or CSA 225 (maximum 10% current rating). The NEC definition of "objectionable current" is any current not suitable for a particular installation; which would include leakage current limits, grounding conductor size, electrochemical potential between dissimilar metals, etc.
Grounding requirements for the Metrocell is to keep the total return current on the grounding network below 5% of the total system DC current draw. This is done by:
1.Making the desired return path a much lower resistance than the undesired return path (that is, current divider principle). Eliminating the grounding conductor at the power plant will help discourage return current flow through the supplementary grounding conductor.
2.Minimize equalization currents between frames via the grounding conductors and antenna coax, etc. This is achieved by adhering to an isolated mesh grounding concept. The mesh concept means that all the metal surfaces (frames, shelves, PCP ground planes and module chassis) within the system are bonded together with ideally as little contact resistance as practically possible.
Isolation means that the system grounding mesh only makes contact with other grounded systems at the local ground reference or BPG. This helps to reduce the chance of ground currents from other systems from flowing through the Metrocell grounding conductors. Isolation from building steel should be facilitated by providing an isolation pad underneath each frame.
