RCD

Residual Current Device. Wikipedia definition.

From this post: http://www.controlbooth.com/forums/l...ml#post142745:

Quote:
Originally Posted by church
For some additional explanation of grounding (earthing) you can check the following link.

Untitled

although it is an on-line book that provides explanation for Electricians to assist them in understanding the Institution of Electrical Engineers Wiring Regulations the U.K. equivalent of the U.S. NEC and the Canadian Electrical Code it provides a good explanation of the principles.

North American technicians should be very careful with this document, as a great deal of it is not allowed under the NEC. This is particularly true of the wide variety of earthing systems found in the UK and Europe. In addition, there are no RCD devices in North America, only GFCI and GFP devices. RCD's are often used in Europe to create ungrounded or impedance-grounded systems that are still safe. This is not allowed in the US or Canada.

In general, North American practice is to hard-ground the neutral as close to the transformer or service entrance as possible. Any number of delta-wye transformers can be installed in a facility, creating "separately derived" neutrals that are hard-grounded at each transformer.