{"id":7472,"date":"2013-12-27T08:00:26","date_gmt":"2013-12-27T12:00:26","guid":{"rendered":"http:\/\/www.engineeringradio.us\/blog\/?p=7472"},"modified":"2023-03-29T13:51:48","modified_gmt":"2023-03-29T17:51:48","slug":"the-isolated-ground","status":"publish","type":"post","link":"https:\/\/www.engineeringradio.us\/blog\/2013\/12\/the-isolated-ground\/","title":{"rendered":"The Isolated Ground"},"content":{"rendered":"\n

We get requests to install Isolated Ground outlets from time to time, especially with sensitive equipment. TELCO likes to have isolated grounds on their fiber MUX’s.\u00a0 It can become an issue with branch circuits in split-phase or three-phase services that share the same ground and neutral conductor.\u00a0 This can lead to a ground loop between neutral and ground, which will create all sorts of havoc in a broadcast facility.<\/p>\n\n\n\n

\"20<\/a>
20 amp, 120 volt, Isolated Ground Outlet<\/figcaption><\/figure>\n\n\n\n

The National Electrical Code covers Isolated Grounds (IG) and sensitive equipment in several sections.\u00a0 The first is section 250.146(D), which states that the installation of isolated ground receptacles is permitted. \u00a0 The grounding conductor connected to such receptacles is permitted to pass through one or more panel boards, boxes, conduit bodies, etc without being bonded to them.\u00a0 However, said panel boards, metallic boxes, conduit bodies, raceway, etc must also be grounded separately.\u00a0 That means running two ground conductors, usually, the isolated ground conductor is green with a yellow stripe or spiral.<\/p>\n\n\n\n

\"Studio<\/a>
Studio electrical diagram isolated ground<\/figcaption><\/figure>\n\n\n\n

The second is section 640.9(A), which refers to separately derived power systems.  This section deals specifically with balanced power; 60 volts AC to ground.  In such cases, a separate ground conductor is allowed as outlined in section 250.146(D) and in 647.6(B), which states that the grounding buss should be connected to the grounded conductor on the line side of the separately derived systems disconnecting means.<\/p>\n\n\n\n

Other sections of the NEC that may apply to broadcast radio and television facilities:<\/p>\n\n\n\n