Question on isolated grounding?

[Dennisc]

Hello, I am not an electrician and am not doing a job. I am going to school to be a Technician and have a question about something I've read. What exactly is an isolated ground? I've heard of something like a computer or soundboard for example requiring it's own isolated ground. Does this mean that the circuit that one of these components are on would have its own bare ground wire that runs back to the main panel and connects to the grounding bus bar? Or does an isolated ground mean that this circuit would run back to the main panel and stay isolated from the rest of the panel and connect to its own grounding device (like a driven ground rod)?

Thanks Dennis

 

[ibew441dc]

Good Question!!

Good Question!!

What exactly is an isolated ground? I've heard of something like a computer or soundboard for example requiring it's own isolated ground. Does this mean that the circuit that one of these components are on would have its own bare ground wire that runs back to the main panel and connects to the grounding bus bar? Or does an isolated ground mean that this circuit would run back to the main panel and stay isolated from the rest of the panel and connect to its own grounding device (like a driven ground rod)?

Thanks Dennis

250.146(D) Isolated Receptacles. Where installed for the reduction of electrical noise (electromagnetic interference) on the grounding circuit, a receptacle in which the grounding terminal is purposely insulated from the receptacle mounting means shall be permitted. The receptacle grounding terminal shall be connected to an insulated equipment grounding conductor run with the circuit conductors. This equipment grounding conductor shall be permitted to pass through one or more panelboards without a connection to the panelboard grounding terminal bar as permitted in 408.40, Exception, so as to terminate within the same building or structure directly at an equipment grounding conductor terminal of the applicable derived system or service. Where installed in accordance with the provisions of this section, this equipment grounding conductor shall also be permitted to pass through boxes, wireways, or other enclosures without being connected to such enclosures.

This may be of use to you:smile:

 

[augie47]

Dennis, It's important to remember that for the overcurrent device (normally breaker in these situations) to operate on a fault, there must be a low impedeance path back to the source. So at some point, there needs to be a equipment ground to grounded (neutral) connection. Early in the conception of "isolated grounds" some used to call for that equip, ground to go only to a ground rod. Due to ground resistance, this will not provide the path required.

 

[Smart $]

What exactly is an isolated ground?

An equipment ground which is isolated from other equipment grounding means between load and source grounding. Electrically all equipment (non-current-carrying metal parts) grounds supplied by the source are bonded in one way or another to each other, but in the case of an "isolated" ground, the grounding conductor's current path is directly to the source ground. It is intended to be the only path for fault, objectionable, RFI, and EMI-induced current to flow to the system ground for the circuit's loads.

 

[bob]

http://ecmweb.com/mag/electric_demystifying_isolated_grounding/