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from the Instru department...
Power Supply Grounding/Earthing Concepts
Application Questions and Problems topic
Posted by kk on 25 November, 2007 - 6:47 pm
What are floating and grounded power supply systems?

Is the UPS output floating or grounded?

Is the output from a 230VAC/110VAC transformer floating or grounded?

What are the advantages/disadvantages of floating/grounded systems?

Do such concepts exist for AC and DC systems both?

What is the difference between Neutral, ground and earth?

regards


Posted by Phil Corso, PE on 26 November, 2007 - 11:03 pm
Responding to kk's 25-Nov (18:47) query... two excellent references are:

1) IEEE "Green" Book, ANSI/IEEE Std 142-1982 (or later), "Recommended Practice for Grounding (Earthing) of Industrial annd Commercial Power Systems"

2) Eustace C. Soares, "Grounding Electrical Distribution Systems for Safety"

Regards, Phil Corso (cepsicon@aol.com)


Posted by Michael Griffin on 26 November, 2007 - 11:23 pm
> What are floating and grounded power supply systems? <

Grounded power supplies have one conductor which is grounded, and floating ones do not.

> Is the UPS output floating or grounded? <

It depends upon whether it is grounded or not. Did you ground it? Did the manufacturer ground it?

> Is the output from a 230VAC/110VAC transformer floating or grounded? <

See above.

> What are the advantages/disadvantages of floating/grounded systems? <

Grounding is sometimes safer. Floating is sometimes safer. Grounding sometimes avoids electrical noise and interference problems. Floating sometimes avoids electrical noise and interference problems. The advantages and disadvantages depend upon the application.

> Do such concepts exist for AC and DC systems both? <

Yes.

> What is the difference between Neutral, ground and earth? <

Neutral is intended as a grounded electrical path. A grounding conductor is usually not a normal electrical path, but acts as one in the event of some types of electrical faults. This is why an electrical outlet will have both neutral and ground wires. An earth ground is a ground that is connected to the earth. A chassis ground may connect to a common point, but not connect to the earth.

If you want to know whether and how to ground a power system, please refer to the electrical codes of the country you live in. Electrical codes in Canada have very extensive and detailed rules on this subject which must be obeyed. No doubt this is the same in many other countries as well. This is a very broad subject and the correct answer depends upon the details of the application.

Grounding is also used in instrumentation and communications applications, which have different considerations than power applications.

If you have a particular application in mind, perhaps you could phrase your question to suit.

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