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Anonymous Poster #1

Grounding

05/23/2013 7:34 PM

Dear All,

For designing grounding for instrumentation ( horn, switches, control vlv, tx ) is it acceptable to connect the grounding onto the cable tray then connect to main earth bar or from instrmunet to earth bar. which preferable and accordance to norm.

Regards

Abdu

Saudi.

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Guru

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#1

Re: grounding

05/23/2013 7:42 PM

Something's fishy here, Abdu.

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Guru
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#2

Re: grounding

05/23/2013 7:45 PM

No, that sounds illegal to me.

Best you follow your local electrical codes and standards of practice.

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Guru
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#3

Re: grounding

05/24/2013 3:27 AM

The only way of determining acceptability is to read the end Client's instrumentation installation standards and the local nation's electrical standards for that is to what the proposed installation will be inspected. Those standards cannot be seen from here.

The above proposal involves mixing-up instrument earthing and power earthing, which is not best practice, and introducing the possibility of a number of additional earthing connections, which increases the chances of shock should a number of them be open at the same time as there are rather more of them than would otherwise be the case. So, notwithstanding any Client standard or national standard that may be applicable, the technique is a poor one and is best avoided.

Best practice involves tying the instrument earth conductors together at an insulated "clean instruemnt earth bar", probably in the main control panel or a local marshalling panel, and running a separate earth cable to the main earth point; this earth connection is kept separate from the main power earth connections and the two only ever meet at the main earth point. The reason for doing it is to keep the fault current, which appears in the power earth conductor for such time as it takes for the circuit protective device to operate and disconnect it, out of the instrument earth conductor. The outcome is that fault surges that might affect the instrumentation are kept away from it as far as is reasonably practicable, meaning the instruments all survive the surges and such plant as is required to operate after the fault has been disconnected stands the best chance of so doing.

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Guru
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#4

Re: Grounding

05/25/2013 5:05 AM

NO. You should not ground through Cable Tray. Cable Tray is to support the cable only. Safety Regulations will not allow this.

DHAYANANDHAN.S

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#5

Re: Grounding

05/28/2013 8:34 AM

Perhaps you are asking if cable tray can be grounded or not?

It is never from instrument to earth bar, It is always the other way out to have Ground to instrument case if instrument is designed in this way. Some instruments are connected internally to earth line and will automatically pick the connection as soon as power is connected to the instrument. Some high voltage instruments do provide extra point to be wired to proper earth for safety purpose only.

I think, you need to go by the standards of the electrical wiring diagrams. Make sure you do not have leakage current into Earth else Earth leakage relay may trip the power.

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#6

Re: Grounding

05/28/2013 9:31 AM

Abdu,

Doing that is generally not acceptable, I would sugegst you contact a qualified electrical or instrument engineer to design the required connections.

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Guru
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#7

Re: Grounding

11/01/2024 9:30 AM

If in doubt, consult a local qualified Electrician, which occupation has the skills to design, install, test, and certify as safe.

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