Chromatography Forum

For a long time I haven't seen any care regarding earth connection of our equipments in the lab including 6890 I am working with. A friend of mine works on a company deals with earth wells and related stuff. I asked him to check or outdoor earth well ohmic resistance and also earth connection of our 6890. He said what ohmic resistance do you need and I didn't know what to say. I checked manual and found nothing. Anyone here knows what is the acceptable ohmic resistance of the power plug earth connection should be or what ohmic resistance of the earth well is acceptable for such instruments?

I have checked electrical before installing instruments (in the US) and have not checked resistance of the earth ground. I would expect that as many outlets in a building contain an earth ground, the resistance for such an outlet would be covered by building codes. And I would expect instrument manufactures to build instruments that will work in the allowed ranges of building codes. (There may be instruments with special electrical requriements that would have to have an earth ground - in wich case the manfacturer would be able to tell you.)

Check with your friend and see if this might make sense.

I am very sensitive to what is written in an instrument manuals and documents. Most of the problems happen because instrument documentation either is not complete or has not been written in fluent English. I think there should be an ASTM standard for writing scientific instruments manual and documentation. Specially when instrument is made in Germany for example and they trying to write an English manual for it you will get a lot of problems understanding it specially if you are not a native English person.

In the manual under "Earthing requirements" it says Earth terminal should be suitably grounded. What does this "suitably" means? What will you do if you see this?

In the US I would, at most, ask an electrician to confirm the outlet is properly wired. If an outlet that will handle a 6890 (using the electrical cord provided by the vendor) is properly wired, there is an appropriate earth ground.

This would mean no home built extension cords or adapters to plug the instrument into a service that fails to include an earth ground.

Check between the earth and neutral terminals of the wall socket with an AC voltmeter.
You must not read more than 0.6 volts if the earth connection is good enough.

Then check the connection between the earth terminal on the instrument plug and the instrument chasis with an ohmmeter. You have to see a short circuit .

Now , it is safe to connect the instrument to the wall socket.