Ground or Earth Leakage Voltage 1

[bbleiler]

We have a customer from Singapore requesting the "earth leakage current" of the machinery that we manufacture. We are in the U.S. and we understand that there is a small leakage current to ground, but have never had a customer be concerned about it. Can anyone help me with this request? Can this current be calculated? Would the onsite facilities have an effect on this current? Why is it important?

 

[OperaHouse]

Capacitive effects of motors and transformers are the largest source of leakage currents. This is probably for a CE requirment if it is an assembly of a larger machine. UL also has a spec for leakage currents. If the device has any line noise filters, like corecom, these have capacitors in them from line to ground which are a source of small current leakage. All you need to do is to electrically isolate the machine from the floor and measure the current from the ground lead to a good ground. The purpose is to establish that the machine will not be a shock hazard if the ground is accidently disconnected.

 

[peebee]

Would the onsite facilities have an effect on this current?
Yes. In particular, if there's a high level of harmonic distortion on the voltage source, this could increase the level of harmonic currents measured on the ground conductor. Similarly, if there's a high level of voltage imbalance, this could also contribute to increased ground currents.

Why is it important?
Beyond the safety issues mentioned by OperaHouse, ground currents can cause problems for other reasons, including:
* Increased neutral-ground voltages, which can cause electronic equipment to malfunction.
* Increased magnetic coupling and EMI radiation, which can cause electronic equipment to malfunction.
* Increased liklihood of ground-fault detection & tripping.
* Arcing at conduit-junction box connections.
* Higher rate of corrosion at earthing terminals (ground rods, etc.).
* Ground currents can be felt by fish, wildlife, farm animals, etc. This problem has been well documented with cows, who will stop drinking water rather than recieve a shock from it. Fish can also be severely affected.

 

[wall33]

to prevent any shock voltage, I suggest using a larger earth conductor. In case of harmonics causing leakage an earth plate would do the trick.

 

[peebee]

wall33,

I agree with your statements, but keep in mind that bb is an equipment manufacturer and therefore has no control over the building installation.

 

[skills]

The way to measure this would seem to be fairly straightforward. If machine mains 1phase, or 3 phase and the neutral were to be run through a current transformer or CT, then the current should read zero unless you have current flowing to ground. I would measure ground leakage this way. A small deflection will be indicated and that is your leakage current. Hope this helps you!

 

[DanDel]

bbleiler, this is a common request for electrical devices used in the medical field in patient care areas. There are several instruments that are used to measure the leakage current (in mA). One manufacturer is Bio-Tek. Their website is

http://www.biotekbiomedical.com/.

I believe they have been purchased by Fluke recently.

 

[dwayned]

dwayned (Electrical)

Measuring the earth or enclosure leakage current of a device ia a common Product Safety Test that is most often specified as a "type test" or engineering test. This test is designed to measure the leakage current that could flow through a person under various single fault conditions, such as open ground, open neutral, and reversed polarity on the input, or any combination of the above. The leakage currents are measured through an impedance model that simulates the impedance of the human body called a (MD) or Measuring Device. Depending upon the prduct safety standard and the application of the product the MD may vary. You can find several articles on product safety testing and line leakage testing on the Associated Research Inc. Web-site:

http://www.asresearch.com.

They also manufacture equipment to perform this test.

Dwayne