Generator Ze test

[sparky1888]

Evening everyone,

Looking for a bit of advice with generator earthing/testing.
An 80kva generator supplying a small site with a few portacabins.
I am aware that the genny needs an earth electrode with an Ra lower than 20ohms as per bs 7430 tested with an electrode tester.The chassis bonded to star point of the windings.
My question is how is the Ze test carried out at the genny? I have read on other forums that a Ze test on the genny will give unusual readings. Only looking to find out what to write on the cert for the origin of the installation as the rest of the tests (R1+R2, RCD etc) are self explanatory.
Any advice would be greatly appreciated!

 

[davesparks]

You cannot test Ze (external EFLI) because there is no external installation to test.

For practical purposes you would need to find out the impedance of the source from the data sheet for the alternator. And the prospective fault current from probably the manufacturer of the generator.

Though at 80kVA the generator will not be able to provide enough fault current for ADS, the engine will stall before most mcbs operate on fault current.