1st Generator install

[Parker27]

I have been installing a 3 phase 60KvA generator connected to a MDU with a 100A 0.1A RCD, when I test the earth electrode resistance (Ra) using the earth fault loop impedance tester I get a reading of 1845 ohms, as this does not meet the Ra x Ia less than or equal to 50v, 1845 * 0.1 = 184.5 , it fails this test.

The ground seems quite dry and the earth electrode rod is under trees, I have tried moving the earth electrode, but still cannot get the Ra value less than 1845 - Have you got any suggestions as to how I can reduce the Ra ?

 

[RyanCheetham]

How deep are you into the ground with your rod?

 

[Parker27]

one metre, I have also tried moisting the area with water, this does bring the reading down a little but not substantially

 

[sparkx]

You can't use a normal earth loop impedance tester, there's no loop ffs.

You need an earth rod impedance tester

 

[Parker27]

Hello sparkx, sorry but what are no loop ffs.

 

[iamelectric]

screw another metre rod on and bang it in deeper

 

[sparkx]

1. You are not competent to be installing a large genset such as this without some knowledge of earthing.

2. Please see my earlier post, you cannot use an earth loop impedance tester on this set up, draw a diagram if that'll help you..

 

[Marvo]

one metre, I have also tried moisting the area with water, this does bring the reading down a little but not substantially

One meter...??? A one meter rod is nowhere near long enough. Even if by some miracle you got a decent Ra value it won't be stable at only 1 meter depth.

Organize at least 2 x 2.3 meter rods and a threaded brass coupling. Knock in the first rod, attach the coupling and screw the second rod on top of it. Knock the second rod in so your depth is around 4.5 meters. Now take a new Ra reading with an earth rod tester.

 

[jamie-spark]

one metre, I have also tried moisting the area with water, this does bring the reading down a little but not substantially

Water lol.

Do you have a copy of OSG. If so look at page 21 this has a LITTLE INFO to get u started

 

[Engineer54]

Do as suggested by Marvo, and move the earth rod position away from any tree's, the roots will rob the surrounding ground area of moisture around the rod. Do not use the thin 3/8'' twigs if that's what you have installed they are the next best thing to being completely useless, apart from not being able to extend them. Use extendable 5/8'' 1.2m rods, which you'll probably need at least 3 if you take Marvo's good advice, or better still 2 X 2.4m rods. Depth is the real key to obtaining both a good Ra value and to ensure the overall stability of a TT system....