Busting the 90° Myth – The Grounding Rule

Bet you have been told that when connected conductivity (direct connection) you MUST place the earth stake at 90° to the target line and as far away as possible – unfortunately, this is total rubbish.

The criteria should be that you have “Good” current on the target line – by good current I mean that the reading needs to be steady with zero or minimal fluctuation. This then allows you to commence locating; if you do not have good current then changes need to be made to the transmitter setup to improve current levels.

As professional locators we need to take into account other information that can and will affect our locate. For example, are there other services present in the vicinity of our target line. I am sure that we would all agree that one of the key points when locating is to achieve an accurate locate, and that this is best achieved by reducing the amount of interference that may affect the electromagnetic field around our target line. If we follow the 90° rule and stretch the earth cable across existing underground utilities, we run the real risk of mutual induction or bleed onto these services.

The manufacturer and some locating manuals that I have seen and read claim that by placing the earth stake far away from the target line produces an increase in the current on the target line, but is this true? Mike Parilac, owner of Staking University in the US and one of the foremost utility locator trainers in the world, conducted a series of experiments around this topic and recorded the outcome in Volume 29 Issue 6 of his Underground Focus magazine. I quote from this article:

Conclusion 1:Following the “grounding rule” increases signal strength by a maximum of 5%, a nominal amount.”

Conclusion 2: “The grounding rule” increases bleed-off when there are nearby conductors.”          

 The rule of thumb: Do not stretch conductive (direct connect) leads by placing the grounding device as close the access point as possible.

 In my next article we will look at times when this rule can be modified to suit various circumstances.

Locating Unlimited Pty Ltd (RTO ID 45518), Australasias leading provider of Underground Damage Prevention Training is committed to providing training and information to help maintain safe work practices around buried utilities and prevent damage to this infrastructure.

 Contact Jeff at Locating Unlimited 0419 44 66 27 or jeff.moore@locatingunlimited.com.au