Hi Nuttanon,
Thank you for your question regarding Professor Dwight’s formula, it is our pleasure to help.
Professor H. R. Dwight of the Massachusetts Institute of Technology developed a simplified formula for calculating the resistance-to-ground of an electrode in uniform soil conditions. The problem with the formula is that uniform soil conditions simply do not exist in nature and as such, hand calculations using this or other formulas seldom work. Here is the formula: Continue reading
Hi Shachidevi,
Thank you for your question regarding proper grounding at cellular stations, it is our pleasure to help.
Proper grounding at cellular stations is quite complex and detailed. There are many requirements for extensive bonding and a typical cellular station and getting into each of them would be far to much to cover in a simple blog. But needless to say, virtually every single piece of metal must be connected to a dedicated equipotential grounding system which is in turn bonded to an earthing system. Continue reading
Hi Ankomah,
Thank you for your question regarding the purpose of the earthing portion of the grounding system in a proper functioning electrical system, it is our pleasure to help.
In a properly designed electrical system, the Over Current Protection Devices (OCPD) such as fuses and circuit breakers will indeed continue to function even without a connection to earth. In other words, if you have a good electrical system, you can remove the connection to the ground rod and the power will still flow and the circuit breakers will still trip in the case of a fault. This is all true, but that is not the purpose or function of the earthing system, now is it? Continue reading
Hemendra tells us:
I am dealing with helping our chemical plant facility technicians do the site ground grid resistance measurement for various grounding safety related matters. System grounding, Equipment grounding for ground fault return path, grounding for Lightning protection and grounding for static electricity mitigation. Some facilities have multiple buildings and I am not sure if all the building ground grids are tied to have a common ground grid.
From available drawings (these plants goes back to 1950s) and site visits, What I have observed is there are accessible ground wells and a ground wire is running around the perimeter of building/structure.
1) My first step in this process is establishing facility “Primary ground reference” and measure its resistance to ground using 3 point fall of potential method or Selective stake less method (If I choose not to isolate the ground well from ground grid my disconnecting the ground wire termination to the electrode in the ground well.).
2) Next I have to establish several “Secondary ground reference” points through out the plant where I am measuring resistance of equipment grounding conductor resistance to ground or process piping ground path integrity whose liquid flow can produce static electricity in a NEC 500 classified hazardous areas.
This “Secondary ground reference” points resistance I measure using a 2-point ground resistance test between “Primary ground reference” point and “Secondary ground reference” point and adding the result to Primary ground reference value measured in 1) above.
WITH THIS MUCH INTRODUCTION ABOUT WHAT I AM UP TO NOW THE QUESTIONS.
Q1) If I the site does no have visible ground well nor the drawing showing the grounding how can I determine or locate a “Primary ground reference” point. Is it correct to use Incoming Utility Power service substation transformer neutral grounding can be used as “Primary ground reference”?
Q2) To establish ground resistance value of this service entrance transformer neutral ground point I need to measure ground resistance using either the 3-point fall of potential after isolating the ground rod from service transformer neutral OR using selective stake less method.
Q3) When I have multiple power distribution transformers in the facility each transformer secondary neutral point is grounded to ground grid can be established as “Secondary ground reference” points for those areas of the plant right?
Thanks for your help.
Hi Emmanuel,
Thank you for your question regarding earthing systems and lightning protection systems, it is our pleasure to help.
Lighting protection systems are an above-grade conductor network designed along the lines of a Faraday Cage, that is used to protect a structure from the effects of lightning discharges (direct or indirect). Continue reading
Hi Kevin,
Thank you for your question regarding the 20-ft grounding rule for cable antenna grounding, it is our pleasure to help.
There are really no special rules or exceptions for cable and antenna grounding in the National Electrical Code (NEC). In the end, your cable must be bonded to the main electrical grounding system and be in compliance with NEC Article 250. The primary purpose of the grounding is to ensure that there are no hazardous differences in potential between your cable system and the building. Continue reading
Hi Cris,
Thank you for your question regarding the testing of Ufer grounds on homes. It is our pleasure to help.
The term “Ufer” ground is another word used to describe what the National Electrical Code (NEC) calls a “concrete encased electrode”. It is also commonly referred to as “building steel”. Whatever you call it, we are talking about the rebar in the concrete foundation. Here is a link with some additional information you may find useful: Continue reading
Hi Slamat,
Thank you for your question regarding resistance-to-ground calculations for parallel electrodes, it is our pleasure to help.
The simplified calculation for predicting the resistance-to-ground (earth) of a given length grounding rod is: Continue reading
Hi Ken,
Thank you for your question regarding routing neutral wires separate from the hot wires, it is our pleasure to help.
Your question is a bit out of our expertise, but we can tell you that it is not only a very bad idea to route a neutral separately from the hot wires, but is illegal under that National Electrical Code (NEC). Please see NEC Articles 215.4(B), 300.3(B), and 300.20(A). Continue reading
Hi Tommye,
Thank you for your question regarding the testing of 55 gallon drum static electricity bonding, it is our pleasure to help.
In any static grounding system, there are generally three (3) systems we are worried about. The first one is the primary ground source that leads back to the first service disconnect. The second is the resistance-to-ground of the grounding electrode. And the last is the required resistance, if any, of the ground connections. In static grounding, there is often a specific resistance required so that the static that is formed will be removed from the system slowly. In your case, you probably do not have a resistance requirement and should have a very low impedance ground path. Continue reading
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