Hi John,

Thank you for your question regarding green bonding screws, it is our pleasure to help.

No.  You may not replace the green bonding screw with a silver one.  NEC Article 250.28 (B) clearly states that the bonding screw (either the Main Bonding Jumper and/or the System Bonding Jumper) must be green in color and that it must be visible when installed.

Remember that the Main Bonding Jumper and System Bonding Jumper perform the same engineering function, in that they are the two (2) and only two (2)  mandatory neutral-to-ground bonds that must occur in your electrical system.  The Main Bonding Jumper is the name for the bond that occurs inside the transformer, the System Bonding Jumper is the name for the bond that must occur in the first service disconnect.  See NEC 250.28.  In your case, you are talking about the System Bonding Jumper which must be a visible green screw.

Sorry for the bad news, but your going to have to run to the shop and grab a few green screws!  Good luck!

Best regards,

The Engineering Team at E&S Grounding Solutions

Hi Allistair,

Thank you for your question regarding boat lightning protection systems, it is our pleasure to help.

Many boats use imbed strips of copper to the outside of the hull, so that the copper is in direct contact with the water.  This becomes the primary electrode.  From that point, copper wires are run to the tip of the mast for use as an aerial.  Other key components, electrical generators, electronic systems, etc., are additionally bonded back to the same copper system so they are at the same potential, thereby protecting the them.

We at E&S Grounding Solutions are certainly not experts in boat lightning systems, there are many others far more capable than we.  But, that should get you the basic theory for protection.  You can also review NFPA 780 for more information regarding boat lightning systems.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: http://www.flickr.com/photos/rahimageworks/7685762104/sizes/o/in/photostream/

Hi Allistair,

Thank you for your question regarding separate earthing systems, it is our pleasure to help.

You may not have truly isolated grounding systems, these two systems must be bonded together in at least one place.  Even when a specification calls out for an isolated or dedicated ground, it still must be bonded back to the first service disconnect at some point.  This is primarily for safety reasons as you do not want to generate differences in potential from one ground system to another.

If you were to test your two grounding systems by conducting a simple point-to-point resistance test, they must show that they are positively bonded to each other.  Now, when the bond is temporarily removed, you should see a very high resistance.  This indicates that the two ground systems are isolated from each other.  But are still systems that are bonded in parallel.

We hope this helps.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: E&S Grounding Solutions

Hi Jeffrey,

Thank you for your question regarding residential grounding, it is our pleasure to help.

The latest National Electrical Code has recently made some changes to the grounding requirements for homes.  You are now required to install two (2) 10-ft ground rods at least 6-ft apart, even if you have a copper water main.  E&S Grounding recommends a 20-ft spacing between these rods.

There are a few exceptions to this rule.  If you can test for resistance-to-ground and can demonstrate that one (1) ground rod by itself is under 25 ohms, you don’t need the second rod.  Also, if you are willing to dig 18-inch deep holes and completely bury your ground rods, you can use 8-ft rods (you must use connections rated for direct burial).

Keep in mind, you still MUST bond to the steel rebar in the foundation, the gas main, the water main, the cable entrance, the telco ground, any lightning protection system, your swimming pool ground, and any other ground system, just as before.  It is just that you may not count these as grounding electrodes anymore.

We hope this helps.  Good luck!

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo Credit: http://www.flickr.com/photos/mamchenkov/278154924/sizes/o/in/photostream/

Hi Melissa,

Thank you for your question regarding step and touch voltages around your transformers.  It is our pleasure to help.

Yes, your engineer is correct.  A Single Line to Ground (SLG) fault at your transformer will create a significant Ground Potential Rise (GPR) which could in fact result in both step and touch voltage hazards to the public.  29 CFR 1910.269 mandates that these hazards be mitigated to protect personnel working near the transformers, and/or the public.

Your conductive soil can be beneficial, but it can also be harmful, given certain conditions.  If the conductivity gets worse with depth, the electrical energy is going to want to stay near the surface of the earth, creating a larger step voltage concern.

You will need Soil resistivity data, and electrical fault data to analyze these hazards properly.  We recommend a series of Wenner 4-point soil resistivity tests with spacing’s at least as large as your transformer area.  For electrical data, you will need the SLG fault current, the X/R ratio (or zero sequence impedance), and the fault clearing time.

We are of course more than happy to help you with this important project.  But if not us, please get someone with the proper simulation software and expertise to help you design a safe and effective grid that is in compliance with 29CFR1910.269 requirements.

Please feel free to call us at 310-318-7151 if you should have any further questions.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: E&S Grounding Solutions

Thank you for your question regarding Ground-Fault Circuit Interrupter (GFCI) outlets and water coolers, it is our pleasure to help.

The National Electrical Code (NEC) Article 422.51 and 422.52 are very clear on this subject, you must have GFCI protection for water coolers.  In fact, machines manufactured after January 1, 2005 must have integrated GFCI protection inside the circuitry of the system (see NEC 422.51).  Depending on how your local inspector interprets the code (see NEC 422.52), you may be required to provide a dedicated GFCI outlet, even if the cooler has integral GFCI protection. 

We would recommend that you install a GFCI and Arc-Fault Circuit Interrupter (AFCI) (see NEC 210.12) for your water cooler.

We hope this helps.  If your should have any further questions, please do not hesitate to contact us again.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: E&S Grounding Solutions

Thank you for your question regarding 50% ground bars, it is our pleasure to help.

Busways have two ground conductors.  One is an actual additional copper or aluminum bus bar in the stack with the phase conductors inside the housing.  The other is when the protective metal housing around the bus bars is bonded and used as a ground path.

The housing can be a 50% rated ground, and the ground bus bar can be the other 50% rated ground.  Together they make up 100% of the ground path.  According to Eaton, in applications with heavy microprocessor-based loads or large computer installations, grounding isolation is essential.  In these cases, the housing ground can be insulated from the bus bar ground.

Isolated grounding is used with sensitive electronic equipment.  Specifically, this type of equipment grounding configuration is only intended to be used for “reducing common-mode electrical noise on the electronic load equipment circuit.”   It keeps ground noise from other equipment from coupling onto the ground used for sensitive equipment.  However, in some circumstances, the isolated grounding configuration can actually make your noise worse.  It is important to understand all the potential repercussions of isolated ground before designing one into your system.

Keep in mind that you may not associate an external insulated Earth cable with the busway as an isolated ground.  The isolated ground (IG) must be inside the busway while using the busway housing as the normal equipment grounding conductor, or in the case of conduit, the isolated ground (IG) must be inside the same the same conduit as the phase conductors and the normal equipment grounding conductor.

An external isolated ground would not follow the exact same path as the busway conductors and create a large loop.  In normal conditions, this loop would induce noise on the isolated ground making it worse for electronic equipment.  In fault conditions, this loop would be a high-inductance (a loop is a giant inductor) and thus a high-impedance, ground-fault return path.  This is a dangerous and counter-productive design.

Design of a system using isolated ground should not be attempted by an engineer without suitable experience because of the many potential problems.  A better solution to ensure clean power and ground is to install a grounded isolation transformer very near to your sensitive electronic loads.  Again, I recommend IEEE Standard 1100-2005 – IEEE Recommended Practice for Powering and Grounding Electronic Equipment (which is available to purchase online as a PDF).  This standard discusses many grounding methods for sensitive electronic equipment that are alternatives to isolation grounding.

An Isolated Ground (IG) conductor can be run parallel to the Protective Earth (also called the equipment grounding conductor) and they are only bonded one point: either at the service entrance or a separately derived source such as an isolation transformer.  The electronic equipment and its chassis must be physically isolated from building ground if it is to be plugged into an isolated ground receptacle (IGR).  When this equipment grounding configuration is used, “the enclosing metal raceway must still be properly grounded.”

The busway enclosure can be used as a 50% rated ground path.  This means that the housing is capable of being an equipment ground conductor at up to 50% of the rated current of the phase bus bars.  This is sufficient ampacity for most grounding systems.  In the isolated ground configuration, the ground bus bar would be the Isolated Ground, and the busway housing would be used as your normal equipment grounding conductor.

If you want to learn more about applications of isolated grounding, please refer to IEEE Standard 1100-2005 – IEEE Recommended Practice for Powering and Grounding Electronic Equipment.  This is part of the Industrial Applications Society’s (IAS) Color Book Series and is often referred to as the “Emerald Book.”

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: E&S Grounding Solutions

Hi Jeff,

Thank you for your question regarding the welding of steel rebar, it is our pleasure to help.

Not all rebar can be welded, particularly with the exothermic welding process as it must be able to heat the surface of the metal rebar to the melting point in order to ensure adhesion.  In general, only steel rebar that is “Grade W” can be welded.

According to Wikipedia: The American Welding Society (AWS) D 1.4 sets out the practices for welding rebar in the U.S.  Without special consideration the only rebar that is ready to weld is W grade (Low-alloy — A706).  Rebar that is not produced to the ASTM A706 specification is generally not suitable for welding without calculating the “carbon-equivalent”.  Material with a carbon-equivalent of less than 0.55 can be welded (AWS D1.4).

Rebar cages are normally tied together with wire, although welding of cages has been the norm in Europe for many years, and is becoming more common in the US.  High strength steels forprestressed concrete may absolutely not be welded.

Here is the link: http://en.wikipedia.org/wiki/Rebar

We hope you find this information useful.  Feel free to contact us again should you have any further questions.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: http://www.flickr.com/photos/brockamer/5433065406/sizes/o/in/photostream/

Thank you for your question regarding lightning protection and ferrite chokes, it is our pleasure to help.

Ferrite chokes are used to filter common-mode noise and interference on data lines such as CAT5 Ethernet.  Ferrites operate on low-power high-frequency signals that are coupled onto the line from neighboring cables or wireless transmissions.  They are not designed to protect from high-power surges such as lightning or short-circuit events.  In high-power surges, ferrite chokes become saturated and become ineffective as filters.

For lightning protection, you need a transient voltage surge suppressor (TVSS) for Ethernet, such as those offered by PolyPhaser and Transtector (see link).

http://www.protectiongroup.com/Surge/Data-Line-Protectors/Application/Ethernet-protector

Of course, the best way to protect the sensitive electronic equipment tied to your Cat5 cable, is to make sure that the difference in potential between the two pieces of equipment is very low, something less than 0.1 ohms.  If there is no difference in potential, than no harmful voltages can form in the first place.  Good bonding between these points, along with a low-impedance electrode, will be one of the best methods of protection.

We hope you find this information useful.  If you should have any further questions, please do not hesitate to contact us again.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: http://www.flickr.com/photos/picofarad-org/2132207664/sizes/l/in/photostream/

Hi Nilushka,

Thank you for your question regarding ground grid voltage variations, it is our pleasure to help.

Unfortunately, we are not very familiar with PSCAD as there are a number of similar programs in this category that can be used for power system simulations.  Many of these software programs come with grounding/earthing modules that are intended to help the electrical engineer design a proper ground system.  But, all of these types of software programs that we have been able to look into, are lacking in some very serious ways.  You have found one of those issues.

Now, we can’t speak directly to PSCAD as we have yet to analyze this program, but if it is like the other programs in its category, it uses a theoretical ‘super conductor’ for its ground design.  In other words, the software can only calculate two of the three parts of ohm’s law; current and resistance.  Voltage drops across the conductor length cannot typically be calculated by these types of programs.  This is of course a direct-current (DC) issue, these types of programs can’t even begin to analyze the impact that alternating-current (AC) will have on the system (inductance, capacitance, impedance, magnetism, etc.).

The reason for this is many fold, but you can easily imagine trying to hand calculate electrical energy flowing through a simple 100-ft long bare copper buried conductor.  Figuring out the current and resistance is easy… calculating the leakage current into the earth as the current flows down the conductor, now that is hard!

You would need to look at each and every foot of the conductor and calculate its impedance, the amount of current ‘leaking’ into the surrounding soil, the voltage drop that would occur, the magnetic fields that would form and collapse, etc.  And of course all of this is based on the soil resistivity of the surrounding earth.  Things get really complicated when you have vertical electrodes that pass through multiple layers of differing resistivity soil.

The bottom line is that calculating the voltage drop across the conductors is very difficult and can take hours of calculations using a high-speed computer.  If your software is giving you results in the blink of an eye or after a few seconds, it is not capable of conducting the level of simulation you need to figure out the voltage variations in your grid.

Here is a link to a recent blog you may find useful:

http://www.esgroundingsolutions.com/blog/939/according-to-my-knowledge-gpr-provides-information-about-the-maximum-potential-that-can-happen-under-a-faulty-condition-but-how-can-we-find-the-potential-distribution-within-the-grid-i-e-in-the-soil

To our knowledge, only the CDEGS program from Safe Engineering Services ltd is capable of conducting this level of analysis.  This is why CDEGS is used by the IEEE, NFPA, ANSI, IEC and many other regulatory bodies for the development of their standards.  We could be wrong and perhaps PSCAD has this ability, we simply do not know as we have yet to analyze it.  However, there is no doubt that PSCAD is a fine program for what it is designed to do.  But like the other programs in its category, it may not be designed to calculate voltage drops across the conductors, and would therefore not be able to accurately calculate Step & Touch Voltage hazards for human safety.

If you should need help in this area, we would be glad to assist you.  Please feel free to call us at 310-318-7151 California time, or simply email us back, and we can start discussing your project needs.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: http://www.flickr.com/photos/philmanker/3147835563/sizes/o/in/photostream/