TECH | On Solid Ground
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2015 EMI Conference
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About the AuthorHanna Peterson, P.E.

Welcome to EMI TECH:

Good bye ACDP, Hello EMI Network

In 2015 the ACDP is making a big transition to a new name – the EMI Network. The former Association of Christian Design Professionals was officially discontinued at the 2014 ACDP conference in Colorado Springs. Since then, we have been working on a new strategy to continue to draw together design professionals who want to engage with EMI around the world. So, you may be wondering, what’s changed?

First, the name. ACDP is now the EMI Network. Our hope is that the name ‘EMI Network’ will more closely identify with the organization, EMI, and eliminate any confusion about who we are. Second, the monthly ACDP newsletter is now EMI Tech. This new quarterly publication will focus on technical issues to help guide us toward better design in the developing world.

Regardless of the name and newsletter, we appreciate your partnership with us in this great ministry. We look forward working with you to advance the name of Christ through design around the world.







Bongolo Hospital

On Solid Ground

Located in rural West Africa, Bongolo Hospital of the Christian and Missionary Alliance is a 160-bedded hospital providing the only medical care for tens of thousands of people from surrounding villages and neighbouring countries. Over the past years the hospital has experienced problems with its electrical system which serves over 40 buildings on the campus. These have included electrical shocks to individuals living on the campus, electrical fires , and damage to valuable and sensitive medical equipment. These serious problems led Bongolo Hospital to seek the help of Engineering Ministries International. In February 2015, EMI sent a team of volunteer Electrical Engineers specifically to investigate Bongolo’s electrical system.

After examining the site, the team determined that improving the grounding of the electrical system was the best first step towards eliminating the issues. The lack of adequate grounding was seen to be the primary cause for individuals being shocked at various locations, as well as a contributing factor in electrical fires. Additionally, since the area is prone to lightning strikes, a poorly grounded electrical system increases the risk of damage to any equipment plugged into it whenever lightning causes an electrical surge in the line.

The purpose of electrical grounding:

  1. Ensures that any surface of electrically powered equipment that comes into contact with humans is at the same electrical potential as the ground the person is standing on when contact occurs.
  2. Prevents fires by creating a return path that allows for quick activation of circuit protection (such as a circuit breaker) in the event of a short circuit to any conductive surface that is not intended to carry current.
  3. Provides some protection from power surges, including those caused by lightning.

What does a well-grounded electrical system look like?

In a well-grounded system all conductive surfaces surrounding wires and enclosing electrical equipment should be connected to ground via equipment grounding conductors, also known as EGCs [NEC250,VI]. The EGCs should be connected back to the ground bus inside the main panel enclosure for each building. For example, in a well-grounded system, if a short circuit occurs such that the enclosure of a drying machine is energized, current will flow back to the source through the ground wire (EGC) tied to the enclosure of the dryer and cause the circuit breaker to trip. If there was no ground wire (EGC) tied to the enclosure, the short circuit-energized drying machine enclosure would shock the next person to touch it or cause a fire due to arcing.

Well-grounded systems must also have adequate earth grounds. An earth ground creates a path to the earth of at most 25 ohms and ideally under 5 ohms electrical resistance. How to achieve this low resistance electrical path is highly dependent on soil resistivity and the grounding materials that are readily available. This low resistance path to ground ensures that all of the grounded components remain at the same electrical potential as earth. It also acts to suppress electrical surges in the line. If the location has a lot of lightning activity, it is wise to put in multiple earth ground rods at each building to reduce the surge impedance even if only one is needed to achieve an acceptable resistance. The grounding electrode conductor going from the earth ground to the main panel should be sized according to the NEC [NEC250.66]. Metals that are susceptible to corrosion should not be used in the grounding system. Copper-coated steel rods, copper wire and clamps intended for this purpose should be used.

Inspecting building wiring at Bongolo Hospital.

Electrical investigation at Bongolo Hospital:


Field-testing ground resistance with the AEMC 3731.

After inspecting the wiring inside most of the building electrical panels at Bongolo Hospital, it was discovered that only one was wired correctly. In this building, every outlet and light was wired to ground and all the ground wires were tied to the neutral at the main panel of the building, where a single connection to earth ground was made. But most panels had no grounding at all. Some had grounds that were tied together to a bus bar inside the panel, but not connected to neutral inside the panel or to an earth ground. In some cases the physical ground rod connections to earth were built using inappropriate materials such as aluminium wire. To quickly measure the ground resistance, a clamp-on ground tester (AEMC 3731) was used.* The few earth grounds that were found were tested and it was discovered that most of them were over the 25 ohms resistance maximum. Since moisture impacts resistance, the earth ground connections outside of buildings where there was moisture were better than the ones driven inside buildings. High resistance on earth ground means there is a higher risk of shock and a higher risk of damage from lightning surges. At a local supplier, 3 meter or 8-10 ft copper ground rods were not easily available. However, 4 ft copper ground rods were readily available.

Recommendations for improved grounding:

Bongolo Hospital has over 40 buildings spread over a radius of approximately 400 meters around the transformer/generator. It was recommended that four wires (3 phases and a neutral) be run for the main lines coming from the main distribution panel at the transformer/generator. Each individual building will have its own earth ground and main panel where the neutral and ground will be tied together.

This type of grounding is TN-C-S which is also known as Multiple Earthed Neutral (MEN) or Protective Multiple Earthing (PME). This method of grounding does not require a ground wire to be run from the main distribution panel, lowering costs on this large system. It is also the easiest transition from an ungrounded system because grounds can be added at each building one at a time without having to add a fifth wire (ground wire) to all their distribution lines first. In addition, this ensures that the ground and conductive surfaces in each building is as close as possible in electrical potential to the ground a person would be standing on.

Due to the materials available and the fact that driving multiple earth grounding rods for each building will provide more protection from lightning surges, it was recommended that each earth ground be made up of two copper ground rods of 4 ft length each spaced 10 ft apart. These would be driven into the earth and connected electrically in series with each other and to the main electrical panel in the building with copper wire sized according to table 250.66 of NEC 2011.

Implementing the grounding improvements recommended by EMI will greatly reduce the risk of shock, reduce damage to medical equipment from surges and lightning strikes, and reduce the risk of electrical fire on the Bongolo Hospital campus.


ARTICLE BY
Hanna Peterson, P.E.

HEADER
Ground rod connection installed at Bongolo Hospital.

EMI TEAM:
Lead/Electrical Engineer: Andy Engebretson; Electrical Engineers: Dave Onstad, Fenton Rees, Josiah Moore, Hannah Peterson; Architects: Jordan Cox, Tipton Housewright; Mechanical/Civil Engineer: Kathryn Stok; Civil/Master Planner: Bill Kelly; Structural Engineer: Kevin Winner

SOURCES
Carpenter et al. (2010) NFPA 70 National Electric Code 2011. Quincy, MA: National Fire Protection Association.

Carpenter, R.B., Lanzoni, J.A. (2007) Designing for a Low Resistance Earth Interface (Grounding). Retrieved here.

Guthrie et al. (2004) NFPA 780 Standard for the Installation of Lightning Protection Systems. Quincy, MA: National Fire Protection Association.

*After returning from the trip, a side-by-side experiment was performed on the clamp-on ground tester versus a 3-point fall of potential ground tester in various scenarios. Although the clamp on tester is much easier to use, it is not the best method to test earth grounds. In the future, a lighter weight 3-point fall of potential tester like the Fluke 1621 should be used.

Hanna Peterson, P.E.
Volunteer Electrical Engineer

Hannah received her electrical engineering degree from Rose-Hulman Institute of Technology in 2004. She started her career in the United States Air Force working in their research labs. She then worked for Cummins Power Generation doing diesel engine controls for Gensets. After that she worked in the solar power industry in module manufacturing and system design/installation and then for a solar inverter manufacturer, Fronius, as a trainer and field engineer. She has joined EMI on two projects in the last six months. Hannah is a licensed PE and currently lives in the Los Angeles area with her husband.




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