A geodesic dome is a customizable, multi-purpose, and semi-portable structure that can be used for private or business projects. These domes can be placed on various surfaces and come in different sizes. For instance, a geodesic dome can be an excellent outdoor camping solution. It has a spacious, open-concept interior due to its unique design. Depending on the situation, a geodesic dome can be connected to an electricity and water supply, which makes it a more comfortable living place.
However, by using electricity, it has been observed that there is a chance of the structure being electrically energized, which is a serious concern. This problem may cause a severe accident if it is not dealt with and resolved. How to deal with this issue? The best answer is to ground and bond the steel frame of the dome. This article provides an overview of the significance of grounding, multiple risk factors for the dome’s structure, and the general concept of using this technique.
Geodesic Dome Structure and Potential Risks
Geodesic or glamping domes are built with galvanized steel pipes and PVC coated polyester membrane that make the structure of the dome lightweight and self-supporting, which enables it to withstand various weather conditions. The domes are often built directly on the ground or on a platform that may be made of wood or concrete. The best recommended practice is to use a wooden or concrete platform matching the diameter of the dome, which provides support for your dome’s foundation and flooring as well as enables a watertight seal around the base.
With the use of power plugs and electrical equipment, the galvanized steel frames of glamping geodesic dome tents have a risk of getting in contact with electrical wires and becoming "live."
The Significance of Grounding and Bonding
The importance of grounding and bonding concerns people's safety, equipment safety, and lightning defence. In the event that the metal cover of an appliance gets electrically energized, the grounding serves as a safeguard against electric shock. Similarly, bonding protects from unexpected electric shock and it is mostly used where a number of electrical devices with conductive exteriors are installed closely together.
Bonding does not provide protection by itself, but rather serves as a part of a system in combination with grounding and is an important part of the protection process. The purpose of bonding is to remove the electrical potential difference between two conductive metal bodies, and it is recommended when installing electrical equipment or appliances. However, this potential difference cannot be eliminated through bonding. A conductive path to the ground, or grounding, is necessary to eliminate static charge as a result of this potential difference.
Grounding is the flow of excess current from metal bodies or electrical lines to the ground wire without causing harm to humans because the current flows from a high potential point to a low potential point and, in this case, the ground wire serves as a low potential medium. The human body does not attract excessive current while there is grounding because it has equal positive and negative charge, hence declared as a neutral object. Otherwise, it gets shocked due to a fault current. If a conductive surface somehow gets energized, then the proper grounding conducts the electricity into the ground of the earth. The grounding of a glamping geodesic dome frame makes it more shockproof and safe for living.
A glamping dome without grounding or with improper grounding may have a risk of fire and electrical shocks, which can result in injury or death.
Factors that may cause the dome frame to be electrically energized
Installing power plugs and cables directly onto the steel pipe structure, overhead power lines, and lightning can cause the dome frame to become electrically energized.
NEVER INSTALL ANY ELECTRICAL PLUGS, CABLES, APPLIANCES OR DEVICES DIRECTLY ON THE DOME STEEL FRAME STRUCTURE.
The best recommendation is to build interior wooden frame walls and install the power cables/plugs in them just like in a conventional house (Figure-1).
Fig. 1
Overhead, bare power lines may produce a high magnetic field due to the flow of current, and that may energize the structure of the dome.
Lightning mostly affects buildings or steel structures with a height of 30 meters (approx. 100 ft) or more, but residential structures with a height of 15 meters (50 ft) should also have a lightning arrester system which includes a lightning rod connected to a grounding cable (Figure-2). A large geodesic dome structure falls into this category as well, where a lightning rod must be installed at the top centre of the frame.
Fig.2
The Use of High Reflective Bubble Foil Layer as Insulation
To insulate the walls of a dome tent, a durable reflective bubble foil layer stitched with a layer of canvas (Figure-3) is used.
Fig. 3
The purpose of this insulation is to reflect the infrared radiation (heat) and to minimize the load on heating and cooling systems due to which the dome’s inside environment remains warmer in winter and cooler in summer. It is quite lightweight and durable and has a long service life.
This insulation is produced through the bonding of polyethylene air bubbles between two layers of highly reflective metallized aluminium polyester film.
The word "metalized" gets people confused about whether it is conductive or non-conductive, but it is actually the process of coating a thin layer of metal on any object. This film is produced by depositing a thin layer of aluminium in the range of 0.5 micrometers onto the surface of a polyester substrate and then achieving a bright, shiny film. Hence, it is non-conductive as the same film is used as a dielectric medium in the capacitors, in the NASA spacesuits, and in the proximity suits of fire-fighters to reflect the heat radiation and protect them from high amounts of heat.
Here is a Continuity Test performed on the Reflective Insulation Layer - TEST VIDEO.
How to ground and bond a dome tent?
Now we will learn how to do the grounding and bonding of a glamping geodesic dome tent. While doing this job, there are some key steps to keep in mind.
- Conductors which are used for grounding or bonding of the dome frame should be checked for electrical continuity and be able to carry current. For this purpose, visually check all connections to the grounding path and, if necessary, use a digital multimeter to check the continuity by connecting its test leads across the conductor or component being tested.
- Ensure that there is no coating, i.e. epoxies, ceramic coating, enamel paint, etc., on the grounding electrodes.
- The ground rod must be driven below permanent frost level, if possible. The length of the conducting rod should be 8 feet, which must be driven all the way down in contact with the earth. Make sure there are no underground communications of any sort. Call your local authorities to make sure there are no electrical, gas, water, or telecommunications lines in the vicinity.
- The National Electrical Code (NEC) section 250-56 establishes a requirement for a single ground rod or ground plate to have an earth resistance of 25 ohms or less.
- Use an equipment grounding conductor that runs on the same cable or that runs with or encircles the circuit conductors to ground all electrical appliances. (Figure-4). LEARN ABOUT WIRING COLOR CODES
Fig 4.
For bonding of electrical devices, use at least a #6 AWG copper conductor to connect electrical objects and metal bodies.
The grounding of the galvanized steel pipe dome frame of the dome can be achieved by connecting a #6 or #8 AWG copper conductor to the bottom hub of the structure (Figure-5) and an 8-foot long copper-coated steel rod vertically buried in the ground. In rocky soil, drive the rod 45 degrees from vertical; otherwise, bury it horizontally in a trench at least 2.5 feet deep (Figure-6).
Fig 5.
Fig 6.
The grounding should have a total resistance of below 1 (one) mega-ohm, which can be measured with a "Clamp-on Ground Resistance Tester" (Figure-7). The resistance of the rod is affected by the soil moisture. Therefore, it is mandatory to check the grounding system to ensure continuity and proper resistance.
Fig. 7
Glamping Dome Store recommends using a licensed electrician to inspect and approve any electrical work inside or in the vicinity of your geodesic dome tent.
Additional sources:
- Shetty, P., & Alkonda, V. (2022). Glamping–understanding a new tourism trend in Maharashtra.
- Pierce, A. (2010). The use of grounding and bonding to reduce the risks of static electric potentials and help in preventing them.
- Vijayaraghavan, G., Brown, M., & Barnes, M. (2004). Practical grounding, bonding, shielding and surge protection. Elsevier.
- Vlad, A., & Balducci, A. (2017). Porous materials get energized. Nature materials, 16(2), 161-162.
- Cain, J. B., & McKay, N. (1991). Thermal radiative properties of metallized films. Journal of Thermal Insulation, 14(3), 221-240.
- Li, D., Tai, Q., Feng, Q., Li, Q., Xu, X., Li, H., ... & Xiong, C. (2014). Highly reflective and adhesive surface of aluminized polyvinyl chloride film by vacuum evaporation. Applied surface science, 311, 541-548.
- Durham, R. A., Szczecinski, S. J., & Durham, M. O. (2020). Factors impacting selection of grounding and bonding conductors. IEEE Transactions on Industry Applications, 56(5), 4652-4661.
- Durham, R. A., Szczecinski, S. J., & Durham, M. O. (2018, September). Grounding and Bonding Conductors: Solid, Stranded, Bare or Insulated?: Copyright Material IEEE, Paper No. PCIC-2018-03. In 2018 IEEE Petroleum and Chemical Industry Technical Conference (PCIC) (pp. 19-28). IEEE.
- Ufer, H. G. (1964). Investigation and testing of footing-type grounding electrodes for electrical installations. IEEE Transactions on Power Apparatus and Systems, 83(10), 1042-1048.