Grounding connection design
The two most important impacts of correct grounding layout are the following.
- The circuit has a zero voltage reference point, the ground. (Green, 2014, para. 1)
- The ground is critical for safety.
If a heater’s insulation wears out, then touching the metal of the heater gives a shock unless the heater has been grounded. The metal heater housing is where the conductor is installed. The conductor is then connected to a ground. The ground may be in the building or far away from the location of the heater. The ground can be a panel or an electrical outlet. (See fig. 1) White or gray insulated wires are the color used for the ground conductor. (OSHA) The grounding conductor for the equipment is green with a yellow stripe or green so they will be distinguished from the ground conductor. (OSHA)
Figure 1 An example of distribution panel (www.osha.gov)
A rated conductor needs to be used. Conductors are rated by the ampere capacity (size) and the highest operating temperature (insulation temperature rating). An example from Square D is #2 Cu, 60/75ºC, Cu stands for copper. The conductor’s rating is useful for appropriate use. The rating is also useful just in case, current passes to the grounding device. The idea is to keep the resistance low to avoid a drop in the voltage. (Green, para. 2) The wire used for the ground is copper or aluminum because both are good conductors of electricity.
Figure 2 The ground symbol (Google images)
Electricity occurs when the current flow (the flow of electrons) is caused by voltage. Circuit grounding ensures that at least one point is safe to touch. (See fig. 1) The functioning of voltage is dependent upon 2 points, so a person feels an electrical shock when voltage passes from one point to a second point through a person’s body. (See fig. 2)
Figure 3 Voltage passes between two points (Kuphaldt, 2008, p. 80)
Current flowing through a wire has the potential to cause a shock, so a disconnect-switch needs to be added to “break the circuit” when there is too much current. (See fig. 3)
Figure 4 A temporary ground and a permanent ground (Kuphaldt, 2008, p. 93)
Voltage = (Current)(Resistance) so that V -= (I)(R). When the ground conductor is sized appropriately, R = 0, and remains 0 when the values for I and V change. An ideal circuit design does not register any voltage drop, regardless of the current’s magnitude (I*R). (Kuphaldt, 2008, p. 59)
Superconducting wire used for a loop in a short circuit measures zero voltage, because there is zero resistance. (Kuphaldt, p. 43) A zero measurement by the voltage meter could also be due to no difference in the voltage between the heater and the ground; which is not the same as zero voltage. A ground loop leak far from the heater housing and its ground can give a faulty reading. When a leak occurs in a shared ground on the facility there is a danger of the heater’s circuit introducing interference through the ground. (Green, para. 8) That is why the best strategy is to ground every electrical circuit separately.
The heater’s ground connection
The grounded point is the point of the circuit that is at ground potential 100 percent of the time. Ground potential amounts to zero voltage between the electrical outlet and the grounded point of the circuit. The metal conductor connects electrically using a thick wire to reach the correct connection point on the circuit. Copper wire and insulated copper wire are suitable.
References
Green, K. (2014) “Grounding and your Heater” Tutco Heating Solutions Group, Farnam Custom Products, http://www.farnam-custom.com/library/engineer-talk/grounding-and-your-heater
Hunka, G. (n.d.) “Circuit Grounds and Grounding Practices” Department of EE, University of Pennsylvania,
“Applying Intrinsic Safety” (n.d.) Scientific Technologies, Inc. http://www.futek.com/files/pdf/Media/IntrinsicSafety.pdf
Kuphaaldt, T. R. (2006; 2002) Electrical Safety Volume 1 – DC, 5th Ed.“Safe Circuit Design” (n.d.) All about Circuits, http://www.allaboutcircuits.com/vol_1/chpt_3/8.html
OSHA General Industry Standards, Subpart S, Electrical https://www.osha.gov/dte/library/electrical/electrical.html#guarding
“Wiring Conductor Ampacity to Temperature Rating” (2001) Data Bulletin Square D Schneider Electric, Bulletin No. 0600DB0103 May 2001 Cedar Rapids, IA, USA http://www2.schneider-electric.com/resources/sites/SCHNEIDER_ELECTRIC/
