Understanding the intent behind Rule 10-210 • Code File, September 2018
September 27, 2018 — With the rewrite of CE Code Section 10, a number of questions spring to mind. In my opinion, the most important are what is the intent of Rule 10-210 and what is it really saying?
To answer these questions, we first need to clarify some terminology and how it is interpreted by different utilities and authorities having jurisdiction (AHJs).
What is a grounded conductor? By definition, it is a conductor that is intentionally grounded. Rule 10-210 stipulates that the conductor in a solidly grounded system supplied by the supply authority shall be connected to ground at one point only at the consumer’s service.
To understand why that is, we need to understand why Section 10 was rewritten and we need to clarify some other issues that may arise with the changes to the grounding systems. One of the major reasons for the rewrite was issues caused by the long-acceptable, yet unchecked, unsafe and undesirable, effects of neutral return current flowing through bonding conductors, grounding conductors, other metallic surfaces like municipal water lines and even the Earth.
Look at a typical residential installation of overhead services with each conductor grounded through a municipal water system. What happens when one consumer loses their grounded system conductor? They use the municipal water line to the neighbour’s grounded system conductor back to the X0, because it is in parallel to their own broken grounded system conductor.
It is also important to understand the utilities do not fall under the scope of the CE Code. So, if a utility understands the issue and decides to change their installation methods, then it is imperative that we understand how to connect to these installations properly. Otherwise, we just make a bad situation worse. And if the consumer installs the cables to the utility transformer, then the CE Code has authority over the installation method and the grounding requirements, which are still undergoing changes as we speak.
So, back to my question — what is the grounded conductor? In a typical utility feed to the consumer, it is the conductor that is intentionally grounded and functions as the fault return path and, “if required,” also functions as the neutral return path. This conductor is typically white or bare. It must be grounded and have a system bond jumper installed at the consumer’s service to create the fault return path to the X0 of the system transformer. It must be connected at one single point only.
Why is that? Well, we are striving to achieve the safest system possible by ensuring we have “single point system grounding,” which eliminates all possible parallel neutral paths back to the X0—or, in this case, back to the grounded system conductor.
But what if the utility or the consumer supplies a neutral conductor and a bonding conductor? The utility transformer already has a system bonding jumper installed at the transformer. This system already has “single point system grounding.” So then why would we ever want to re-ground either of these conductors? Sub-rule (d) of Rule 10-210 clarifies it shall have no other connection to ground on the supply side or the load side of the connection. Doing so would create another parallel neutral return path and wouldn’t serve to mitigate the concerns that have led to these changes in the first place.
So, understanding the intent behind “single point system grounding” helps the inspector and the installer understand the goals and methods for achieving a safer installation and eliminating parallel neutral paths.
However, there are systems—such as overhead distribution systems—that already exist. These are not going to go away overnight. Consequently, each AHJ needs to formulate a plan to deal with them on a case-by-case basis as services are updated and changed.
The next concern that comes into play is the grounding of the facility at the location of the service. On a farm, for instance, you may have extended a service 120 m beyond where the service grounding occurred. What is the soil resistivity between these two points? How would a lightning strike affect it? What would the issue be with a ground potential rise (GPR) fault on the utility system?
This is where the issue of equipotential grounding comes into play. An equipotential ground is a connection between an electrode and the metallic surfaces of the electrical equipment.
To answer these questions, we may require engineering ground studies or we may simply install equipotential grounding at each out building to help mitigate the concerns with lightning, GPR, soil resistivity and other issues that may arise when services are grounded at only one point and connected by a bond conductor to a distant or remote location.
But the question then becomes how remote is remote? If the grounding takes place in the utility transformer and you are unaware of the lightning effects or soil resistivity in your area, then installing an equipotential ground at each facility should help mitigate these effects, regardless of the distance. So if the transformer is 3 m from the building or 100 m from the building and a bonding conductor interconnects the grounding at the transformer, I would recommend installing an equipotential ground at the building’s main service entrance and for all other buildings that service feeds. Because these equipotential grounds are interconnected by the bonding conductor, we also inadvertently increase the grounding area to help stabilize the utility system, which makes it a win-win.
This article originally appeared in the September 2018 issue of Electrical Business Magazine.
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