i was just looking these questions up...
i was just looking these questions up...
1.
I'm trying to understand this grounding and bonding issue and have watched Mike's videos on the subject dozens of times and gained a lot of clarity on the subject but i still have some questions....I've heard him say the only way to 'clear a ground-fault' is to "turn it off"....Makes sense!....but In the event of a ground-fault on the line-side of the service is there some sort of OCPD in the transformer?? How does it turn off? or does it?
2.
Question #2 If the neutral conductor back to 'the source' is the effective ground-fault current path to trip the breaker on the line side of an OCPD what exactly is the purpose of grounding electrodes?? If anyone else can assist I'd appreciate it.
Hope this helps.
1. For a fault on the LOAD side, it'll "turn off" because the breaker has tripped and there are no loads drawing power, and therefore no more fault.
Line side fault, I can't help you there, other than saying yes there is an OCPD there but the POCO owns it.
2. Does this make sense? The GEC being connected to the grounding electrode keeps the voltage at zero for all the EGCs connected to it (unless of course there is a problem).
But now I have another question- so then the customer's main service OCPD is protecting the customer side (LV) of the service xfmr, and the POCO's fuses are protecting the MV side?
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/bregnd.html#c3
In the event of an electrical fault which brings dangerous high voltage to the case of an appliance, you want the circuit breaker to trip immediately to remove the hazard. If the case is grounded, a high current should flow in the appliance ground wire and trip the breaker. That's not quite as simple as it sounds - tying the ground wire to a ground electrode driven into the earth is not generally sufficient to trip the breaker, which was surprising to me. The U.S. National Electric Code
Article 250 requires that the ground wires be tied back to the electrical neutral at the service panel. So in a line-to-case fault,
the fault current flows through the appliance ground wire to the service panel where it joins the neutral path, flowing through the main neutral back to the center-tap of the service transformer. It then becomes part of the overall flow, driven by the service transformer as the electrical "pump", which will produce a high enough fault current to trip the breaker. In the electrical industry, this process of tying the ground wire back to the neutral of the transformer is called "bonding", and the bottom line is that for electrical safety you need to be both grounded and bonded.
The term "ground" refers to a connection to the earth, which acts as a
reservoir of charge. A ground wire provides a conducting path to the earth which is independent of the normal current-carrying path in an electrical appliance. As a practical matter in household
electric circuits, it is connected to the electrical neutral at the service panel to gaurantee a low enough resistance path to trip the
circuit breaker in case of an electrical fault (see illustration below). Attached to the case of an appliance,
it holds the voltage of the case at ground potential (usually taken as the zero of voltage). This protects against
electric shock. The ground wire and a fuse or breaker are the standard safety devices used with standard electric circuits.
