Here's a typical US arrangement ...
It's fairly common for there to be no disconnects or overload protection at smaller PoCo pole mounted, single phase transformers. At various points in the line, the PoCo will have 'automatic cut-outs' that act like breakers - but also automatically re-set after a few seconds. Only after multiple faults with they stay 'open.'
The winding on the secondary side of the transformer has a connection at either end, as well as a center tap. Thus, there are 240 volts between the end (insulated, "hot") wires, and 120 volts between either 'hot' and the center (bare, 'neutral') wire.
The neutral wire also has a direct connection to a ground rod at the nase of the pole.
The bare neutral wire is aluminum on the outside, and steel on the inside. Thes "ACSR" (Aluminum Cable Steel Reinforced) is intended to support the wires to the service mast. You cannot cut it with most cable cutters without the steel core damaging the cutters.
Your very first overcurrent device is located just AFTER the meter, as part of the service disconnect. This disconnect is the first part of the system that is not sealed, and is accessible to the consumer. The meter is before the disconnect.
The meter typically will have four jaws - two to interrupt each 'hot' wire - and the entire current load will pass through the meter. The neutral (the ASCR was spliced to insulated wire at the top of the mast) will not pass through the meter at all.
At the service disconnect there is also a connection between the neutral, and another ground rod at the building.
What you call 'selectivity' is called 'selective co-ordination' here. We do not always do this. When we are required to have 'selective coordination,' it is necessary to either do an engineering study, considering the various trip curves of the components, or to purchase everything from the same manufacturer, who has had UL evaluate the equipment combinations for selective coordination.
Testing of ground rod impedance is not usually done; if in doubt, we simply add another ground rod at least 6-ft away, and assume that we have a good ground.
There are "surge suppressors" sold that either attach to the main panel, or replace a few of the breakers in the panel. If true lightning protection is desired, it is necessary to install a complete system, with 'electrodes' on the roof, etc. That work is usually done by a specialty contractor.
There is a second sort of surge protection that can be provided at each appliance.
We do not have to demonstrate any trip time. Our product standards require ordinary breakers to trip within 6 cycles (1/10 second). Fuses are typically represented by their manufacturers as clearing a fault within a fraction of a cycle (less than 1/100 second).
Last edited by renosteinke; 01/13/11 12:21 PM.
