The standard arrangement in the U.S. is equivalent to British TN-C-S, with the neutral of the transformer secondary connected to earth locally and a rod at each service entrance connected to the incoming neutral. The connection must be made at or before the service-disconnecting means, which in practice means that it's usually connected either to the neutral busbar in the main distribution panel or at the meter base.
Can you clarify that we are actually using TN-CS system here in the U.S.
The problem that I see is this - in the UK if I'm correct they use L1+ separate neutral & separate earth wire all the way to xtrm and drive a rod at both locations . or do they piggy back the earth wire onto the neutral for the ride back to the xtrm?
In the US. We have two hots one neutral we should have a fourth wire going all the way back since the we can't rely on a ground type TT system back through the earth. To much earth impedance to effively take out the fuse
So our system shouldbe four wire to xtrm other wise it looks like a TT system
does anyone have a drawing of UK and U.S. System to confirm all of this confusion
Example , they are run mostly overhead from a pole mounted utility transformer. There is only one wire feeding the primary side of the utility transformer located 300' away from the meter socket mounted on the side the house.
This can vary from place to place. Many utility companies distribute the HV neutral and have local transformer primaries connected phase to neutral, but there can also be phase-to-phase connections for the single-phase transformers used to feed regular residential neighborhoods. Some places do not distribute the HV neutral at all, so all local primaries are phase-to-phase connections, as in the U.K.
We use the same basic type of earthing connection as UK for new construction.
There are several types of earthing arrangement in the U.K. though, TN-C-S resembling the American system. The TT arrangement which is common in Britain is not permitted under the NEC.
What type or system are we using if it's not TT?
wondering if Ze test would read too high of an impedance through the earth 300' to the xtrm ??
Not if the service conductors are sized properly.
We don't install the ground wire needed(earth conductor ) all the way back to the xtrm to preform Ze test this is the problem not the size of the conductors
It's not at all unusual for the 240/415V distribution in the U.K. to run for much longer distances than that, since British practice tends toward installing one large transformer and running a 4-wire 3-phase network around a whole neighborhood, whereas American practice leans more to using a larger number of smaller single-phase transformers, each feeding only a few homes (although this is changing gradually in some newer subdivisions).
Thoughts on why we don' test Zs ??if a plumber is require to pressure test his pipe surely the electrician would be required to loop test his wires for high impedance and leaks to prevent fire, after floods rather then a Hail Mary blessing!
Also we typically drive two 8'rods six feet apart with hopes of arriving at 25 ohms or less no test here either??
Remember that the NEC specifies the use of two rods only if a single rod cannot be brought below 25 ohms by itself. It is curious though that if 25 ohms cannot be achieved with a single rod, the rule then just says to install a second rod without any further stipulation!
