Separate earth for USA devices

[AusLee]

Hi,

A number of devices from the USA have different voltage than in Australia.

The guy has his own transformer from 415V at the primary side L-L to 208V at the seconday.

There is a distribution board at the secondary taking tge one output fron the transformer and distributing it via single phase and 3 pgase breakers to the loads.

The question is: those devices require earthing. Shall it be the same earth as the primary or a separate dedicatex earth?

In Australia earthing is imperative for class I equipment even if there is a GFCI/RCD protection.

A link to some correct litterature is very much appreciated.

Thanks.

 

[waross]

208 Volts is derived from a wye connection of three 120 Volt windings. 120 Volt rated loads are connected from one line to the wye point or neutral. Panels typically (but not always) have a neutral bus and a ground bus. The wye point or neutral is connected to the ground electrodes as a "system" ground. There are specific code rules for system grounding. This connection may be at the transformer or at the panel, it depends. Conductors are run from the ground bus to equipment as equipment grounding conductors. There are specific code rules for equipment grounding.
The same ground grid may be used for both the 415 Volt system and for the 208 Volt system.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

I bet this guy's transformer doesn't change the line frequency from 50Hz to 60Hz, so simply matching the voltages may not be the smartest move if there is anything with an iron core involved, e.g motor, transformer, etc.

 

[AusLee]

Hi,

Well spotted Scotty, thanks will call his attention. There seems to be a mix of small motor and small electronic loads.

Waross thanks for the clarification, we're trying to figure out what the term "dedicated earth" means in this case. We thought that they meant a separate earth grid, remote from the one for 415V but as you say it can be the same, with or without GFCI/earth fault differential protection.

What could they be asking for?

 

[cranky108]

The small motors may be universal motors, in which case the frequency dosen't matter. Or in some cases, like my electric lawn mower, they use a rectifier to drive a DC motor. So don't jump to conclusions that 50 HZ is bad the the loads.

I've had a little time to think about this, because my wife wants to move to another country where the voltage is 220 V with no ground reference.


Strange how there 220 V light bulbs look like they might fit where we use 120 V light bulbs.