Another translation, another question.

Original German: Antriebssysteme dürfen nicht direkt an TT-, IT- und an TN-S Netzen mit geerdetem Außenleiter betrieben werden!

Rough translation: Drive systems are not permitted to be operated directly on ......

We received feedback from a German-speaking engineer that what we are looking for is "...corner-grounded TT, IT and TN-S systems".

"corner-grounded TT" comes up with 2 hits in Google, leading me to question the suggestion.

The 1:1 English translation would be something like "...TT, IT and TN-S system with a grounded line conductor." Unfortunately, I know about as much about this topic as I know about designing aircraft. Can anyone out there help sort this out?

  • \$\begingroup\$ After checking some stuff on line, I would say "drive system may not be operated on TT, IT, or TN-S nets with grounded phase." But, I' m not an expert in that area so I'm not going to make this an answer. It seems to me that a wrong translation could destroy equipment or hurt people, so please be danged sure you get the right translation. \$\endgroup\$ – JRE Mar 23 '16 at 15:15
  • \$\begingroup\$ It seems that "corner-grounded (delta)" is the correct term, see e.g. here, here, or here. \$\endgroup\$ – JimmyB Mar 23 '16 at 15:40
  • \$\begingroup\$ If you are in EU, you will find this stuff very rare (if). see: bmillerengineering.com/elecsys.htm they are more common in USA. \$\endgroup\$ – Marko Buršič Mar 23 '16 at 16:46
  • \$\begingroup\$ This link provides examples in commercial wiring that is relevant to three phase corner grounded delta power in the United States: examples and discussion on same \$\endgroup\$ – Greg Dec 14 '16 at 15:38

A corner grounded power system is a system that is fed from a delta transformer winding with one phase grounded. The other two phased are at the line voltage above ground. A grounded wye system has each phase at line voltage divided by the square root of three above ground.

This Wikipedia article explains TT, IT and TN-S power distribution systems. The terminology is used with IEC and EU standards and practices. In the USA and Canada, NEMA and UL standards and design practices are used.

It seems like the drive system should have no connection made at the drive terminals to ground (earth) if the supply is corner grounded delta. You would have much better guidance if the instructions listed the configurations that are acceptable and provided explanatory diagrams. Rather than trying to work with a manual that you need to translate, try to obtain an English manual.

If it is your task to translate the manual, you are in a difficult situation. Technical manuals are best translated by someone who's first language is the target language and who also understands the technology plus the standards and design practices of the target region of the world.

It is not uncommon for technical manuals that have been translated to English elsewhere to require further refinement of the translation to make them acceptable in the USA and Canada markets.


Someone may need to consider whether this equipment is acceptable in the various English-speaking target markets. There are a lot of drive manufacturers supplying products in the USA and few if any have installation restrictions like the ones described. The link supplied by Marko Buršič shows a variety of systems that are occasionally used. Being used only occasionally does not mean that customers with those systems expect problems connecting equipment. It was once common to supply a drive isolation transformer for every drive, but today customers expect to connect drives directly to power systems without more than sometimes adding line chokes.


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