Fachgebiet  Elektronik und Elektrotechnik, Geowissenschaften  Anmerkung  electricity 
 de 
Terminus Induktionsspule mit Mittenabgriff 
Zuverlässigkeit 3 (Zuverlässig) 

 en 
Terminus tapped induction coil
Zuverlässigkeit 3 (Zuverlässig)
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Fachgebiet  Landverkehr, Elektronik und Elektrotechnik, VERKEHR  
 de 
Terminus Masse 
Zuverlässigkeit 3 (Zuverlässig)

 en 
Definition the conducting mass of the earth or a conductor connected to it through a very small impedance.  

Terminus earth 
Zuverlässigkeit 3 (Zuverlässig) 
Terminus ground 
Zuverlässigkeit 3 (Zuverlässig) 
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Anm.:
1. Masse kann aucun ein geerdeten Gestell (frame) oder eine Potenzialschiene sein.
2. Die gleichen Bezeichnungen sind auch in Budig, Fachwörterbuch Elektrotechnik und Elektronik zu finden und kenne ich aus meiner Erfahrung als Elektroingenieur.

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Note added at 10 hrs (2017-08-15 07:16:06 GMT)
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It was common practice with tube type fullwave rectifiers to connect the secondary centre tap to the equipment chassis,& hence to the Mains Earth.
https://www.eevblog.com/forum/beginners/connecting-center-ta...

From what I can uncover by searching here and elsewhere, connection of the center tap to the chassis, which is ultimately connect to earth ground via the AC earth ground, protects against electrocution at 120VAC in the event of a short between the primary and secondary windings of the transformer.
https://forum.allaboutcircuits.com/threads/step-down-transfo...

In all installations, however, we connect the center tap to earth ground
http://boards.straightdope.com/sdmb/archive/index.php/t-4396...

If the line stage has an output transformer with a centre tap, it is very tempting to connect the centre tap to earth.
https://books.google.de/books?id=eddy7svanhcC&pg=PA554&lpg=P...

The third option (my preferred) would be to connect the centre tap to earth and earth all exposed conductive parts to this. That way you would reduce the potential to earth to 115V.
http://www.theiet.org/forums/forum/messageview.cfm?catid=205...

110Vac systems including 110V centre tap to earth (55V phase to earth) can be tested on the secondary winding.
http://uk.rs-online.com/web/p/loop-impedance-rcd-combined-te...

If one of the Load lines is earthed you must not take the center tap to earth
The E/S terminal can always be safely taken to earth
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

110 V a.c systems including 110 V Centre tap to earth (55 V phase to earth) can be tested on the secondary winding, either at 110 V or 55 V on the centre tap to earth.
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...
(And other 734,000 Goggle results)