METREL MI 3399, Instruction Manual With Exercises

Page: 271 / 272

Abbreviations APPENDIX
– MI 3399
271
R
T
Resistance of the transformer
RVC
Rapid Voltage Changes
S
Apparent power
SB
Switch board
SELV
Separated or safety extra-low voltage
STC Standard Test Conditions
THD
Total Harmonic Distortion
TN Earthing system earthed at the power source and/or
distribution points.
TN-C Earthing system earthed at the power source and/or
distribution points. PE and N conductors are combined
comprising a PEN conductor.
TN-C-S Earthing system earthed at the power source and/or
distribution points. Exposed conductive parts are partly
connected to the PE conductor and partly to the PEN
conductor.
TN-S Earthing system earthed at the power source and/or
distribution points. N and PE conductors are separated.
TRMS True RMS
TT All accessible metal parts are connected to basic grounding
system.
t
Δ
Trip-out time of a RCD
U
C
Contact Voltage
U
CL
Contact Voltage Limit
U
CSF
Contact voltages at single fault on earthing
U
LN
; U
L-N
Nominal mains voltage
U
L-PE
Rated fault loop voltage or nominal supply voltage
U
N
; U
Nom
Nominal voltage
U
OC
Open (o) Circuit (c) Voltage (U)
USB
Universal Serial Bus
WEEE
Waste Electrical and Electronic Equipment (Directive)
Z
LINE
; Z
LN
; Z
L-N
; Z
L-L, L-N
Line impedance
Z
LOOP
; Z
L-PE
Fault loop impedance
Z
N
Impedance of the neutral conductor
Z
REF
Reference line impedance
Z
S
; Z
S RCD
Loop impedance of a RCD protected system
Z
T
Transformer secondary impedance
ΔU; dU
Measured voltage drop
η
Efficiency
ρ
specific resistance of conductor's material