Thursday, March 3, 2011

Voltage classifications

Electrical engineering terminology is rife with references to such voltages as MV (medium voltage), LV (low voltage) and HV (high voltage). It is often confusing and frequently misleading for new engineers to assess which is which. The problem is made more complicated by the fact there is no unanimous agreement among standard-making bodies regarding this classification. It is typical for an engineer in India to consider its own domestic network (240/415 V) as medium voltage (MV) while that in the U.S. (110 V) as LV. This is far from the truth. Any voltage less than 1 kV is LV according to all institutions making standards. The following table illustrates various categories in the table below.

Authority
Document/ clause ref.
LV
MV
HV
IEC
IEC 60269-1:2006
IEC 62271-200:2003
Less than 1 kV

1 kV to 52 kV
IEEE
IEEE 141:1983
Clause 3.1.1.2
Less than 1 kV
1 kV to 100 kV
100 kV to 230 kV
NEMA
NEMA C84.1:1995
Clause 2.1.3
Less than 1 kV
1 kV to 100 kV
100 kV to 230 kV
India
IS 10118-1:1982
Clause 5.1
Less than 1 kV

Above 1 kV
Shell
DEP 33.64.10.10
Clause 1.3.2
Less than 1 kV
1 kV to 36 kV
Above 36 kV