POWER & ENERGY EFFICIENCY HANDBOOK
Don’t be confused by line and neutral fuses David Norton | TDK-Lambda Americas
It pays to know when the use of a single fuse is less hazardous than fusing both hot and neutral wires.
For many years ac-dc power supplies for
Dual fusing
the medical market have been safety certified to the IEC 60601-1 medical standard and to the industrial IEC 60950-1 /IEC 62368-1 standards. Dual certification reduces the number of
Line
Fuse F1
Neutral
Fuse F2
Load
individual model numbers manufacturers must produce and stock. A point to note is that two ac input fuses are needed in many medical applications, one in the Line side and one in the Neutral side. Dual fusing is necessary to guarantee full protection if the polarity of the Line and Neutral wiring to the power supply should be reversed. This condition might arise due to a wiring error at the building’s ac socket or in the wiring feeding the power supply. Nevertheless, supply manufacturers such as TDK-Lambda now offer a single (Line) fuse option on new medical/industrial power supplies. Here is the explanation why: If an industrial system is consuming more current than a regular ac socket can support, it would have to be permanently connected to a
32
DESIGN WORLD — EE NETWORK
TDK — P&EE HB 10-19.indd 32
10 • 2019
Earth ground
Distribution panel
Power supply
Voltage relationships in a phase-to-phase connection (208 Vac).
A power supply connected to the ac input, its Neutral connected to the earth ground at the panel.
eeworldonline.com | designworldonline.com
10/10/19 9:15 AM
