Fuse blows when powering up an ION/PowerLogic meter

Issue
Every time an ION/PowerLogic meter is powered on, the fuses are blown.

Product Line
PowerLogic/ION Metering Devices

Environment
Control power for ION/PowerLogic Devices

Cause
The inrush current may go up to 40A for a 1/2 cycle at maximum input voltage. Regular fuses (Fast-acting Fuses) cannot withstand this condition.

Resolution
Schneider Electric recommends the FNQ-R-2 (slow blow) OR the ATQR-2 (at UTSW). There have been no reported cases of nuisance blowing with these fuses. From the Installation manual, the recommended amperage for the fuse is 2A. It is critical that the fuse is of type SLOW BLOW, otherwise inrush current when powering up will cause nuisance blowing.

The ION8600 pre-wired enclosure from SquareD Services uses an FNQ-R-5 fuse (5A). The Potential/Voltage Transformers (PT's) may inherently limit the inrush current on start-up, however SLOW BLOW fuses are still required.

A slow blow fuse can tolerate high voltage levels for a short period without shorting the circuit. This means that when a short or a sudden change in voltage occurs, a slow blow fuse doesn’t blow immediately but rather withstands the high current for a short time, allowing a sufficient and reasonable time to complete tasks prior to disconnecting the power source. On the contrary, a fast (or quick) blow fuse is a fuse that blows instantly when high power voltage is passed through it. This fast-acting fuse is the common fuse found in frequently used electrical equipment that is sensitive to changes in the flow of electricity.