Fuses and circuit protection

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For products see:
Circuit Protection
PV Combiner Boxes

The fitting of adequate fuses or circuit protection in all DC circuits is essential. These must be big enough to carry the maximum expected current, but not over-sized for the current rating of wire used. 

Suitably rated fuses of the types listed below should be used between the battery and load or charge circuits, placed as close as possible to the battery. Fuses need to be sized based upon the length of time the maximum current will occur taking into account surge ability of the inverter or other devices.

Currents need to be 10% to 20% lower than fuse ratings to avoid nuisance fuse blowing. Also inverter efficiency needs to be considered. eg. if this is 85% at high load a 3 kW AC load would draw 3450 W from the DC battery, (ie. 288 A @ 12 V; 144 A @ 24 V).

DC rated circuit breakers can also be used. These can then act as safe and convenient disconnect switches if servicing is required.

Time vs.Amps Fuse Chart (for class T fuses)
FUSE BLOW POINT
(in Amps)
Time 200 Amp Fuse 300 Amp Fuse 400 Amp Fuse
1 second 670 1060 1450
6 seconds 530 800 1100
1 minute 370 580 800
4 minutes 340 520 710
8 minutes 310 500 690
16 minutes 300 475 650
32 minutes 275 435 600
1 hour 250 400 550
1 to 3 hours 200 300 400
Long Term Load Handling 3 hours or more 160 240 320