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Selecting a DC Input Fuse or Circuit Breaker
DC Disconnects
and Over-
Current Devices
975-0556-01-01
The DC cables from the battery to the inverter need to be provided with
overcurrent protection, in the form of a fuse or circuit breaker, located as
close as possible to the DC positive battery terminal.
Because your batteries can provide thousands of amps of short-circuit
current, you need a DC-rated fuse or circuit breaker that can safely
interrupt the short-circuit current that the batteries can produce.
The DC circuit from the battery to the inverter must be equipped with a
disconnect and over-current device. This usually consists of a circuit
breaker, a "fused-disconnect," or a separate fuse and DC disconnect. Do
not confuse AC circuit breakers or fuses with DC-rated ones. They are not
interchangeable. The rating of the fuse or breaker must be matched to the
size of cables used in accordance with the applicable installation codes.
The breaker or disconnect switch and fuse should be located as close as
possible to the battery, in the positive cable. Applicable codes may limit
how far the protection can be from the battery.
To select the correct fuse type and size:
1. Determine the total short-circuit current rating for each battery, based
on the battery manufacturer's published short-circuit current sourcing
ratings for the battery. Then determine the total for your battery bank.
For example:
•
If you are using one battery to power your inverter and its short-
circuit current rating is 500 A, the total short-circuit current rating
is 500 A.
•
If you are powering your inverter with two 12 V batteries
connected in parallel, and each battery has a short-circuit current
rating of 500 A, the total short-circuit current rating is 1000 A.
•
If you are powering your inverter with two 6 V batteries
connected in series, and each battery has a short-circuit current
rating of 500 A, the total short-circuit current rating is 500 A.
Important:
For batteries connected in parallel, the total short-circuit current
rating is the sum of the short-circuit current ratings of all of the batteries
connected in parallel. For batteries connected in series, the total short-circuit
current rating is equal to the short-circuit rating of the battery with the highest
short-circuit rating. It is not the sum of all the short-circuit current ratings taken
from each connected battery.
This guide for use by qualified installers only.
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