Owners manual

MNPV2, MNPV3, MNPV4, MNPV6 Instructions (continued)
5 | P a g e 10- 0 1 0 - 1 R E V : G
Circuit breaker selection.
When selecting breakers for use with the MidNite combiners, first check with the PV manufacturer to determine the
proper “series fuse”. The term fuse is used even though you are probably using breakers. This is a carryover from UL
terminology. MidNite Solar offers PV combiner breakers rated at 150VDC and 300VDC. The 150V breakers come in
these amp ratings. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 30, 40, 50, 60 and 63. Other sizes are available on special
order. Part numbers for breakers are as follows: MNEPV10, MNEPV15, MNEPV20 etc, the last 2 digits being the
amperage rating of the breaker.
The 300VDC breakers are twice as wide as the 150 volt versions and use two positions in the combiner.
The wire input and output are located on the top side. These breakers come in 7,10,12,15,20,30 and 50 amps.
Part numbers: MNEPV12-300 is a 12 amp 300VDC breaker, MNEPV15-300 is a 15 amp 300VDC breaker etc.
IMPORTANT! Polarity of the din rail DC breakers. The DC breakers supplied by MidNite Solar are custom
manufactured in Lesotho Africa by CBI. These breakers are polarity sensitive. This means that they need to be
installed correctly in order to insure that they will be able to trip if called upon to do so. In a PV combiner the +
sign marked on the breaker connects to the PV positive output. The same breaker when hooked up to the
battery circuit (not in a PV combiner) hooks up a little different. The + sign hooks up to the battery plus. This
hook up is not obvious. The + sign designates the highest potential should be connected there. This is an easy
one to determine in a PV combiner. Follow the current path through the combiner, into the PV input of a
charge controller and out of the controller to an output breaker and then into the battery plus. You would think
that the end of the output breaker connected to the controller would be at a higher potential than the battery
plus. In normal operation this is true. The main job of this output breaker is to trip when and if there is a
catastrophic failure. (Any manufacturer of power electronics will tell you that power electronics can fail). If the
output breaker fails to trip, you are at risk of fire from the output wires burning up. When a charge controller
fails, they always short from positive output to negative output. Since these two terminals inside the charge
controller are normally connected up to a very large battery bank, you have a direct short across the battery
bank if the controller fails. During this condition, the controller is acting like a piece of wire. The battery positive
terminal is the highest potential! Make sure that the plus (line) of the breaker is connected to the battery plus
terminal. If the breaker is connected backwards, it can fuse in the closed position as it attempts to open. That
could ruin your entire day!
FUSES/FUSEHOLDERS.
The MidNite MNPV3 & MNPV6 can also utilize touch safe fuse holders and fuses
rated for up to 1000 volts DC for high voltage strings.
Fuseholders are wider than circuit breakers.
The MNPV6 can hold four fuseholders and comes with a special busbar that has
four legs to accommodate four USM1 type fuse holders made by Mersen (Ferraz
Shawmut).
The MNPV3 can hold two USM1 type fuseholders. The busbar on the MNPV3 has
two sides, one side for circuit breakers and one side for fuseholders.
A plastic adapter is included for use with fuseholders.
Fuses are available from 1 to, 30 amps. (80 amps total MNPV4, MNPV6,
60 amps total MNPV2, MNPV4). Use MidNite Solar 1000 Volt fuses.
These devices are not polarity sensitive, but do not open them under load.
You WILL have a fire on your hands!
USM1 Fuse touch safe fuse holder