30 amp Jayco 195RB has 40 amp fuse. Why?

[Whistleroo]

My newly purchased 2021 Jayco 195RB has the following spade fuses in the fuse panel:

(3) 15 amp
(1) 30 amp
(1) 40 amp

Would the 40 amp fuse be a mistake, since this is a 30 amp unit?

Why would there be 30 amp and 40 amp protection? One would expect one (total system) 30 amp fuse, and several 15 amp circuits.

The "2021 Jay Flight & Jay Flight SLX Owner's Manual is of no help here.

[craigav]

When someone has a 30a or 50a RV, the reference is to the 120v side where you have a 30a main "breaker" for a 30a RV. The fuses are to the 12v system and the size of the fuse chosen is based on what is being protected such as the slides, furnace, lights, converter, etc., in particular, protection for the wiring going to those types of items. ~CA

[ttavasc]

The 40amp fuse would be the reverse polarity fuse that protects things in the event that the batteries are connected incorrectly. On my 195RB the fuse was clearly labeled on the distribution board with "Reverse Polarity Protection".

[bankr63]

And to be clear, it's really all about the power (in watts). Roughly P(w)=V*i(a) or Power (in watts) = volts (potential) times current (i in amps). That is really for DC power, AC power has some other factors too, but the DC equation is pretty close for AC calculations.

So 30 amps of AC current at 120 volts is roughly 3,600 watts of power that your TT can pull from the pedestal. Step that down to a much lower voltage through the converter and 40 amps of DC current at 12 volts is only 480 watts of power. So a 40 amp 12V DC circuit is well within the capacity of a 30A (120V) service trailer. Theoretically you could actually have about 300 amps of 12v fuses on a 30A AC service, but there are other factors that come into play that would limit that (your converter probably can't supply 3,600 DC watts).

Remember that if it's fused it is DC (low) voltage and if it's a breaker ir's AC (high) voltage.

[JimD]

Surprised that the fuses aren't labelled. My rig has 30 amp fuses for the slideouts.