2005 Jayco 24SS: Tank heaters are wired in series - normal or mistake?
Each tank (black, gray, fresh) has a single Ultraheat TH-726 heater pad, nominally 13.5 volts @ 8.6 amps. The total heater current draw is about 12.5 amps on a circuit fused at 15 amps. It appears the black and gray tank heaters are wired in series, as each draws only 4.3 amps, instead of 8.6 amps. I haven't measured the fresh water tank heater, but since the remaining heater current is 8.2 amps (12.5 - 4.3), it's probably getting the full 13.5 volts.
If they are in series, the black and gray tank heaters are producing only 28 watts each, instead of the 116 watts each if they were in parallel with the fresh water tank heater, and also getting the full 13.5 volts. That's a lot less wattage, so I'm thinking these tanks are not going to be protected very well.
1) Are the two tank heaters supposed to be wired in series?
2) If not, is there an easy way to correct the situation? I could run two extra wires between the tank heaters to put them in parallel, then change the 15 amp fuse to 20A, but maybe someone has a better idea.
3) Is there good way to add insulation to the tanks? The bottoms of the black and gray tanks are fully exposed, so I'm thinking of strapping some 1/2" pink building insulation foam to the bottom of each, and wrapping the drains with heat tape and pipe insulation. The fresh water tank is harder to reach, but pink foan could glued to the metal plate supporting it.