Given the chart Bertus has posted, I would be very cautious about powering short pieces with 12 V. The temperature reached could be destructive within a very short time. It rather looks like the chart is hinting that 60 cm is the shortest piece that should be run on 12 V (i.e. 1.3 A is the maximum current) - and at that, 90 °C is certainly enough to cause burns to skin.

 

Am I the only one who noticed that in the picture the two heating strips are jumpered together with a small jumper? If we're talking about high currents then my question is: "Can that jumper handle the current?" Or "Can it be introducing some losses?

 

Am I the only one who noticed that in the picture the two heating strips are jumpered together with a small jumper? If we're talking about high currents then my question is: "Can that jumper handle the current?" Or "Can it be introducing some losses?

Rough guess jumpers like those pictured are generally AWG 20 to AWG 22 so short run open air stranded wire 5 Amps down to 3 Amps easily. So based on the original numbers my best guess is yes assuming they aren't getting hot. Now if the jumpers are more inline with AWG 18 (about 7 Amps) then no problem at all. Again, purely a guess.

Ron