2 heating cables, separate shower

[qwertyjjj]

You often see manufacturers suggest one heating cable for the room and a separate one for the shower in case the shower one fails.
Is the cable really so fragile that you can't just use one long one?
Also why are they always assuming the shower one would fail first?
Seems weird for a manufacturer to suggest this.

[Tile & Stone Guild]

It's more about if it does fail then the outside floor and stall floor have to be removed. Part of the reason asks for a megohmeter to he used, reality is if it passes it shouldn't ever fail. It's a warranty cya more than anything.

[jadnashua]

One reason why Schluter wants theirs covered by Kerdi when used in a shower. The insulation should be good, but keeping it dry adds a little more reliability. If the sensor or end point cap land in the shower, that's also a weak point.

[tilemanct]

They aren't talking about the cable they are talking about the sensor that regulates the control. Its a fail safe issue. A quality non Chinese manufactured heating cable will last indefinitely. The sensor will also. I have had one sensor fail in 15 years of installing these systems. For the price of another sensor its cheap insurance.
Getting back to your original question/statement I always run two different cable systems and controls for main bath floor and shower. Usually two different installs. One may be in an uncoupling membrane and the shower in a mud bed. Both react to radiant heat differently. One control/system would be hard to maintain each area to a consistent temp and comfort level.

[jadnashua]

FWIW, Ditraheat essentially ends up with a spare sensor...one comes with the thermostat, and a second one comes with the heating wire. They recommend you install both and just leave one disconnected in case something fails down the road. That's something you could do with any brand, but might have to buy a second one.

[Tiger Mountain Tile Inc]

That's a good point about them heating up at two different rates. The other thing is that a wire/uncoupling system is usually preferred for the floors these days but inside the mud bed of the shower I would rather have a cut & turn mat to install in there. So two different mats just kind of makes sense.