On Saturday, December 15, 2018 at 9:50:53 AM UTC-5, Kristy Ogilvie wrote:
I'm in the process of fitting a Triton electric shower, and was being nosy. I noticed it has a thermal cutout situated where the water leaves the heater unit, this: http://www.datasheet-pdf.info/entry/36TXE11

That cuts out at 105C (ouch!) and it's also switching 20 amps when it's rated at 10 amps, AND it only cuts off ONE of the two elements.

It does have another cutout on the other end of the heater unit, which cuts them both off.

1) Why have two cutouts?
2) Why overload the first one?
3) Why only cut off half the power?

I think I have part of your answer. If you pull up the actual datasheet,
it says this:

36Ts (automatic reset) are supplied to customer specified open and close calibration set points with a tolerance on both set points.


It has a table showing the various versions and the temp ranges, tolerance
they can be *set* to. So, I think what you have is a part that is marked
as the generic, ie 105C cut-off, but the cut-in and cut-off can be set
by the manufacturer to the customer's reqts. What you have could certainly
be set to a lower cut-off temp. But having said that, the range of 71C
to 105C still sounds very high for a shower water heater. Any chance you
have the exact part number wrong? One letter or number difference matters.

If you have the current figured out correctly and it's really 20A, then
this part should not be in there.

As to having two cut-offs, that's very common. Typically there is a thermostat
for normal operation, then one or two thermal fuses that blow if it exceeds
normal operating range, eg it's being run with no water. If there are
two elements, it's also common in water heating applications for there to
be two thermostats to regulate the two elements, at least in tank type
heaters.