On Saturday, December 15, 2018 at 12:25:03 PM UTC-5, Kristy Ogilvie wrote:
On Sat, 15 Dec 2018 17:04:34 -0000, trader_4 wrote:

On Saturday, December 15, 2018 at 12:03:16 PM UTC-5, trader_4 wrote:
On Saturday, December 15, 2018 at 11:20:32 AM UTC-5, Kristy Ogilvie wrote:
On Sat, 15 Dec 2018 15:44:12 -0000, trader_4 wrote:

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.

Ah, I didn't read that far down.

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.

That makes sense.

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.

Well presumably that's what it CAN be set to, and like you said, they haven't.

But the whole *range* is too high. I didn't read the whole thing, but I'm
assuming that any given one can be adjusted within that range, ie 71C to 105C
and why would a shower water heater ever have an output anywhere in that range.
You'd think the max you'd want would be, IDK, 120F? And that assumes it's
getting mixed with cold after.




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

An estimate, but I knew it was more than the 10A I thought the stat was rated at. The shower is 8.5kW (35.5A at 240V), and I measured the resistances of the elements (when cold) as 11.3 and 14.75 ohms, with the stat switching the 11.3, which would be more than half the full load, i.e. more than 17.75A. I see further down the datasheet that the stat's actually rated 10A for 100,000 cycles and 16A for 30,000 cycles. Since it probably only kicks in if you overheat the shower, 30,000 cycles is ok. Maybe it's wired up wrong and it should be switching the smaller element? Or at 20A it can handle maybe 15,000 cycles?


How do you know it's there for the case where you overheat it and not as
part of normal operation? If it's really operating at a lower temp range
then it could be the normal thermostat. What strongly implies that is
that you say it only works one element. If it's an over temp cutoff,
one that means something is wrong, then it should cut off both elements.




As to having two cut-offs, that's very common. Typically there is a thermostat
for normal operation,

I don't think it's normal operation for the stat to operate - this is a basic shower where the element should be on all the time (1 or both depending on the user setting), the fine temperature control is by a water pressure control. So I assume if you overheat it slightly, then in warm mode the heater goes off, and in hot mode it cuts to half power, then if it overheats further, the other stat cuts both off.

I've never seen that in any appliance. When it reaches a true high limit
cutoff, it stops the whole thing, very often permanently.





then one or two thermal fuses that blow if it exceeds
normal operating range, eg it's being run with no water.

They're both stats as far as I can see, which auto-reset when it cools back down. It would be damn annoying if you had to replace one every time you overheated it.

The point is, if it overheats something is wrong. Your statement above
suggests that overheating it is frequent? For example, I had one
of those instant hot water dispensers for the kitchen sink. It quit and
it turned out the thermal fuse had blown out. But there was no reason,
it had not gone empty, etc. The new part was a different design. Which
lead me to believe they had a problem, the original ones were set too
low or failed for another reason. But that's how it worked. Thermostat
for normal operation, thermal fuse for when things go wrong. Had an
electric kettle, same kind of design.

Forgot to add, if you really want to know and have easy access to it,
put a volt meter on the thermostats and watch what happens vs water
temp.

Good idea. Tested. They switch as I thought. Both elements stay on permanently unless I turn it to an uncomfortably high temperature, then one cuts out for several seconds. I couldn't get the other to cut out, that's probably if the mains pressure drops lower.

Uncomfortably hot 105c







If it cycled all the time it would be annoying, as incandescent lights would dim and brighten each time it switched it

Any heater like that is going to cycle and FF it causes your lights to dim, you have bad wiring.




- in fact I remember as a kid my parents' shower did the same as mine but much faster - it only had one heating element, 7kW, but the switching was for 1 second, as the lights would dim and brighten quite often when you turned it too high. It's basically just an anti-scold (or damage to the heater perhaps) feature to protect against water pressure dropping, or you turning the dial too high.