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:
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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?
Are you sure about the part number? The 36T is a thermostat that can be ordered with various set points. I doubt they would use the 105C version for a shower. Perhaps other versions can switch 20A. As for your last question, it is not being used as a safety cutoff like the other one. It is being used as a thermostat. Leaving one element on full time while switching the other probably works well for their intended use.
Well presumably that's what it CAN be set to, and like you said, they haven't.
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?
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.
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.
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.
If it cycled all the time it would be annoying, as incandescent lights would dim and brighten each time it switched it - 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.
But as you've said, it doesn't have to be 105C, and it isn't. It cuts out at about the temperature I'd consider my skin about to be damaged,.
Yet it doesn't, as the temperature is fine tuned by pressure. The heater is either off, 4kW, or 8kW, and remains that way or the whole showering session.
It doesn't take much of a voltage drop for you to see lights dimming, only a couple of volts. And drawing over 30A on a 100A system tends to do that.
The 105C/71C was what I saw in the introduction, I guess it's the default. The table on page 11 of the pdf shows it can be set from 2-220C.
They'd need to switch faster with a smaller hysteresis than the shower stats do.
That would require a smaller hysteresis, and a more expensive stat - both to give less hysteresis and to switch double the current.
How else could you prevent it, considering different houses have completely different water pressures. The bottom end of the pressure scale (for the hottest water) may be correct or a high pressure house, but will burn you in a low pressure house.
Because it annoys me when someone replies to 5 points in my post, then at the end, after I've read and replied back, informs me they've killfiled me. Killfiling should just be done silently, instead of the childish behaviour of getting the last word in.
Me?! It's the people plonking me just because they disagree with something I said, and then also declaring it publicly, and after having made me read through their entire 5 point reply. If I killfile something I simply do it silently, or just say "I'm fed up with you".
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