Shower related: watts and amps.

[amfisted]

Issue not resolved, but just put off as it has been since I purchased the new shower in mid 2017.

The old shower is still working, albeit when the On button is pressed the delay before the flow reduces and the temperature corrects itself is considerably longer than it was when we first bought the house. Indeed, sometimes you have to turn the shower off then back on again to make that correction happen.
Its still on my to-do list, though the new shower will probably be out of warranty by the time I get round to it.

 

[Simon35]

I agree the MCB ought to have been swapped out in my case for a larger one, but there is nothing unsafe about an MCB which is rated for less than the load and less than the cable rating, as bourn out by the fact it has never tripped. The MCB survives without tripping, because a shower's load is not continuous one and because the shower's load is modulated. Tighter fuse or MCB protection is always better/ safer.

Sizing the MCB to suit the load is always better, such that Ib <= In and is in fact compliant with the regs.

Unlike your method.

 

[DetlefSchmitz]

MCBs run for long periods above their ratings tend to go brown and become damaged and can even damage their neighbouring MCBs in my experience.

 

[Harry Bloomfield]

I never suggested it was 'my method' simply that tight protection to the load is better / safer than one that is higher rated. MCB's (and other fuse types) are rated on there trip current versus time curve. So long as an MCB is large enough that it can reliably sustain the load, without itself suffering damage, then all is fine. It has suffered neither damage, nor has it ever tripped.

 

[ban-all-sheds]

I never suggested it was 'my method' simply that tight protection to the load is better / safer than one that is higher rated.

In < Ib is not "tight protection", it is an overloaded device.

MCB's (and other fuse types) are rated on there trip current versus time curve. So long as an MCB is large enough that it can reliably sustain the load, without itself suffering damage, then all is fine.

Does "fine" mean the same as "non-compliant"? And how can you tell that it won't suffer damage?

 

[JohnW2]

... tight protection to the load is better / safer than one that is higher rated.

Safer for the cable, and maybe even the load, but definitely not 'safer' for the MCB itself. As has been said, running an MCB beyond its rated current, even for short periods, will inevitably result in increased heating - which may or may not be enough to damage (or alter the characteristics), and/or shorten the life of, the device (and/or adjacent devices)

MCB's (and other fuse types) are rated on there trip current versus time curve. So long as an MCB is large enough that it can reliably sustain the load, without itself suffering damage, then all is fine. It has suffered neither damage, nor has it ever tripped.

As above, running an MCB beyond its ratings can have consequences - merely avoiding the situation in which enough current flows for long enough to result in a trip does not provide a guarantee against those possible consequences. Most manufacturers say something like this, relating to currents "at or approaching" the MCB's rating, let alone in excess of that rating ....

Adjacent thermal-magnetic MCBs should not be continuously loaded at or approaching their nominal rated currents when mounted in enclosures. It is good engineering practice to apply generous derating factors or make provision for adequate free air between devices.....

Kind Regards, John

 

[flameport]

The MCB survives without tripping, because a shower's load is not continuous one

Yes it is - when the shower is on, it's on continuously.

and because the shower's load is modulated.

There is no 'modulation', an electric shower is at the full load 100% of the time it's on.

Shoving more than the rated current through an MCB or fuse for an extended time will cause overheating, that heat will damage the device and the cable attached to it, and in some cases cause damage to other adjacent devices.

 

[Harry Bloomfield]

Yes it is - when the shower is on, it's on continuously.


There is no 'modulation', an electric shower is at the full load 100% of the time it's on.

Shoving more than the rated current through an MCB or fuse for an extended time will cause overheating, that heat will damage the device and the cable attached to it, and in some cases cause damage to other adjacent devices.

Well, I can only say you are wrong...

My shower rather cleverly is certainly able to modulate both the water flow and the Kw (using a triac) input to achieve the temperature the user sets on the dial and it does so very, very accurately winter and summer. How it modulates the water flow I don't know, because I have never needed to investigate, but it doesn't use solenoid valves, aside from the on off valve. The old basic unit which it replaced, used a dial (tap) to simply adjust the flow, flow was dependent on pressure at any instant so it needed constant tweaking to get a comfortable shower - this is perhaps the type you are basing your understanding upon. If SWMBO turned a cold tap on in the kitchen it would be too hot. It has three mode buttons, max/med/min - for water and energy saving which reduces the flow, but each precisely maintains the set temperature. We only ever use it on max and the temperature on the dial of 5.5. It has been the best and most reliable shower we have ever had, but it was expensive.

If the pressure should drop too low, this one behaves nicely, shutting down and indicating a fault without scalding. Absolutely no excess heat in being generated in the MCB, during the course of a shower, I checked long ago in order to dismiss my own early concerns about apparently over running the MCB's rating.

 

[JohnW2]

Well, I can only say you are wrong... My shower rather cleverly is certainly able to modulate both the water flow and the Kw (using a triac)...

Make and model?

Kind Regards, John

 

[Harry Bloomfield]

Make and model?

Kind Regards, John

From memory, a Mira, but I cannot recall the model after all this time..

 

[JohnW2]

From memory, a Mira, but I cannot recall the model after all this time..

Oh, you wrote in the present tense, so I thought you were talking about your current shower, rather than an "after all this time" one. How long ago did you have this 'modulating' shower, then?

Kind Regards, John

 

[Harry Bloomfield]

Oh, you wrote in the present tense, so I thought you were talking about your current shower, rather than an "after all this time" one. How long ago did you have this 'modulating' shower, then?

Kind Regards, John

It IS the current shower.

 

[JohnW2]

It IS the current shower.

Why can't you tell us, with certainty, at least the make, if not also the model, then?

Kind Regards, John

 

[Harry Bloomfield]

Why can't you tell us, with certainty, at least the make, if not also the model, then?

Kind Regards, John

Why are you so obsessed John, it a shower, just a particularly good shower? Are you looking to buy one, I think it cost a bit over £400?

 

[Harry Bloomfield]

For the benefit of John...

It is a Mira and marked 'Advance'. Checking Miras showers, 'Advance' would seem to be the name they use for their more capable units, rather than a specific model. No doubt the actual model could be identified by opening it up, which I have absolutely no intention of doing without a good reason. Besides it will not be a current model, they change them almost annually.