RCBO query

[pete01]

A 2kw heater cant suddenly decide to be a 3kw.....can it?

 

[EFLImpudence]

I would say "No".

 

[morqthana]

Even more pointless jabbering!

I've learnt that a 32A MCB does not trip the instant the current gets to 32A, but it will trip at some current greater than that after some period of time.

So in the context of the question posted by the OP about whether he should put his 9.5kW shower on a 32A MCB, you wrote this:

The thing about a shower, is that they only run for a matter of minutes

And I thought that you might be wrong. Or at least you might not always be right. So if your theory is that a 9.5kW shower on a 32A MCB is OK because showers "only run for a matter of minutes", then I thought that should be examined, in case it is wrong. Which I think it could be.

Obviously it's crucial what you mean by "a matter of minutes", so I asked you, but twice you've dismissed the question as "jabbering".

What do you really think is most helpful? To attempt to logically, and with reason, and in the full light of known facts, examine suggested courses of action, or to accuse people who try to do that of jabbering?

 

[pete01]

A 32 amp will run at 36 amps forever ish, over that it will trip instantly, I think (memories going),

 

[morqthana]

He thinks every single question posed should be a learning experience for the poster. It is MANDATORY that the poster learns something.

No, not "mandatory". But why do you react to strongly against the idea that learning can be a good thing?

I suggested to you, without calling you an idiot or anything like that, that you might have found it helpful to be able to work out 9500÷240 yourself.

Be honest - is that really an unhelpful, outrageous, crap idea?

You responded, likening "9500÷240" to

What you need to do is get a spec sheet for the screws and the ply. Multiple the tensile strength of the screws and the ply, then divide by 8.482. Add the humidity level for whatever day you intend to do the work, then subtract it. What number do you get? That'll give you the answer you're looking for.

Who do you really think is being the most rational here?

 

[EFLImpudence]

A 32A B type MCB, for example, must:

not trip up to 1.13 x 32 ( 36.16A )
trip within a hour at 1.45 x 32 ( 46.4A )
and instantly at 3 to 5 x 32 ( 96 up to 160A )

That doesn't mean running it at 45A for half an hour is good for it.
Like having a fuse permanently red hot but not quite melting.

 

[morqthana]

A 32 amp will run at 36 amps forever ish, over that it will trip instantly, I think (memories going),

Well this is a 40A load, and since Harry reports

I have a 9.5Kw which has been running on a 6mm/32amp MCB, for many years and without any issues.

it won't trip instantly at 40A. But will it run forever (ish) at that current?

Why, when I tried to find out what informs Harry's view that 40A through a 32A MCB will be fine because showers "only run for a matter of minutes" did you laugh and agree with Harry when he described that as pointless jabbering?

 

[pete01]

Well this is a 40A load, and since Harry reports



it won't trip instantly at 40A. But will it run forever (ish) at that current?

Why, when I tried to find out what informs Harry's view that 40A through a 32A MCB will be fine because showers "only run for a matter of minutes" did you laugh and agree with Harry when he described that as pointless jabbering?

I did laugh because Harry made me laugh, you was jabbering on about nothing....probably.

No need for some long messages proving otherwise I won't be reading it

 

[Harry Bloomfield]

Why, when I tried to find out what informs Harry's view that 40A through a 32A MCB will be fine because showers "only run for a matter of minutes" did you laugh and agree with Harry when he described that as pointless jabbering?

Quite simply, no one, but no one, will run a shower for in excess of one hour. In fact most will be in, and out within minutes - that is the point of a shower, speed for most people. The worst that can happen is that if you exceed the 'on time', is that the MCB/RCBO might eventually trip. Inconvenient, if you happen to still be in that shower, but perhaps a reminder to get out?

All MCB's/RCBO's, in the same range, are built with the very same internal components, able to carry the maximum current of the same range, all that varies is the sensing/trip components, suggesting that overheating due to overload, should not be an issue.

After decades of use of a our 9.5kw shower, supplied via a 32amp RCD, last year I decided it was time to upgrade our consumer unit with a larger item, including RCD's, and all new MCB's. Once that was done, out of curiosity, I took the opportunity to closely examine the old 32amp MCB, which had supplied our shower, and never once tripped. As expected, there was absolutely no sign of any wear, damage or any sort of issue at all.

 

[morqthana]

In fact I'd like to open my question out to SUNRAY, diy_fun_uk, Jurassicspark and whoever the 1 other person was who thanked Harry Bloomfield for saying I was jabbering.

If there's a space between running forever ish and tripping instantly, what is wrong with looking into how long a shower might run, and whether it might run for long enough for the MCB to trip?

Maybe it won't - maybe that time is several hours. Maybe it's 20 minutes.

I don't know. But I do know that maybe what Harry meant by "a matter of minutes" merited examination.

So to SUNRAY, diy_fun_uk, Jurassicspark and ano - what was your real reason for agreeing that I was jabbering when I asked?

Do you really think that it doesn't matter how long "a matter of minutes" is because it's always going to be the case that a 40A shower on a 32A MCB will be fine? Or was there another reason for agreeing that I was jabbering?

 

[morqthana]

Quite simply, no one, but no one, will run a shower for in excess of one hour.

I agree, or at least agree that it is so unlikely that it can be discounted.

In fact most will be in, and out within minutes - that is the point of a shower, speed for most people.

But "within minutes" still needs better qualification. I can assure you that sometimes it's "within 10 minutes". Or "within 20 minutes".

Not everybody, always, zooms in and out in "within 5 minutes", or whatever the time is you're envisaging, which is why I though that your advice should be scrutinised a bit.

The worst that can happen is that if you exceed the 'on time', is that the MCB/RCBO might eventually trip. Inconvenient, if you happen to still be in that shower, but perhaps a reminder to get out?

All MCB's/RCBO's, in the same range, are built with the very same internal components, able to carry the maximum current of the same range, all that varies is the sensing/trip components, suggesting that overheating due to overload, should not be an issue.

Do the regulations say anything about deliberately designing an overload into a circuit?

 

[Jurassicspark]

As in a time you'd more likely state in minutes than fractions of an hour? Yes.

As in only a few minutes? No.

What are you jabbering on about, do you even know?

Even more pointless jabbering!

In fact I'd like to open my question out to SUNRAY, diy_fun_uk, Jurassicspark and whoever the 1 other person was who thanked Harry Bloomfield for saying I was jabbering.

Mr Morqthana its been quiet a time. I can recall you saying that you had me on block so I don't think there is a valid reason of quoting and replying to you but as you have mentioned my name I would like to insist. You said I was out and done or maybe blocked, like there was no way back or no reason to speak right? It feels like you wanted a reaction but still want to act above it, like poking at something and walking off like your hands are clean. If I was so out the way, why are you dragging me in sideways like this? Say things straight please or don’t say them at all this halfway mess just shows you’re not done.

And regarding last time it’s not about drama nor about wanting attention, it’s about how you can’t say you’re done and still do things that open up the same door you said was already shut. If my name wasn’t meant to pull anything then why use it? You don’t drop something you’ve been holding back without knowing it’ll get seen, noticed, or reacted to. I didn’t ask to be part of the conversation again, but now that I’ve been pulled in -- even by something small, I’m not going to sit quiet like nothing happened.
So now here we are, and I’m not showing up out of nowhere, not crashing in just because. I’m responding to something that clearly had a spark behind it, even if it came covered in calm.

If there's a space between running forever ish and tripping instantly, what is wrong with looking into how long a shower might run, and whether it might run for long enough for the MCB to trip?

Nothing wrong with that There is absolutely nothing wrong with looking into how long a shower might run and whether it can run long enough to trip the MCB. If there’s a space between something running forever and tripping immediately it doesmake sense to understand exactly where the shower fits.

Maybe it won't - maybe that time is several hours. Maybe it's 20 minutes.

Depends on the shower and it depends on the type of MCB. Would running 40A continuously through a 32A type B MCB trip it? And when would it trip the MCB? Look at the trip curves.

I don't know. But I do know that maybe what Harry meant by "a matter of minutes" merited examination.

Well what really matters isn’t debating the length of a shower but whether the system is built to handle normal use safely. So spending too much effort on interpreting “a matter of minutes” is a pointless when the bigger picture should be about proper installation and reliable protection.

So to SUNRAY, diy_fun_uk, Jurassicspark and ano - what was your real reason for agreeing that I was jabbering when I asked?

Well how do you know that its "as in a few minutes" and how do you know it’s not just a few minutes? People’s shower habits can be very different some might take quick showers and others take longer. Saying it’s only a few minutes assumes everyone is the same, which isn’t true. Saying its for like a fraction of an hour assumes everyone is the same, which isn't true. Without real data or measurements, you can’t just decide the shower only runs for a short time.

So is it jabbering?

And does it matter though?

Do you really think that it doesn't matter how long "a matter of minutes" is because it's always going to be the case that a 40A shower on a 32A MCB will be fine?

What exactly do you mean by "fine"

 

[SUNRAY]

So to SUNRAY, diy_fun_uk, Jurassicspark and ano - what was your real reason for agreeing that I was jabbering when I asked?

Don't bring me into your row, all I did was agree with someone who knows what he's talking about.

 

[pete01]

In fact I'd like to open my question out to SUNRAY, diy_fun_uk, Jurassicspark and whoever the 1 other person was who thanked Harry Bloomfield for saying I was jabbering.

If there's a space between running forever ish and tripping instantly, what is wrong with looking into how long a shower might run, and whether it might run for long enough for the MCB to trip?

Maybe it won't - maybe that time is several hours. Maybe it's 20 minutes.

I don't know. But I do know that maybe what Harry meant by "a matter of minutes" merited examination.

So to SUNRAY, diy_fun_uk, Jurassicspark and ano - what was your real reason for agreeing that I was jabbering when I asked?

Do you really think that it doesn't matter how long "a matter of minutes" is because it's always going to be the case that a 40A shower on a 32A MCB will be fine? Or was there another reason for agreeing that I was jabbering?

Stop jabbering

 

[ebee]

A 32 amp will run at 36 amps forever ish, over that it will trip instantly, I think (memories going),

No not really.
Our basic design (with fuses) would be to allow a 13% overload and not trip. A 45% overload must trip. Anything in between then it depends. Please note it does not mean will trip instantly or near instantly, but "within the conventional time" (which is often 2 hours but could be 4 hours.
Follow the curves on a MCB and you will find more info on that particular MCB rating, you might be surprised.
I would never advise running anything over 32A on a 32A MCB as you will be running it on its curve - a big no.
Select your MCB (or RCBO) according to the cable rating max and your design current max and breach neither.