RCBO query

[diy_fun_uk]

I consider that tyre "analogy" a very poor one compared to a simple bit of knowledge about how much current an XkW appliance draws.

Knowing that isn't really deep and involved effort to learn about electrical installation work. It's GCSE level science. It's one very simple calculation.

And think how much time it would have saved you if you could have answered this:

yourself.

Goodbye ...

 

[morqthana]

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

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

As in only a few minutes? No.

 

[ebee]

the amber may just be suitable for the heater if you have 230V but would not be correctly protected by a 40A MCB/RCBO

Hi Sunray,
With a bog standard electric shower you might need to protect against 1/ Short circuit, 2/ Earth fault but not 3/ Overload ( just to advice the DIYers that these 3 things are what we might use a fuse or breaker etc for, but we might not use the same device for those things - note we might use an RCD for Earth Fault and it might be the only thing we can use for an Earth Fault (such as in a TT system) but we can certainly use it for additional protection (back up protection if you like) . A device for Short Circuit and/or Earth Fault protection we would always use at the origin of the L of the circuit. In theory overload protection could be anywhere in the circuit including the N conductor and it would actually still give overload protection but we do not actually put it in such a place for obvious reasons.

anyway after that long ramble my point was - is overload protection actually required for a fixed load such as a bog standard electric shower? No not as such it isn`t.

Places like a ring or radial circuit we would usually do so whether we have three or thirty or three hundred socket outlets on the same circuit (or light fittings etc etc), that is when we usually require overload protection (Electric Motors are another one good example too).

 

[Harry Bloomfield]

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?

 

[pete01]

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

 

[morqthana]

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

Yes, I know, and I would have thought you would too, as I wasn't in any way "jabbering".

You said "The thing about a shower, is that they only run for a matter of minutes."

I asked if you meant a time which would be stated in "minutes" rather than "hours" or fractions of hours, or if you meant just a few minutes.

If some examples would help, does your "matter of minutes" encompass, say, 20/35/50 minutes, or is it limited to 3/5/10. That sort of thing.

I didn't think it was that complicated.

 

[Harry Bloomfield]

You said "The thing about a shower, is that they only run for a matter of minutes."

I asked if you meant a time which would be stated in "minutes" rather than "hours" or fractions of hours, or if you meant just a few minutes.

If some examples would help, does your "matter of minutes" encompass, say, 20/35/50 minutes, or is it limited to 3/5/10. That sort of thing.

Even more pointless jabbering!

 

[flameport]

Sparky has advised it should be on a 32A RCBO.

They are wrong.

Checking the shower installation manual, it states 40/45A MCB for their 9.5kW model,

It would, as that 9.5kW shower is 40A, which is a lot more than 32A.

however if running on a 6mm cable they further state circuit protection should be 32A

No instruction book can possibly know how the cable is installed, so that should be ignored.

 

[EFLImpudence]

however if running on a 6mm cable they further state circuit protection should be 32A.

 

[diy_fun_uk]

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

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

Person: Hi, will these screws do for securing 6mm ply to my wooden floor?

Morqthana: 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.

 

[SUNRAY]

however if running on a 6mm cable they further state circuit protection should be 32A.

View attachment 390311

As I mentioned earlier that is a list of cable maximum current ratings under differing installation methods, on it's own it is not an instruction on what size over current device to use for a particular appliance, for example where would one obtain a 38A or 69A MCB? However from that table we are able to identify which MCB, fuse etc. is suitable to protect the cable against overload.
For example the row in blue

working left to right we could use 40A, 50A, 63A MCB depending on the installation method but that is not the same as saying all 3 of those MCB sizes would be suitable for say a 13KW load (~56A) which runs for significantly longer periods of time.

 

[ebee]

is overload protection actually required for a fixed load such as a bog standard electric shower?

I ask yet again, is overload protection required by an Overcurrent Protective Device such as a fuse or MCB for example ?

 

[EFLImpudence]

No.

 

[SUNRAY]

I ask yet again, is overload protection required by an Overcurrent Protective Device such as a fuse or MCB for example ?

The regulations say no... But having encountered an oven heater and a shower heater going low resistance and causing an overload, I don't do it.
I did intend to retain the shower heater to investigate further but I haven't seen it since so suspect it went for scrap

 

[EFLImpudence]

But having encountered an oven heater and a shower heater going low resistance and causing an overload, I don't do it.

Genuinely interested in how this would work.

I presume that by "heater", you are referring to the element.

How did this caused overload manifest itself in these two quite different appliances?