Maximum Wattage for Shower

[ericmark]

No, it isn't.

Showers are primarily quoted at 240V, e.g. 9.5kW @ 240V = 39.6A.
This is not a coincidence. It is so they may be on a 40A MCB.

The quote may also mention that 9.5kW @ 240V = 8.7kW @ 230V. This latter figure is only 37.8A.
Therefore you may have a slightly higher wattage if you are designing at 230V, although this may not be wise, as (as Winston is always telling us) the actual voltage is likely to be around 240V.

Some heating appliances have a voltage and wattage range, my cooker has this, and as such one can work out what the watts are at a set voltage, however unless the range is published, one can't assume, we also can't rely on the voltage being less than 230 +10% or 253. Yes often it is at 230 volt, but with micro generation the voltage can today cover the whole range 216.2 to 253.

So all we can do is work it out at 230 volt and expect manufacturers to allow for the permitted under or over voltage.

 

[JohnW2]

Some heating appliances have a voltage and wattage range, my cooker has this, and as such one can work out what the watts are at a set voltage, however unless the range is published, one can't assume ...

I think that when a wattage is quoted, one is nearly always told the voltage to which that relates, and if one assumes that the load is a simple passive resistive one (which will usually be essentially the case with "heating appliances"), one can work out what the wattage would be at any voltage.

... we also can't rely on the voltage being less than 230 +10% or 253. Yes often it is at 230 volt, but with micro generation the voltage can today cover the whole range 216.2 to 253.

In electrical terms, that's all true. However, in contrast with the 'mirror image' situation in relation to fault protection (for which we are now required to design so that protection is adequate down to a supply voltage of 218.5V), I am not aware of any requirement to design on the basis of the currents that could flow if supply voltage were as high as 253V.

Kind Regards, John

 

[deadshort]

Knowing nothing about this I can't believe there are so many varying views. I would have thought this was pretty standard. Anyhow maybe I'll go with a 9kw Mira sport airboost in the hope the air boost will give me the power I'm after? Any thoughts? Thanks!

Great shower ! I have one, constant temp and looks Ok!

DS

 

[ban-all-sheds]

I am not aware of any requirement to design on the basis of the currents that could flow if supply voltage were as high as 253V.

There never has been - I think this was discussed here a year or two ago, and the consensus was that there must always have been adequate tolerances in everything.

 

[JohnW2]

There never has been - I think this was discussed here a year or two ago, and the consensus was that there must always have been adequate tolerances in everything.

Indeed so.

Good to see you again - even if it turns out to be a temporary phenomenon!

Kind Regards, John

 

[SUNRAY]

Some heating appliances have a voltage and wattage range, my cooker has this, and as such one can work out what the watts are at a set voltage, however unless the range is published, one can't assume, we also can't rely on the voltage being less than 230 +10% or 253. Yes often it is at 230 volt, but with micro generation the voltage can today cover the whole range 216.2 to 253.

So all we can do is work it out at 230 volt and expect manufacturers to allow for the permitted under or over voltage.

One of the issues I have come across a number of times is people sourcing/bringing home from abroad when it was 220V, armed services are good at this. So a typical 3.3KW washing machine at 220V is around 15A and 13.8Ω. Plug this into good old blighty leccy at 240v and suddenly we're looking at 17.3A [4.16KW] and where I used to live [2nd house of 40ish from the sub] it was more like 250V or more and 18A [4.5KW] before long the 13A plug is either burnt out or welded solid into the socket.
Even a 3KW @ 220V = 13.6A 16.13Ω, 240V = 14.8A 3.57KW & 250V = 15.5A 3.87KW.
I have installed a 15A socket on a 16A radial a few times for this.

I've found a number of coffee machines in offices where the rating plate quotes 220-240V, 3KW, 13A and they have a melted moulded plug, clamp meter usually shows around 14.5 - 15A at 240V
And a make of water boiler, similar sort of rating plate plus a 1KW 4.4A boost listed, proudly sporting a big '3KW for perfectly boiling water at a touch' sticker. Invariably they are on a 13A fused switch with repeated blown fuse report and current measured at around 18A.

 

[ban-all-sheds]

One of the issues I have come across a number of times is people sourcing/bringing home from abroad when it was 220V, armed services are good at this. So a typical 3.3KW washing machine at 220V is around 15A and 13.8Ω. Plug this into good old blighty leccy at 240v and suddenly we're looking at 17.3A [4.16KW] and where I used to live [2nd house of 40ish from the sub] it was more like 250V or more and 18A [4.5KW] before long the 13A plug is either burnt out or welded solid into the socket.

However one works it out it is quite clear that it should never have a BS1363 plug on it.

I've found a number of coffee machines in offices where the rating plate quotes 220-240V, 3KW, 13A

It can't possibly be all of those.

and they have a melted moulded plug

So what you've found were a number of dangerous electrical appliances which should not have been on sale, and re which the sellers should have faced prosecution. Did you ever report any of them to Trading Standards?

And a make of water boiler, similar sort of rating plate plus a 1KW 4.4A boost listed, proudly sporting a big '3KW for perfectly boiling water at a touch' sticker. Invariably they are on a 13A fused switch with repeated blown fuse report and current measured at around 18A.

What have the installation instructions said?