Advice on space heating passive house

[Radian]

34 minutes ago, TerryE said:

@Radian, a kettle is on for no more than the minute or so need to boil a litre or two. A Willis is designed to be on for hours.  These cases differ in time profile and therefore in thermal dynamics.

 

That's the exact point I was making earlier:

20 hours ago, Radian said:

It seems that people can be misled by thinking that if a 3kW kettle is OK using a three-pin 13A plug then any 3kW load is similarly safe. The kettle, however, is only operating for seconds and any warming of the lead and plug goes unnoticed as the heat has insufficient time to build up.

 

Even 2kW heaters (the maximum usually available from reputable suppliers) are pushing it. I could only find one "13A" smart socket that was built with robust enough components to handle 8 Amps comfortably. A FLIR camera comes in very handy for this kind of exercise.

[SteamyTea]

10 minutes ago, TerryE said:

very uncomfortable leaving a 12A load connected through a standard UK plug for many hours

A 10A load would be OK as that is what the continuous load rating is.

 

We had some old 3 kW storage heaters wired in like that.

Luckily they only had 2 or the 4 elements working in them.

Kept the inflammable resin and acetone at a usable temperature.

Looking back the things we got away with in the 1980s is quite impressive.

One lad we employed was so keen to wire in a 7 kW sunbed when there was not a dedicated supply that he just split the wiring up, top and bottom.

Then a bit of flex to plugs and found a double wall socket, plugged it in, told the customer that it was commissioned and left.

 

[Nickfromwales]

1 hour ago, Radian said:

it cannot be denied that both 3kW electric kettles and 3kW Willis heaters look absolutely identical as an AC load. Yet, as you point out, one is routinely equipped with a 13A plug and the other " would absolutely never be on 13a plugs" - in your own words.

One is a product produced for the consumer eg plug n play, thus they’re typically fitted with a ( often moulded and irreplaceable ) 13a plug. So no, apples and oranges in your explanation which is misleading and may confuse readers unnecessarily   

 

1 hour ago, Radian said:

But this kind of 'gotcha' persists throughout the self-build environment and I've seen other members making mistakes along these lines so feel compelled to maintain its visibility wherever I see it arise.

The self build world is rife with part or ill informed hero’s who attempt to carry out work which is either illegal for them to do, or just bloody stupid of them to even attempt. A Willis heater is a plumbing part not a domestic appliance, so nobody should buy one, let alone fit one, if they know nothing about basic / core electrical principals.

Some have the sense to seek out information from resources like Buildhub, even though at that stage they should really be searching tor a good electrician, but if they do end up here it is important that what they read is sound, robust and relevant. Comparing domestic appliances with heating parts is none of the above, and nobody should ever take what is written on the ‘net as gospel…….always consult a qualified electrician and at the very least have that person plan the install with you, and test / commission it for you.   
 

Be safe people!!

[Radian]

 

4 minutes ago, Nickfromwales said:

So no, apples and oranges in your explanation which is misleading and may confuse readers unnecessarily   

 

You're certainly confusing me with apples and oranges, apples and apples and so on. No wonder we seem to be spinning our wheels ?

 

? But I've been agreeing with you all along! My "explanation" continues to be that the heating effects (dynamics thereof as @TerryE puts it - while even he seems to think I'm disagreeing when I'm not?!?) are different, and therefore that the products are intended for different uses and require different electrical installation methods as a consequence. I just don't get how what I've written here might confuse readers - the only reason I keep littering this thread with my responses to you is because I have a passion about achieving clarity on this very issue.

 

Again, I entered this thread with the observation that anyone not requiring the full 3kW on offer from a single Willis (or indeed 6kW from two) and who were considering plumbing in two for redundancy (possibly only connecting one to the electrical supply) has the option of wiring two in series with the advantage of safely making it 'plug and play' with a 13A plug. This also opens it up to control with standard time-switches, smart sockets etc. and may be particularly attractive for temporary use before full commissioning. This would be the only safe way to power Willis heaters without installing a new 16A/32A radial in 2.5mm/4mm cable - which would otherwise require the services of a qualified electrician.

 

[SteamyTea]

2 minutes ago, Radian said:

But I've been agreeing with you all along

I have had that with people on here.

Agree with them, but saying it differently seems, for some, to be the polar opposite.

[TonyT]

 

 

having a 3kw immersion heater on a plug top is plain silly for lots of reasons.

30 years in the trade and never used a 13 amp plug on an immersion 

 

done plenty with 15amp plug and sockets! Via 20 amp double pole switches 

 

[TerryE]

3 hours ago, Radian said:

he seems to think I'm disagreeing when I'm not?!?

 

? ? Don't worry. I think you're one of the good guys.  And yes, rereading I think that I did misunderstand your thrust.

[Radian]

2 hours ago, TonyT said:

having a 3kw immersion heater on a plug top is plain silly for lots of reasons.

 

Quite right. How about two in series?

[dpmiller]

Something must've changed over the years-  3-bar electric fires  and various other 3kW heaters also used to work off a plug just fine back in the day, but nowadays a 2.5kW tumbledryer overheat a plug.

And don't start me on 3kW elements in Water stills that run all day long, on a 13A plug...

[Nickfromwales]

2 hours ago, dpmiller said:

Something must've changed over the years-  3-bar electric fires  and various other 3kW heaters also used to work off a plug just fine back in the day, but nowadays a 2.5kW tumbledryer overheat a plug.

And don't start me on 3kW elements in Water stills that run all day long, on a 13A plug...

C’mon…….you could instantly tell which socket the fire was plugged into as it was brown instead of white!!  I’d be interested to know how many deaths from fires were attributed to these, back in the day….

 

3 hours ago, Radian said:

How about two in series?

In principal we both know this would work. Then you put your sparky hat on and things change significantly.  
If someone were to come in to work on this, and one heater had failed, they may then, mistakenly, drop the dead heater out and run the working one off the plug top. They’d think they were being a hero, but they then put you at risk.

What you / we do for ourselves is not something we can do for 3rd parties, particularly when there is a liability trail and a warranty / commission of a new CU. The chat here is just a little ‘loose’ in terms of who “could” do “what”. You can set fire to your own house or electrocute a family member, but I cannot do that for a client. 
If somebody wants to DIY this as you suggest, then that’s fine, in principal, but imo not a good idea at all.

 

I like your posts, don’t take me wrong, it’s just a huge no-no from a sparky PoV to have 2x 230 volt devices connected up in series in a residential domestic setting, unless they came that way from the manufacturer and the unit was supplied with 1x 230 volt input and then split this after the incoming connection. Technically you could ask a sparky to give you the 13a socket and then plug into it whatever you wish, but then the liability and responsibility lays with you for whatever happens downstream. 

[Ajn]

On 16/02/2022 at 14:20, ProDave said:

13A fuses get hot at close to 13A and in some makes of FCU they get hot to the point of destroying it when on for a long time.  If ever you smell a fishy smell check your FCU's for overheating.

If this is the case then the fuses maybe fake and do not comply with BS1363 or there is a fault with the fuse connections The rating given in BS1363 are not intermitant ratings they are continuous ratings.

There are a lot of fake plugs and fuses out there.

As an aside the other issue that is not so obvious to a lot of people is the 13A twin socket. The rating is not 13A per socket.

Edited February 18, 2022 by Ajn