Manufacturer question : 3kW installation - easier than 4.4 kW

[Mike McHugh]

Hello everyone - new member here, from a manufacturer/distributor trying to understand how our products get installed and what we can do to make it easier.

I own a manufacturing company, we currently sell instant water heaters and other space and water heaters to electrical wholesalers - nationals and independents.

Specifically, we have just had a debate in the office about whether it would be more attractive under UK wiring Regs for electricians to install a 3kW instant undersink water heater rather than a 4.4kW unit.

The benefit we imagine is that (a) 3kW could be hard wired to a fused spur off an existing ring main, whereas (b) 4.4kW needs a cable all the way back to the distribution board. What do the regulations say on this ? What do people do in practice ? If everyone runs a cable back anyway, clearly not much saving between 3.0 and 4.4kW.

There are other issues making sure a 3kW instant water works well, but that we are on top of those. Its just the possible installation advantage we are unsure about.

I hope you don't mind the question - we are genuinely trying to take on board what people want.

Mike

 

[MJPD29]

Although possible, i would rather have a dedicated circuit even for a 3kw heater, it will burn out the fuse spur over time as i have seen time and time again and is better suited with a dedicated 16a mcb and 20a double pole switch. I personally would not take it off the ring circuit regardless so 3kw/4.4kw would make no difference to me

 

[Taylortwocities]

The maximum device you can attach to a ring final circuit will be fused at 13A (3KW approx).
There is a specific Appendix (15) in the regulations (BS7671) which provides guidance on how not to put too much load on a ring final circuit. In particular, it provides guidance that one should avoid connecting immersion heaters, space heaters or loads of a similar profile to a ring final. It goes on to say that loads greater than 2KW would be better on their own radial circuit.

But that's guidance. If you look at the market, there are lots of similar products that are rated at 2 and 3KW. The load profile of an instant water heater isnt much different to a common kitchen kettle, and they all plug in to a ring final.

Without a doubt a 4.4KW device will need its own dedicated circuit. Many of these will be installed in existing kitchens/etc where running a whole new circuit will be an issue. I'm thinking about places like village halls, community centres etc where you are stuck with the supplies that are there.
Given the above, I would say that you'd have a smaller market for the 4.4KW device because of that.

PS Where do I send the invoice for my consultancy fee?

 

[Wilko]

Hi MM - if the unit was for occasional use, like hand washing in toilet (say) then a 3kW model might be able to be attached to an existing circuit, depending on survey. But if the unit was used frequently / continuously in a kitchen (say) it should have its own circuit for either kW model, in my humble opinion.

 

[richy3333]

BS7671 says you should avoid running 'immersion heaters, comprehensive electric space heating or loads of similar profile from the ring circuit'. I suppose its whether as a manufacturer you feel any of those conditions apply to your unit?

As mentioned before I've seen a few burnt out FCU's from these types of instant water heaters over the years.

 

[Mike McHugh]

Some great replies thanks, it does seem a little of a grey area which is rather what we expected. To answer richy's point we do not envisage constant use or anything like in the vast majority of cases. The product is for hand washing only in washrooms, so a burst of 15 seconds every minute would be high use, but that brings average load down to 3kW x 15 seconds /60 seconds = 0.75 kW. Note an instant water heater is very different to say an immersion storage water heater or a space heater which could run at full load for hours at a stretch. Of course we cant absolutely guarantee no one will leave the tap running and just walk away, drawing the full 3kW indefinitely. But equally I suppose we cant guarantee no one will plug 2kW fan heaters in every single socket in a ring main either !

 

[Taylortwocities]

The product is for hand washing only in washrooms, so a burst of 15 seconds every minute would be high use,

In that case, limit your product size to 3KW. Otherwise, as I said above, with a larger than 3KW product you’ll not get business from a large proportion of the market, who will not or cannot install a new dedicated circuit.
Remember that a new circuit is notifiable works, which needs a registered electrician to carry out.
A 3KW unit can be installed by any local handyman into an existing circuit.

 

[Mike McHugh]

Thats another good point for the 3kW, and another surprise to me - I had imagined even the fused spur would require a registered electrician.

 

[Taylortwocities]

It depends on where! In England, The only things that require notification are new circuits, new or replacement consumer units or electrical work in bathrooms.
Other (and I think preferably) more stringent regulations apply in the Colonies.
Note that all electrical work is supposed to be certified, but any competent person can do that.