80l unvented water heater

[mbev51]

Hi, my electrician finally turned up to view the work in my outbuildings. He says the 80l unvented presurized water heater ive just bought will have to go on its own circuit because its more than 15l. The info from the page of the ebay seller says a 13amp fused spur. Its a 2000w heater european style. Ive been trying to find the building regs on the internet without success. At the end of the day i'll let him do it his way. Im still keen to know the regs

 

[ericmark]

In the appendix 15 of BS 7671 it suggests items 2 kW or more which are fixed, should have a dedicated circuit so the load current in any part of the circuit will be unlikely to exceed for long periods the current-carrying capacity of the cable (Regulation 433.1.5 refers).

433.1.5 Accessories to BS 1363 may be supplied through a ring final circuit. With or without unfused spurs, protected by a 30 A or 32 A protective device complying with BS 88-2.2. BS 88-6. BS 1361. BS 3036, BS EN 60898, BS EN 60947-2 or BS EN 61009-1 (RCBO). The circuit shall be wired with copper conductors having line and neutral conductors with a minimum cross-sectional area of 2.5 mm² except for two-core mineral insulated cables complying with BS EN 60702-1, for which the minimum cross-sectional area is 1.5 mm². Such circuits are deemed to meet the requirements of Regulation 433.1.1 if the current-carrying, capacity (Iz) of the cable is not less than 20 A and if. under the intended conditions of use, the load current in any part of the circuit is unlikely to exceed for long periods the current-carrying capacity (Iz) of the cable.

sorry don't have current edition. Note the long periods, for a 40 gallon cylinder it clearly is a long period, but what about a tumble drier, it is over the weight to be considered portable, and does not have wheels, and can run for 90 minutes or more, so I would class that as a long period, but how many dedicated circuits have you seen feeding a tumble drier?

If supplied near the centre of a ring final I see no problem, any overload will trip the overload device, only when located near the consumer unit, so the two legs of the ring final don't fully share the load could there be a problem.

 

[EFLImpudence]

It definitely does not have to have its own circuit.

Connecting it to the socket circuit is presumably what the electrician is worried about and there likely will be no other circuits that it could happily share, so...

 

[winston1]

A

In the appendix 15 of BS 7671 it suggests items 2 kW or more which are fixed, should have a dedicated circuit so the load current in any part of the circuit will be unlikely to exceed for long periods the current-carrying capacity of the cable (Regulation 433.1.5 refers).


sorry don't have current edition. Note the long periods, for a 40 gallon cylinder it clearly is a long period, but what about a tumble drier, it is over the weight to be considered portable, and does not have wheels, and can run for 90 minutes or more, so I would class that as a long period, but how many dedicated circuits have you seen feeding a tumble drier?

If supplied near the centre of a ring final I see no problem, any overload will trip the overload device, only when located near the consumer unit, so the two legs of the ring final don't fully share the load could there be a problem.

A 2kW load will never overload one leg of a ring where ever it is fitted. At just over 8 amps it is far less than the rating of 2.5mm2 cable. There is no reg saying loads over 2kW have to go on their own circuit either.

 

[Taylortwocities]

Back in the past (16th edition, I think) had a reg that said what your electrician had said.
But the requirement for 15litre+ water heaters to be on their own circuit does not appear in the 17th.
The last OSG that I have (green/17th) includes a GUIDANCE that vessels over 15litres should(not must) be on separate circuits, but there is no corresponding reg marker in that OSG.

My conclusion is that your sparky is not up to date and remembering a time when T Rex were in the charts.

Of course, he may have surveyed your ring final circuit and concluded that there isn’t enough capacity to add another 2kW. But I doubt it.

Further to the “appendix 15” references above. This section of the regs book is informative only and is there to provide simple guidance on how loads on ring circuits can be provided. It’s not a regulation.

 

[Taylortwocities]

A

A 2kW load will never overload one leg of a ring where ever it is fitted. At just over 8 amps it is far less than the rating of 2.5mm2 cable. There is no reg saying loads over 2kW have to go on their own circuit either.

Thanks for the helpful input, Winnie. Keep it up

 

[Agile]

I would have thought that it would be best to treat it like an immersion with a dedicated switched fused spur ( with a double pole switch with the contacts spaced at least 3mm when open if I remember correctly ). I don't see why that spur could not be supplied from an existing ring circuit but opinions seem to vary on if any, and how many, spurs can be added to a ring main.

What potentially worries me more is how it is to be plumbed in as we have quite strict regulations in the UK on the way unvented cylinders are protected and I expect that they may be more strict here than in the rest of the EU.

During the training for installing unvented cylinders they used to show a photo of a French school which had been largely destroyed when an UV cylinder exploded.

They should normally be fitted by someone who has done the training and assessment and then notified to Building Control.

An 80 litre UV cylinder at 100 C would produce 40,000 litres of steam at NTP ! Quite a scope for a large explosion!

 

[EFLImpudence]

I would have thought that it would be best to treat it like an immersion with a dedicated switched fused spur ( with a double pole switch with the contacts spaced at least 3mm when open if I remember correctly ). I don't see why that spur could not be supplied from an existing ring circuit

Immersions are not normally on a "dedicated switched fused spur" - either the correct or often used incorrect meaning.

 

[winston1]

Thanks for the helpful input, Winnie. Keep it up

That’s OK. As it was not directed at you I don’t understand why YOU are thanking me.

 

[conny]

Because it was a helpful reply?

 

[ericmark]

In 1954 when my parents house was built, there were demarcation lines, unions would not let electricians to do plumbing work, or plumbers to do electrical work, so the supply to the immersion heater went into a 15 amp socket and the immersion had a 15 amp plug so the plumber did not have to do anything other than plug it in once fitted.

The 15 amp socket went to a 15 amp fuse in the fuse box, and was a dedicated supply, and since no fuse in the airing cupboard there was nothing to produce heat.

Moving to using the 13 amp plug and socket, would result in there being a fuse in the plug, and a fuse clearly has enough heat to melt the fuse wire inside it, so must always be in free air, or fan assisted air with a built in oven. In the airing cupboard hard to ensure free air, so need the wall to dissipate heat, so need the fused connection unit, so it is built into a wall and can get rid of the heat.

Or of course a cooker connection unit could be used, and a 16 amp MCB/RCBO in the consumer unit.

However with a radial supply having an immersion heater on the supply worse case scenario is it may together with other items cause the MCB/RCBO to open.

A 2kW load will never overload one leg of a ring where ever it is fitted. At just over 8 amps it is far less than the rating of 2.5mm2 cable. There is no reg saying loads over 2kW have to go on their own circuit either.

That is true of course, but I did not think I had to add "together with other current using items" and this is the problem with the ring final, designed to use 7/0.029 cable, but latter we reduced the size to 2.5 mm² and increase the overload setting from 30 to 32 amp. In the main this is not a problem, as cable still rated 20 amp or more, and two cables so cable good for 40 amp, and overload set to 32 amp.

However we are permitted around 106 meters of cable, (was from memory 88 meters) and if we have a number of items near the origin of the cable we can get over the 20 amp on one leg, but as long as the items don't run for long, this is not a problem, it takes time to heat up the cable, and a kettle at 3 kW runs for such a short time, the cable does not over heat, I know I switch on two cup boilers powered from the same 13 amp fuse, to make 2 cups of coffee in the adverts, and it does not rupture the 13 amp fuse.

So we are looking at both overload and time, and only with a ring final, if using 20 amp radials it does not matter. Only with a ring final can there be a problem, and at 15 litres using this calculator it says it will take around 50 minutes which is less than the time set with tumble driers, so either tumble driers need a dedicated circuit i.e. not on the ring final, or your heater is OK on the ring final.

So personally I think OK on a ring final, but I have tried to show why I feel it is OK. Rather than make some unhelpful statement like.

A 2kW load will never overload one leg of a ring where ever it is fitted. At just over 8 amps it is far less than the rating of 2.5mm2 cable. There is no reg saying loads over 2kW have to go on their own circuit either.

I had already stated "it suggests" not the regulations say, and "appendix 15" OK missed it was quoted from the 2008 edition. I was trying to show why some one would consider not permitted, rather than simply say they are wrong.

 

[ericmark]

Oh as as far as the 15% better than rival water heaters, the Willis system works on time, so the longer it runs for, the more hot water you have, so with a 200 litre tank you can decide if you leave it on for 5 minutes to give enough hot water to wash hands, or 2 hours so enough for a bath, the user has the option, so can be far more efficient to other systems, but it seems only the tick Irish have worked out how to install them!

 

[Taylortwocities]

That’s OK. As it was not directed at you I don’t understand why YOU are thanking me.

I was actually being complimentary and supportive.
But you obviously can’t see that, so I will revert to my usual attitude.
Have a nice time.

 

[flameport]

Back in the past (16th edition, I think) had a reg that said what your electrician had said.

The 15 litres thing is in the 15th edition 1981, appendix 5, so wasn't a regulation then.
It disappeared from the 16th edition 1991, but was included in the on site guides from when they were first published in 1992.
17th and 18th editions have it in the appendix again.

The only reference in the 14th edition is Table A.3, where for a radial circuit serving one room of less than 300 ft² which is not a kitchen, the maximum number of socket outlets is 6, provided that no fixed water heating appliances are connected. The same appears in both the original 1966 version and the 1976 metric reprint.

Earlier editions from the 10th in 1934 to the 13th have nothing on immersion heaters of any capacity.
The only references to water heaters are of the electrode type, where uninsulated elements are immersed directly in the water.

The conclusion is that it was never a regulation, but was guidance introduced by someone from somewhere around 1980, with no credible source or explanation as to why.

 

[mbev51]

Hi, ive read through your discussions on the topic with intetest. There is no harm in my electrician putting it on its on circuit and so we may well do that. I will talk to him about it. As for the plumbing in, i have to use a plumber with g3 certificate. I have installed one of these in in our old french house about 20 yrs ago, not hard to do just have to follow the instructions. It has a pressure vessel and a blow out valve. Sadly also i have a hetas stove fitter coming to install a woodburner and a new twin wall chimney. Again ive done these before, was hoping we could do this one and get it inspected by building control. Unfortunately that is not possible here. We are developing part of an outbuilding to be a rentable holiday let. Everything has to be above board and certificated.