Radial / Ring conversion.

[3Riversparky]

Hello everyone. I've just joined. I am a retired [20yrs] spark and have just come to live in a static caravan lodge.
The sockets are wired in two radials through one breaker including the kitchen which was set up for dishwasher and washing machine! Wiring is 2.5mm and a single 25A breaker. 16 sockets some double. Plus gas boiler and built in microwave, electric oven and fridge freezer. The lounge has a plug in 2KW convector heater.
Floor area approx less than 50m2.
Washer and dishwasher not fitted but I'm wanting to use their socket outlets for two instaflow water heaters and reduce my reliance on gas. The anticipated total load will be approx 6000W from the heaters but could be more continuous than the departed washers. These loads come after the oven kettle and toaster !
Is there a reason why I can't change the radial into a ring with a 32A breaker and leave a few sockets on the existing radial which I will reduce to 20A. can identify the routes.
Sorry but it's 20 yrs since I last worked and want to stay within the regs whatever edition is now current !! I personally don't think the installation should have been certified in the first place!! Outside supply is 40A.

Hoping for some interesting and helpful comments . 3RS

 

[ericmark]

I do not understand your reasoning, you can't run a 6000 watt appliance from a ring final, there is a 3 kW max, and the appendix recommends any fixed appliance over 2 kW is fed from it's own supply.

Whole idea of the ring final is to save copper, it allows 106 meters on a single ring final which could supply the whole post war home, it was 88 meters until the volt drop rules changed. In a caravan one is hardly likely to use that much cable, with 25 amp radials 24 meters would be the max length, it would cause an increase of the loop impedance of 0.65Ω between incomer and the last socket.

I used an under sink water heater in my caravan, with the element swapped to 1 kW it held 7 litres of water, which was ample. Latter caravans had a carver water heater that was duel fuel either electric or gas, fitted under the bunk beds.

I noted on holiday there are some specials for static caravans, but with a 40 amp supply instant water heaters are not really a good idea.

As to regulations wise, only real change for caravans is now any metal clad unit similar to a caravan is banned from having a PME supply, but little else has changed for caravan like accommodation.

 

[Rodders53]

What size gas cylinders and what cost to refill? Or what unit price are you charged if piped gas on site?
A 47kh propane cylinder holds around 656 kWh of energy. Prices online range from £90 to £125.
So at worst case = 19p per kWh say 80% efficiency = 24 p per kWh into the water. Could be less (or more) depending on what you pay.

What unit price is the electric? It'll need to be less than the above to work out cheaper to heat. Many static caravan sites are charged at commercial rates so considerably more than domestic SVR (currently an average of 24.5 p per kWh). {That is due to reduce a bit in July, and then increase again for winter.}

3kW (13A) or even 6kW (26A) instant heaters will never give a satisfactory shower, of course.

Three Rivers is, potentially, my old stomping ground (although there is more than one 'three rivers' in the UK).

 

[securespark]

What you can draw depends on the breaker feeding your static.

My parents-in-law have one and the supply is only 16A, rather making a mockery of the consumer unit in the static.

I would rely on gas for heating the rooms and the water.

The water heaters are too heavy to include on the socket circuit, plus, surely gas must be cheaper, even though it's bottled?

 

[JohnW2]

I do not understand your reasoning, you can't run a 6000 watt appliance from a ring final, there is a 3 kW max, and the appendix recommends any fixed appliance over 2 kW is fed from it's own supply.

The OP is talking about two water heaters, so probably 2 x 3,000W and that would theoretically be OK on a ring if there were no other 'significant' loads on that circuit and if the water heaters were connected to appropriate points on the ring.

Indeed, 6 kW would be theoretically OK on a 2.5mm² (Method C) radial if it were protected by a hypothetical 26A or 27A MCB, so maybe the OP's concern is that 26A is 1A more than the rating of the nearest available MCB (25A) ? I realise that the guidelines in the OSG do not suggest any allowance for diversity with instantaneous water heaters unless there are more than two of them, the fact that they would be operative only for for relativity limited periods of time means that I would personally lose no sleep mover that "1A".

I realise that it would be unconventional, and therefore probably controversial, but if instead of using a new bit of 2.5mm² cable to turn the 25A radial into a 32A ring, the OP installed that cable in parallel with the existing one (for the entire circuit) then he could theoretically have a 50A radial, more than his total supply !

 

[3Riversparky]

Thank you those are pretty much my thoughts but I admit to being s little out of date with the passage of time so I searched for comments.

 

[JohnW2]

..... t I'm wanting to use their socket outlets for two instaflow water heaters and reduce my reliance on gas. The anticipated total load will be approx 6000W from the heaters but could be more continuous than the departed washers.

I think that you may need to re-consider that.

Quite apart from the cost of electricity in comparison with LPG, I think you may well be over-estimating the adequacy of 3 kW, or even 6 kW of instant water heating.

I am currently using an electric instant water heater as a temporary measure (prior to installation of definitive CH and DHW systems) in a house I am renovating. It is a 9.5 kW (about 41 A) unit, with 2 x 4.75 kW elements, with the choice of having one or both of the elements operative. With just one element (4.75 kW) the water it produces is no more than 'luke warm' at any usable flow rate, although it produces 'properly hot' water at good flow rates with the full 9.5 kW.

On the basis of that experience, I would imagine that a 3kW one would be completely useless, and that even 6kW of instant water heating might fall short of being ';adequate'.

Kind Regards, John

 

[ericmark]

When I lived in a caravan I paid a set price for electric it did not matter how much I used, so I did my best to only use electric, the thing I found used the most gas was the fridge, a small bottle would last 3 weeks, once I fitted an electric element my gas lasted months, the main problem was renewing the gas, no spare bottle, so had to wait until site office open to get replaced, so good reason for all electric.

Unless one has solar, battery, and split tariffs, today the reverse is often true, but I have two electric showers, two cookers, three story house on a 60 amp fuse, so can't really say much about using electric rather than gas or oil when on a small supply, but never blown the DNO fuse so why worry?

I have looked at saving money with some what on reflection were daft ideas, but I know my supply is not enough to heat home with electric, I have to use oil, as my supply is simply not big enough, be it oil or LPG unless to can stop using it completely, may as well use it as cheaper than electric.

 

[Harry Bloomfield]

I am currently using an electric instant water heater as a temporary measure (prior to installation of definitive CH and DHW systems) in a house I am renovating. It is a 9.5 kW (about 41 A) unit, with 2 x 4.75 kW elements, with the choice of having one or both of the elements operative. With just one element (4.75 kW) the water it produces is no more than 'luke warm' at any usable flow rate, although it produces 'properly hot' water at good flow rates with the full 9.5 kW.

On the basis of that experience, I would imagine that a 3kW one would be completely useless, and that even 6kW of instant water heating might fall short of being ';adequate'.

I think the OP's best solution, might be a stored HW system. My own touring caravan includes 10L of stored water, Truma system - 12v pump pressurised, it is heated by either gas, electric, or both simultaneously, consuming around 1Kw when on electric. Both that, and the CW system are fed by the same pump, so the same pressure at the mixer outlets, including the shower. We find the shower more than adequate, providing time is allowed for it to recover between usage.

 

[JohnW2]

I think the OP's best solution, might be a stored HW system. My own touring caravan includes 10L of stored water,

Indeed so. A house I know (needing serious refurbishment!) with no other water heating has an ancient Redring heater which, like yours, stores around 10 litres of heated water, and must be 3kW at most, since it is 'plugged in' That is fine for just providing hot water to sinks/basins.

Truma system - 12v pump pressurised, it is heated by either gas, electric, or both simultaneously, consuming around 1Kw when on electric. Both that, and the CW system are fed by the same pump, so the same pressure at the mixer outlets, including the shower. We find the shower more than adequate, providing time is allowed for it to recover between usage.

10 litres will not provide much of a shower and, as I have indicated, my experience is that even 4.75 kW of 'real-time' heating is totally inadequate to maintain a useful HW temp.

 

[Rodders53]

10 litres will not provide much of a shower

Thousands upon thousands of touring caravans and motorhomes have / do run with such HW tanks and people shower in them quite happily. It needs users to operate a 'wet' 'soap' and 'rinse' system, so not a continuous stream of water, but we used to cope well with it when we had such a system. (Cold water barrel - external - was no more than 40 litres as was the waste tank).

Ours was 850W/1300W electric and one could run gas at the same time to reheat quicker still if desired. Water was at 70C.

More than adequate as a shower when mixed with cold via the DC pump. We could shower one after the other (first towelled off and dressed before second undressed to shower giving the HW some 'recovery' on electric only).

Far better than the rubbish Mira instant heat electric one in the holiday let we went to a couple of weeks ago. That was pathetic.

 

[JohnW2]

Thousands upon thousands of touring caravans and motorhomes have / do run with such HW tanks and people shower in them quite happily. It needs users to operate a 'wet' 'soap' and 'rinse' system, so not a continuous stream of water, but we used to cope well with it when we had such a system. (Cold water barrel - external - was no more than 40 litres as was the waste tank).

Fair enough. It's not a world I know, and I suppose that I probably would not think of what you're describing as 'having a shower' - I think the latter typically/ideally requires 10-15 litres/minute, so, if mixed 1:1 )or even 1:2) with cold water, 10 L of hot would not provide for a very length 'continuous shower'. However, as you say, in such an environment one doesn't have all that much water to heat, anyway, so I suppose what tyou say makes sense in that context.

Ours was 850W/1300W electric and one could run gas at the same time to reheat quicker still if desired. Water was at 70C. ... More than adequate as a shower when mixed with cold via the DC pump. We could shower one after the other (first towelled off and dressed before second undressed to shower giving the HW some 'recovery' on electric only).

Again, fair enough. If I've done my sums right, then to heat 10 L of water through 50 degrees (say from 20 to 70 degrees) with a 1,300 W heater should theoretically take about 27 minutes - but that time would obviously reduce if one used gas in addition to the 1,300 W of electrical heating.

 

[Harry Bloomfield]

10 litres will not provide much of a shower and, as I have indicated, my experience is that even 4.75 kW of 'real-time' heating is totally inadequate to maintain a useful HW temp.

It's not 10 litres though is it? 10litres really hot water, mixed with cold is around 20 litres. I have never managed to exhaust it all yet..

 

[JohnW2]

It's not 10 litres though is it? 10litres really hot water, mixed with cold is around 20 litres.

Indeed. In fact, as I wrote, maybe even 30 litres ...

.... I think the latter typically/ideally requires 10-15 litres/minute, so, if mixed 1:1 )or even 1:2) with cold water, 10 L of hot would not provide for a very length 'continuous shower'.

I have never managed to exhaust it all yet..

As above, if one is talking about a 'continuous shower' (which is what most people understand by 'traking a shower'), at a recommended flow rate of 10-15 litres/minute, 20 litres of (hot+cold) water would last for 1.33- 2 minutes, and 30 litres (of less hot water)would last for about 2-3 minutes - which may be adequate for you (even though certainly not for my daughters ).

 

[Harry Bloomfield]

As above, if one is talking about a 'continuous shower' (which is what most people understand by 'traking a shower'), at a recommended flow rate of 10-15 litres/minute, 20 litres of (hot+cold) water would last for 1.33- 2 minutes, and 30 litres (of less hot water)would last for about 2-3 minutes - which may be adequate for you (even though certainly not for my daughters ).

Much, much longer than that, they use a fine spray.