new CU or retrofit RCBOs for new water heater circuit?

[bertle]

i

I have tried to search for the advice already but couldn't find it. Any point in the right direction appreciated.

Sadly I have Economy 7 and it has been causing me a great deal of difficulty with switching on at the wrong times and now the boiler has also packed up. I have a small flat and want to recover some space so have decided that I want to get rid of my PulsaCoil III 205 litre boiler. I want to replace the boiler with an on demand instant water heater, and gain cupboard space.

I am aiming for a 12kW Redring Powerstream, 50A. or something similar. (any recommendations?) I had considered 3phase power and getting a much larger capacity heater. There is 415V 200A in the power distribution room, where my mains lives which is three/four metres away from my front door and CU. Is this feasible?/approx cost?

I have a HAGER consumer unit installed in a new build flat from 1998/1999. There is no RCD protection but just standard MCBs. I have a 100A mains supply.

I want to know to meet current regulations whether or not I need a new Consumer Unit or if I can retrofit with RCBOs to bring a new circuit, feeding a new 50A water heater circuit. The water heater/boiler cupboard is a short run from the CU that is above the front door, maybe 2.5m. Any ideas on how much this would be?

Any advice is welcomed, although I really want the boiler to go and some more space.


Best regards

Bertle

 

[mrloy99]

Hi,
Your main fuse may say 100amp on the side of it but it is most likely that there will be an 80amp fuse inside.As you have crappy E7 heaters anyway I would suggest you get rid of the lot and forget about the electric water boiler and just get the full gas package in.However in response to your query you can retrofit rcbos but I've not come accross one rated at 50amps.Splitting the tails into Henly block and installing a separate rcd/mcb "shower unit" may be easier and then you maybe wont have to suffer the cost of providing rcd protection to the rest of the circuits(unless you want to).Your 3 phase idea will probably be very expensive

 

[pennywise]

Hager RCBO Type B SP 50A 30mA by Hager

 

[baldsparkies]

As the lads have said, just wanted to add wire in 16mm if your going for the 12kw unit. They are instantaneous power gobblers and you will find they run much more efficiently with 16mm cable.

 

[bertle]

Thanks for the advice. I cant have gas as there is no gas in the building. About the mains: I measured the diameter of the mains cables from the meter: Measuring from the inner red insulation layer I get a diameter of 0.98cm. I also measured the diameter from the outer grey insulation but cant remember it.

Does this sound like 100A cable? You are right:- I dont know what the actual supply fuse is. Is there a way of finding this out without being on hold to the electric company (southern electric). If I do have 100A mains and a 50A water heater, 30A induction hob. I am worried about voltage drops causing flickering lights, or is flickering lights only when you are maxing out the supply? Or perhaps I miss the point: Circuits should have same voltage as supply voltage because its all in parallel? Flickering lights has another cause?


thanks
B.

 

[baldsparkies]

Max demand shouldn't be an issue, as far as volt drop goes 16mm suggested is for that very reason. Flickering lights are more likely caused by poor connections although high frequency electronic flourescents can be fussy about voltage supplies. You could ask the supply authorities what size fuse is in your cut out head, but they will probably keep you on the phone for hours and then guess.

 

[bertle]

Thanks for your replies. I will ask for 16mm2 cable, and will look into the advised Hager 50A RCBO and separate shower RCD unit. I really appreciate the advice. Will be glad to gain boiler cupboard space, and no more Economy 7. Thanks again!

Best regards,
B.

 

[mrloy99]

Thanks for your replies. I will ask for 16mm2 cable, and will look into the advised Hager 50A RCBO and separate shower RCD unit. I really appreciate the advice. Will be glad to gain boiler cupboard space, and no more Economy 7. Thanks again!

Best regards,
B.

I'm not sure what you are intending to do about your heating,ie do you require your instantaneous 12kw water heater to run a wet central heating system as well as your hot water or is this for hot water alone?Also not sure if you have an existing electrically heated shower already?Heatrae sadia do one called amptec but in their literature they still show a hot water cylinder.As previously stated all these high kw boilers are very heavy on the juice,and incidently they also recommend a 63amp mcb to be used for their 12kw boiler.If you were to sacrifice your cupboard space you would be able to take advantage of the E7 or E10 tarrif.If I was you I would do a full costing on your options including running costs.Presumably bottled gas is not an option too?
But after rereading your post its the cupboard space you are really needing...You should be prepared for a drop in pressure,rather than having tons of stored hot water at mains pressure from your thermal heat store.But then again maybe it will all save you money by only heating what water you need to use straight away.

 

[bertle]

Thanks MrLoy.

I have Economy 7 serving a Gledhill Pulsacoil III boiler that heats the water over night via an immersion heater to supply a shower and sink. No wet CH, just wall mounted convection electric types. So i wanted a instant heater for a shower and sink. (not at the same time!!)

Actually, I saw this:
Eemax UK Tankless Electric Water Heaters

The 15kW model. Same sort of thing as 12kW powerstream. I have a tiny flat in central london so any spare space is needed. Dont want to remodel bathroom for a electric shower, the pipe run from boiler cupboard to shower is very short already.

with a little more power and going on the literature seems promising. I also thought that two 30A cables is better than one larger 50A cable for a few reasons - less power losses, and also the cables might run a little cooler. I also thought something that heats with two elements might be a little more effective. Of course, I am learning and open to any products you have experience with. But - is a 60A+ heater going to BBQ my mains if it is 80A and not 100A as stamped on the main fuse? I thought maybe it draws a huge current to start with with then no more than 40-50% once the elements are fired up. For short showers, no more than 10 minutes, or filling up a kitchen sink. I could get the supply fuse upgraded, but dont want to wait around for the electric company.

Best,

B.

 

[mrloy99]

Thanks MrLoy.

I have Economy 7 serving a Gledhill Pulsacoil III boiler that heats the water over night via an immersion heater to supply a shower and sink. No wet CH, just wall mounted convection electric types. So i wanted a instant heater for a shower and sink. (not at the same time!!)

Actually, I saw this:
Eemax UK Tankless Electric Water Heaters

The 15kW model. Same sort of thing as 12kW powerstream. I have a tiny flat in central london so any spare space is needed. Dont want to remodel bathroom for a electric shower, the pipe run from boiler cupboard to shower is very short already.

with a little more power and going on the literature seems promising. I also thought that two 30A cables is better than one larger 50A cable for a few reasons - less power losses, and also the cables might run a little cooler. I also thought something that heats with two elements might be a little more effective. Of course, I am learning and open to any products you have experience with. But - is a 60A+ heater going to BBQ my mains if it is 80A and not 100A as stamped on the main fuse? I thought maybe it draws a huge current to start with with then no more than 40-50% once the elements are fired up. For short showers, no more than 10 minutes, or filling up a kitchen sink. I could get the supply fuse upgraded, but dont want to wait around for the electric company.

Best,

B.

hi Bertie,
I think that your 80amp supply should do the job especially as you say....it will only be on for a short time.I googled powerstream there now and I see they can be got for around £180 for the 12kw model.But if you were going to upgrade to 100amps to keep everything right your main meter cables(tails in electrician speak)should be sized at 25mm sq.As previous posters suggests 16mm sq would be best to supply your heater...but as its a very short run I can't off the top of my head think of any reason not to use 2 x 6mmsq cables.provided they are supplied off the same mcb 63amp.....Although looking at the literature for the dual jobbie it woul seem to be 3x 30amp supplies...My concern would be that future maintenance personnel wouldn't be aware that for full isolation it would be necessary to isolate two circuits....You would need to have a notice stating this fact on the dual unit and at the consumer unit.
Your maximum loading of the rest of your house should be easy enough to work out....your max cookerampage loaded up is probably less than 20amp,kettle,say 10 amp,microwave,12amp,washing machine 12amp and a couple of covecter heaters 15amp.Computer,tv,electric blanket,lighting,fridge/freezer,another 15 amp....But what all will you be using at the same time?
Only you can know.....I know that if I was going for the 15kw model I would get it upgraded to 100amp. Also dont forget that as you are situated in London all your proposed works is part p notifiable.....good luck.

 

[bertle]

Thanks Loy. sorry to bother you again, but you've been really helpful.

Re mains supply fuse.

Have a Connecting Block RDL CB3, believe to be rated to 100A after googling this model. Have a RDL CB6 Henley block, 100A stamped on it, I think this splits the supply somehow as one set of tails goes into the Economy 7 teleswitch. Meter tails 9.8mm diameter, measured at coloured red inner sheath insulation with vernier calipers. EDF meter installed in 2003. Says its rated between 20 - 100A. CU split into two rows of MCBs, each row has a 100A circuit breaker a the end of it.

Can I safely guess that I have 100A supply? Have been onto power company about service fuse, but calling after work they are too busy, and when I call at work Im on hold for too long.

Is there any sure fire way to determine supply, bar getting DNO to check service fuse, or trying to draw 80A from my appliances, and then 100A to see if I can pop the service fuse?

Thanks

bertle.

 

[mrloy99]

Thanks Loy. sorry to bother you again, but you've been really helpful.

Re mains supply fuse.

Have a Connecting Block RDL CB3, believe to be rated to 100A after googling this model. Have a RDL CB6 Henley block, 100A stamped on it, I think this splits the supply somehow as one set of tails goes into the Economy 7 teleswitch. Meter tails 9.8mm diameter, measured at coloured red inner sheath insulation with vernier calipers. EDF meter installed in 2003. Says its rated between 20 - 100A. CU split into two rows of MCBs, each row has a 100A circuit breaker a the end of it.

Can I safely guess that I have 100A supply? Have been onto power company about service fuse, but calling after work they are too busy, and when I call at work Im on hold for too long.

Is there any sure fire way to determine supply, bar getting DNO to check service fuse, or trying to draw 80A from my appliances, and then 100A to see if I can pop the service fuse?

Thanks

bertle.

Yes bertle,you are quite right the only way of confirming that you have a 100amp service fuse is to cut the seal and withdraw the fuse.It wasn't me,it was like that! It wouldn't be the first one I've come accross.
Also from what I can make out from your previous corespondence you said you have convector heaters,and NOT storage heating.If this is indeed the case then the only circuit supplied is your water heater?? So when you take this out your E7 will be completly redundant. So you should contact your supplier and get onto normal tarrif.The way E7 works is that they charge you more on your day rate and less on your night tarrif. The normal tarrif is less.