Central Heating cable size

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Hi

Need a bit of help/advice regarding the current wiring of my oil-fired central heating system, which was installed by the previous owners.

Basically, there is a white single flex cable running underground in conduit from my house to the shed to feed a warmflow 70/90 oil boiler, boiler stat and a Wilo Gold 50 pump.
The flex cable is stamped "JSL H05VV-F 3X1), which I assume means that it is a 0.5mm flex cable, (please correct me if I'm wrong).

At the house the flex cable rises from underground and is wired directly into a mechanical timeclock. The timeclock is then just plugged into the ring main.
I want to relocate and renew the timeclock and hence extend this existing flex cable to the new timeclock location (via a junction box from the point where it enters the house)

My query is, assuming I am correct with regards to the cable size, is there a maximum distance that this 0.5m flex cable serving my boiler and pump can be?
Currently the cable is already approx. 16-17m long (13m underground, 2m exposed in house and 2m exposed in shed.

By the way, the only other controls for my central heating system is one motorised valve on the radiator circuit and it too is wired directly into the existing timeclock. There is currently no room stat or cylinder stat on my system.
 
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H05VV-F 3X1

It's the 3x1 which is the size - 1mm²

You don't need to worry about voltage drop.
At 3A you're good for over 50 metres.

Are you sure you don't have a tank stat?
It must have some means of switching off when hot enough.

Edit - With 3A in my mind I used 3% instead of 5% so even more than 50m but it doesn't matter.
 
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Hi EFLImpudence
Thanks for your reply.
I thought that the HO5VV-F part stood for the cable size ie. 0.5mm, but your telling me that its actually the 3x1 which is the cable size.
Is there any way to double check the cable size ie by measuring/checking the physical size/diameter of the cable, no offence I just want to double check?

Regarding stats, no , there are absolutely no stats what so ever on the heating system, except for the high limit boiler stat. When the boiler switches on, it runs constantly until I turn it off or until the boiler stat cuts out.
This is the reason why I want to relocate the timeclock, as I want to upgrade the system by adding another motorised valve, proper wiring centre, room stat and cylinder stat as per the sundial 'S Plan'.
Which raises another question, I am going to wire all the new stats, timeclock, motorised valves in 5-core, 0.75mm heat resist flex, again is there a maximum distance the 0.75mm cable to each of these items can be?
 
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As far as I can tell the ratting you quote matches a range of cables from 0.5mm to 6mm see here.
As to size of cable it will depend on current draw. At 1mm the volt drop is 44 mV/A/m and at 16mm it's 2.8 mV/A/m and we can only work it out once we know the amps drawn and size. It is considered that 5% volt drop is maximum acceptable.
Having said that where a item like a central heating boiler is powered one would normally look at the manufactures plate to see what it's limits are.
As well as volt drop we also look at the protection. We would expect should a short circuit accrue then it will auto disconnect (fuse will blow) and for this to happen we measure the impedance (AC resistance) to ensure under fault conditions the fuse will blow.
A 3A fuse needs a resistance (impedance) of less than 16.4 ohms to blow in the required time. As electricians we have meters able to direct read this so it's just a case of connect up and press test button. Without these meters it gets rather involved with calculations.
To control central heating we will normally follow one of the Honeywell plans which again can be complex with a timer or thermostat controlling a valve with in turn controls the boiler.
Although the information given rings alarm bells as likely it does no comply it does not as related break any rules and it is impossible to answer your questions with so little information.
 
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Is there any way to double check the cable size ie by measuring/checking the physical size/diameter of the cable, no offence I just want to double check?
Look on this page
http://www.yegpowercords.co.uk/uk_powercords.php
You will see that different sizes are all H05W-F
The cable size is given as 3(cores) x the actual size.

The only way for you to find out is to measure each strand with a micrometer and do the maths. Compare it to 1mm² T+E.

I did have a page with the wire codes i.e. what the H 05 W & F mean but I cant find it. Try Google.

I am going to wire all the new stats, timeclock, motorised valves in 5-core, 0.75mm heat resist flex, again is there a maximum distance the 0.75mm cable to each of these items can be?
There is a maximum distance but you do not need to worry about it in a 'normal' house with such a small current. That's what the cable is made for.
 
P

Paul_C

I thought that the HO5VV-F part stood for the cable size ie. 0.5mm, but your telling me that its actually the 3x1 which is the cable size.

The "05" part refers to the voltage rating, in this case a maximum of 300V to earth and 500V between conductors. The whole breakdown for your flex:

H = Harmonized coding system
05 = 300/500V rating
V = PVC insulation
V = PVC sheath
F = Finely stranded
3x1 = 3 conductors of 1 sq. mm each
 
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Cable size is measured is cross sectional area the easy way is to try and slide a orange, red, blue, or yellow crimp which are 1mm, 1.5mm, 2.5mm and 6mm over the cable. Since stranded hard to measure and calculate but of course you can measure one strand and multiply. Missed the 3X1 reference which as said likely means 3 times 1mm.

To add more control does seem a good plan. Using radiator thermostatic valves will mean once room is hot then hot water will be returned which will turn off the boiler with it's built in output thermostat.

However there will be some cycling problems. Although gas fired I have same problem and have selected to use radiator thermostatic valves upstairs but a thermostat/timer down stairs. Today one can buy a combined thermostat and timer so it changes temperature rather than just on/off.

I use one of these which as long as you change batteries once a year works well.

However my water is a separate boiler so no need for any plans. The motorised valve often has a micro switch which means it rather than the thermostat controls the boiler.

These micro switches are often more complex than the simple diagram shows and have caused me some problems in the past. All I can say is good luck.
 
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You must use the valve's auxiliary switch to turn the boiler on. This ensures that the valve is fully open before the boiler fires.

More importantly, if there is a fault that stops the valve from opening, the boiler cannot fire (as it would if driven from the timer/thermostat).
 
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You must use the valve's auxiliary switch to turn the boiler on. This ensures that the valve is fully open before the boiler fires.
Some boilers have only local control from a flow switch in the pipe work of the boiler, they only fire if there is power AND the water is flowing.
 
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Look on this page
http://www.yegpowercords.co.uk/uk_powercords.php[/QUOTE]
Alternatively look in our very own Wiki.


I did have a page with the wire codes i.e. what the H 05 W & F mean but I cant find it. Try Google.
Alternatively try our very own Wiki.


The whole breakdown for your flex:

H = Harmonized coding system
05 = 300/500V rating
V = PVC insulation
V = PVC sheath
F = Finely stranded
3x1 = 3 conductors of 1 sq. mm each
Alternatively refer the OP to our very own Wiki.


I did have a page with the wire codes i.e. what the H 05 W & F mean but I cant find it. Try Google.

http://www.eland.co.uk/cable-genius/1/an-introduction-to-harmonised-cables.html[/QUOTE]
Alternatively refer EFLI to our very own Wiki.
 
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Alternatively look in our very own Wiki.
Alternatively try our very own Wiki.
Alternatively refer the OP to our very own Wiki.
Alternatively refer EFLI to our very own Wiki.
This really is a serious point, so hopefully you'll take it seriously ... I agree with you totally that it is silly for people to repeatedly post identical or very similar material when they could so easily refer people to the wiki (and create new wiki entries for this purpose when they saw the need).

Without wanting to repeat any of the discussion about it, we know that, for several years, you have been advising people not to undertake electrical work unless/until they have learned enough and acquired the necessary skills to be 'competent', and you have an extensive list of suggested reading for them. I wonder therefore, why you have not done as you preach and put all that into a wiki entry, so that you can simply refer people to it, rather than littering the forum with so many, so similar, posts?

Kind Regards, John.
 

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