C/H supply - spurred or dedicated cct?

[Carter]

OK then, long story short; relative has had her old (housing assoc prop) back boiler removed and a new combi installed. The plumbers left the combi's flex temporarily dogged into a plug top and plugged into a socket outlet over the worktop with the assurance that the sparks would be along the next day to make the final connection. I thought I'd show my face when they pitched up and was relieved to find them attempting to pull what I assumed was to be a new circuit through the over-packed mini trunkings and back to the existing C/H mcb in the C/U. I returned at day's end to find all working as per and Carter's aunt more than happy with it.

I then got a late night call from her talling me that all the sockets were tripping out, after running her through a few basic checks it seemed like the Cent Htg breaker was taking no part in proceedings at all???

Next morning confirmed that they hadn't run a seperate circuit at all and their switched FCU was in fact spurred off the washing machine spur which sits on the kitchen ring cct. Carter's sainted aunty then informed me that "...yes they were struggling to get one of their cables through the 'ole, I think they gave up in the end."

hmmmm. that'll explain that then.

So a call to their clerk of works ensued followed by him attending and I quizzed him along the lines of "so why didn't you pull a seperate cicuit? What about cumulative earth leakages? and more importantly if a fault develops with the ring circuit then she'll lose all heating and vice versa?"
A few days later following his consultation with their engineer he came back proffering...

"...that circley drawing at the back of that red book you showed me."

He was referring of course to the illustration at Appendix 15 as justification for the validity of the circuit arrangement. He also offered the fact that...

...we've done over 4oo of these so far; all the same way...

as if this was going to impress or somehow nullify the existence of BS 7671 sec. 314 completely.

So gents, where does this practice (of spurring a central heating supply off a ring circuit) sit in relation to sec. 314 Division of Installation? Just can't see how it satisfies the requirements here?

 

[Spudnik]

Technically, there is nothing wrong with a switched spur fused at 3A for CH.

 

[SirKit Breaker]

Jason is right, but if at all practical it is best practice to run a seperate circuit for the boiler for the reasons you state, but sometimes it is just not practical to do it.
I have even seen boilers tapped into the lighting circuit, not ideal but not strictly wrong either as far as i am aware.

Cheers...Howard

 

[telectrix]

as long as it's not an electric boiler!!!!

 

[SirKit Breaker]

as long as it's not an electric boiler!!!!

Do you mind that is my wife you are talking about

 

[paturback]

Imo dont think its best practice but technically ok depending on the load,is the washing machine spur fused down?

 

[Carter]

Technically, there is nothing wrong with a switched spur fused at 3A for CH.

But that's my point Jason; sec.314 states...

Every installation SHALL be divided into circuits as necessary, to:

(i) avoid hazards and minimise inconvenience in the event of a fault...

Fails here absolutely in my view, in summer it would undoubtedly range from an inconvenience to the single 'man about town' to a massive and life disrupting PITA for a family with four kids or something. For the housebound elderly in the week-long freezing grip of a British January the 'incident' curve gets rapidly steeper and the consequences a lot more serious. how many suffer an accelerated demise every year through just 'mild' hypothermia? Thousands?

(ii) facilitate safe inspection, testing and maintenance...

Fair enough so long as the spark in attendance actually removes the fuse from the spur unit to ENSURE safe isolation rather than just flick it off. At this point we're back to dobs of red tape over the switch!

(iii) to take account of danger that may arise from the failure of a single circuit...

...see (i) and (ii) above...

(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents...

Well it certainly failed on this one, cured by buying a replacement kettle! And let's remember that first sentence of 314, the operative word here is "SHALL" be divided into circuits... not "should" be which is of course merely advisory in intent. That being the case I still can't see how a principal circuit such as a dwelling's whole heating and hot water supply is allowed to be deemed merely a sub-circuit. ??? It's a pretty fundamental one if you ask me. As a side note to this; I ramped the kitchen ring RCBO and found that it tripped repeatably and consistently at 19mA!

Jason is right, but if at all practical it is best practice to run a seperate circuit for the boiler for the reasons you state, but sometimes it is just not practical to do it.

That's hit the nail on the head Sirkit. In this case it was entirely practical, there was the newly vacated breaker that controlled the old rig and even a spare way adjacent! The only problem was the fact that their specifying engineer failed to pick up on the fact that the existing MT runs in these properties might/would be packed tight and omitted the requirement for bigger containment from his tender. Either that or their subbies couldn't be @rsed to strip and fit a bit of MT4.
Once again; from the wording of 314 I'd have to say that the requirement is for something beyond a matter of 'best practice'. It's a requirement.

I have even seen boilers tapped into the lighting circuit, ...

Eek!

...not ideal but not strictly wrong either as far as i am aware.

Apart from the non-compliance with the spirit if not the word of that pesky sec.314

Cheers...Howard

And thank you for the input Howard.

 

[Carter]

as long as it's not an electric boiler!!!!

Well this is the other point that gripped my grapes on this one, along with the back boiler they stripped out the immersion tank which meant that where once the property had the ability to independantly store a quantity of hot water it now has none and she's reliant on a single instantaneous/on demand (?) arrangement. If it goes down she's down to kettles or in the worst case, pans on hobs, which is even more dangerous. At the moment she's OK, hale and hearty but things inevitably change in that regard and the consequences of her dumping pans of boiling water... Me no likey!

 

[Carter]

Imo dont think its best practice but technically ok depending on the load,is the washing machine spur fused down?

Nah it's wired into the ring and controls an unswitched socket under the worktop into which the washing machine is plugged. Their spark took a pair (2.5mm sq) and a CPC from the feed terminals of that spur to another one he'd fitted immediately below for the C/Htg.

 

[Spudnik]

I see what you are saying, but sec 314 (i) is in regards to one RCD protecting a whole installation for eg.

Which is why we use dual CU's to spread the circuits.