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.

 

[Carter]

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

Sorry Jason I'm not seeing that anywhere There's no mention of that regulation's specific applicability to RCD protected circuits only. They get their mention at 314.1.(iv) and it fails to comply with that too.

I should have made it clearer in the first post but t's pretty much all of sec.314 that I believe is in conflict with the practice of installing spurred C/H feeds, well all bar 314.3 and even that depends on correct isolation being followed re removal of the cartridge fuse.

So at this point I still say it fails.

 

[Dunc]

If they stripped out an immersion cylinder I would assume that there would now be a redundant immersion supply? Why the hell didn't they just extend the immersion supply to the new boiler seeing as how it would he surplass to requirement and already wired back to the CU.

 

[Des 56]

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?
The installation as a whole would still function with circuits unaffected by the disconnection of others


(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!



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.



Eek!



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



And thank you for the input Howard.

1/ If there was a split rcd board with up and down sockets, the seperate central heating mcb would lose power when a fault on one or the other took out the rcd relevant to the central heating circuit, unless your saying each circuit should have single rcbos as well
A split rcd board minimises inconveniance,it wont remove inconveniance,only a non fault system ( if it were possible) could do that and we would all love one of them

2/
This is more to do with the competence of the person who will work on the system
isolation of the spur can be at the distribution board
3/
Lights throughout go off and granny takes a tumble
Split the circuits up so that gran can plug a lamp in a working socket
The central heating spurred off the ring goes off and danger doesn't appear to be imminent
4/
Are you saying that you had a kettle that uses a functional earth as part of its design
54.3.7 will define these requirements

 

[Carter]

If they stripped out an immersion cylinder I would assume that there would now be a redundant immersion supply? Why the hell didn't they just extend the immersion supply to the new boiler seeing as how it would he surplass to requirement and already wired back to the CU.

That baffled me as well, I probably would have let it slide if they'd tagged onto/extended the existing cable. And like I said there was a spare way in the board anyway! For a few mtrs of MT2 they compromised the whole install. Oh and they've done the same thing 400 odd times previously.

 

[Carter]

1/ If there was a split rcd board with up and down sockets,

Sorry Des should've said; it's a flat, single storey. the board is one of those old Square D jobbies, 8way I think from memory. I'll scribble down the cct arrangement tomorrow but I know there was one 'Spare' breaker and also a ruddy blank plate to insert an 8th breaker if needed! The previous C/H circuit was terminated into a 16A type B not an RCBO.

...the seperate central heating mcb would lose power when a fault on one or the other took out the rcd relevant to the central heating circuit,

Exactly; that's the problem.

...unless your saying each circuit should have single rcbos as well

Well I'm definitely saying that a dwelling's only means of heating and generating hot water deserves its own dedicated circuit to which no extraneous equipment should be added unless it's a functional element of the heating system. It just makes complete sense now that homes no longer have the diversity of solid fuel ranges, gas water heaters, or whatever by which to generate hot water should the supply go down.

A split rcd board minimises inconveniance,it wont remove inconveniance,only a non fault system ( if it were possible) could do that and we would all love one of them

Agree there.

2/
This is more to do with the competence of the person who will work on the system
isolation of the spur can be at the distribution board

Well you can't (or more precisely, positively shouldn't) legislate for the lowest common denomination of idiot that's for sure but handymen do love to whip the covers off stuff and to them Flip the spur = Pilot lamp goes OFF = Safe to proceed. That's a foreseeable scenario, the fuse remains in situ, matey boy is scrambling around on the worktop and a careless knock energises the boiler, Mr. DIY gets a ******.

3/
Lights throughout go off and granny takes a tumble
Split the circuits up so that gran can plug a lamp in a working socket
The central heating spurred off the ring goes off and danger doesn't appear to be imminent

I get the point you're making Des, that imminent danger is more likely in that fault scenario but that doesn't devalue the argument I'm making. It'd be interesting to find some stats on that proverbial; staircase light fails - people sustain serious/fatal injury, montage and see exactly how many times a year that actually happens? 10? 20? maybe, I don't mean cracking your shin on the coffee table. On the other hand I hear some horrendous figures given for proven cases of accelerated death in the elderly caused by mild hypothermia and these are mean averages.

4/
Are you saying that you had a kettle that uses a functional earth as part of its design
54.3.7 will define these requirements

Nope, course not, it was in the preliminary stages of developing a short to earth in its element due to the corrosion and encrustation of scale. If you'd ever tasted the caustic witch's **** that Severn Trent serve up round here you'd understand why. It was contributing its own residual current to that of the washing machine and the boiler and that was enough (I'm guessing) to trip the kitchen ring RCD which as I said had an effective trip current of 19mA upon doing a ramp test on it. My point was that tacking the C/H onto the kitchen ring compromised the integrity and functionality of the installation.

 

[londonlec]

Its perfectly compliant.

I wish someone would come and put a new boiler in for me, for free.

 

[Carter]

Its perfectly compliant.

Well apart from sec.314 that is.

I wish someone would come and put a new boiler in for me, for free.

This is more about a landlord's (social or otherwise) legal obligations and a prudent business policy's rolling maintenance/improvement program and after 35 odd years of tax paying I think she's deserved it.

 

[Spudnik]

I agree Mr C.

I now see that the installer has spurred from an outlet which has a 13A switched spur controlling it.

Well, personally, i cannot see anything wrong, apart from the fact that if the washing machine trips, it will take the CH with it.

This i cant see as being a hazard, electrically.

The key words we have to look at are "shall" and "minimise".

"Shall" is not "must" and "minimise" is not "remove completely"

Not ideal, but not a hazard.

All IMHO.

 

[Carter]

I agree Mr C.

I now see that the installer has spurred from an outlet which has a 13A switched spur controlling it.

Not quite Jason, he hasn't spurred off the washing machine socket outlet, he's spurred off the feed side of the sw/spur that controls it and that feed is part of the kitchen ring.

Well, personally, i cannot see anything wrong, apart from the fact that if the washing machine trips, it will take the CH with it.

...apart from the fact that if the... which kinda makes my point; from a design point of view it shows a disregard for the functionality of the installation and the convenience (and in some circumstances the health) of the end user. It wouldn't pass muster in a commercial or industrial situation would it? In fact if it appeared on one of the engineer's/architect's dis-board schedules or drawings it'd be an open invitation to gather round, point and laugh!

This i cant see as being a hazard, electrically.

Well not an electrical hazard per se granted that it isn't going to immediately explode in a ball of flame and sparks and subject to the various degrees of 'hazard' that can be defined but that's not the issue I'm raising. I'm saying at most that it's a hazard of an electrical nature in as much as it involoves an electrical system and the design thereof.

The key words we have too look at are "shall" and "minimise".

"Shall" is not "must"...

Well actually it is. In any fair reading and particularly in regard to legal interpretations, the word "shall" is imperative, there is no conditional or optional element implied at all. The authors of BS7671 seem to have adopted the American grammatical habit of freely interchanging "will" and "shall" without regard as to whether they are speaking in the first, second or third person.
My Webster's gives its definitions as...

1. plan to, intend to, or expect to: I shall go later.
2. will have to, is determined to, or definitely will: You shall do it. He shall do it.
3. (in laws, directives, etc.) must; is or are obliged to: The meetings of the council shall be public.
4. (used interrogatively in questions, often in invitations): Shall we go?

Which seems pretty unequivocal; number 4 merely demonstrates its use as an interogative not a conditional.

...and "minimise" is not "remove completely"

True, they're completely different objectives and I'm not trying to conflate the two, the only way to completely remove the electrical risk from a dwelling is to pull the service fuse. I contend that (where facility allows) not installing a seperate circuit for a dwelling's heating/hot water system actually does the opposite to minimising inconvenience, it in fact increases the potential for serously inconveniencing the end user so therefore falls foul of 314.

Not ideal, but not a hazard.

All IMHO.

And I know what you're saying but it comes down to two things here, an assessment of the scope of the word 'hazard' and whether sec. 314 applies or not and if not... why not?

Cheers fellahs, your input much appreciated because I've yet to get the definitaive answer on this one.

 

[sparks1234]

Got to say that you really are barking up the wrong tree here. If they had spurred off the switched side of the spur for the W/M that would have been foolish but seems as though they have just spurred off the ring circuit.....Really cant see a problem