your thoughts please

[kme]

Scenario:

3 storey property used for bedsits.

Did a PIR last year; customer now wants remedial costs.

There are seven bedsits; each with its own DB - 6A 60898 for lights, and one or two 61009 20A/30mA for S/O.

Each bedsit is fed via a 6mm T+E, buried in the structure, from the ground floor bedsit; containing the HED and front-end DBs. The 6mm subs are fed through 30A 3036s (no RCD protection). Supply is single phase TN-S.

Now - if I used 32A 61009s for sub-main protection; 2 problems occur to me:

1 - the 20A 61009s in the bedsits are redundant.

2 - should an RCBo trip on a sub-main, access would be required to the ground floor bedsit to reset it.

As far as I can see, the only other option is to renew the sub-mains, in either trunking on surface, or SWA (or similar).

Your opinions would be valued guys.

KME

 

[Chr!s]

Hi KME

Firstly, if you use MCBs on your distribution you'll have no Fault discrimination(Short circuit or Earth Fault Current) with upstream MCBS, so best to stick with fuses for distribution.

As you say if you place a 30 Ma RCD on the distribution again you will your discrimination/selectivity.

Have you read the DPC ?

522.6.7.102 Where Regulation 522.6.6101 applies and the installation is not intended to be under the supervision of a

skilled or instructed person, a cable installed in accordance with Regulation 522.6.6101(v), and not complying with

Regulation 522.6.6101(i), (ii), (iii) or (iv), shall be provided with additional protection by means of an RCD having the

characteristics specified in Regulation 415.1.1. An exception is permitted for minor works where the designer is satisfied

that there would be minimal increased risk of damage to the circuit cable due to penetration by screws, nails and the like.

The decision shall be recorded under part 2 of the Minor Works Certificate or the comments section of the Electrical

Installation Certificate.

 

[kme]

Thanks Chris -

I have indeed perused (and submitted my comments on) the DPC; however I would (possibly) have concerns using it as a reference until the amendment is published; as it is still a draft.

Fair point on the fault discrimination mate - I hadn`t designed that far yet; and plonked that into my post "off the cuff" so to speak - but I`d agree that fuses would be better in that scenario.

Now; as regards the RCD situation. If we accept that we cannot use the draft ( I`d look a bit daft if I gave my reasons for not installing an RCD on the sub as a reg which turns out to not be included in the final publication!) as a reason for omitting an RCD, then we either omit it anyway; and note it as a deviation; or, as per earlier post, run surface wiring for the sub-mains.

The 6mm subs had, in a couple of cases, code 3 insulation readings - less than 200K to earth. Further, the lighting circuits (individual bedsits AND communal lighting) are without CPC (although all fittings are class 2 ).

(sorry - food on table - back soon.........)

continued post-food.....

Right. So I think its agreed(?) that utilising a prospective reg isn`t a good idea; I`m heading in the direction of surface trunking for the sub-mains, TBH. Any alternate thoughts or suggestions appreciated



KME

 

[Chr!s]

Well if the insulation reading on the subs are low then you may as well renew the distribution circuits, regardless of the dpc.

---------- AUTO MERGE Post added at 19:25 ---------- Previous post was at 19:22 ----------

Oh just oner otherthing is it defo Tns, eon state only Tncs even though the presentation is that of Tns. Many Dnos heading this way

 

[sprocketflup]

Sorry to butt in fellas - whats DPC stand for please?

 

[m4tty]

Damp Proof Course lol:CWet Fish

 

[Chr!s]

Sorry to butt in fellas - whats DPC stand for please?

draft public comment

 

[Manator]

Its a Draft for Public Comment, and should not be used as this could even now be changed.

Giving it in an answer is like saying charge 20% VAT in December because it is going up in January anyway.

 

[kme]

Sorry to butt in fellas - whats DPC stand for please?

As the guys have said - Draft for Public Comment is the version of the amended regs. that is placed in the public domain for any interested parties to peruse, and make suggestions on. It is then re-hashed, taking into account the comments made, before its release as a general amendment.

KME

 

[safedepth]

Its a Draft for Public Comment, and should not be used as this could even now be changed.Giving it in an answer is like saying charge 20% VAT in December because it is going up in January anyway.

Are you saying I shouldn't have been doing that?

Oops:Blushing:Blushing

 

[Chr!s]

Its a Draft for Public Comment, and should not be used as this could even now be changed.Giving it in an answer is like saying charge 20% VAT in December because it is going up in January anyway

Not really, i spoke to a chap at the iee and most things are done and dusted, though i do take your point.

Well other point is when will he want the work carried out, we all know these things can drag on, so it may be worth considering.

 

[professional]

The proposed exemption from rcd protection is currently being blocked pending further review.

With so many totally untrained individuals working in the electrical industry, such an exemption could be a "kitchen fitter's charter to bodge".

Such an exemption should only be available to those with the training, qualifications and experience to carry out the required risk assessment ....

 

[sprocketflup]

So if its not in the regs yet, surely it shouldnt be adhered to? after all, installs that were put in when the 15th edition was the regs probs didnt take into account the stuff that is now current in the 17th?

Or am I completely off the mark here?

 

[m4tty]

If the certificate is signed to bs7671:2008 then the amendment doesn't come into it.

 

[Sidewinder]

KME,

I "guess" you coded the subs 2 at the PIR?

Did we discuss this when you were doing the PIR?



I don

 

[NozSpark]

I don't quite understand the reasoning behind the remedials i.e. changing the 3036's for 61009's specifically...

I guess the original install was before the BRB and therefore burried cables do not need RCD protection (unless TT)???

Re any subs with 200K ohms IR, I can understand it in these instances, rip out and replace! --- Sidewinder speaks wise words re subs run in communal areas only ---

And the DPC (is that regs now)

 

[Megaohm7]

Are you saying I shouldn't have been doing that?Oops:Blushing:Blushing

It appears you haven't been alone!! :Blushing

 

[SPECIAL LOCATION]

[ No matter what, IF the supply origin is in a discrete residential unit IMHO it cannot comply with the

 

[kme]

Thanks guys - Snakey & trailer boy are thinking as I was.....

Though the moving of the incomer was further than I was considering, TBH (underground incomer in the furthest corner - and I don`t think we spoke about it, though I could well be wrong!)

I believe the best possible solution (not to be confused with the best solution possible!) is to put the subs on the surface in trunking / MI, and leave the fuses where they are.....

For info: each bedsit has a coin meter adjacent to the DB - 61009 for sockets and 60898 for lights...... I had the DNO out to the job, as when I attended to do PIR, the floor below the HED had a mound of pitch on it, and the HED was showing bare conductors - think it`d been getting a tad warm.....

Thanks, one & all

KME

 

[M107]

Protek do a 100A 30mA TD rcd

Part number is T100/30-2TD

EDIT:

Found it

http://www.protekuk.co.uk/portal/default.asp?id=1041〈=ita&sez=prodotti