Todays work

[NozSpark]

You TTing it M??

 

[M107]

You TTing it M??

Yep

And this will be used on my assessment in June, so we shall see what the assessor makes of single pole RCBO's on a TT.

 

[Sidewinder]

I have a TT install that has some intermittent tripping on an old single RCD board.

Client is willing (would prefer) to update to a fully RCBO board, but single poles on a TT.

I am still doing my research.

 

[Graham Lister]

Why would an RCBO not be suitable for a tt when MCBs are? The main switch meets the double pole requirement.

 

[steptoe]

Im 99% certain TT requires ALL LIVE conductors to disconnect,

there is a reg IIRC that specifically states this,

tho if Im wrong it wont be the first time.

Graham, you could use DP RCBOs, but not widely available in the UK,

another Q for my list next week.

 

[Sidewinder]

Graham,

The main switch does not meet the double pole requirement for ADS.

 

[Andy™]

dual split and your sorted. or 100mA TD incomer

 

[steptoe]

[quote name='Andy

 

[RB2004]

correct me if im wrong, but the reason why Single pole MCB are acceptable, but not single pole RCBO are because when an MCB is used in conjunction with an RCD which is double pole, if the RCD trips it disconnects the live via the mcb and the neutral, which in effect disconnects in a similar way as a double pole RCBO.

Main switch doesnt meet requirements as it is a means of isolation rather than automatic disconnection in the event of a fault.

 

[steptoe]

correct me if im wrong, but the reason why Single pole MCB are acceptable, but not single pole RCBO are because when an MCB is used in conjunction with an RCD which is double pole, if the RCD trips it disconnects the liveline via the mcb and the neutral(which is also live), which in effect disconnects in a similar way as a double pole RCBO.Main switch doesnt meet requirements as it is a means of isolation rather than automatic disconnection in the event of a fault.

more or less.

 

[a1]

Has anyone put this in an e-mail to their Scheme Provider?

 

[a1]

I did. And here is the first reply, Thanks to ECA:

Single pole devices such as circuit breakers and RCBO

 

[steptoe]

532.1 (i) - condition 2

 

[M107]

I didnt email but I did phone the tech line, I got the same reply as admin...

So sounds like two providers are on the same lines.

Now I shall give my reasoning for not using DP rcbo's (remember it's all down to individual interpretation of the regs, but I am open to any criticisms & learnings).

The DP main switch satisfies the requirement of 537.2.1.1 To isolate every circuit from each of the live supply conductors.

The single pole rcbo's also meet the requirements of 411.3.2.1 by dissconnection of the line conductor under fault conditions & 411.5.2 (i)

 

[Sidewinder]

Quick summary of all the relevant reg numbers anyone?

 

[Graham Lister]

See M107s post for reg numbers and sound reasoning. Lets not overcomplicate things with double pole rcbos on each circuit.

 

[steptoe]

so you want to cause inconvenience by switching off the whole installation to change a light switch?

doesnt do it for me,

maintenance anyone? surely that requires DP isolation that shouldnt require turning off the whole installation.

 

[a1]

And here is the reply from NICEIC:

Thank you for your email. We are unable to provide email responses to enquiries of this nature from businesses that are not registered with NICEIC. Please contact our technical helpline via telephone on 0870 013 0391.

If your business is registered with NICEIC, you can access our technical experts for email enquiries via the secure area of our website.



Please note, response times from our technical helpline may vary.

Should you require any further support or advice please contact our customer service team on 0870 013 0382

Kind Regards

 

[Andy™]

And here is the reply from NICEIC:

NIC.... about as useful as a cholcolate fire guard....

 

[M107]

Ok here we go (why am I doing this..... feels like I'm painting a target on my forehead :^O ) this could be a long one so stay awake....Hopefuly this will point some new peeps to the industry in a direction that they can then decide & interpret the regs for themselves...

So a Domestic TT system first thing lets take a look at

411.5

411.5.2 One or more of the following types of protective device shall be used, the former being preferred:

(i) An RCD

(ii) An overcurrent protective device

Now my take on that is an RCBO fits the bill to cover both (i) & (ii). no mention of double pole requirements, so again I would be happy to use either single or double pole devices.

Next is 537.1

This section provides requirements for:

(i) non-automatic local and remote isolation and switching measures for the prevention or removal of dangers associated with electrical installations or electrically-powered equipment and machines, and

(ii) functional switching and control.

So here I am reading the regulation as, the mainswitch can give the provention & removal of dangers by means of isolating both line & neutral of the supply. But no mention of single or double pole requirements (for that we need to read on)...as a side note for those at college or just starting out Table 53.2 gives excelent guidance of switches, their BS numbers & a yes/no guide to their uses for isolation,emergency switching & functional switching.

537.1.4 A main linked switch or linked circuit-breaker shall be provided as near as practicable to the origin of every installation as a means of switching the supply on load & as a means of isolation.

A mainswitch intended for operation by ordinary persons, e.g. of a household or similar installation, shall interrupt both live conductors of a single-phase supply

Well here I take the BS EN60947-3 main switch meets the requirements for Isolation as it does indeed interrupt both Line & Neutral.

So far this is the only requirement for double pole switching, but only for isolation & not for automatic dissconnection under fault conditions. No mention of individual circuits needing to be isolated by means of DP devices as opposed to the whole installation.

537.2

Isolation is a function intended to make dead for reasons of safety all OR a discreat section of the electrical installation by seperating the electrical installation or section from every source of electrical energy.

The magic word here is OR, for a little word it can make a big change in your final installation choices.

Anyway as you see it doesnt say you have to isolate individual circuits, you can isolate the whole installation.

537.2.1.1

Every circuit shall be capable of being isolated from each of the live supply conductors. In a tn-s or tnc-s system, it is not nessesary to isolate or switch the neutral conductor where it is regarded as being reliably connected to earth by a suitably low impedance.

Provision may be made for isolation of a group of circuits by a common means, if the service conditions allow this.

This I feel is the one that people decide gives rise to the requirement of DP isolation of individual circuits...

But reading the first sentence it says "EVERY circuit" & not "every INDIVIDUAL circuit", so again I would say the main switch meets the criteria of this regulation.

411.3.2 Automatic disconnection in case of a fault:

411.3.2.1Except as provided by regulations 411.3.2.5 and 411.3.2.6 a protective device shall automatically interrupt the supply to the line conductor of a circuit or equipment in the event of a fault of negligible impedance between the line conductor & an exposed conductive part or a protective conductor in the circuit or equipment within the dissconnection time required by regulation 411.3.2.2, 411.3.2.3 or 411.3.2.4

Again no mention of supply types or the requirement to switch the neutral under fault conditions... only the line needs to be interrupted.

Remember you as the electrician need to look at the property type as well as think about the installation....for example a thatched building I would consider DP rcbo's due to rodents, electrical conductors, & the increased risk of roof fires

Having said all that the above doesnt mean you disscount double pole RCBO's as a waste of time & money, they are a regulatory requirement in some installations...for example

Agricultural sites maybe an option to loose single circuits by means of DP rcbo as opposed to the whole installation when an RCD trips (705.422.7)

And the isolation requirements of 705.537.2 point to DP rcbo's as a way of complying.

Well I hope I've not made a numpty of myself :^O :Blushing

Seriously I do hope this has given a nudge to people to take a look at their BRB & make a decision for themselves..............Now ladies gentlemen I shall put on the tin hat & take cover. :Salute