Splitting circuits accross RCDs

[sellers]

Over the past 2 days I've changed a CU, installed a V Phase along with a fair few other bits at a property.

To cut a long story short, customer supplied materials and the way in which I could wire the V Phase was to supply 1 of the RCD's,

So on one side we have the cooker and hob, and then the other side kitchen sockets, house sockets and lighting which are supplied via the V Phase

Sound fair? Or would you say I haven't split the circuits well enough?

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V Phase is fed from the non RCD 50Amp MCB then out to the right hand RCD. Interestingly, the incoming voltage yesterday was 248 and outgoing was 220, then today it was around 240 compared with 212. TBH I thought it would stabalise the volage at a fixed value.

 

[Manator]

I have never used these V phase things but I thought that they were wired prior to the CU so that the supply was regulated before connection to the CU. Forgive my ignorance.

 

[NozSpark]

I know for a fact that the NIC wouldn't like you having the whole house sockets on the same RCD as the lights...

Division of circuits to minimise inconvenience in the event of a fault springs to mind!

(can't remember the reg no. But those words are still ringing in my ears)

I thought that the vphase gave a stabilised 220v output??

Doesn't look too difficult to install TBH

 

[sellers]

That was my thinking, but they have to take their feed from an MCB. The instructions stated a 50amp, the terminals would just about take the 10mm. Unsure if they do other sized V-phases, I would imagine one wired into the tails would be a lot better with maybe a 100amp switch fuse prior

 

[steptoe]

I would say putting all the sockets and lights on one RCD is not compliant with the 'so as not to cause inconvenience' bit of the regs.

I usually put house sockets and cooker on one side, then kitchen sockets and lights on t'other, that way table lamps can be used if one RCD goes, or the lights will work if other RCD goes.

just my tuppence.

EDIT - too slow

 

[NozSpark]

I thought that they were only good for resistive loads????

 

[ian932]

Have you adjusted your Zs max to allow for a new nominal of 220v as the tables in the books are based on a nominal of 230v

 

[Doc Hudson]

On one of the old threads about V-Phase it was pointed out that you cannot use them for high power items, cookers & showers etc, which is why it cannot go before the CU. I would have thought you should have used RCBO's for sockets & lights. If that one RCD trips then all power & light is going to disappear.

Doc H.

---------- Post Auto-Merged at 09:38 ---------- Previous post was made at 09:36 ----------

But there again if the 50A MCB trips most of the property power goes anyway.

Doc H.

 

[sellers]

Rcbo's would be favourable, regs state ' every installation shall be divided into circuits as necessary to avoid hazards and minimize inconvenience in the event of a fault'

I understand it is not the best way to split the circuits but it's the best for the v phase operation and does minimise inconvenience to some extent, will be taking my NIC AC inspector to this job to have a look.

 

[NozSpark]

Rcbo's would be favourable, regs state ' every installation shall be divided into circuits as necessary to avoid hazards and minimize inconvenience in the event of a fault' I understand it is not the best way to split the circuits but it's the best for the v phase operation and does minimise inconvenience to some extent, will be taking my NIC AC inspector to this job to have a look.

then expect him to comment on it!

Mine did the other week and that was only looking at the paperwork! Had a twin RCD board the u/s lights, d/s sockets one RCD and d/s lights, u/s sockets & kitchen skts on other.... There were a few other circuits, but it did get commented on

!!!!

 

[ian932]

Ian are the tables in BS 7671 not to a nominal 230 +10% -6%, so a device supplying a constant 220 V would still fall within the nominal voltage range.

Nope see BRB 411.4.7, i.e Uo / 5xIn for a bs60898 type B, so the Vphase would make it say for a 32a mcb 220/5x32 = 1.375ohms

 

[ian932]

Hi Ian411.4.7 states Uo of 230V

Definitions, Voltage, nominal, page 31

Also note - The actual voltage may differ from the nominal value by a quantity within normal tolerances.

Where does that say you can apply the +/- range to the table 41.2, 41.3 & 41.4, it doesn

 

[nsbs]

http://www.ecobuild.co.uk/var/uploads/exhibitor/2081/18o1kirh0l.pdf

try this, it mentions how to install and what it can be used on.

ian

 

[NozSpark]

OK then,,, what would you do if your supply voltage just happened to be 220v???

All the max Zs tables are calculated on 230v!!!!!

And I'm talking NO vphase here.

 

[ian932]

OK then,,, what would you do if your supply voltage just happened to be 220v???All the max Zs tables are calculated on 230v!!!!!

And I'm talking NO vphase here.

Noz are you asking because you don't know the answer?

 

[NozSpark]

Noz are you asking because you don't know the answer?

:red card

 

[PC Electrics]

It's rather difficult to explain in just words - if we had a blackboard and could write stuff down and draw curves and diagrams I could explain it better, but here it is:

The nominal figures used in 7671 are there for our benefit. They allow us to design our circuits to fixed parameters, keeping the engineering and the maths simple.

The design and engineering of MCBs, however, includes for the allowable nominal tolerances in the supply voltage and allowable voltage drop within an installation. MCBs are designed and engineered to work at the lower extremes of these tolerances without the need for us to take this into account in the basic design of our circuits.

In other words, the engineering has already been done for us.

 

[ian932]

:red card

I have 2 balls neither are crystal!!, I asked because your post could have been interpreted in several way's and also it was unclear who you were directing the question at if in fact you were, don't really know why you had to react like that to a genuine question.

Surely it

 

[wozz]

I really dont get the minimize inconvenience bit of the regulation. A dual RCD board i dont really consider to minimize inconvenience , all RCBOs would but only if the installation was divided up enough in the first place. I realise the regs cant be specific but this hardly points us in the correct direction, dual RCD board become available around the time of the 17th edition and become known as 17th edition boards so everyone fits them.

Am i the only one that thinks like this?

 

[Sidewinder]

OK,

Both sides of this "argument" have points.

The nominal voltages are there for the designs to be based upon.

The VPhase device does not hold a constant voltage.

Thus it modifies the nominal voltage values that are delivered to the install.

Thus by rights you "SHOULD" recalculate the required impedances.

Will this make a difference?

That is the designers shout.

IF you are using these then you should get confirmation in writing from the manufacturer.

Especially of you have borderline impedance values.

Oh, & I don't personally consider an RCD a suitable cop out for poor EFLI design.

Though perhaps the scams & the brb disagree, but I never got on that commitee!