Upgrading old MK Sentry installation

[AAAMUSEMENTS]

My Sister has an old but good condition metal MK Sentry CU, apart from sorting out some of the wiring and changing some MCBs to the correct ratings it is fine and I would rather not have it changed.

There are some RCBOs but no overall RCD protection and no space for it. Would it be acceptable to have an ELCB in the incoming supply, to protect the system?

If so, what rating?

There will be, once the wiring is sorted, Circa:

1 x cooker 32Amp

1 x immersion 16Amp

1 x garage/outdoor 16 Amp

Probably:

2 x 32 Amp power ring

2 x 5 Amp lighting ring

The new shower is going on a separate new CU on it's own tails.

Thanks in advance.

 

[Lee321]

yes a rcd could be fitted to the incomer however the potential for nuisance tripping is increased

 

[fletchflash]

its not a good idea to have a 30mA RCD supplying 30ma rcbo's.

Also this would not comply with 17th edition as there is no RCD discrimination, a nuisance trip from a kitchen circuit would knock everything off including lights.

Which circuits are RCBO protected?

It wouyld be better to fit any other circuits which require RCD protection with RCBO's.

Why not put the shower in the existing CU if theres space?

 

[sparkytim]

Often found its just cheaper to change the lot for a duel RCD board.

 

[AAAMUSEMENTS]

There isn't space in the existing CU for the shower. The old shower feed, long disused, had a separate, ancient switch with plug in fuse. This switch had been wired with meter tails into the main switch in the other CU. To make the tails fit in the switch they had taken out about half the strands in each...



As the meter tails right back to the meter need replacing (undersized) it made sense at the time to put 2 new pairs of tails through and use a new CU just for the shower.

RCBOs may well be the way to go, not really familiar with them to be honest, I assume that as long as all the circuits are on RCBOs then there is no need at all for an RCD? Can lighting rings still just go on an MCB? Would this setup satisfy 17th Edition?

RCBOs certainly make sense as the state of the wiring throughout the house, although generally very sound, is a little sketchy in places.

However the correct RCBOs needed for this old CU may be more difficult to track down... to add to the mystery on one of them the label has fallen off so I have no idea what rating it is...

?:|

 

[Zeespark]

What about installing a Henley block and then a small 1/2 way CU with RCBO's amuse?

AndyGuinness

 

[AAAMUSEMENTS]

What about installing a Henley block and then a small 1/2 way CU with RCBO's amuse?AndyGuinness

Sorry Andy I am confused!

There will be a Henley in the meter cupboard, with two pairs of tails going into the house; one for the new dedicated shower CU, and one for the main existing CU, which will probably have to be at least 9 way, assuming RCBOs are used.

 

[Zeespark]

I may have gotten the wrong end of the stick..........as per blinking usualWet Fish. Apologies if I have confused you.

AndyGuinness

 

[fletchflash]

generally lighting circuits need to be RCD protected too, unless there deeper than 50mm in a wall, or surface mounted.

sounds like its probly a type 1 board which wouild mean rcbo's are a bit tricky to find.

Sounds like the whole installation needs a good testing really, and after doing that, messing about with a new shower CU, as tim said, probly would be better to just replace the lot with a 17th ed CU. Would be cheaper, and not much more work. Much neater to have everything combined in one fuse board too

 

[ianmacd]

My local John Cribbs are doing 10 and 15 way dual rcd wylex boards with 8 or 10 (depending on if its 10 or 15 way) MCB's for about 50-60 quid. Thats probably 2-3 rcbo's worth.

 

[AAAMUSEMENTS]

I am certainly coming round to the idea of replacing the Sentry, but the new shower CU is staying as it has already been bought.

That's a good price - but is VAT included in that? We don't have any John Cribbs up here unfortunately.

 

[sparkytim]

Try Denmans they have some pretty good offers on Crabtree 17th Edition bds

 

[AAAMUSEMENTS]

Try Denmans they have some pretty good offers on Crabtree 17th Edition bds

Thanks, still a bit of a trip as the nearest to me looks to be Kings Lynn.

:|

The Sentry is definitely going anyway, it makes no sense at all to spend 90 odd quid on rcbos that would not fit properly anyway. I tried a Wylex in there today and the busbar does not line up, and the cover will not close. Other than that they are a perfect fit!

Least I can get some money back for my sister by flogging the old RCBOs from the Sentry on Ebay... :^O

On a separate note, the Wylex RCBO I was looking at today in Newey and Eyre had an earth fly lead - described as "functional earth". What is the purpose of this? It's a new feature to me and is presumably only there for the purpose of making the test function more realistic?

?:|

 

[sparkytim]

Hi again

Yes most of the newer single pole RCBOs have a functional earth lead which is required for the electronics to function you just connect it to the related circuit way earth terminal

 

[AAAMUSEMENTS]

Just been googling and found a quote from a manufacturer saying that the functional earth is required to provide "loss of neutral" protection.

Now mildly confused!

 

[Lurch]

Just been googling and found a quote from a manufacturer saying that the functional earth is required to provide "loss of neutral" protection. Now mildly confused!

If the incoming neutral goes the potential between N and E will rise from whatever it is (less then a few volts at the most generally) to around 230V. IIRC the Merlin RCBO's tripped if the N-E potential rose to above 50V.

 

[AAAMUSEMENTS]

If the incoming neutral goes the potential between N and E will rise from whatever it is (less then a few volts at the most generally) to around 230V. IIRC the Merlin RCBO's tripped if the N-E potential rose to above 50V.

Right yes I think I understand... this would depend on the earthing method used presumably?

 

[Lurch]

Right yes I think I understand... this would depend on the earthing method used presumably?

Nope.

By incoming neutral I mean on the incoming terminal on the RCBO, not the main incoming neutral from the DNO.

 

[AAAMUSEMENTS]

Nope.By incoming neutral I mean on the incoming terminal on the RCBO, not the main incoming neutral from the DNO.

Right, I think I have got my head around it now... so it would mean there was still protection in the event that the circuit neutral was broken, AND there was a live-earth fault?

 

[Andy™]

Right, I think I have got my head around it now... so it would mean there was still protection in the event that the circuit neutral was broken, AND there was a live-earth fault?

as soon as the neutral fails, RCBO would open. or the L-E fault would cause it to open

either way, itll trip