Merlin gerin type b rcbo

[KNIPEX]

I installed a ringmain in an office flush in the wall in pvc conduit, tested the circuit and its over the max zs allowed for a type c 32a rcbo.

no prob i thought i will get a type b, after searching i cant get one, spoke to merlin gerin they said they dont make them, i said what if my zs is over max allowed for type c to table 41.3,

they said the max allowed is stated in table 41.5 which is 1667 i said no that refers to TT systems not PME system, they said no you can use that table for all zs reading, i then tried to explain about the other tables ie 41.3 and they said to ignore them and use table 41.5 again i said this refers to tt systems it even states about earth rods below the table.

basically that was the end of the conversation and told them i was going to speak to the niceic about it, which im yet to do as i couldnt get through on friday.

anyone else had these problems, with merlin gerin and what are your thoughts on the above.

thanks.

 

[Des 56]

Because of the low value of Zs of Tn systems,the Rcds electronics, can become much more prone to failure than it could with the lower fault current of a TT system
Zs of a TN system should be within limits for this reason if nothing else
A high fault current with an increased rcd operating failure and a Zs over limits makes it less safe than a TT system with reliance on an RCD

 

[Spudnik]

I do agree with Des, however, there seems to be this unwritten reg that basically says Zs can be up to 1667 ohms on a 30mA RCD, regardless of supply type.

I think it depends a little on how much over your result is.

 

[Sintra]

531.3.1 In a TN system, where, for certain equipment in a certain part of the installation, the requirement of reg 411.4.5 cannot be satisfied, that part of the installation may be protected by an RCD.

 

[IQ Electrical]

I don't agree with Des but the only 'evidence' that I can produce is taken from the ECA Guide to the 17th Edition Wiring Regulations:-

"A common source of misunderstanding is that of either specifying or measuring values of ELI where the circuit also has an RCD fitted. ELI measurement under these circumstances is a futile excercise.

The circuit will have been checked for continuity, and this is all that is needed together with, of course, functional checks of the RCD.
This criterion satisfies requirements for automatic disconnection.

The subject is somewhat confused by the inclusion of RCBO's in table 41.3 and for clarification, circuits with RCBO's do not need to meet the specified ELI values."

I expect the NICEIC helpline will confirm this.

 

[malcolmsanford]

This is another BRB grey area. If you look at reg 411.4.9 which is for a TN system it clearly states that a BS 61009-1 when used on a circuit not exceeding 32amp, is not a delayed type, that it will disconnect in time, then the EFLI can be taked from table 41.5 and for a 30mA is 1667.

The Table 41.3 gives figures when the overcurrent 'part' of the RCBO is being used to against fault protection. In reality, the RCD 'part' operates and, as, the 50 Volt equation 1666 x 0.03 = 49.98 volts 'takes over' and provides protection. 1666 ohms is correct for a 30 mA device.

Merin Gerin were correct.

 

[davelerave]

merlin guerin 32amp B type rcbos


pretty sure i fitted a few recently

 

[KNIPEX]

keep the replies coming guys, links please dave so i can buy them

 

[m25maintenance]

mk make rcbo to fit mg boards i bought a 32 and 40 b type a few days ago

 

[davelerave]

http://www.global-download.schneider-electric.com/852575A6007E5FD3/all/7B047EBD608F28B38525770B005A169D/$File/91943e%20%28web%29.pdf

are these the ones - type AC ,curve B

schneider and merlin are the same i think?

they're the ones i fitted anyhow

 

[Deleted member 9648]

Because of the low value of Zs of Tn systems,the Rcds electronics, can become much more prone to failure than it could with the lower fault current of a TT system
Zs of a TN system should be within limits for this reason if nothing else
A high fault current with an increased rcd operating failure and a Zs over limits makes it less safe than a TT system with reliance on an RCD

Where is the unreliability of an RCBO on a TN system actually stated in an official source? ,I've never come across any such thing.
It strikes me that if this is really the case they are not fit for the purpose.

 

[KNIPEX]

mmm thats an rcd dave, not rcbo it takes up 2 ways in the board aswell and room i just havnt got mate.

dont think they will go with diff make rcbo in a mg board mate but thanks for the tip.

 

[davelerave]

mmm thats an rcd dave, not rcbo it takes up 2 ways in the board aswell and room i just havnt got mate.

dont think they will go with diff make rcbo in a mg board mate but thanks for the tip.

they're actually rcbos - b and c curve if you scroll down the previous link to 19618
Schneider Electric eCatalogue

they're the same make-mg have become schneider
http://www.schneider-electric.com.eg/documents/company/brand-migration/migration_flyer_english.pdf

i've fitted loads of mg b type rcbo -dont use the solid -neutral afraid

 

[KNIPEX]

erm they still seem to take up two ways in the db from the picture though which i havent got capacity for.

 

[davelerave]

ya- i got ya

i wouldn't be depending on rcds for ADS on a L-E short-circuit for Tn -that's my opinion anyhow
i would prefer to meet the disconnection time for the mcb


don't think the separate make is a big deal really-assuming the BC is right-it's manufacturers hype afaik