RCD OVERLOAD

[sparkiedave]

Was called to a job the other day, MK sentry board (RCCB takes up 4 ways), shower switch had burnt contacts from loose connection as normal, noticed at the board that there were a lot of RCCB's and not many breakers, had a closer look, 2 ring mains, 1 cooker circuit and 1 shower circuit, all wired into their own RCCB, with no breaker, typed up a letter and took it straight to landlords, other stuff noted, 25mm tails, 63 amp isolator, 6mm Main Bond, just couldn't believe that someone would do somethin like that

 

[ricicle]

6mm² is acceptable as a main bond under certain circumstances. Whats wrong with 25mm² tails on 63A ?

 

[electronicsuk]

are you sure these RCDs were not in fact RCBOs?

 

[electronicsuk]

Are you sure these RCDs were not in fact RCBOs?

EDIT: Ok, seems that I like the sound of my own voice...!

 

[securespark]

Look carefully at the devices. What BS or EN numbers had they?

BS 3871 or EN 60898 for MCB's.

BS 4293 or EN 61008 for RCD's

EN61009 for RCBO's.

 

[sparkiedave]

main bond size should be 10mm if neutral meter tail is 25mm, potentially 100amp demand, because we're not supposed to examine the main fuse to ascertain it's size, we have to assume that it's not 60amp therefore a 63amp isolator is not up to the job, RCCB's are definately not RCBO's, old LN5780,
30mA, 2 pole BS4293 so there's no overload/short circuit protection

 

[electronicsuk]

main bond size should be 10mm if neutral meter tail is 25mm, potentially 100amp demand, because we're not supposed to examine the main fuse to ascertain it's size, we have to assume that it's not 60amp therefore a 63amp isolator is not up to the job, RCCB's are definately not RCBO's, old LN5780,
30mA, 2 pole BS4293 so there's no overload/short circuit protection

Even with 25mm tails, 10mm bonds may be permissable on a TT system.

FWIW, would love to see a picture of the CU - finding it hard to imagine the logistics of fitting RCDs in place of MCBs, as you'd still have to deal with the neutrals.

 

[sparkiedave]

It's TNS, they've sawn the stubs off the bus bar where the neutrals were, then brought a neutral down from the neutral bar to feed in from below, someone had put a lot of thought into getting it wrong, in fact, thinking even further, the output should be at the bottom, so they wouldn't even work as an RCD! Think I'm gonna ring the landlord tomorrow!!

 

[Spark123]

Don't think it matters a lot of the time which way round an RCD is connected, as long as both the feed is at one end and supply at the other.
Some new ones don't like it as much tho. You'd have to check the manufacturers instructions.

Not advocating what has been done tho - it is wrong to only have RCD protection and no overcurrent protection.

 

[ericmark]

On commercial I have seen this many times. Someone reads 63A on unit and jumps to conclusion it will trip at 63A. It has been happening for years the old loadmaster MCB also had an isolator rated at 100A and I have seen these fitted instead of a MCB.
Not the first and I expect not the last.