converting DB to comply with 17th edition

[leep82]

Been to look at a job and the customers consumer unit is split load 100a 100ma time delay rcd, which is acting as the main switch and 80a 30ma rcd. Upstairs and downstairs lights are protected via the 100ma rcd, with the rest of the installation via the 30ma. Ive been asked to do some work on the upstairs lighting circuit including in the bathroom. What i want to do is remove the 100ma rcd and replace it with a 100a double pole main switch and then install an additional 80a double pole rcd.

Obviously i am going to use up an extra two ways in the board, but there is the capacity to do this. Just wondered if i would need to buy any extra kit, additional bus bar or maybe links to feed the new rcd?

 

[Pete999]

Are you an Electrician, or a DIYer

 

[R G]

Whats the earthing arrangements , why not keep the unit as it is and install RCBOs for the lights ??

 

[Leesparkykent]

Is the 100mA RCD time delayed?

 

[R G]

Is the 100mA RCD time delayed?

He says so...

 

[Leesparkykent]

He says so...

Haha oh yeah...skim reading

 

[leep82]

TT system, doing it the way i suggested would still leave spare ways for any future work whilst already having rcd protection in place. Didnt want to go down the rcbo route and make the board look a mess. In an ideal world i would like everything on an rcbo, just seemed easier and tidier to essentially make the board a dual rcd one

 

[Leesparkykent]

TT system, doing it the way i suggested would still leave spare ways for any future work whilst already having rcd protection in place. Didnt want to go down the rcbo route and make the board look a mess. In an ideal world i would like everything on an rcbo, just seemed easier and tidier to essentially make the board a dual rcd one

What make is the board?

 

[leep82]

Another reason for me wanting to go down this route is that i have a 80a 30ma wylex rcd on my van from a recent strip out, its good as new.

 

[leep82]

Wylex DB

 

[Leesparkykent]

Wylex DB

SPSN RCBO jobs a goodun.

 

[Andy78]

What's the reason for getting rid of the 100mA RCD ?

 

[davesparks]

Another reason for me wanting to go down this route is that i have a 80a 30ma wylex rcd on my van from a recent strip out, its good as new.

So put it at the far end of the CU and route the lx circuit that you are working on through it.

 

[Welchyboy1]

Should really be a double pole rcbo with an upfront 100mA rcd

 

[Leesparkykent]

Should really be a double pole rcbo with an upfront 100mA rcd

How come? What's wrong with a single pole switched neutral RCBO? When you have a 100mA S type upfront.

 

[leep82]

What's the reason for getting rid of the 100mA RCD ?

at the minute any problems, nuisance tripping with that and the whole installation goes off

 

[davesparks]

at the minute any problems, nuisance tripping with that and the whole installation goes off

But removing it removes the backup fault protection it provides when the 30mA fails to trip.
By removing it you are making the installation less safe than when you found it.

 

[telectrix]

RCBO all the way, in my book. keep trhe spare RCD for another job.

 

[Kamikaze]

What would be the point of making any changes to the distribution board, since in four months time, it wouldn’t comply again?

 

[telectrix]

What would be the point of making any changes to the distribution board, since in four months time, it wouldn’t comply again?

because it will comply when he makes out the cert. sod next year.

 

[netblindpaul]

Wylex NHXSBS type RCBO is single pole solid neutral not switched, as are 90+% of those in the market place.
There are VERY, VERY few double pole or single pole switched neutral RCBO's.
SPSN = Single Pole Solid Neutral, NOT Single Pole Switched Neutral.

 

[Plonker 3]

What would be the point of making any changes to the distribution board, since in four months time, it wouldn’t comply again?

It will comply exactly the same in years time as it does right now, he is on about swappong a RCD for a main switch not swappping the whole DB.

 

[leep82]

What would be the point of making any changes to the distribution board, since in four months time, it wouldn’t comply again?

forgive my ignorance but what will be happening in four months time?

 

[telectrix]

New years eve pi$$ up, followed by heavy metal CUs.

 

[leep82]

Done a little research and read that 100ma time delayed rcd acting as a main switch on a TT system is no longer required providing that all circuits are 30ma protected and the DB is of an all insulated material

 

[leep82]

New years eve pi$$ up, followed by heavy metal CUs.

ha ha, i was aware about the consumer unit changes

 

[richy3333]

Ok, I've skip read and drunk the best part of a bottle of wine but something doesn't bode well with the op's questions

 

[davesparks]

.
SPSN = Single Pole Solid Neutral, NOT Single Pole Switched Neutral.

Depends which manufacturer you look at, they seem to use the acronym SPSN interchangeably

 

[davesparks]

Done a little research and read that 100ma time delayed rcd acting as a main switch on a TT system is no longer required providing that all circuits are 30ma protected and the DB is of an all insulated material

But if it's there already why remove it? You will only be removing an additional layer of protectection

 

[leep82]

at the minute any problems, nuisance tripping with that and the whole installation goes off

But removing it removes the backup fault protection it provides when the 30mA fails to trip.
By removing it you are making the installation less safe than when you found it.

i would be installing a 30ma rcd to protect the lighting curcuits currently protected by a 100ma rcd. Does this make the system any less safe? Removing the 100ma rcd and replacing with a main switch would also allow the installation to be divided better so in the event of a single fault the whole installation would not be lost

 

[davesparks]

i would be installing a 30ma rcd to protect the lighting curcuits currently protected by a 100ma rcd. Does this make the system any less safe? Removing the 100ma rcd and replacing with a main switch would also allow the installation to be divided better so in the event of a single fault the whole installation would not be lost

Yes it makes it less safe, the 100mA RCD would provide a second level of fault protection if left in place. Being time delayed it will only trip if the 30mA RCD fails to trip due to being faulty.
If the 30mA RCD works correctly then the 100mA RCD will not trip

 

[Andy78]

i would be installing a 30ma rcd to protect the lighting curcuits currently protected by a 100ma rcd. Does this make the system any less safe? Removing the 100ma rcd and replacing with a main switch would also allow the installation to be divided better so in the event of a single fault the whole installation would not be lost

The time delay on the 100mA RCD should take care of any discrimination issues. As Dave says, leave it in. It won't cause inconvenient tripping, the 30mA RCDs should be able cause enough nuisance while being left well alone by the main RCD.

 

[leep82]

So we are effectively saying that if we had a new install, TT system, we could use a dual 30ma rcd, fully insulated board, all acceptable to current regs but this isnt as safe as the scenario ive described?

 

[davesparks]

So we are effectively saying that if we had a new install, TT system, we could use a dual 30ma rcd, fully insulated board, all acceptable to current regs but this isnt as safe as the scenario ive described?

Exactly
Compliance with the regulations is a minimum standard, not an absoloute

 

[leep82]

Thinking of using an rcbo after all. Question now though is do i need a double pole device? Been searching for similar threads and it seems its open to debate, maintaining the 100ma time delay rcd would give me an isolation point that isolates all live conductors ( as required in a TT), but this isolates the whole of the installation and not individual circuits?

 

[Leesparkykent]

Thinking of using an rcbo after all. Question now though is do i need a double pole device? Been searching for similar threads and it seems its open to debate, maintaining the 100ma time delay rcd would give me an isolation point that isolates all live conductors ( as required in a TT), but this isolates the whole of the installation and not individual circuits?

The problem you have if you don't use a double pole or single pole switched neutral RCBO is in the event of a neutral earth fault on the circuit the 100ma "S" type RCD will still see the neutral earth fault and trip taking out everything because the neutral of the circuit hasn't been disconnected when the RCBO has tripped.

Edit: from post #21 I'm not sure if Wylex make a single pole switched neutral RCBO without looking.

 

[telectrix]

Done a little research and read that 100ma time delayed rcd acting as a main switch on a TT system is no longer required providing that all circuits are 30ma protected and the DB is of an all insulated material

the reason that the 100mA RCD was installed on a TT system was to provide fault protection when all circuits were not RCD protected ( 16th). if all circuits have RCD protection, it's no longer required, but useful as a back up if the 30mA tripe was liable to not tripping on a fault due to being gummed up from never having the test button pressed.

 

[leep82]

Thanks for tour replys guys, things have changed once again with regards to this job. Customer now wants switch moving in dining room ( downstairs lighting circuit ). Now thinking of using the 80a 30ma rcd i have to protect the two lighting circuits i intend to work on but as mentioned leaving the 100ma time delay rcd main switch in place. Checked wylex catalogue and as thought there double pole rcbo's are two module, now im working on both lighting circuits i havnt got the room to fit these.

 

[7029 dave]

What ra are you measuring.? (out of interest) Leave the s type 100ma rcd in situ IMO.

 

[leep82]

Yeah i am going to leave it in place