just a quick one

[Zeespark]

I stand corrected. Thanks Lurch.

AndyGuinness

 

[tom1]

whoever put the cu in would have been best to put in insulated cu with four 30ma rcbo,

as you have come along after to put some sockets in garage, my only consern relating to rcd is that the sockets are protected by 30ma rcd,

if its one 30ma for whole install put a note in the comments box.

if its one 100ma td rcd as main switch put a 30ma rcbo in and quote for 3 more

if not interested put a note in the comment box. am i wrong?

 

[switch10]

cheers lurch, think thats just answered my question, and i have also gone and got my osg which explains a few things i was unsure off.

 

[switch10]

thanks to everyone for the replys, very much appreciated

 

[Apache]

So if this was wired to the 16th could you get away with protection with a 30mA RCD with no 100mA TD in sight? Not ideal, but would it have complied at the time?

 

[kme]

Yup. There are loads of TT down here, with 6, 8, or 10 way boards, with 30mA front-end RCD main switch.

It isn`t ideal (and never was), but it WAS compliant.

Not for a "recent" install, though, which the O/P says this is....

 

[SPECIAL LOCATION]

So if this was wired to the 16th could you get away with protection with a 30mA RCD with no 100mA TD in sight? Not ideal, but would it have complied at the time?

Depends upon how you interpret regulations such as 314-01-01 (i)

page 29 of the old Yellow book.. (16th)

Avoid danger and minimize inconvenience in the event of a fault

Would a single RCD minimize or increase inconvenience?

Same level of ELECTRICAL SAFETY tho? :|

 

[NozSpark]

Would a single RCD minimize or increase inconvenience?

Same level of ELECTRICAL SAFETY tho? :|

But if push comes to shove, safety comes above inconvenience..

as we are talking about TT & RCD... SP RCBOs and DP fault isolation anyone?

 

[batty]

I see metalclad consumer units on Tns sytems with either 100mA or 30mA

main switch RCD's in my area there are whole estates like it.

 

[SPECIAL LOCATION]

...talking about TT & RCD... SP RCBOs and DP fault isolation anyone?

Sharp intake of breath!!!!!!!!!!!!!!!!!!!!!!!!! :O:O:O

 

[batty]

But if push comes to shove, safety comes above inconvenience..as we are talking about TT & RCD... SP RCBOs and DP fault isolation anyone?

Will the main switch not be double pole.

 

[steptoe]

But if push comes to shove, safety comes above inconvenience..as we are talking about TT & RCD... SP RCBOs and DP fault isolation anyone?

Im sure I have voiced my concern about SP RCBOs before on TT systems.

Will the main switch not be double pole.

yes, but it doesnt offer fault protection for direct contact(is that the correct term these days?), you require an RCD or DP RCBO for this purpose

 

[switch10]

sorry to drag this one back up guys.. some conflicting advice, and looking through the regs book, osg and electrician guide to building regs it gets more confusing lol.

on the consumer unit im looking at is a fully insulated mk unit, short length tails, from isloation switch to consumer unit. main switch , and then mcbs, with 1 x 30ma rcd protecting lighting and sockets. (no cooker, or electric shower etc present), the cables are all buried in the wall, with no earthes conduit etc, however from reading up on this it appears that i do not in fact need a 100a 100ma Rcd incomer as this went out with the 16th edition?

im keen to get this sorted as using the sockets im adding for my NICEIEC assessment, and dont want to get shot down for adding to a system which could be deemed inappropriate

 

[Lurch]

So are you saying there is a single 30mA RCD covering everything?

 

[switch10]

So are you saying there is a single 30mA RCD covering everything?

yes lurch, there is only 3 cicuits, very old house, 2 sockets in living room, 2 sockets in kitchen, 2 in bedroom, and a total of 6 lights. all covered by 1 30ma rcd.

 

[Lurch]

From an electrical point of view it's all covered by the 30mA RCD as is required. However, as it stands it falls foul of the 'circuits should be arranged so as to minimise inconvenience' regulation.

 

[switch10]

i understand what you are saying lurch, just hard to put sockets on 1 RCD and the lighting on another 1, The last circuit is currently used, soon to be attached garage sockets.

so there is no need for the td 100ma RCD incomer as previously discussed as this is where im confused.

 

[Lurch]

i understand what you are saying lurch, just hard to put sockets on 1 RCD and the lighting on another 1, The last circuit is currently used, soon to be attached garage sockets.

Use RCBO's.

so there is no need for the td 100ma RCD incomer as previously discussed as this is where im confused.

No. The 100mA incomer would be used to protect anything not protected by the 30mA RCD, e.g. distribution circuits tapped off before the 30mA RCD (if they didn;t require a 30mA RCD anyway). In your case no TD RCD is required, from what I can gather.

 

[switch10]

cheers lurch, your comments have been very helpfull. cleared up what i thought, allways like to make sure im on the correct lines, and sometimes best to ask for confirmation..

 

[spinlondon]

Domestic TT installations require a minimum of 100mA RCD protection.

Circuits of special locations require a minimum of 30mA RCD protection.

Socket-outlets for general use, require a minimum of 30mA RCD protection.

Cables concealed in walls may require a minimum of 30mA RCD protection.

All these requirements can be met by using either a front end 100mA RCD, and individual 30mA RCDs as required. Or by using a single front end 30mA rcd.

With either of these methods, there will be no discrimination where fault currents are above 100mA. A fault on one circuit will affect all circuits.

The usual solution is to use a time delayed front end 100mA RCD to cover the whole installation, and individual 30mA RCDs as required.

With the OP's case, they are not concerned whether the existing installation meets the requirements of BS7671, just whether ther addition meets the requirements.