RCBO needed or not???

[sparkytim]

The only way to provide discrimination with 2 RCDS in series is by time delay one fitted at the supply end.

They do not make a 30 m A Time delay RCD and the 100 m A will not comply if the sub main requires 30 m A as it seems.

I would remove the Garage end RCD and replace it with a Main switch and go with RCD at the main C Unit.

 

[tom1]

Yeah, was a bit.I didn;t assume anything, hence our differing conclusions.

 

[ianmacd]

The only way to provide discrimination with 2 RCDS in series is by time delay one fitted at the supply end.They do not make a 30 m A Time delay RCD and the 100 m A will not comply if the sub main requires 30 m A as it seems.

I would remove the Garage end RCD and replace it with a Main switch and go with RCD at the main C Unit.

Or remove the requirement for one at the house end and fit one the the garage.

 

[kme]

So whith a 31mA or larger imbalance which will trip?

31mA doesn`t appear all at once; it ramps up. So the 10mA *should* see and remove problem before the leakage reaches 31mA

As said, 30mA(S) aren`t generally available, and if you MUST have 2 RCDs - and the upstream MUST be 30mA (17th OR 16th TT), what are your alternatives?

As an example:

My house is TT. Therefore, even if I use surface wiring / SWA, I must protect that cable with a 30mA device. I`ve got SWA down to the garage. I don`t want a fault on something plugged into the garage to take out the RCD in the house (even if I used an RCBo, I`d have to go all the way back to the house to re-energise).

So, the only option, as far as I was concerned, was a 10mA device - 16th allowed for RCD discrimination to be 3X value. 16th has been superseded, but that doesn`t make that information any less valid, does it?

KME

 

[sparkytim]

10 m A will just give a lot of trouble think it can operate at anything just over 5 m A and it WILL NOT DISCRIMINATE. I think you may be getting mixed up with Overcurrent faults where discrimination can be obtained by ratio between MCBS / Fuses in series.

 

[spinlondon]

31mA doesn`t appear all at once; it ramps up. So the 10mA *should* see and remove problem before the leakage reaches 31mAAs said, 30mA(S) aren`t generally available, and if you MUST have 2 RCDs - and the upstream MUST be 30mA (17th OR 16th TT), what are your alternatives?

As an example:

My house is TT. Therefore, even if I use surface wiring / SWA, I must protect that cable with a 30mA device. I`ve got SWA down to the garage. I don`t want a fault on something plugged into the garage to take out the RCD in the house (even if I used an RCBo, I`d have to go all the way back to the house to re-energise).

So, the only option, as far as I was concerned, was a 10mA device - 16th allowed for RCD discrimination to be 3X value. 16th has been superseded, but that doesn`t make that information any less valid, does it?

KME

There is no reason why you cannot use a 100mA time delayed RCD to protect surface wiring. Using 10mA along with 30mA will not offer discrimination in the event of a fault. Only time delayed RCDs will offer discrimination.

 

[ianmacd]

There is no reason why you cannot use a 100mA time delayed RCD to protect surface wiring. Using 10mA along with 30mA will not offer discrimination in the event of a fault. Only time delayed RCDs will offer discrimination.

Indeed (as I said in #4). Remember we are discussing a distribution circuit not a final circuit here.

 

[a1]

I have a similar situation to this...

Brother in Law, is on a TT system, 6mm Cooker cable from house CU to Garage (CU) Contactum CU at house end has 30ma RCD Main Switch.

Garage end is an old MK Sentry CU with 32A RCBO protecting the S/O. (5)

RCBO passed all except for the x5 test (No Trip - Both sides of the waveform - 0

 

[netblindpaul]

Admin,

I would put a 100mA TD RCD up front.

Supply garage via MCB UNLESS cable runs require 30mA protection.

Fit 30mA RCD as main switch in garage CU, or use RCBO's

HTH

Paul

 

[a1]

Admin,I would put a 100mA TD RCD up front.

IIRC 100ma is for fire protection? 30ma for Shock Protection, Yes?

So, what would happen for the Shock protection in the house if they did fit a 100ma Time Delayed RCD (Main Switch)?

Also, had a google search, and as yet, I can't find one.

Supply garage via MCB UNLESS cable runs require 30mA protection.Fit 30mA RCD as main switch in garage CU, or use RCBO's

HTH

Paul

You mean, Supply for Garage off of an MCB at House End? Or MCBS in the CU at Garage end?

All ccts in Garage are run in PVC Trunking (except where they enter and run in the ceiling).

With regard to the RCBOs, Paul - Wouldn't they trip the same as the house (If both are 30ma)? Or would they trip first, being newer? ]

Thanks for your reply.

PS. matt.leung - Sorry for hi-jacking your thread.

 

[netblindpaul]

MCB in house, RCD in garage.

Forget about discrimination with instantaneous RCD's NO MATTER what the rating!

If you want to achieve discrimination use a time delay up front.

The only requirement for 30mA protection at the supply side of the garage sub-main is if it is run in such a manner the regs require it.

Else as long as it is 32A or greater then you can treat as a sub main dist. cct and supply accordingly.

Paul

 

[a1]

Thanks Paul.

Currently, the Garage is supplied off of a 32A MCB at the House End, but all the ccts (House End) are proctected by the RCD Main Switch.

 

[netblindpaul]

Re-arrange the board?

Can you fit a main switch and then the MCB, then the RCD, then the "house"?

 

[a1]

Re-arrange the board?Can you fit a main switch and then the MCB, then the RCD, then the "house"?

No Mate.

6 Way all being used - and RCD Main Switch.

 

[superspark]

Hi

my view is

6mm t+e from cu on none protected side as no room on rcd side protected by 32amp rcbo through wall into adaptable box armoured cable glanded into this and cleated outside glanded into c/u for garage 4 way board normal 63a main sw, surely only one rcd is needed,at main c/u if supply cable is concealed in wall, or if supply cable is surface clipped then i would put this on mcb and have rcd in garage.

1 ring for garage sockets or two radials and 1 lighting circuit unless their growing green plants in their 32amp should be ample.

 

[netblindpaul]

Hmmmm,

All I can suggest then is change RCD main switch for a main switch and change the "house" mcb's to RCBo's.

EXPENSIVE!!!

Can't immediately think of any other way to supply from this board...

Another option would be to add some Henleys and fit a secondary supply to the garage?

Try this.

Meter>REC Isolator>100mA time delay RCD>Henleys to:--->>

---------------------------->House with RCD main switch

---------------------------->Second DB with main switch & CPD for garage

A small "garage" type CU would do. Remember to ensure that the CPD is big enough for a "long" disconnection time!

WPD charge <

 

[batty]

Is any of feed cable buried? If not put seperate consumer unit with 100mA TD Rcd main switch with suitable MCB house end and at garage end depending what is wanted to be spent either a 30mA Rcd main switch with Mcb's or Main switch board with Rcbo's. If feed cable is buried you will either need to replace it or you will have to have 30mA Rcd protection house end but that also could be in seperate board.

 

[a1]

Use the 100ma as the Incoming Isolator (Main Switch) before the Henley?

 

[a1]

Thanks Guys,

House CU is just below ceiling Height, 6mm Garage Supply disappears into ceiling, along the joists and out of the bedroom wall, Clipped to exterior wall, into a JB in the SHED, Then inside alont the top og the shed wall, out through the shed wall, into A length of Round PVC Conduit, and into the Garage wall and directly into the Garage CU where it enters the garage.

 

[netblindpaul]

YEP use the 100mA as an installation main switch for the lot, however, it MUST be time delayed, S type.

This type of install is familiar I can show you one if you want not far away from your location!