RCCB as main switch?

[Noob2013]

Hi all,

I have been to a property where the tails come out of the meter and into an RCCB which then feeds the main switch of the consumer unit. All circuits are protected by MCBs.

If I'm adding a new circuit, is it best put in an RCBO instead of an MCB?

Thanks

 

[Guest77]

Not that I am aware, have you?

What make would you like?

 

[Guest125]

Well for a start a simple adjustable RCD will give you tripping currents from 10mA up to 1A (or more) and time delays of 0.1S up to 10S (or more)

Plus a company called FDB will manufacture any RCD to any specification. We use them a lot for DC immune RCDs.

 

[telectrix]

My point was if he installs a new circuit to a board which has a RCD main switch (and doesn't need it) then in affect he will be making the existing circuits worse by adding to the problem of one RCD protecting the whole installation. I know it is not clear cut and is only my interpretation so I think a board change would ensure all the new work is compliant.

i agree, but you border on persuading the customer to spend more than necessary if a less costly solution is available whilst still leaving the installation safe. a bit like condemning 3036 boards because they're not to current standards, although safe for continued use.

 

[davesparks]

Where would you use one?
I know where you find them, next to the rocking horse sh*t lol

Main and sub distribution units used for temporary power distribution in outdoor events will often incorporate adjustable RCDs which can be set to give 30mA time delayed operation along with a whole host of other possible settings.

Most rental generators now have adjustable RCD protection as standard too.

 

[davesparks]

Not that I am aware, have you?

I've never used a fixed 30mA S type, but plenty of adjustable ones that could give that kind of operation. And I am sure it wouldn't take me long to find one if I needed one.

 

[Guest125]

i agree, but you border on persuading the customer to spend more than necessary if a less costly solution is available whilst still leaving the installation safe. a bit like condemning 3036 boards because they're not to current standards, although safe for continued use.

Safety first

 

[TJ Anderson]

What make would you like?

MK, Crabtree, Wylex, BG, or Hager please

 

[JD6400]

Main and sub distribution units used for temporary power distribution in outdoor events will often incorporate adjustable RCDs which can be set to give 30mA time delayed operation along with a whole host of other possible settings.

Most rental generators now have adjustable RCD protection as standard too.

Hi Dave

But why would you want to set it at 30mA delayed as opposed to 100mA delayed , as by delaying it you will have lost the benefit of the 30mA anyway ?
Is this something to do with the regs you have to follow for events

 

[davesparks]

find me one!

Take one of these www.hobut.co.uk/earth-leakage-relays , add a suitable core balance CT and connect to a shunt trip on an MCB or MCCB of your choice.

 

[TJ Anderson]

Ok. I think we can safely say the OP's client will not have a bespoke "specialist order" variable ma RCD on the front end of his install. More like a crusty old 60A Crabtree ELCB that don't trip when the button is pressed!!

 

[davesparks]

Hi Dave

But why would you want to set it at 30mA delayed as opposed to 100mA delayed , as by delaying it you will have lost the benefit of the 30mA anyway ?
Is this something to do with the regs you have to follow for events

To ensure discrimination with 10mA RCDs installed downstream of it. The same way you would use 100mA S type in front of 30mA in a TT setup. It depends entirely on what it is protecting and why.
You are building installations out of pre-built standard distribution boards unlike fixed installations so you almost always end up with multiple RCDs in series. Sometimes you have to set one as a 30mA time delay just to stop a fault on one circuit from tripping out 2 or 3 RCDs upstream of it but still give discrimination with a 100mA upstream of that.


There is no regulatory reason for using them though, just the individual electricians design/method for ensuring that faults cause minimum disruption.

 

[davesparks]

Ok. I think we can safely say the OP's client will not have a bespoke "specialist order" variable ma RCD on the front end of his install. More like a crusty old 60A Crabtree ELCB that don't trip when the button is pressed!!

No he won't, but you stated that such things do not exist, so those of is who know better have disagreed.

 

[Noob2013]

I will have a look at the RCD when I go back and update you all.

It looked like a fairly new RCD with a test button. Definately not 10+ years old! Also no adjustments available on it.

So the general verdict is;

If it's a 30mA RCD then use an MCB for new circuit.

and

If it's 100mA RCD then use a 30mA RCBO for new circuit?

 

[Guest77]

MK, Crabtree, Wylex, BG, or Hager please

I could easily get my wholesaler to find one, a quick google and I found a protec, MK do one as well if you look throught their range in the catalogue
[h=1]RCD, DP 2 Module Time Delay[/h]

Catalogue No1:	T100-30-2TD
Size:	100A 30mA
Range:	Circuit Protection RCDs

 

[Guest125]

it is not quite that clear cut. You will need to interpret the regs on this one as there is a little disagreement.

I would say to be 100% sure just change the board. You cannot be wrong then. Other methods are open to a little interpretation.

Prepare 2 quotes and give the customer the pros and cons of both.

 

[Guest125]

Mental note: "Never say you can't"

 

[JD6400]

it is not quite that clear cut. You will need to interpret the regs on this one as there is a little disagreement.

I would say to be 100% sure just change the board. You cannot be wrong then. Other methods are open to a little interpretation.

Prepare 2 quotes and give the customer the pros and cons of both.

Or go and check what is there and then quote . I would say it is still a little early for building up the old bank balance ready for next christmas ! mg_smile:

 

[JD6400]

To ensure discrimination with 10mA RCDs installed downstream of it. The same way you would use 100mA S type in front of 30mA in a TT setup. It depends entirely on what it is protecting and why.
You are building installations out of pre-built standard distribution boards unlike fixed installations so you almost always end up with multiple RCDs in series. Sometimes you have to set one as a 30mA time delay just to stop a fault on one circuit from tripping out 2 or 3 RCDs upstream of it but still give discrimination with a 100mA upstream of that.


There is no regulatory reason for using them though, just the individual electricians design/method for ensuring that faults cause minimum disruption.

Thanks for that Dave , always good to see the reasoning behind how it is done in different sectors of our industry .
I can see how it would give you some discrimination if the fault was not to large .

 

[davesparks]

Thanks for that Dave , always good to see the reasoning behind how it is done in different sectors of our industry .
I can see how it would give you some discrimination if the fault was not to large .

With the time delay being selectable you can get a fairly good discrimination between multiple RCDs used for fault protection.

At the end of the day in this part of the industry it is going to boil down to doing the best you can when you're up to your knees in mud in the middle of nowhere.

 

[Noob2013]

With the time delay being selectable you can get a fairly good discrimination between multiple RCDs used for fault protection.

At the end of the day in this part of the industry it is going to boil down to doing the best you can when you're up to your knees in mud in the middle of nowhere.

So a 30mA time delayed RCD with a standard 30mA RCBO would be acceptable?