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

 

[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?

 

[davesparks]

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

Sorry, we've gone off at a bit of a tangent there talking about temporary distribution for events.

It would be utterly pointless in an installation, the cost would be ridiculous for a start

 

[Simlec]

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.

So when you have your 30mA time delayed Setup, what is it protecting ?
As the max for personal shock protection is 30mA.
Your 10mA RCDs on final circuits will protect life in damp/wet areas for your outdoor event.

 

[Guest125]

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.

I think there is going to be a lot of change in this sector in the 3rd AMD.

 

[davesparks]

I think there is going to be a lot of change in this sector in the 3rd AMD.

No there won't, nobody gives two hoots about what 7671 has to say!

 

[baldsparkies]

Until all facts and that deffo includes earthing arrangement are known.
A definitive answer can't be given.
So everything so far is surely hypothetical which could mean another long thread lads.

 

[Guest125]

Until all facts and that deffo includes earthing arrangement are known.
A definitive answer can't be given.
So everything so far is surely hypothetical which could mean another long thread lads.

Yeah but all these threads cannot give every detail and any advice should be verified by the installer anyway.

I like to think of it as a chat amongst collegues at lunch.

 

[Guest125]

No there won't, nobody gives two hoots about what 7671 has to say!

Present company excluded no?

 

[baldsparkies]

Yeah but all these threads cannot give every detail and any advice should be verified by the installer anyway.

I like to think of it as a chat amongst collegues at lunch.

Or killing time before going to bed because there's FA worth watching on the telly.

 

[davesparks]

So when you have your 30mA time delayed Setup, what is it protecting ?
As the max for personal shock protection is 30mA.
Your 10mA RCDs on final circuits will protect life in damp/wet areas for your outdoor event.

It's protecting other parts of the site from losing power when a fault occurs downstream of it.

Damp/wet areas? We're talking about outdoor events in the UK, we'll be lucky if it's merely damp! Torrential rain is far more likely.

 

[davesparks]

Present company excluded no?

Not really, I'll consider the requirements of 7671 and 7909 a bit more than most do but I sure as hell don't stick to them as if they were gospel!