Can RCDs function as CU's isolator

[trey]

Just a question - not planning to do anything myself.

Does a CU require an isolator module and an RCD if all the circuits are on the RCD (ie isolator->rcd->mcbs)? The reason for doing this would be to free up extra MCB space or to allow for a pre-17th split load box to have two RCDs (one for each neutral block) without losing module space.

The only functionality that I can you losing is the ability to isolate the RCD if it failed and needed replacing. But as replacing an RCD is in the same league as fitting a CU in terms of required competency, whoever does the job would have to isolate the CU the alternative way (pulling main fuse or unscrewing load from henley block).

Views?

 

[plugwash]

My understanding of the situation is.

RCDs can be and often are used as main switches for consumer units.

However generally there should be one device which isolates everything in a consumer unit and if there isn't then there needs to be clear warnings to inform the user of this fact and how they should isolate things.

 

[skenk]

If you are feeding the second RCD from the load side of the first, there would need to be discrimination between the RCD's or a fault could trip the whole installation which isn't allowed. If both RCD's you mention are supplying final circuits with a 30mA trip and normal disconnection times then I don't think you can do this.

If you are feeding the second RCD from the feed side of the first there would need to be a nearby main switch to isolate the whole installation.

 

[ban-all-sheds]

If you replace the main switch in a traditional split-load CU with an RCD then the 2nd one will be downstream of it....

 

[Taylortwocities]

You could create a dual tariff board

Meter tails into a 100A main switch in separate enclosure
This goes into a henley block
two sets of meter tails one set to each of the two RCDs with their associated circuits

That way you have a single point of isolation and 17th edition compliant (oh yes it is, oh no it isnt ) CU.

 

[plugwash]

Just make sure you clearly label which switch does what..............