New Regs regarding RCD's

[gazzer23]

My friend just moved into a new build flat and its for a disabled person with a hydraulic lift to go to the upper floor.
There was/is a leak (cause unknown as yet) that shorted out the fire alarm which caused its RCD to break but also the main breaker for the whole CU.
When I questioned the contractor about it, he told me there was new regulations that if any RCD trips they have to trip the main breaker which seems total -------- to me but I am gullible.
The whole point of the RCD is to isolate the circuit leaving other circuits up.
As in this case her fear is being in the lift and everything trips and getting stuck.

What he told me is rubbish isn't it ?

Thanks Gary

 

[Rockingit]

I would say that you've been fed a line, there. It's not impossible for an upstream overload device (which I assume is what you mean by 'main breaker') to activate at the same time as a downstream RCD (eg, introduce a load of dirty water and one is sensing a short going L-E [RCD] and the other is sensing a short going L-N [MCB] at the same time) but there's no interlink between them. In fact, we actively design circuits to not introduce what we call nuisance tripping for exactly these type of reasons.

I'd be asking this contractor to show you the regulations that they're claiming.....

 

[Avo Mk8]

The electrician's explanation is wrongly worded, but there is an element of truth about RCD tripping not being the full story.
Firstly, when you say RCD, is that actually what tripped, or was it an MCB or RCBO? A 'main breaker' is normally a switch, which doesn't trip!

Protection devices are typically MCB's, RCD's and RCBO's
MCB for overcurrent protection
RCD for leakage current (but not overcurrent) protection
RCBO for a combination of the above.

In a modern CU you might expect each circuit to be protected by an RCBO, which would prevent the problem your resident is worried about.
But if the consumer unit has MCB's and one or two RCD's, a leakage fault on one circuit will take out the RCD protecting that group of MCB's, hence all lose power.
So the residents worry is valid.

The CU needs all RCBO's if they aren't already in it!

Rockingit got there first, but I thought I'd post anyway

 

[Rockingit]

The electrician's explanation is wrongly worded, but there is an element of truth about RCD tripping not being the full story.
Firstly, when you say RCD, is that actually what tripped, or was it an MCB or RCBO? A 'main breaker' is normally a switch, which doesn't trip!

Protection devices are typically MCB's, RCD's and RCBO's
MCB for overcurrent protection
RCD for leakage current (but not overcurrent) protection
RCBO for a combination of the above.

In a modern CU you might expect each circuit to be protected by an RCBO, which would prevent the problem your resident is worried about.
But if the consumer unit has MCB's and one or two RCD's, a leakage fault on one circuit will take out the RCD protecting that group of MCB's, hence all lose power.
So the residents worry is valid.

The CU needs RCBO's if they aren't already in it!

I wasn't contemplating that someone would be so stupid as to install a split board in this situation to start with!!!.......

 

[Rockingit]

My friend just moved into a new build flat and its for a disabled person with a hydraulic lift to go to the upper floor.
There was/is a leak (cause unknown as yet) that shorted out the fire alarm which caused its RCD to break but also the main breaker for the whole CU.
When I questioned the contractor about it, he told me there was new regulations that if any RCD trips they have to trip the main breaker which seems total -------- to me but I am gullible.
The whole point of the RCD is to isolate the circuit leaving other circuits up.
As in this case her fear is being in the lift and everything trips and getting stuck.

What he told me is rubbish isn't it ?

Thanks Gary

Can you post up some pictures of the system for us to see?

 

[snowhead]

Stairlifts have a built-in battery for use in the event of power loss.
I would expect a hydraulic lift would also have one so it could at least be lowered to the lower floor in the event it suffered power loss between floors.

 

[gazzer23]

I would say that you've been fed a line, there. It's not impossible for an upstream overload device (which I assume is what you mean by 'main breaker') to activate at the same time as a downstream RCD (eg, introduce a load of dirty water and one is sensing a short going L-E [RCD] and the other is sensing a short going L-N [MCB] at the same time) but there's no interlink between them. In fact, we actively design circuits to not introduce what we call nuisance tripping for exactly these type of reasons.

I'd be asking this contractor to show you the regulations that they're claiming.....

Thanks that is exactly what I thought.
So the MCB detects a short between L and N, that I couldn't remember but I knew an RCD detects an imbalance of current going out and coming back.
The problem is my friend who told me about this problem, her story keeps changing slightly so it is hard to find out what exactly happened. An electrician went over yesterday and tested it and said everything is fine so maybe she is exaggerating ?
I told her if it happens again to take photos of the CU and to video and test the lights, lift etc. to show what is working and what isn't.

Thanks for your reply as my main concern was my sanity and what he said did seem daft and like you said there is no interlink between the RCDs and MCB so they can't make it trip.
I guess its possible if water got in the smoke detector that all 3 terminals could be shorted and trip both but more likely just one should trip.

 

[littlespark]

Any new build flat, with NEW consumer unit… one of the main things is that circuits are labelled up correctly… so even an untrained homeowner can see what is controlled by which breaker.


It is confusing as to what has been said by who to whom… Chinese Whispers come to mind.

 

[gazzer23]

I will go over and get some photos, the CU is well labelled and very long with many breakers.
I never seen one that big in a small flat but then I am not an electrician ;-)

The contractor did say the lift would go to the bottom if power out but after his other remark it is hard to know if it is true or not.
it should be hopefully, she should test it and see.