New single RCD consumer unit

[JohnW2]

Ah - so, as far as you know, that MCB does not actually trip on it's own?

I will confirm that with the tenant. I know it needs to be left off to get up and running again. Hence the thinking that the two are in someway connected.

That would be helpful. As I've been discussing with others here, the whole thing gets even more difficult to understand if some fault is causing an MCB as well as the RCD to trip. If it's only the RCD, then that's a somewhat more common, and more sane, situation to contemplate.

It would be interesting to know whether the kitchen sockets MCB has to be in the 'off' position for the RCD to be resettable even if nothing is plugged into any of the kitchen sockets (or is otherwise connected to that circuit).

Kind REgards, John

 

[nairb123]

An electrician "up the road" from the tenant says the rcb is too sensitive. I should use a 100a 100ma. ?? is 30ma to 100ma really going to solve the problem?.

If the 'leakage' causing the RCD to trip were fairly marginal (between 30mA and 100mA) then changing to a 100mA one might well 'cure' the problem. However, it would be totally contrary to the regulations and would leave people exposed to a theoretical risk of death - the whole point of having 30mA RCDs is that 30mA is the magnitude of electric shock above which death becomes an increasingly serious possibility!

Kind Regards, John

Wow I dident realize it was that low. I really thought it took amps. So it would defeat the whole object of the rcd. I had the rcd put in because there were to youngish kids moving in. And young lads do like to play.

So the 30ma one is staying

Thanks for that

 

[JohnW2]

Wow I dident realize it was that low. I really thought it took amps. So it would defeat the whole object of the rcd. I had the rcd put in because there were to youngish kids moving in. And young lads do like to play. So the 30ma one is staying Thanks for that

You're welcome, but that's right. It takes very little - even 30mA through a person can be lethal if it persists - that's why a 30mA RCD is required to trip within a small fraction of a second at leakage currents of 30mA or more. 'Amps' would probably cremate as well as kill

However, one needs to be aware that RCDs are no panacea. If someone connects themselves between live and neutral, then there is no way that any clever devices can realise that the resulting current is due to anything other than a 'legitimate load' - so no device, RCD or otherwise, could protect anyone from that. RCDs sense the situation in which there is a fractional difference (e.g. 30mA) between currents in the L and N conductors - the implication being that some of the current flowing through the L is getting back to the supplier's transformer via a route other than the N wiring - the most obvious alternative route being from L to earth (maybe via a human being).

Kind Regards, John

 

[nairb123]

To follow up on this. I have spoken to the the electricians who installed the CU and asked why a single RCD installation was used.
The reason was the existing wiring would need to have been re-wired to split the upstairs lighting/sockets from the down stairs lighting/sockets. This would have been a significant additional cost. So I think its a fair compromise. I understand that a dual RCD would typically have upstairs lights/down stairs sockets on one RCD and the other way around on the 2nd RCD.

There is going to be a check if the certificate has been released from building controls and another one sent. The work was submitted within a week of completion.

I am awaiting news from the tenant regarding the MCB status when the RCD trips.

To summarize the situation....
The single RCD will trip if there is an imbalance on any ring (lights/kitchen etc) but may not trip an individual MCB on the ring.
An individual MCB could trip if the load is too high or a thermal temp is reached. But this might not trip the RCD.

Its all neat stuff and good to know. Now I will ensure that the tenant gives the correct info.

Thanks
Nairb

 

[ericmark]

Having now read more I would agree neutral - earth fault is likely causing at least some of the problem.

The higher the load with a neutral - earth fault the more likely it is to trip. The problem is this fault could be in any of the Class I appliances brought into the property.

So for example a bit of bread stuck in a toaster left plugged in but switched off could cause the RCD to trip when using the shower.

It is often a nightmare trying to find out which item has the fault normal for me is to use the PAT tester to check each item with an earth and plug as so easy for the offending item to be unplugged when one tried to test.

Even switching off an MCB will not help as neutral is still connected.

Although likely something the tenant owns that is causing the problem it really does not help. The real point is cost and to me swapping the RCD for a Isolator and fitting all RCBO's if they will fit in the board is likely cheaper than trying to find out which item is faulty.

One can clearly test the common things which are likely to cause the problem already said toaster is first item on the list followed by cooker and immersion heater.

This is were experience counts a mature electrician has likely seen it all before and can cut down testing time by selecting likely items first. A younger one may have to resort to one item at a time until he finds the one causing the problem and clearly it's helpful to be able to blame it on something belonging to the tenant but it's still costing you getting every item tested and likely fitting RCBO's will be more cost effective.

Sorry I am not really a domestic electrician so I don't know if that consumer unit will take RCBO's but if it will that's the easy way forward.

As a foot note a RCBO is a MCB and RCD combined.

 

[JohnW2]

Having now read more I would agree neutral - earth fault is likely causing at least some of the problem. ... Although likely something the tenant owns that is causing the problem it really does not help. The real point is cost and to me swapping the RCD for a Isolator and fitting all RCBO's if they will fit in the board is likely cheaper than trying to find out which item is faulty.

Maybe - but don't forget that, even if it were possible to change it to all RCBOs, that would not necessarily tell one which item was faulty - it will only indicate which circuit has the fault (and there aren't all that many to choose from, anyway!).

Kind Regards, John

 

[AndyPRK]

So if its a neutral earth fault, why does the kitchen MCB (which isolates line) have to be left off to reset the rcd?

I guess one appliance may have a large surge current.

I would put the fridge on an extension lead to the other socket circuit and see what happens.

 

[nairb123]

Maybe - but don't forget that, even if it were possible to change it to all RCBOs, that would not necessarily tell one which item was faulty - it will only indicate which circuit has the fault (and there aren't all that many to choose from, anyway!).

Kind Regards, John

But knowing that it could be 1 or more toasters/kettles on a ring thats faulting is a huge help.
Would a fridge on load (cooling) have the same electrical properties as at idle?
I calculated that the shower pulls between 30-40 amps(max). Would a high current device leak more that an iron or kettle?

The RCBO route does seem tempting... Does an RCBO come after the main RCD.or sit in parallel?

 

[nairb123]

So if its a neutral earth fault, why does the kitchen MCB (which isolates line) have to be left off to reset the rcd?

I guess one appliance may have a large surge current.

I would put the fridge on an extension lead to the other socket circuit and see what happens.

The fridge sits on the second kitchen ring. It has run for days on an extension lead from living room sockets fine.

I now want to make sure the labels on the front match whats in the CU. You know a sanity check.
The tenants house is 80 miles away so I will need a to do list next time I am there which is shortly I suspect.

 

[AndyPRK]

You would replace the rcd with a red main switch.
And replace the Mcbs with rcbos which are about £25 each
Which rearly should have been done in the first place but would have cost u more.

 

[JohnW2]

But knowing that it could be 1 or more toasters/kettles on a ring thats faulting is a huge help.

As I said, it would be of some help to know what circuit was at fault - but it still could be difficult to locate the fault. Don't forget, the fault could be in the wiring, not necessarily a tosater, kettle or other appliance.

The RCBO route does seem tempting... Does an RCBO come after the main RCD.or sit in parallel?

I think eric was suggesting that you should get rid of the RCD (replacing it with a 'main switch') and then change all the MCBs to RCBOs - if that is possible in your CU. I think that Wylex RCBOs cost around £28 each.

Kind Regards, John

 

[JohnW2]

So if its a neutral earth fault, why does the kitchen MCB (which isolates line) have to be left off to reset the rcd?

Goodness knows - but the story about the MCB does seem a bit confused/ confusing/ uncertain. Switching off a SP MCB would obvioulsy not islate any N-E fault on that circuit.

I would put the fridge on an extension lead to the other socket circuit and see what happens.

Or plug the fridge (and, if necessary, other appliances) in through a (ideally 10mA) plug-in RCD.

Kind Regards, John

 

[RF Lighting]

Where's the house? Pay my mileage and day rate and I guarantee I'll find the fault.

Got called out bank holiday monday to an Intermittent RCD fault. It had tripped 3 times during the morning. Tracked it down to a failed X&Y capacitor in the tumble dryer. On site 2 hours including a natter with the customer (my sister)

 

[bernardgreen]

On site 2 hours including a natter with the customer (my sister)

Only a natter, didn't she have tea and choccy biscuits for you. ?