MCB/RCBO Lock off Kit

[333rocky333]

Thanks for clarifying. That presumably means killing at least half of an installation (with a DP RCD), if not the whole installation (with a Main Switch, if there are no RCDs or all-SP RCBOs), which must often be somewhat of an inconvenience.

I do not do domestic but it must be a pain now with all these Rcd main switches doing multiple circuits, from experience you barely need to touch a Neutral nowadays to trip the Rcd, So i would quess its prudent to lock off The Two pole Rcd, rather than it trip inadvertently and P off the homeowner.
I quess on a longer job you would drop the circuit Neutral out at the board

 

[JohnW2]

I do not do domestic but it must be a pain now with all these Rcd main switches doing multiple circuits, from experience you barely need to touch a Neutral nowadays to trip the Rcd, So i would quess its prudent to lock off The Two pole Rcd, rather than it trip inadvertently and P off the homeowner.

Yes, I almost mentioned that it might 'make sense' to isolate the neutral in order to avoid that ominous 'click' one hears when doing something to the neutral However, what I was talking about was BS7671's view that DP isolation was need with TT (but not with TN-S) for 'safety' reasons.

Mind you, I'm not sure if/why the homeowner would be any less P-off'd by your switching off (and locking off) the RCD than they would be if the same RCD was (possibly) inadvertently tripped by your working

Kind Regards, John

 

[ericmark]

I would be happy in my own home putting insulation tape over the RCBO for a circuit being worked on, unless there were contractors working in the house, in which case I would use locks, if I touch a neutral it will only trip a circuit I am working on.

However elsewhere one needs to do a risk assessment, and where I work the safety officer is an electrician, so I would always drop the tails.

However as far as disruption due to isolating a RCD this would not be an option for an electrician he would drop tails, but isolation it not only done for electricial work.

 

[333rocky333]

Mind you, I'm not sure if/why the homeowner would be any less P-off'd by your switching off (and locking off) the RCD than they would be if the same RCD was (possibly) inadvertently tripped by your working

Kind Regards, John

Watching Eastenders or the like, back in the day i have nearly been lynched on commercial sites for tripping Front end Rcds, knocking out Tills, fruit machines, computers etc

 

[JohnW2]

Watching Eastenders or the like, back in the day i have nearly been lynched on commercial sites for tripping Front end Rcds, knocking out Tills, fruit machines, computers etc

Yes, I understand that, but you seem to have missed my point ...

Accidentally killing all the circuits protected by an RCD (which might well annoy people) by touching L & N together is a risk of something which might (or might not) possibly happen. However, deliberately killing all the circuits protected by that same RCD by switching and locking it off is a certainty

Kind Regards, John

 

[ericmark]

Yep had it last week, refurbishing a kitchen set off smoke alarms and resulted in power being cut to modem which we were unaware was on the same circuit. So the over phone transaction in another building where he was taking credit card details failed as a result.

This will be addressed, clearly there needs to be an UPS when the supply is so important, if tripping out a RCD will cause problems then clearly there will only be one circuit on the RCD, to group multi circuits on one RCD clearly the designer did not deem loss of power a real problem.

 

[JohnW2]

... if tripping out a RCD will cause problems then clearly there will only be one circuit on the RCD, to group multi circuits on one RCD clearly the designer did not deem loss of power a real problem.

As I often say (e.g. in relation to freezers, there's a bit of swings and roundabouts here.

Having just one circuit, maybe a 'dedicated' circuit, on one RCD/RCBO will obviously decrease the risks associated with the circuit failing whilst one is doing something important (like the credit card transaction you mention). However, it also increases the risk of a failure of the circuit when one is not doing something important going unnoticed, so that one doesn't discover the problem until one next needs to use the circuit 'for something important'!

Kind Regards, John

 

[ericmark]

As I often say (e.g. in relation to freezers, there's a bit of swings and roundabouts here.

Having just one circuit, maybe a 'dedicated' circuit, on one RCD/RCBO will obviously decrease the risks associated with the circuit failing whilst one is doing something important (like the credit card transaction you mention). However, it also increases the risk of a failure of the circuit when one is not doing something important going unnoticed, so that one doesn't discover the problem until one next needs to use the circuit 'for something important'!

Kind Regards, John

That is very true, personally I have a rechargeable torch in same supply as freezers, so if I loose power the torch auto switches on, one can easy miss some thing not showing like no display on freezer, less likely to miss a torch shining.

The bigger problem is the designer often does not consult the user, with the cheap re-wire of mothers house, one sub-consumer unit in kitchen was going to be left untouched, and it had 4 RCBO's in it, the electrician doing the job was going to put the SWA feed to this CU on one of the pair of RCD in main consumer unit until I said no, there is no need for the SWA to have RCD protection. Why he as the designer felt it was correct to have the RCD's doubled up I don't know.

So often the answer to why did you do that is well we always do it that way.

Clearly with most new builds the user is not available at design stage, so he has to use a genetic design to suit most users, but so often a consumer unit is charged without really taking into account what the user wants. Only after the RCD trips does the user find out there were options.

If we think back to the 80's with TT supplies it was common to fit a 100 mA RCD and they rarely had nuisance tripping, it was only when we went to 30 mA the problem raised its head. Today with a TT supply we can use double pole single width RCBO's allowing one circuit to be isolated for electrical work, with a TN supply no need to isolate neutral so only talking about a TT supply. But the cheaper consumer units like fuse box don't do double pole single width RCBO's so looking at some think like Wylex, so around £32 each. So typical 10 way consumer unit gets expensive, not only due to RCBO cost but also the SPD cost, which jumps from £30 to £100, so £20 extra for each RCBO Plus £80 extra for the SPD so with a TT installation RCBO protection gets rather expensive, at least £250 more than a simple twin RCD box.

Most users would flinch at the extra, they don't consider the cost of a lost freezer full of food should it trip when no fault on that circuit, or the problems finding a fault before you can reset the RCD. Even when you know the fault, bath over flowed for example, drying out before all power is restored takes time, but this is rarely pointed out to the user, the designer by this time is long gone.

So we went from

314-01-01 Every installation shall be divided into circuits as necessary to:
(i) avoid danger and minimize inconvenience in the event of a fault, and
(ii) facilitate safe operation, inspection, testing and maintenance.
314-01-02 A separate circuit shall be provided for each part of the installation which needs to be separately controlled for compliance with the Regulations or otherwise to prevent danger, so that such circuits remain energised in the event of failure of any other circuit of the installation, and due account shall be taken of the consequences of the operation of any single protective device.

to

314.1 Every installation shall be divided into circuits, as necessary, to:
(i) avoid hazards and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Section 537)
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation
(v) mitigate the effects of electromagnetic interferences (EMI)
(vi) prevent the indirect energizing of a circuit intended to be isolated.
314.2 Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of other circuits, and due account shall be taken of the consequences of the operation of any single protective device.

And the designer has to decide if twin RCD protection complies with the current regulations, sorry don't have 2018 version, but since 2008 it is debatable as to if twin RCD's comply.

Yes I know if we get a power cut we loose all power anyway, so the take account of danger that may arise from the failure of a single circuit such as a lighting circuit seems a bit odd, but the take account could be emergency lights does not need to be split into circuits, but a RCD is an over current device, it does not measure current in the circuit but it does measure the current imbalance so since it is an over current device it does form a circuit.

If you accept the RCD forms a circuit then it is down to the designer to consider 314.1 and since it says "reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation" it is clear IET considered the RCD as forming a circuit, so the designer has to consider "facilitate safe inspection, testing and maintenance" so needs to provide a method to isolate.

In commercial premises this is considered, I have worked in many an office with a suspended ceiling where each lamp with plugged in with a klik plug in ceiling rose so we could isolate one lamp and change it without turning off all the lights,

even in just the one room. Some one in the design stage had considered maintenance.

So with where I work there was clearly an error, no one had considered what would happen if internet lost when the router was installed, so now we know the error, a UPS will be fitted, the problem is the wrath was aimed at the person who caused power cut, not the designer who did not allow for a power cut.

 

[JohnW2]

That is very true, personally I have a rechargeable torch in same supply as freezers, so if I loose power the torch auto switches on, one can easy miss some thing not showing like no display on freezer, less likely to miss a torch shining.

As I've often said, I'm a great believer in 'over-temperature' alarms for freezers. On at least the last 2-3 occasions on which I would otherwise probably have lost the contents of a freezer, it has been due to death of the freezer itself, not loss of its electricity supply. The over-temp alarm saved the day on all those occasions in a way that no number of torches, 'dedicated circuits' or even 'power failure alarms' would not have done!

If we think back to the 80's with TT supplies it was common to fit a 100 mA RCD and they rarely had nuisance tripping, it was only when we went to 30 mA the problem raised its head.

That obviously makes sense although, as I always say, 'experiences vary' - since, even having lived with many 30 mA RCDs for many years, I have experienced very few, if any, 'nuisance trips'.

Today with a TT supply we can use double pole single width RCBO's allowing one circuit to be isolated for electrical work ...

Theoretically, yes - but I have personally never seen a TT installation which uses such devices, and nor are they things one commonly sees being offered by suppliers.

... with a TN supply no need to isolate neutral so only talking about a TT supply.

As I recently said/asked, I don't really see why BS7671 thinks that SP isolation is OK for TN-S but not for TT. In both cases, any risk is incredibly small, but I don't really see why they dismiss the theoretical risk with TN-S. Any thoughts about that?

If you accept the RCD forms a circuit ...

We've been through this before, and I don't think that any sensible person would 'play with the language' such as to argue that an RCD 'forms a circuit'. As you say yourself, an RCD looks at current imbalances (and operates if that 'imbalance current' is 'over' a certain value), but I would suggest that no sensible person would believe that BS7671 would regard an RCD as a device which "protects against overcurrent" as mentioned in its definition of a "circuit".

Kind Regards, John

 

[AndyPRK]

Here you go John. So you can see with your own eyes...

A very cautious install.

Chose crabtree as double pole (over his usual hagar)

 

[JohnW2]

Here you go John. So you can see with your own eyes...

Thanks, but I never denied that the devices exist (and that some people therefore presumably use them) so the video does not really alter what I wrote:

Theoretically, yes - but I have personally never seen a TT installation which uses such devices, and nor are they things one commonly sees being offered by suppliers.

Kind Regards, John

 

[ericmark]

I would agree with you John I don't know why TT singled out, if anything it is the TN-C-S which I thing needs some extra protection. I note with EV charging points there is a device which if the voltage goes out of limit 207 to 253 disconnects line and neutral then earth, and I question why only used on the EV charging point supply? If a PEN is lost then really want to switch off whole house and protect my equipment, never mind the shock danger.

But this is beyond my pay grade, I just in the main follow the rules.

I do see times where one questions the rules, father-in-laws house had the motor caravan parked only one meter from the meter cupboard where the gas meter is earthed to the house TN-C-S supply, to have the motor caravan TT to my mind would be dangerous, and in ones drive is not really a caravan park so see no problem with using the TN-C-S earth. It was not my shout, but there are times when one needs to use some common sense.

However with a customer to break the rules is asking for problems. If we read about court cases so often we say there by grace of god go I. I would have had no qualms in getting my 14 year old son to plug in a loop impedance meter and write down the results, by that point he had his RAE and pushing a button and writing down the results is not rocket science.

But we read about Emma Shaws death and see how the court felt an electricians mate could not be trusted with that job.

I had a close call working in Sizewell, I feel I was in the wrong, but lucky cleared, I switched off a motor supply in three places to a crane, the locks on two were worse for the sea air and would not work, the third one did work, so locked off and gave the site foreman the key so he could give it to which ever electrician came to replace it, the plant fitter got the key off the foreman and tried the motor, lucky only sparks, no one injured. I as said felt I had done wrong, and I should have brought the key back to the office. But my boss felt the fitter was wrong to have requested the key without checking why locked.

 

[JohnW2]

I would agree with you John I don't know why TT singled out, if anything it is the TN-C-S which I thing needs some extra protection.

As you probably know, the argument in BS7671 for isolation of neutral not being required in TN installations is that, with such systems, there is minimal risk of the CPCs/exposed-c-ps within the installation being at a significantly different potential from the neutral.

With TN-C-S that is obviously the case, since the installation's CPCs are directly connected to neutral at the MET - so, even if there is a PEN/CNE supply fault, leading to the incoming neutral and TN-C-S 'earth' being at a very high potential relative to true earth, then (also assuming that any required main bonding is in place) there will be no significant N-E PDs within the installation.

However, I understand less with TN-S - since I would have thought that some supply neutral faults could then result in appreciable N-E PDs, just as they could with TT.

Kind Regards, John

 

[Jupiter01]

Sorry guys, I meant to post this link
MCB RCD Lockout / Off Leaderman Kit for Consumer Unit Circuit Breaker - LDM-BCK | eBay

Would you recommend this kit as it has both types of lock-offs which presumably covers me for all the eventualities. It also has the sign and lock, etc.

 

[flameport]

It's a basic set containing the absolute minimum for some types of circuit breaker.

It most certainly will NOT cover 'all eventualities'.