Use of isolators with showers, oven, and other fixed stuff.

[mfarrow]

Quite - which makes me a bit confused as to why are you concerned that the 'big red switches' cannot be locked off?

Because there are members of this forum who believe they can be used as a point of isolation, and in the real world this will extend to the lazy electrician as well.

If they cannot be used as a point of isolation, do not satisfy the requirements for an emergency switch, and serve no functional switching purpose (i.e. with showers) then I see no point in having them. You then also remove the temptation to rely on them when working.

 

[JohnW2]

Because there are members of this forum who believe they can be used as a point of isolation, and in the real world this will extend to the lazy electrician as well.

...but aren't there some situations (e.g. if the switch is within the eyesight of the person doing the work, or if there is no-one else in the building etc.) when it is reasonable to use it for isolation?

If they cannot be used as a point of isolation, do not satisfy the requirements for an emergency switch, and serve no functional switching purpose (i.e. with showers) then I see no point in having them.

Perhaps (although there are a good few points one could debate), but 'point' or not, just as with 'fan isolators', MIs often require them and, at least until next year, many feel constrained to follow MIs to the letter.

Kind Regards, John

 

[AndyPRK]

they are usful as an emergency switch

and should a fault occour, allow isolation to allow the RCD to remain on, to power other circuits.

 

[JohnW2]

they are usful as an emergency switch. and should a fault occour, allow isolation to allow the RCD to remain on, to power other circuits.

I'm inclined to agree. On balance, I think that, certainly with cookers, there is probably more to be said for them than against them. It's probably much more debatable in the case of showers.

Kind Regards, John

 

[EFLImpudence]

'point' or not, just as with 'fan isolators', MIs often require them and, at least until next year, many feel constrained to follow MIs to the letter.

As I raised recently, surely there is a difference between 'Manufacturers' Instructions' and 'Information'.

After all, it makes absolutely NO difference to the well being and operation of a shower whether there is a switch or not.
Nor does the inclusion of an RCD so this 'instruction' is clearly just advice for the safety of the user.

Aren't some of these so called instructions just a method of installation that the manufacturer thinks should/may be/is done and merely a guidance for those who may not be familiar with the work (and possibly written by the marketing department).

 

[JohnW2]

As I raised recently, surely there is a difference between 'Manufacturers' Instructions' and 'Information'. ... After all, it makes absolutely NO difference to the well being and operation of a shower whether there is a switch or not. ... Nor does the inclusion of an RCD so this 'instruction' is clearly just advice for the safety of the user.

I can't really disagree with the the logic, or common sense, of any of that. However, the sort of statements we're talking about often include words like "must", and it's hard to see that one can interpret that as anything other than an 'instruction'.

Whatever, it seems that the IET have realised that an insistence on 'blindly obeying' MIs is inappropriate and that, if current proposals persist, there will be far more scope for discretion come next year.

Kind Regards, John

 

[mfarrow]

...but aren't there some situations (e.g. if the switch is within the eyesight of the person doing the work, or if there is no-one else in the building etc.) when it is reasonable to use it for isolation?

If you don't have insurers to worry about, a boss to fire you (I've heard of electricians get thrown off the books for less), can see the switch, are the only person in the building and/or trust your wife/husband to do as their told, and remember to check it's still off after your coffee break, then you can do what you like if you are confident it it sufficient to avoid the hazard. Many DIYers would do the same, however I personally avoid the cooker switch and don't have an isolator at the shower. The downstairs loo is the only place I have one for a fan as I suspected BCO would get cranky if it didn't, and it's nice to have those guys on side.

You may like to have them for RCD trip avoidance but I've not heard of many cookers tripping RCDs on neutral-to-earth fault.

 

[JohnW2]

You may like to have them for RCD trip avoidance but I've not heard of many cookers tripping RCDs on neutral-to-earth fault.

If there is an element-to-earth fault (which I would have thought was fairly common), will that not manifest itself as a N-E fault if the element is switched off by SP functional switching in the cooker?

Kind Regards, John

 

[AndyPRK]

I was glad I had a cooker isolator recently when the element went, tripping the RCD.

 

[mfarrow]

If there is an element-to-earth fault (which I would have thought was fairly common), will that not manifest itself as a N-E fault if the element is switched off by SP functional switching in the cooker?

Yes, I'm rather inclined to agree with that . In which case I will change my plea to exclude cookers!

 

[JohnW2]

If there is an element-to-earth fault (which I would have thought was fairly common), will that not manifest itself as a N-E fault if the element is switched off by SP functional switching in the cooker?

Yes, I'm rather inclined to agree with that . In which case I will change my plea to exclude cookers!

Does the limited extent of that exclusion mean that you are confident that the functional switching in showers is DP?

Kind Regards, John

 

[mfarrow]

Does the limited extent of that exclusion mean that you are confident that the functional switching in showers is DP?

Internal shower switches are SP, by and large. Given the relative complexity of an electric shower unit, the failures I've seen have not been due to an element failure giving rise to a neutral-earth short.

I think it also must come down to the considerations one must take in designing an installation. If you design a cooker circuit to the minimum 'bare bones' requirements for RCD protection, where RCD is required, i.e. an RCD protecting multiple circuits, then there is a strong case for an isolator to minimise fault inconvenience. If you have a full RCBO circuit, or like me armoured cable to your cooker (so no RCD) then there's an argument perhaps for not needing one to isolate the supply due to neutral faults. What the relative cost merits are between an RCBO, versus chasing/wiring/terminating one more accessory are I wouldn't like to say.

I've also seen charred wires from insulation-smothered ceiling lights causing insulation to go brittle and circuits to pop. We don't do anything currently to protect against this occurrence (or other faults in Class I light fittings), but maybe DP light switches are the way forward? All the more reason for Class II lighting circuits, I'd say!

 

[JohnW2]

Does the limited extent of that exclusion mean that you are confident that the functional switching in showers is DP?

Internal shower switches are SP, by and large.

As I'm sure you realise, that was the assumption behind my largely rhetorical question ...

Given the relative complexity of an electric shower unit, the failures I've seen have not been due to an element failure giving rise to a neutral-earth short.

I really haven't got enough experience of failed shower units to be able to comment. However, as you will realise, my point was that if the shower developed an element-to-earth fault, with SP functional switching within the unit, that would manifest itself as a N-E fault when the shower was functionally-switched 'off'.

If you design a cooker circuit to the minimum 'bare bones' requirements for RCD protection, where RCD is required, i.e. an RCD protecting multiple circuits, then there is a strong case for an isolator to minimise fault inconvenience.

Exactly my point. That 'bare bones' arrangement is, I would imagine, easily the most common and, with SP switching in the shower, that would mean that an element-to-earth fault (or any other N-E fault) within the shower would take out all other circuits protected by the same RCD - hence, as you admit, a strong case for having a DP isolator.

Kind Regards, John

 

[mfarrow]

My case is that the requirement for them should be engineered out at source (i.e. at the consumer unit). I'm not a fan of these split RCD units and don't see the logic of having fault protection across 5+ circuits: "Yes Mrs Jones, we've split your house into 3x 32A ring mains, 2x lighting circuits, 1x immersion, 1x cooker circuit, 1x shower circuit, and a loft supply, in case of the unlikely event you'll ever overload one of them, but we've bunched them all onto 2 RCDs so if someone puts a nail through the cable or your cooker element goes pop you'll loose half the house".

IMHO the isolators can also encourage the tradesman to be lazy about their taught 'safe isolation' procedures ("I'll be here all the time, I can keep an eye on it") and present another link in the chain of terminals that can cause fault. One day we might see a loose/burnt connection on one of these (not uncommon) set fire to some loft dust/bees nest.

 

[AndyPRK]

Imagine what it was like when there was only 1 rcd prior to the cu.

At least with many rings it allows easier fault finding.