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Topic Title: Double Insulated and 2 core flex.
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Created On: 25 May 2014 09:02 AM
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 25 May 2014 09:02 AM
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alanblaby

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Twice this week I have fitted equipment and not been too happy doing it.

Under cabinet lighting, supplied with a soldered in 2 core flex, and a boiler condensate pump that had a 2 core flex as its switching cable.

Both items were marked as double insulated, but the cables were plain 2 core flex, no earth. (of course, UK mains voltage, not SELV)

Even though the equipment is Double Insulated, I've got it in my head that the cable should have an earth core.

Could someone please point out the failings in my thoughts?

Thanks
Alan.
 25 May 2014 09:27 AM
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daveparry1

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If the items are double insulated and officially marked as such (square whithin a square) why would you think there should be an earth conductor present Alan? There would be nowhere to connect it to would there!
 25 May 2014 09:38 AM
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CopperRod

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I think he's looking at the flex having an earth incase it's damaged etc as it's at mains voltage?
 25 May 2014 09:45 AM
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alanblaby

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Yes,the flex, especially on the pump.
On the lighting, if you cut through it, the over current protection should cut it off as it is L+N cores. With the pump, there is a permanent live and switched live coming back. Cut that, and nothing will trip, leaving a live cable dangling.
 25 May 2014 09:48 AM
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CopperRod

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Does the pump not have a 'parking' earth terminal?
 25 May 2014 09:50 AM
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Avatar for potential.
potential

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: Double Insulated and 2 core flex?
A most sensible combination I would have thought.


Originally posted by: CopperRod

I think he's looking at the flex having an earth incase it's damaged etc as it's at mains voltage?

In what way does an earthed conductor protect a 3 core flex?
If the flex is damaged so one, two or three conductors are exposed it doesn't mitigate the potential risk in any way does it?
If the whole cable or one or two conductors are severed how does it protect the cable in any way?
Relying on a fortuitous contact between conductors if a cable is severed is not a satisfactory method to guard against a cut cable being left in a live state IMO.
 25 May 2014 10:01 AM
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CopperRod

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I'm not suggesting it is a best method. I was merely trying to follow Alan's thinking?
 25 May 2014 10:30 AM
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phantom9

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It is the point about the reason for a cpc. A cpc is a circuit protective conductor. If the appliance being served is double insulated usually the manufacturers state that no means of earthing should be introduced in to it, I take that to include a redundant cpc. So it is not an appliance protective conductor. As for the flex requiring a cpc I don't agree. You can see it where it enters the device and where it starts. Same for the u/c light or the pump. The point made by potential is absolutely valid.
 25 May 2014 12:01 PM
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geoffsd

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Originally posted by: alanblaby
With the pump, there is a permanent live and switched live coming back.

 25 May 2014 04:44 PM
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potential

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Originally posted by: CopperRod

I'm not suggesting it is a best method. I was merely trying to follow Alan's thinking?


point taken.
 25 May 2014 08:41 PM
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aligarjon

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Originally posted by: geoffsd

Originally posted by: alanblaby

With the pump, there is a permanent live and switched live coming back.


[IMG][/IMG]


Which bit do you find confusing then Geoff. How long do you think a cable should be before it needs to be protected by a cpc ? Its quite possible the flex be installed behind tiles if its to a boiler which gives the potential for some numpty to put a screw through it.

Gary

-------------------------
Specialised Subject. The Bleedin Obvious. John Cleese
 25 May 2014 09:00 PM
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mapj1

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I'd read that as him being puzzled as to the choice of words, of a pump between live and switched live. Personally I'd prefer a switched live and a neutral, or in a European moment, perhaps phase and switched neutral.

coming back to the OP, the CPC is not there to protect the cables - if it were singles rattling about in plastic tubes would not be considered equivalent. It is there is case the load needs it - and if it doesn't, perhaps in case the load is changed for a different model that does.
AS the 2 core cables are generally captive, and cable and core get changed together that thinking does not apply.
Unlike for example the CPC to the plastic ceiling rose, not needed today, but 'on standby' for when someone moves in with a hideous brass monstrosity...

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regards Mike
 25 May 2014 09:24 PM
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aligarjon

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Maybe Mike, i took it as being disrespectful but i might be wrong in which case i appologise. i suppose that is the problem with using silly faces instead of constructive comments. I pressumed the neutral on a boiler wiring to be already present.

Gary

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Specialised Subject. The Bleedin Obvious. John Cleese
 25 May 2014 09:32 PM
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mapj1

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Ah well I suppose he might have been stirring perhaps - but I think its not likely - unlike one or two others on different threads.. Must admit I read it twice, but made the assumption that the neutral was understood.

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regards Mike
 25 May 2014 10:07 PM
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geoffsd

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I had no intention of being disrespectful and apologise if that was the outcome.

As said, my confusion was concerned with a pump connected by a live and switched live.
 25 May 2014 10:13 PM
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aligarjon

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My mistake Geoff. sorry.

Gary

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Specialised Subject. The Bleedin Obvious. John Cleese
 25 May 2014 10:38 PM
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geoffsd

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No problem. Thanks.
 25 May 2014 11:45 PM
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alanblaby

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It is a condensate pump.It has a 3 core flex supplying the power for the pump, then, it has a separate 2 core flex, both live cores, to cut the power to the boiler if the float switch contacts are broken.

There is an internal tank for the condensate, this fills up to a certain level, then the water is pumped out. If it goes above that level, the float switch opens, to cut power to the boiler.
 26 May 2014 10:50 AM
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bowmandj

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I can sense why your unease for the pump flex carrying two live wires. If cut then there is no chance of a possible over current protection, an earth in the flex would at least provide that opportunity.

Maybe a more secure way would be for an earth screened flex similar to that screened cable that permits shallow embedded cable with no RCD requirement. But I don't know a supply for earth screened flex other then small signal use.

But such extra security is nit commanded by the regs. Double insulated kit is just that, and a cable with just live conductors but us insulated and sheathed us no different to a meter tail.

-------------------------
Derrick B

nanos gigantum humeris insidentes

 27 May 2014 12:05 PM
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AJJewsbury

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Even though the equipment is Double Insulated, I've got it in my head that the cable should have an earth core.

Could someone please point out the failings in my thoughts?

I guess you're thinking of regulations 411.3.1.1 and 412.2.3.2 which require a c.p.c. to be run to and terminated at each accessory and 'point'. Note that it doesn't apply to an appliance, and the 'point' in your case will be where you connect the supplied 2-core flex to the fixed wiring - so all should be well.
- Andy.
IET » Wiring and the regulations » Double Insulated and 2 core flex.

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