Earth clamp on incoming cable

[securespark]

Just revisiting this thread. Good to see the DNO have rectified the pipe clamp connection.

I have reread the stuff about RCDs and, WRT the following,

Yes, but Sunray said early RCDs did use an earth and you answered by describing something that is not an RCD.

, I think that AFAIK, RCDs have never used an earth.

I think was implied was that the VO ELCB was the predecessor to the RCD.

I knew the technical guy at Wylex very well (he has retired now) and he was around when Wylex were developing their first RCD range, which was fitted as an incomer to metal clad consumer units or as a stand alone unit in a plastic case and if memory serves, it was released in 1974. It did not have any earth connections.

 

[EFLImpudence]

Not sure what you are asking, exactly.

I have reread the stuff about RCDs and, WRT the following,

"Yes, but Sunray said early RCDs did use an earth and you answered by describing something that is not an RCD."

I think that AFAIK, RCDs have never used an earth.

Well, some RCBOs have a functional earth connection but only for ensuring they can work in certain conditions - if the supply neutral is lost I think; may be wrong.
Some (all?) RCD sockets (FCUs?) won't switch on without the earth connection connected.

I think was implied was that the VO ELCB was the predecessor to the RCD.

Predecessor, yes, but they use a different method.

Voltage Operated ELCB
- by measuring the Voltage on the earth wire.

RCD or Residual Current Operated ELCB
- by measuring the missing current on the neutral conductor.

I knew the technical guy at Wylex very well (he has retired now) and he was around when Wylex were developing their first RCD range, which was fitted as an incomer to metal clad consumer units or as a stand alone unit in a plastic case and if memory serves, it was released in 1974. It did not have any earth connections.

RCCBs don't.

 

[SUNRAY]

Here's one I found five years ago:

Sorry the RCD is glared out, it's 25A 30mA.
RCBO's invariably have the earth wire too.

 

[JohnW2]

Well, some RCBOs have a functional earth connection but only for ensuring they can work in certain conditions - if the supply neutral is lost I think; may be wrong.

Indeed - but am I right in my impression that this 'craze' may be on the decline? I never really understood why some manufacturers decided that a 'functional earth' was necessary (to ensure enough voltage was available to run the device's electronics in the sort of situation you mention), yet continued to manufacture and sell RCDs which were presumably just as depended on an adequate L-N PD for their electronics to function! In terms of RCBOs, I think that at least some manufacturers decided (presumably without consulting bernard ) that the probability of a fault requiring a 'residual current trip' arising at the very time when a TN-C-S installation had a 'lost neutral' was 'vanishingly small'!

Some (all?) RCD sockets (FCUs?) won't switch on without the earth connection connected.

Indeed, and also 'RCD adaptors' - maybe most/all active RCDs? I suppose it makes sense. If an RCD socket/adaptor is being used in a situation in which residual-current protection is considered particularly desirable, it makes sense for the device to not 'switch on' if there is not an adequate enough earth connection to enable an L-CPC fault to trip the device. We've discussed this before, and it's not at all obvious how they achieve that functionality.

Kind Regards, John

 

[securespark]

Yup, that's probably a Memera 2000 A80 or A100 with functional earth. EDIT: You already mentioned it was 25A.

MEM tech a good few years ago told me the functional earth on their RCDs also helps them detect DC fault current.

I had a raft of "faulty" RCD changes by sparks at work and sent a handful back to MEM for testing. The RCDs were testing OK on their test bench. Therefore the "faults" were put down to faulty/ leaky equipment attached to the RCD when under test.

 

[bernardgreen]

the probability of a fault requiring a 'residual current trip' arising at the very time when a TN-C-S installation had a 'lost neutral' was 'vanishingly small'!

If a TN-C-S installation has a 'lost neutral' and still has a connection to the incoming Live then all the electrical wiring including the CPC and Neutral will be at Live potential if any appliance or other load is switched ON ( obviously the appliance will not work and will appear to be dead ).

In this situation if the Earth Leakage protection device can detect current passing through it on the Live without a matching current on the Neutral and therefor disconnect the Live then it is reducing the risk of damage or harm.

(presumably without consulting bernard )

I didn't expect them to need to consult me .

 

[securespark]

Not sure what you are asking, exactly.

I wasn't asking anything, just trying to explain that maybe Sunray was putting VO ELCBs in the same "boat" as RCDs; I now know he wasn't.

And I completely messed up my post by omitting to make it clear I was talking about the development of early enclosure-mounted RCDs.

 

[JohnW2]

If a TN-C-S installation has a 'lost neutral' and still has a connection to the incoming Live then all the electrical wiring including the CPC and Neutral will be at Live potential if any appliance or other load is switched ON ( obviously the appliance will not work and will appear to be dead ).

In such a situation, the Neutral within the installation will obviously rise to a possibly very high potential relative to earth, but it would only come to be at the same potential as the 'Live' if there were absolutely no 'incidental' paths to earth (such as bonded extraneous-c-ps) - which would be fairly unusual. Depending upon where the PEN fault was, the overall 'incidental path to earth' might consist of many such paths in multiple dwellings in parallel, in which case the Neutral voltage might not necessarily be 'all that high'.

In this situation if the Earth Leakage protection device can detect current passing through it on the Live without a matching current on the Neutral and therefor disconnect the Live then it is reducing the risk of damage or harm.[?quote]Maybe I'm missing something but, as I implied in my previous message, I can't see why that would happen (an RCD operating) unless there were an astonishingly improbable co-incidence of a simultaneous L-E (or L-CPC) fault in one of the circuits protected by an RCD. In the absence of such a coincidental fault, I don't see why there should be an L-N imbalance in any of the installation's RCDs, any more than there would be in the absent of the PEN fault. Am I missing something?

Kind Regards, John