Can anyone explain the purpose of this separate switchfuse and RCD? (Ed.)

[Taylortwocities]

The biggest issue wirh voltage operated ELCBs was that they relied on the CPC of the entire installation being perfectly isolated from earth.

Almost impossible with earthed copper pipes. As a result the VoELCBs were effectively useless, hence their demise.

 

[Ragnar_AT]

Almost impossible with earthed copper pipes. As a result the VoELCBs were effectively useless, hence their demise.

Exactly. Germany required sections of rubber hose to be fitted between earthed water pipes and pumps, immersion tanks, etc., if a voltage operated ELCB was fitted but whether that was actually done is anyone's guess.

 

[securespark]

Hiya Plugawsh,
The term "Switchfuse" was often used to mean a "One Way Consumer Unit" type thingy to put any wylex fuse or breaker in - say adding a shower circuit (and connector block such as Henley or wylex) .
So a 1 way might be called a switchfuse then a 2 way probably called a two way consumer unit and a wylex 604 etc called the consumer unit, so in this example you`d have circuits controlled by 3 (1 + 2 +6) switches and probably loadsa other stuff from different decades too.
and some of those switches were up for OFF and some were down for OFF.
Ho the good old days

And the difference between a "Switch fuse" and a "Fuse switch"?

Never really got to grips with that in the 80s...

 

[plugwash]

The term "Switchfuse" was often used to mean a "One Way Consumer Unit" type thingy to put any wylex fuse or breaker in

Yeah, the OPs "switchfuse" is a WY106 which takes regular wylex standard fuse carriers or MCBs https://www.tlc-direct.co.uk/Products/WY106.html

Wylex also did a 60A model that looked quite similar but used different (presumablly larger) fuse carriers. https://www.tlc-direct.co.uk/Products/WY108M.html

 

[ebee]

The biggest issue wirh voltage operated ELCBs was that they relied on the CPC of the entire installation being perfectly isolated from earth.

Indeed, back in my early working years anybody asking at the trade counter for an ELCB would be asked if they wanted voltage operated or current operated. The voltage types were eventually discontinued in favour of the current type and later on we renamed then RCDs.
Today we sometimes see a circuit illustrated devised to disconnect the PEN (CNE) conductor for a loss of PEN situation and it is, in simple terms, an RCD to act in a way that it monitors voltage not unlike those old voltage types of ELCB. Use in the UK is not allowed on our mains supply though because it disconnects your incoming earth connection on TNC-S or PNB (or PME)