And again...

[JohnW2]

What do you mean by 'all poles' - you presumably don't mean 'all 4', do you (i.e. two neutrals taken through the RCD)? Does the arrangement you're describing even work (in terms of RCD functionality)?

4 POLE RCD, two neutrals and two lives passing through it from two SP services (same phase, not 2 different phases, or split phase),...

I clearly need some educating here. The only 4 pole RCDs with which I'm familiar are designed for 3 phase+neutral use, and I'm struggling to understand how they could work (as RCDs) if you used one of the intended 'phase' paths through it for a second neutral. Are you talking about some other type of 4 pole RCD - or am I just being dim?

But RCD had (from looking at it) cooked from heating on one of the two live poles.

As I hinted before, are you sure that the cooking did not result from a poor connection at that one terminal (rather than from 'overload')?

Kind Regards, John.

 

[Adam_151]

The overheating was localised not around the terminals but kind of in the middle of the RCD where it had deformed the side plastic (it was one of the poles at the edge of the device and you could see where it had blistered and burnt - can't remember if I took pictures or not)

And yes john, it was a standard 4 pole RCD as normally used for 3ph + N appplications, as long as the currents in the conductors through the torioid sum to zero then its happy.

Like a said, it was a badly put together installation, but an RCD will work in that configuration

Theres nothing particualy special about the 4 pole rcds for 3 phase work other than just extra poles on the end with the conductors passing through the trip coil, if you wanted, you could use them for a single phase circuit and disregard two poles (you'd have to pick the right phase pole though, or the test button wouldn't work - it connects an outgoing phase through a resister to the incomming neutral to unbalence the device)

 

[JohnW2]

And yes john, it was a standard 4 pole RCD as normally used for 3ph + N appplications, as long as the currents in the conductors through the torioid sum to zero then its happy. Like a said, it was a badly put together installation, but an RCD will work in that configuration. ... Theres nothing particualy special about the 4 pole rcds for 3 phase work other than just extra poles on the end with the conductors passing through the trip coil, if you wanted, you could use them for a single phase circuit and disregard two poles ...

Thanks. I've never really thought too deeply about what goes on inside a 4-pole RCD, in particular the way in which the four 'windings' are arranged (just straight conductors going through a toroidal sensing coil?) - but what you say makes sense. I guess I'll have to do a little more cogitating

Kind Regards, John.

 

[WabbitPoo]

In layman's terms, then, should the new white box with its rcd built in have been connected from a spare mcb location on the "fuse box" above (I told you I was a layman!)?

And if so, perhaps there wasnt a spare place, so they took an easy route....?

Just trying to understand.

 

[JohnW2]

In layman's terms, then, should the new white box with its rcd built in have been connected from a spare mcb location on the "fuse box" above (I told you I was a layman!)? And if so, perhaps there wasnt a spare place, so they took an easy route....? Just trying to understand.

If you ignore some of the more esoteric discussion here regading suggestions that it is conceivable that one could argue that the setup is OK (I don't think anyone truly believes that), they've done more than "take an easy route". They've left out a crucial element, namely some 'overcurrent' protection for the circuit - as well as the RCD in that white box, the circuit should also have an MCB (which, as you say, might possibly have been one in the "fuse box") or a fuse.

Kind Regards, John.

 

[SUNRAY]

No overcurrent protection.

The bit that really infuriates me with examples like this it there should be space in that partiular enclosure for a MCB

 

[ban-all-sheds]

Certainly looks like there is.

 

[SUNRAY]

Certainly looks like there is.

So why did the numbskull not put the extra £5 bitin there?

 

[Alarm]

Good question, but there is room.

 

[ban-all-sheds]

Because he's a numbskull who doesn't understand the things he's fiddling with.

 

[SUNRAY]

Because he's a numbskull who doesn't understand the things he's fiddling with.

As ever

 

[Adam_151]

John... does this: http://www.interestingengineering.com/2011/03/residual-current-devicerccbrcd.html help?

 

[JohnW2]

John... does this: http://www.interestingengineering.com/2011/03/residual-current-devicerccbrcd.html help?

It does indeed - all is now clear. Many thanks.

Kind Regards, John.

 

[RF Lighting]

Certainly looks like there is.

There was. There is now a 2 pole main switch and a 20A circuit breaker in that enclosure, with the RCD protection having been moved to the garage end.

 

[ABCwarrior]

"Henley" blocks seem to be the favoured name(in much the same way as "hoover" is used for "vacuum cleaner") for jointing blocks. Maybe they're the most commonly used?

I used the Lucy ones, seem much neater and fitted my setup better:

http://www.cablejoints.co.uk/upload/Lucy_Switchgear_MLNS_5_Way_Terminal_Blocks___Specification.pdf