Shed Wiring

[JohnW2]

There are two types of RCD FCU passive and active and the selection is dependent on the loop impedance where the device is fitted. With a good loop impedance a passive type can be used which means after a power cut the shed will still have power. Where the loop impedance is too high an active type is used. This means under fault conditions should the voltage drop below the operating voltage for the RCD it will trip anyway i.e. fail safe.

Absolute rubbish.

Eric, could you possibly explain to me the thinking behind that statement? It sounds almost as if you are saying that it's OK if the EFLI is too high for an RCD to operate (i.e. extremely high), but if that's the case one uses an active RCD just for its 'no-volts-disconnect' functionality. Thanks.

Although I used slightly different language from you, I'm glad to hear that someone agrees with me for once!!

Kind Regards, John

 

[JohnW2]

... the cable to the garage is almost certainly too long to be on a 32A breaker.

??

Kind Regards, John

 

[Greenie9657]

The cable to the shed is approx 3 meters

 

[JohnW2]

The cable to the shed is approx 3 meters

Thanks. However, I wouldn't understand BAS's statement even if it were 300 metres. Sure, the cable wouldn't then be suitable, but for reasons other than the rating of the MCB!

Kind Regards, John.

 

[ban-all-sheds]

Cable with overload protection downstream of reduction in CCC should be no longer than.....

 

[JohnW2]

Cable with overload protection downstream of reduction in CCC should be no longer than.....

Ah, yes, I was slow there (even if I think it's a rather silly {at least, very arbitrary} reg!)! However, if the OP's response is correct, then that argument seems to have been thwarted!

Kind Regards, John

 

[ban-all-sheds]

3m seems rather short to get from a downstairs ring final, up to a safe height for crossing to the shed, crossing to the shed, and then down to the height of the FCU....

 

[JohnW2]

3m seems rather short to get from a downstairs ring final, up to a safe height for crossing to the shed, crossing to the shed, and then down to the height of the FCU....

I agree - but 3m is what we were told! Perhaps he will re-measure and revise the figure.

The irony, of course, is that although you expressed disbelief (as I probably also would have done) when the OP indicated that he had tried his shed supply by plugging it into a socket, apart from the issue of terminating T+E in a plug, that is functionally exactly what he should be doing (with a 13A fuse at, or close to, the point at which the 'spur' connects to the ring)!

Kind Regards, John

 

[Greenie9657]

That's what I've done John. I'm going to leave it connected all day today just to see if the downstairs ring is ok as the upstairs in inaccessible. Thwn i can wire it in properly. i thought 3 meters was generous just to be on safe side but ill re measure later on.

 

[JohnW2]

That's what I've done John. I'm going to leave it connected all day today just to see if the downstairs ring is ok as the upstairs in inaccessible.

As I'm sure you realise, that's not really how it should be done, and it is unlikely to tell you anything about the acceptability or safety of your installation. I really don't know what you think might happen during this one-day 'plugged-in test' to either confirm or refute (in your eyes) the fact that what you've done is OK!! What should be done is proper testing, involving sophisticated equipment, both before and after connecting your new wiring.

Thwn i can wire it in properly. i thought 3 meters was generous just to be on safe side but ill re measure later on.

Fair enough. As BAS said 3m seemed very little to get you all the way from the ring in the house to the FCU in the garage, but only you can know the truth. As you have probably understood, the point is that the Wiring Regulations essentially require that the FCU (i.e. the fuse, which would normally be 13A) should be no more than 3m (cable length, from ring to FCU/fuse) from the point where the spur joins the ring.

Kind Regards, John

 

[ban-all-sheds]

The irony, of course, is that although you expressed disbelief (as I probably also would have done) when the OP indicated that he had tried his shed supply by plugging it into a socket, apart from the issue of terminating T+E in a plug, that is functionally exactly what he should be doing (with a 13A fuse at, or close to, the point at which the 'spur' connects to the ring)!

It wasn't the functionality I was commenting on - it was the notion that that qualified as testing.

 

[JohnW2]

The irony, of course, is that although you expressed disbelief (as I probably also would have done) when the OP indicated that he had tried his shed supply by plugging it into a socket, apart from the issue of terminating T+E in a plug, that is functionally exactly what he should be doing (with a 13A fuse at, or close to, the point at which the 'spur' connects to the ring)!

It wasn't the functionality I was commenting on - it was the notion that that qualified as testing.

I realised that, which is why I said I would probably have expressed the same disbelief that you did. I was merely pointing out the irony that the functionality of his 'testing' setup would (if spur length >3m) be more compliant than his intended 'final' arrangement!

Kind Regards, John