Electric shower tripping rcd/mcb

[riveralt]

Can I fit another manufacturers MCB in the Wylex CB or should I just go for a Wylex 50A

Normally I would say you can fit a Wylex 50A for that distance but it will depend on the cable run - for example is the cable encased in conduit or insulation at any point along it run?

 

[JohnW2]

Would yo say that for a 10.8kw shower using 10mm cable with approximate 18/20 meter run that a 40A MCB would be the normal choice. Or would you go for a 45/50A MCB

As I've said, no matter how one looks at the figures, the current taken by your shower (at 230V or above) will be greater than 40A, which would make the use of a 40A MCB non-compliant with the Wiring Regulations.

The compliant answer is, as I've said, to fit a 45A or 50A MCB (and that may well make your problem go away) - BUT, as I've also said, you can only do that after confirming that the cable size and routing is adequate for the higher-rated MCB.

Kind Regards, John

 

[JohnW2]

Is the required torque setting to ensure we don't leave it too loose or to ensure we don't do it too tight?

As I said, in my experience it would almost seem the latter, but I'm not very happy.

However, if you had an MCB/RCD/Main Switch screw which you could get 'an extra quarter turn' on, by hand and without much effort, would it occur to you that it was even 'tight enough', let alone 'too tight'?

Would you be happy to leave that screw 'as it was' (after torquing), knowing that you could probably easily tighten it more by hand?

Kind Regards, John

 

[EFLImpudence]

Is the required torque setting to ensure we don't leave it too loose or to ensure we don't do it too tight?

As I said, in my experience it would almost seem the latter, but I'm not very happy.

Agreed.

However, if you had an MCB/RCD/Main Switch screw which you could get 'an extra quarter turn' on, by hand and without much effort, would it occur to you that it was even 'tight enough', let alone 'too tight'?

Would you be happy to leave that screw 'as it was' (after torquing), knowing that you could probably easily tighten it more by hand?

Not really, especially as you're supposed to recheck/retighten after a period.

Isn't the purpose of torque settings usually more importantly to ensure that all relatated nuts or bolts are at the same 'tightness' rather than a specific critical value - cylinder head bolts, wheel nuts etc?

If so, it hardly seems relevant to a consumer unit where it would be difficult to damage the tails or bus bar with the cage terminals and protecting the cage terminals would seem to be the wrong priority.

 

[JohnW2]

However, if you had an MCB/RCD/Main Switch screw which you could get 'an extra quarter turn' on, by hand and without much effort, would it occur to you that it was even 'tight enough', let alone 'too tight'? ... Would you be happy to leave that screw 'as it was' (after torquing), knowing that you could probably easily tighten it more by hand?

Not really, especially as you're supposed to recheck/retighten after a period.

Quite so - although if one retightened them to the same ('modest') torques, I suppose my argument would weaken! I'm just not happy that the specified torques are 'adequate'.

Isn't the purpose of torque settings usually more importantly to ensure that all relatated nuts or bolts are at the same 'tightness' rather than a specific critical value - cylinder head bolts, wheel nuts etc?

I would say that's only a 'secondary' purpose, in those relatively few situations where 'balanced tightening' is crucial. The primary purpose is usually (at least, in mechanical circles) to achieve the optimum torque for the nut/bolt/washer/thread/materials (or nut/screw/..., or nut/stud/...., or screw/threaded hole/... etc.) combination in question. For the last few years of his life, my father's work was predominantly concered with 'screw threads' (which would have bored me to death), about which he became quite passionate, and he was always hammering into me the fact that there was only one optimum torque for any combination of nut/bolt/washer/thread/materails etc. combination

If so, it hardly seems relevant to a consumer unit where it would be difficult to damage the tails or bus bar with the cage terminals and protecting the cage terminals would seem to be the wrong priority.

As above, I don't think it's anything to do with 'balancing' torques. It's either to do with ensuring 'adequate' tighetening or to avoid overtightening (which could strip threads and lead to a loose connection). Despite my experiences, I suspect that the intent was probably the former, but they do seem to have specified very modest torques (IIRC, 1.7Nm for MCBs, 2.1Nm for RCDs/Main Switches).

Kind Regards, John