Shower circuit design.

Following your reasoning the CPD for a ring circuit should not be 32A, it should be the maximum current that could be drawn from all the sockets, with cable size to match!  The point is that 32A protects the CABLE sufficiently, even if I plug in 50A of load. This is exactly the same as these showers.

Not exactly the same - if done properly a ring is arranged such that it will adequately serve all the expected loads (as distinct from the number of sockets) without overloading (taking diversity into account) - in the old days it was done by floor area of course, now we're expected to use a bit more nouce, but all the same it shouldn't be expected to suffer small overloads of long duration. It's well know that overload protection often doesn't perform well in that situation - hence the warning of regulation 433.1.

  - Andy.

gkenyon: 
The issue being, that OCPDs heat up. We simply don't have enough information to determine whether it's dangerous … if the mcb's either side of the shower breaker are often well loaded up to a good percentage of their capacity whilst the shower is running the shower breaker ABOVE it's capacity, we really don't know what will happen (except we do, because we've all seen overheating occuring at the CU for various reasons)!

I have had a look at some Hagar data, but this current revision of the forum makes it difficult to paste them in.

32 A MCB: Loss per pole @ rated current = 3.9 W. From which R = 3.81 milliohms.

40 A MCB: Loss per pole @ rated current = 4.3 W. From which R = 2.69 milliohms.

Now run the 32 A MCB at 40 A: Loss per pole @ rated current = 6.1 W. That is 40-odd per cent greater than the loss for a 40 A MCB at 40 A load. (In general this holds approximately true across the range of MCBs.)

It may not seem much, but we do not know whether this is safe. However, as Alcomax points out, if there are no signs of thermal damage (have a close look all round out of the board), it may be appropriate to leave it alone and grade C3. Of course, if there are any signs of thermal damage, it is a C2 from me.

My only issue with Chint is that I could not find a wholesaler who keep their MCBs in stock, Screwfix supply them, but they don’t keep them in stock with them only being available after 24-48 hours.

If Chint and Screwfix ensured there was stock in each branch I would have completely resolved all the issues on Friday and there would not now be unresolved issues to deal with.

I actually have a better stock of 40 amp circuit protective devices in my van than any wholesaler in the United Kingdom have in their warehouse, except a some of the specialist second hand suppliers such as Willrose, but I didn’t have Chint so I have ordered three as  “just in case” van stock.

Jaymack: 
 

Zoomup: 

Chint. Oh 'ek.

Posters should be aware that any form of advertising is not allowed and should be removed by a moderator. Makers have a case for compensation from the I.E.T.!

P.S. Whatever happened to OMS and other valuable contributors who kept up the calibre of posts!  

Jaymack

The I.E.T's official rules and responsibility…..

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Zoomup: 
 

Comments, questions and content

This website enables registrants to post or transmit comments, questions and other content on the site and provides several forums for discussions.
Some of this posting will be moderated and other content posted or facilitated by the site will be checked solely to ensure that the site is not used for commercial exploitation.

The Institution undertakes no responsibility to otherwise screen the comments and other content and does not endorse the comments and other content in any way.

If you rely upon any advice provided by persons participating in the discussion groups or posting information on this site, you do so at your own risk.

Then there is the legal view!!!!!!!!!!!!!!!!

Jaymack

Sparkingchip: 
 

My only issue with Chint is that I could not find a wholesaler who keep their MCBs in stock, Screwfix supply them, but they don’t keep them in stock with them only being available after 24-48 hours.

If Chint and Screwfix ensured there was stock in each branch I would have completely resolved all the issues on Friday and there would not now be unresolved issues to deal with.

I actually have a better stock of 40 amp circuit protective devices in my van than any wholesaler in the United Kingdom have in their warehouse, except a some of the specialist second hand suppliers such as Willrose, but I didn’t have Chint so I have ordered three as  “just in case” van stock.

 

So what is really wrong with fitting a different make of M.C.B. and slightly adjusting a bus-bar finger to suit? Or putting the new device at the end of a shorter bus-bar and linking it by a short wire tail/link? Isn't that just site engineering?  A better quality make of M.C.B. than Chint would be a benefit.

Z.

This is probably the point you may be told I have been seen banging my head against a wall ? 

 

P.S. Whatever happened to OMS and other valuable contributors who kept up the calibre of posts!  

Jaymack

Well, I'm still here and have read this topic with interest.

As a public forum, many journeyman electricians and trainees reading the varied views expressed here will in most cases be confused by members giving what might be regarded as contradictory advice to BS7671.

Legh