Demand

[AndyPRK]

So I was watching an electrican on youtube (CJR)


He was installing a new shower adding a 40A MCB.

The board was a 16th ED.
On the RCD side were 4 B32, all socket rings.

He is adding the B40 onto the RCD side, and is going to reduce the socket rings to
2 B16
1 B20
1 B32 (kitchen)
(he said he used a clamp meter)

He claims test sheets have a box for maximum demand load and this is why he is changing them.
"This can only be calculated by the number and rating of the mcbs and applying diversity"

only other significant load was B32 cooker

Thoughts! ?

I guess there must be a mad calculation to comply

 

[EFLImpudence]

Rubbish ???

How will that lower the demand?
What if there is only a 60A main fuse?
The demand is what it is.

Perhaps he could have made the four rings into one, then all would be well.

 

[Harry Bloomfield]

Have you a link to the video?

It seems an odd thing to do..

 

[AndyPRK]

you won't like the video and get side tracked lol !

He only mentioned it in passing anyway

 

[Harry Bloomfield]

you won't like the video and get side tracked lol !

He only mentioned it in passing anyway

This one?

1:10 on...

Odd thing to do.. What if someone wants to load up one of the rings to the normal capacity of a ring circuit?

 

[AndyPRK]

Yes.

And yes it is bloody stupid.

Ps
Glad it’s not my house. In many ways

 

[EFLImpudence]

At 3.56 he seems to (does) think cable zones do not apply if the cable is >50mm. deep.

Didn't watch any more.

 

[AndyPRK]

Good point.

He is going to be assessed on this install as he mentioned in a previous video.

 

[ericmark]

I may do the same as him, but I would not make a video of doing it, if making a video of your work it needs to be A1. So it is a discontinued Contactum consumer unit so does not matter if MCB or RCD changed you would need to use old second hand units if you can get them. I googled for a 40A MCB but each one I found said out of stock.

The main point is size of the incoming fuse, if 80A or less, then nothing wrong with having a 80A RCD, if over 80A then there are a few ways around the problem, main one is change the consumer unit, but you could fit your own 80A fuse and continue using the one fitted, or use a henley block and use a second consumer unit for shower, and not touch the original unit.

 

[securespark]

At 3.56 he seems to (does) think cable zones do not apply if the cable is >50mm. deep.

This from a web page I found:

Cables That are not in Electrical Cables Safety Zones

Sometimes it is not possible to run cables in these zones. It is allowed so long as the following guidelines are followed:

1. The cable must be over 50mm below the surface. If the wall is made from metal then it will need RCD protection

https://www.diydoctor.org.uk/projects/electrical-safe-zones.htm

 

[EFLImpudence]

Edit -

reread and it does say that with an 'or' after it. It is wrong.

 

[securespark]

Has that reg changed from green book to blue?
Or is it still the case that if you want to run a cable outside of zones, the only way to do it is to run it in earthed conduit or trunking or use an earthed armoured or earthed metal sheathed cable?

 

[EFLImpudence]

I think they might be right. Ooops.

 

[AndyPRK]

Now there is another YouTube electrican following his advice.

And a more respected one kinda too.

There must be something in it. ?

 

[JohnW2]

I think they might be right. Ooops.

Indeed ....

As far as I can see, the concept of so-called 'Safe Zones' [as described in 522.6.201(i)] only exists for cables buried less than 50mm deep. For cable buried deeper than that, the issue of 'Safe Zones' therefore does not seem to arise at all. Is that not correct?

Mind you, in practice, unless one comes out of the back of a back box, how one can get a cable from an accessory to a place which is "≥50mm deep" without it ever being <50mm deep is another question!

Kind Regards, John