shed consumer unit

[Guest77]

6mm2 isn't enough on this occassion if a 40 amp design current, but a 20 amp supply may actually be adequate lol, but what I liked about your initial post was your question regarding why the op doesn't trust his spark, I like to know the answers to those questions, and asked what he did for a living as well, and I wasn't being sarcastic, I genuinely would like to know.

 

[Darkwood]

Sorry darkwood, you are correct, the spec sheet I had was for 90c.
Looks like the 6mm is not good enough for the 40 meter run then.

I think I may stop posting today.... just can't get thing right......

We all do dont fret... just wondered how Elend cables had managed to change the laws of Physics - a first since Einstein did it

 

[Spoon]

Just to say to the OP. The voltage drop for 6mm over 40 meters is not recommended. For 37 meters it's ok.

 

[gsc]

I hope I explained okay...

The House CU is a 10 way split load with 2 RCDs.. running different circuits... He said he would plug the RCBO (40A) into the mains switch of the House CU as there is a spare way and connect it via the busbar. Then run the armoured cable above ground to a CU with RCD on the shed...

It's the bit about the RCBO I am worried about... is that the correct way or is it possible that it could be an issue?

Thanks again..

Also MDJ I am a computer technician but I hope you aren't asking that question as a way to make me feel bad for asking if its safe...

GSC

 

[Spoon]

We all do dont fret... just wondered how Elend cables had managed to change the laws of Physics - a first since Einstein did it

haha... At least it's nearly Friday.

 

[markc123]

What do you do for a living?

Funny isn't it ... there was a time when this thread would actually be quite offending in the fact that the OP doesn't believe what his 'professional' spark is telling him. Undermining him bit ect...

However, with the state of some of the 'electricians' these days + the media stories of 'cowboy tradesmen' - you can hardly blame people for coming online and getting a second opinion now.

...although, some of the 'electricans' online are still dodgy - reference a thread you've literally just been commenting on in the last 10mins mike lol.

 

[Spoon]

OP:
Are you sure he is fitting a RCBO to the house CU as it already has RCD protection so doesn't need it.
What is it about the electrician that makes you want to question him?

 

[Guest77]

I hope I explained okay...

The House CU is a 10 way split load with 2 RCDs.. running different circuits... He said he would plug the RCBO (40A) into the mains switch of the House CU as there is a spare way and connect it via the busbar. Then run the armoured cable above ground to a CU with RCD on the shed...

It's the bit about the RCBO I am worried about... is that the correct way or is it possible that it could be an issue?

Thanks again..

Also MDJ I am a computer technician but I hope you aren't asking that question as a way to make me feel bad for asking if its safe...

GSC

I am just interested in why you have a gut instinct about the design, I think you are right to feel a bit wary, perhaps you just have instincts for these things lol, the reason though why he is using an RCBO in the house is because the armoured is above ground, some may say he should have fitted a small db with double pole rcd protection but others may feel the single pole RCBO enough.

 

[Guest77]

OP:
Are you sure he is fitting a RCBO to the house CU as it already has RCD protection so doesn't need it.
What is it about the electrician that makes you want to question him?

The armoured is above ground and therfore the spark isn't taking any chances lol, if it was 2 foot under he probably wouldn't fit RCD protection at the house end.

 

[Spoon]

But as the OP says "The House CU is a 10 way split load with 2 RCDs.." It already has RCD protection.

 

[Guest77]

But as the OP says "The House CU is a 10 way split load with 2 RCDs.." It already has RCD protection.

yes but I would not add a sub main to an existing Trip myself, especially as power tools will be used, the house lights will be going off otherwise I suspect, with a different RCD nothing else in the house can be effected if a fault occurs mate.

 

[Darkwood]

I hope I explained okay...

The House CU is a 10 way split load with 2 RCDs.. running different circuits... He said he would plug the RCBO (40A) into the mains switch of the House CU as there is a spare way and connect it via the busbar. Then run the armoured cable above ground to a CU with RCD on the shed...

It's the bit about the RCBO I am worried about... is that the correct way or is it possible that it could be an issue?

Thanks again..

Also MDJ I am a computer technician but I hope you aren't asking that question as a way to make me feel bad for asking if its safe...

GSC

With the given info the install would not comply due to it not meeting Volts Drop requirements of 3% ?

A rcbo is an acceptable choice of front end device, I assume you have a spare way in your consumer unit and he is fitting the appropriate rcbo for that board in a part of the board which isn't covered by the 2 existing rcd units?

We sometimes question DIYers or other curious people when they reference an Electrician as it can be a ruse to get free advice to do the work themselves where we would normally advice to use a competent person for their own safety or because the work is notifiable, in MDJ's case he just wondered on this occasion why you had a 6th sense to query the design - so please don't take offense over any questioning.

 

[Spoon]

A rcbo is an acceptable choice of front end device, I assume you have a spare way in your consumer unit and he is fitting the appropriate rcbo for that board in a part of the board which isn't covered by the 2 existing rcd units
.

Now it makes sense.....

 

[Richard Burns]

You have said that the design current is never above 26 A (6 kW) so this is the design current he is using to calculate volt drop which then does comply using a 6mm² cable over 25m (and adding some for the internal circuitry).
If you have a split load CU then there is no spare way that is not already RCD protected so any additional RCDs such as the two suggested (RCBO in board and RCD in shed) are redundant but could be used in case of failure of the primary RCD.
If you have a high integrity CU then there may be a spare non RCD way and this could be protected with an RCBO, but in the shed would be more convenient.
Overall a few minor niggles but each to their own.

 

[gsc]

OP:
Are you sure he is fitting a RCBO to the house CU as it already has RCD protection so doesn't need it.
What is it about the electrician that makes you want to question him?

Hi Spoon,

So I have spoken with him again today regarding this.
He has said that what he wants to do is:
In my existing CU I have a spare slot next to my MainsSwitch, where he wants to connect the RCBO via the a Busbar. Then run 6mm2 3Core Armoured Cable to a length of roughly 38m give or take a couple or metres.From there the cable will fit into a Garage/Shed CU via an RCD which will have 2MCBs connected. One for lights and one for power sockets.

Looking at my equipment and lighting needs for the shed andgarden, he doesn’t feel I will go over 6KW of power usage at any one time andfeels that what he has stated will be ample. The Armoured Cable will go inPlastic trunking down a wall and along a concrete floor.
I am not an Electrician but understand it a bit so wanted todouble check that other people felt this was good enough?


I have been screwed over before by an electrician with ahouse rewire and so am very cautious.



Thanks
GSC