shed consumer unit

[Spoon]

Do you know why the armoured cable is going in plastic trunking?

 

[gsc]

Do you know why the armoured cable is going in plastic trunking?

He just said he will run it through plastic trunking to makeit look nice….

 

[Spoon]

He just said he will run it through plastic trunking to makeit look nice….

ok.
I understand you having doubts if last time you got shafted.

 

[gsc]

ok.
I understand you having doubts if last time you got shafted.

So do you feel that what he has offered is good enough? and seem legit?

Regards,

GSC

 

[Spoon]

All depends mate. Its hard to say exactly over a forum, without looking at what he is doing. Regs say not more than 37 meters, so I cant advise on "roughly 38m give or take a couple or metres". It's the same as I can't say to you it's ok to drive 31mph in a 30 zone.
The way the electrician has recommended seems ok as long as he follows the regs. (CYA.... I'm good at that)

 

[gsc]

All depends mate. Its hard to say exactly over a forum, without looking at what he is doing. Regs say not more than 37 meters, so I cant advise on "roughly 38m give or take a couple or metres". It's the same as I can't say to you it's ok to drive 31mph in a 30 zone.
The way the electrician has recommended seems ok as long as he follows the regs. (CYA.... I'm good at that)

Well it's a better response than no..... at least I know he isn't trying to rip me off or anything

Thanks Spoon.

GSC

 

[Spoon]

He still might be trying to rip you off with the price????? Not my place to ask...

 

[Guest77]

So do you feel that what he has offered is good enough? and seem legit?

Regards,

GSC

The job is probably okay, to get over the problem reduce the breaker size, job done.

 

[NDG Elecs]

The job is probably okay, to get over the problem reduce the breaker size, job done.

My thoughts exactly. I would drop down from 40 to 32A at house end. Hell, you could probably get away with a 20A unless you are an (extremely clever!) octopus and capable of using four power tools at once! Even in winter with a heater on probably no more than 20A will be flowing at any one time.

I am guessing that the spark in question is setting the RCBO up unprotected from the dual RCDs...as a high integrity CU. At least that's what I have inferred.

Should we ask if there is any extraneous metal work in the shed....is it PME.....best not go down that path eh!!

Yeah OK, octopuses are very clever.... I mean even clevererer than that tho!

 

[Guest77]

It will take a lot of power to trip a 20 amp supply, I bet my house only draws 40 at christmas with the cooker on and every socket in the house with something plugged in lol

 

[Darkwood]

This was my argument at the beginning, if the loads are variable then you have to assume the RCBO current rating is your demand as this is what it is possible to load the cable upto, if your supplying a fixed load then agree he could use a lower demand value regardless of rating of RCBO - so even a 32amp rcbo will not comply to VD.

This should be a 10mm cable, putting the cable in trunking will reduce it current carrying capacity as well as costing you more money, I cannot see the set-up but cannot understand why a neatly cleated swa will not do as it is.

The mains end is correct with the RCBO as I suspected you have a high integrity board with a few unprotected ways one of which he is using to feed the out building.

The chancers you would ever load the cable up enough to compromise volts drop is low but the fact is the design should stop you doing and not your usage habits.


I would be happy with his work personally if he fitted a 32amp RCBO with a 10mm SWA this will comfortably cover all the issues we have brought up, he's playing his calculations on the knife edge and he should be giving room for expansion, additional loads as the regulations recommend.

To summarise then -

32amp RCBO would be preferred to give you room for additions.
10mm swa is fine for volts drop at 40m.
The trunking is merely cosmetic and your choice as its just extra cost and if using a 10mm cable it won't compromise the design current as the cable has a lot of room for maneuver.

 

[HandySparks]

...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...

Sounds just fine. If the final circuits in the shed are, say, a 20A socket circuit and a 6A lighting circuit, the VD in the distribution circuit (SWA) can be based on a max load of 26A. In practice, you won't notice or care if the VD is on the limit for lighting (it's only a shed!).

I'd query why he's using an RCD in the shed as well as the RCBO at the supply end. Might as well just fit an MCB at the main board; no need to RCD protect the SWA whether buried or not (unless TT supply).

 

[Darkwood]

Sounds just fine. If the final circuits in the shed are, say, a 20A socket circuit and a 6A lighting circuit, the VD in the distribution circuit (SWA) can be based on a max load of 26A. In practice, you won't notice or care if the VD is on the limit for lighting (it's only a shed!).

I'd query why he's using an RCD in the shed as well as the RCBO at the supply end. Might as well just fit an MCB at the main board; no need to RCD protect the SWA whether buried or not (unless TT supply).

We all know in the real world it probably won't be any issue as you say it only a shed and what are the chances of the load been maxed, the supply will probably be 240 not 230 etc etc but what's the point of having regulations if we are not seen to adhere to them and design installs to meet them (regardless of the actual chances of a breach) the installers proposal has no room for maneuver and this is also in the regulations to allow for possible additions which could be likely.

Good point on the series RCD's, missed that he said the shed board would have one.