Is a Larger MCB needed? Advise d

[Pepe]

I want to add a second light and a second socket to an additional lighting and power circuit in a family members garage.

Currently the power circuit is connected into a 16a MCB in the consumer unit in the garage. This is then connected to a 16a MCB in the main consumer unit in the house via SWA.

The appliances in the garage are a fridge, a chest freezer and a tumble dryer.

My calculations with diversity works out at about 18.8 amps of current.

I think i should swap the 16amp MCB's to 20 amp MCB for garage and 32 amp for the main consumer unit.

The lighting circuit only has two lights. Works out about 0.5 amp drawn.

Any advice would be greatly appreciated.

Also on a separate note. Is it acceptable to terminate Swa cable without a gland and piranha nut? It is just taped into the bottom of the consumer unit.

Also the installer has drilled holes in plastic pattress boxes and feed t&e into the boxes leaving gaps for dust to fall into! Again is this acceptable?

I don't think so, having just done the Level 2 2365 and 17th edition. But just wanted other opinions, as I'm still rather inexperienced.

Cheers for reading

Pete

 

[davesparks]

You cannot just swap the mcb for a larger rating without carrying out the design calculations, the installed cable may not be capable of safely carrying 20A.

How did you arrive at 18.8A? Domestic fridges and freezers are usually a couple of hundred watts at most, tumble dryers I'd expect be be in the 2kW region so unlikely to see above 11A on the circuit in my opinion.
Add this to the fact that it has presumably operated on a 16A mcb without tripping through overload?

Terminating SWA without a gland is not acceptable, a piranha nut is not essential a single there are other methods of connecting an earth to the gland.

 

[Ian1981]

Might help if we knew the size of the SWA and the installation method?

 

[Pepe]

Thanks for the quick replies.

I calculated based on power output of 4kw for dryer and 400w for each of fridge and freezer. Then did the calculations from the onsite guide.
Not currently tripping out, just wanted to make sure correct mcb's were installed. Thanks for clearing that up.

Cable is buried in garden then clipped to wall in detached garage.

Not sure size of swa.

Thanks again for replies

Cheers

Pete

 

[Ian1981]

I doubt your dryer is 4kw pete as that is a draw of around 17 amps!

 

[davesparks]

Thanks for the quick replies.

I calculated based on power output of 4kw for dryer and 400w for each of fridge and freezer. Then did the calculations from the onsite guide.
Not currently tripping out, just wanted to make sure correct mcb's were installed. Thanks for clearing that up.

Cable is buried in garden then clipped to wall in detached garage.

Not sure size of swa.

Thanks again for replies

Cheers

Pete

Where did you get those power ratings from? You will find all appliances have their power ratings detailed on a data plate attached to them somewhere.
Also you don't want the power output, you need the power input.

if the dryer really is 4kW then it must not be connected via a 13A plug as it would be overloaded!

 

[Pepe]

Just found the manual for it and it says it is 2.6kw

 

[Richard Burns]

Because you have an existing circuit the first thing you need to do is find out the size of the cable and the installation method so that you can calculate the current that the supply cable can take. This is slightly backward in comparison to designing a new circuit where you would find out cable length, installation method and design current and calculate volt drop first.
Even if the supply cable was 1.5mm² it could be connected to a 20A MCB (just).
If it was 2.5mm² then it would still be limited to 20A as it could not be connected to a 32A MCB.
Once you know this then you can consider the design current and see if perhaps the load in the garage should be reduced (often not an easy option with customers).
Because you have existing appliances they should all by law be marked with their power rating or current so the calculation should be easy, diversity would be the hard part but could be ignored for such a small arrangement.
Also since you are adding a socket the socket requires 30mA RCD protection if this is not already in place.
From the loads you describe 16A should be OK, whilst realising that there is no discrimination between the house protection and the socket circuit, this is hardly critical in this situation, just something for the owner to be aware of.

SWA should always be glanded, though in certain limited circumstances, such as the formation of TT systems, the earthing may not be continued on into the consumer unit, but it should still be retained securely.

The requirements for accessories are that horizontal top accessible surfaces should be IP4X and all other surfaces IP2X and also they should be suitable for the environment. For a garage sealing them against dust would sound sensible.

 

[Pepe]

Hi Richard

Thanks for the response. I am starting the Level 3 C&G 2365 on Monday. So I'm hoping I will be learning about design currents and diversity in more detail then.

My mum bought a new build from Taylor Wimpy two years ago. Whoever installed the existing plug sockets has cut messy holes in the plastic back boxes and poked twin and earth cable through the holes.
On the level 2 C&G I was taught to use glands with cable running into sockets and light fixings. Firstly to stop any stress on the cable and terminations and secondly to stop any dust getting into the back box. Is that right?

The Swa is wrapped in electrical tape and sellotaped into bottom of the consumer unit!

I'm guessing that time was of the essence for the installer and they subsequently cut a few corners.

 

[Pete999]

Hi Richard

Thanks for the response. I am starting the Level 3 C&G 2365 on Monday. So I'm hoping I will be learning about design currents and diversity in more detail then.

My mum bought a new build from Taylor Wimpy two years ago. Whoever installed the existing plug sockets has cut messy holes in the plastic back boxes and poked twin and earth cable through the holes.
On the level 2 C&G I was taught to use glands with cable running into sockets and light fixings. Firstly to stop any stress on the cable and terminations and secondly to stop any dust getting into the back box. Is that right?

The Swa is wrapped in electrical tape and sellotaped into bottom of the consumer unit!

I'm guessing that time was of the essence for the installer and they subsequently cut a few corners.

Did your Mum get an EIC with the new house pack from the Builders?

 

[Pepe]

I hope so, will check with her and see if I can dig it out.

Why do you ask?

 

[Ian1981]

If it was a new build then you should have received a EIC as builders require it for finishing dates and hand overs as well as being compliant with bs 7671

 

[Pete999]

I hope so, will check with her and see if I can dig it out.

Why do you ask?

Well, if anything is proven to be wrong with the Electrical Installation in your Mother's house, and you said the contractors who did the install belonged to one of the C.P. Schemes, there may be evidence that the EIC is fraudulent, or at the least not worth the paper it's printed on.
She may have cause to sue the builder, not sure if that would work, but it would prove that the Electrical Contractor that has installed the wiring, has done so with little regard to BS7671 the IET Wiring Regulations, this would be something your Mother would need to take up with her Solicitor.
Quite frankly, how these points were not picked up by the inspection She would have had done during the purchasing of the house is beyond me, something that sadly goes on a lot with new builds.

 

[Loki]

If i remember rightly clarkson evans do a lot of the electric installs on taylor wimpey sites in my area so it could be them. They tend to be cheaper in tendars than other companies due to the way they run teams. They usually work in a teams of 3 or 4. One qualified team leader & the others are apprentices at various stages.
The work is fast paced & as such quality of work can to suffer.