Workshop Wiring

[Technomorph]

Hi,

I am not an electrician. 

I am converting my integrated garage into a workshop. The house is three years old.

I need to provide power for two 16A machines, plus add some additional 13a sockets.

This is the current wiring: 

https://drive.google.com/file/d/1yjILTcdCxsTvVzHLnECpI-00qjUhHqlC/view?usp=sharing

This is the proposed wiring:

https://drive.google.com/file/d/1Sje0xiCu-eaPtvU9p7773DDoGvBtnmUx/view?usp=sharing

• Separate CU in garage
  
• Separate circuits for 16a sockets with Type C MCBs
  
• RCD to isolate faults to garage without tripping RCD in house
  

Is this safe and legit?

Is there a better way of doing this?

Cheers

 

[Andy™]

doesnt look too bad. you would be best using interlocked 16a sockets though

you also have no discrimination between RCD's so either or both would trip if there was a fault, so if at all possible and wiring allows id be removing the first RCD

 

[Murdoch]

New circuits fall under part P of the building regs. 

 

[Technomorph]

Thanks for the feedback. The work will be undertaken and tested by a qualified electrician - just want to be informed, plus I'm interested.

In terms of discrimination, could I replace the existing general RCD in the house CU with an S Type RCD like this:

https://www.rselectricalsupplies.co.uk/bg-electrical-double-pole-time-delay-rcd-80a-100ma-cur80100td_3934

and then use the following general RCD in the workshop:

https://www.rselectricalsupplies.co.uk/bg-electrical-double-pole-rcd-63a-30ma-cur6330_3931

Cheers

 

[Evans Electric]

I'd say no .    Your RCD in the main board must be covering other circuits ,  which don't need an S type.

Your electrician can probably reconfigure the main board  to  connect your 4mm garage sub main  to an MCB  only .    The Regs state that all cable buried in a wall  need RCD protection  so run it on the surface  if you want to  comply .  

Otherwise its looking good to go .    

 

[Andy™]

Thanks for the feedback. The work will be undertaken and tested by a qualified electrician - just want to be informed, plus I'm interested.

In terms of discrimination, could I replace the existing general RCD in the house CU with an S Type RCD like this:

https://www.rselectricalsupplies.co.uk/bg-electrical-double-pole-time-delay-rcd-80a-100ma-cur80100td_3934

and then use the following general RCD in the workshop:

https://www.rselectricalsupplies.co.uk/bg-electrical-double-pole-rcd-63a-30ma-cur6330_3931

Cheers

not that simple. the RCD in the house will protect other circuits and will eed to be 30mA without time delay (you cant get a time delay 30mA anyway)

 

[Sidney]

Depending on the layout of the property and the cable run to the garage I would probably be going down the switched fuse route after splitting the tails then off the a DB in the garage.

I would speak to your electrician and see how he would design it.

Is he on holiday?

 

[Sidewinder]

Plus no selectivity between the B32's & probably the C16’s & B32

I'd want to run the curves to know about the 16/32 selectivity.

 

[Technomorph]

Is there any issue with having a single RCD in the main house CU, and not one in the garage CU, thereby not having to worry about discrimination? The 4mm running from the house to the garage is buried in the wall.  It is an integrated garage, so technically part of the house.

In terms of selectivity for the MCBs, the trip curves from the manufacturers aren't very detailed, but if my untrained eye is not deceiving me for the MK curves, it would seem that if I use a C32a MCB in the house and leave the rest as they are, then selectivity between all the MCBs should work i.e. C16 -> B32, B32 -> C32. Does this seem sensible? I appreciate that viewing the curves is probably necessary to make that judgement. If you can be arsed, p585 of the following:

https://www.mkelectric.com/Documents/English/EN MK Technical Specifications/Circuit Protection/Miniatur Circuit Breaker.pdf

Here is an updated proposed wiring diagram:

https://drive.google.com/file/d/1VUy_tvqggusK6ahUOQOnfNT-eIjVFxwQ/view?usp=sharing

 

[kerching]

there any issue with having a single RCD in the main house CU, and not one in the garage CU, thereby not having to worry about discrimination?

Not if you don't mind going back to,the house every time it trips!

i put two emergency lights in my garage and every circuit has its own RCBO

 

[Sidewinder]

I've run the selectivity study for you, using MK data in the design software I use.

In the main board, C32.

In the sub board, C16 & B32 on separate circuits, 15m cable runs, 4mm sq radial on the C32, 2.5mm sq radial on the C16.

The cable sizes and lengths don't have any bearing really on the selectivity between breakers.

C32>C16, partial selectivity achieved

C32>B32, no reasonable selectivity achieved