Jump to content

Installing Consumer Unit into my shed


Al80
 Share

Recommended Posts

My young lad wants to buy an inverter welder.  

 

He has found a welder which has a current range of 20A to 140A.  The supply required  is 16A

 

My shed is currently being fed by a 2.5 SWA cable which runs a number of sockets and a light.  The power is from fed the main house from a 20 A MCB.

 

The main reason for installing the CU is the welder as this needs 16A.

 

I was looking at installing the following

 

1 x 16A double pole 16 amp RCD

1 x 20A MCB - for sockets

1 x 20A MCB - for a welder

1 x 10A MCB - for lights 

 

I cannot see myself using more than 16A at one time.

 

Does the above sound ok?


I know that there is a risk the welder could pul more than 16A this tripping out the MCB.

 

Thanks.

Link to comment
Share on other sites

Very rare you run a welder at full capacity, i run my 140A on a 13a plug. It would only be a problem if continual blasting at 140A but in that case the welder just isnt upto it anyway.

Link to comment
Share on other sites

I have an old style transformer based stick welder. Had issues with it occasionally tripping the 16A breaker in my shed CU. Only when striking an arc first time when the welder is cold. This happens even when welding at very low currents like 40A. Think its an inrush thing.

  • Like 1
Link to comment
Share on other sites

11 minutes ago, Al80 said:

Thanks for that. 
 

I could buy a 120 amp welder that will work on a 13 amp plug but was worried about it blowing the fuse 

go for the 140 and run 2.5mm rods, usually around 60-70A, machine will run pretty much all day and not pop a 13A fuse

Assuming your 2.5mm supply cabe isnt 100m in length etc.

Edited by markc
Link to comment
Share on other sites

45 minutes ago, Al80 said:

was looking at installing the following

 

1 x 16A double pole 16 amp RCD

1 x 20A MCB - for sockets

1 x 20A MCB - for a welder

1 x 10A MCB - for lights 

RCD will need to be rated at a lot more than 16A, it will need to be rated at least as high as whatever protects the feed to the shed.

Link to comment
Share on other sites

Just now, Al80 said:

The MCB currently feeding the shed is 20A. To allow for downstream discrimination I was sizing the RCB in the shed for 16 A. 

 

Tut, tut! It's called selectivity now! ?

Link to comment
Share on other sites

1 minute ago, Al80 said:

The MCB currently feeding the shed is 20A. To allow for downstream discrimination I was sizing the RCB in the shed for 16 A. 

The RCD is a residual current device that trips on earth leakage.  The 16A is NOT a rating at which it will trip, that is just a measure of the maximum current that it can pass.

 

The over current protection is what the MCB's are for.  And with a 20A MCB at source and a 20A MCB in the shed it's pot luck which will trip.

 

With a 2.5mm SWA feed you might be able to go to 25A at the source

Link to comment
Share on other sites

22 minutes ago, ProDave said:

The RCD is a residual current device that trips on earth leakage.  The 16A is NOT a rating at which it will trip, that is just a measure of the maximum current that it can pass.

 

The over current protection is what the MCB's are for.  And with a 20A MCB at source and a 20A MCB in the shed it's pot luck which will trip.

 

With a 2.5mm SWA feed you might be able to go to 25A at the source

As I am not at home I can only guess that the RCD that is on the row where the shed MCB is on is probably 20 A

Link to comment
Share on other sites

Shouldn't your starting point be the load required at the shed then the cable length? 

 

What's your earthing system at the house end?

 

Have you exported the earth?

 

You could perhaps fit a switch fuse off Henley's and take a sub main to the shed...

 

Have you accounted for "discrimination" ? between any upstream and downstream RCDs?

 

Maybe consider a small all RCBO board at the shed? You're welding, at night, and the lights go off! ?

Link to comment
Share on other sites

The load on in the shed will be no more than 16 amps.

 

The earthing on the house is an earth rod.

 

it would be very very hard to run a new line from the current CU to the shed. 
 

To be honest it’s more looking like the welder may not be an option using the  current 2.5 wiring going to the shed without running into issues. I could change the MCB to a type C or D but to accommodate for the surge in power but am not in favour.

 

I will have to look further at selectivity between the rcd between the house and the shed

 

 

 

 

Link to comment
Share on other sites

5 minutes ago, dpmiller said:

an inverter welder will be just fine at sensible current levels.

Totally agree.

ive been using arc welders on very long extension leads for years.

All the above information is valid but to get back to your lad using a welder … get him one, plug it into a 13amp socket and get him welding.

I doubt you will end up drawing more than 10amps with the machine set at 80-90amp and that will do you fine for most steel you will use

  • Like 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...