Adding a second consumer unit to a garage CU - or alternative?

[albuquerque]

Hi all

I've got a CU in the garage, which is fed by 6mm CSA from the house CU on a 32A MCB.

The garage CU is already full with a 32A C MCB going to the welder socket and a 13A B MCB going to a ring.

I'd like to plumb my compressor in as it's currently on a BS1363 plug into the wall but occasionally trips the breaker.

I would add a 16A socket to the 32A line but the protection would be, of course, 32A. Then I though of a 16A FCU but it seems there's no such thing.
So my question is; can I spur another small CU off the 32A line and put a 16A MCB in there?

Now that I've typed this out it seems pretty clear that what I need to do is swap the existing garage CU for a larger one...!

Thoughts appreciated.

 

[ban-all-sheds]

What you need is to properly assess the load in the garage, and properly supply it not from the house CU.

And you need to have the installation in the garage properly implemented, which it currently is not.

And you need to have all this done by someone who knows what they are doing.

You also (if you haven't already got clearance from your DNO) need to keep your fingers crossed that your welder and/or compressor don't cause problems for your neighbours such that the DNO come investigating and find you to blame.

 

[Taylortwocities]

I'd like to plumb my compressor in as it's currently on a BS1363 plug into the wall but occasionally trips the breaker.

Which breaker does it trip?

 

[John D v2.0]

The garage CU is already full with a 32A C MCB going to the welder socket and a 13A B MCB going to a ring.

If the welder is ok for trip time and voltage drop on a 32a mcb, then I'm surprised a ring needs such a small MCB. Rewiring the ring if it's 1.5mm cable might be an option, alternatively similar to your suggestion, update the sockets MCB to 20a to the first socket and an fcu, connect the rest of the sockets to the fcu and plug the motor in there.

However this would all be subject to checking of the zdb at the garage and calculating the trip times. You'd also need to check the upstream mcb is adequate, having two 32a MCBs in series is not useful anyway.
And finally if the motor is over a horse power run directly from the mains you need permission to run it from your dno so they can check if it will affect other customers or the network.

 

[albuquerque]

Thanks John. That seems like a decent option - as it's not "simply" rewiring, I'll get our electrician to look at it.

I'm just going to ignore @ban-all-sheds response as paranoid nonsense. Having read through some of the other threads in this section, I can detect a megaphonic pattern.

 

[ericmark]

You can get 16 amp sockets with a mcb or RCD in the moulding for socket which would allow it to use the 32A supply.

 

[ban-all-sheds]

Thanks John. That seems like a decent option - as it's not "simply" rewiring, I'll get our electrician to look at it.

I'm just going to ignore @ban-all-sheds response as paranoid nonsense. Having read through some of the other threads in this section, I can detect a megaphonic pattern.

What a strange thing to say about what I wrote, when compared to what John wrote:

 

[albuquerque]

@ban-all-sheds I can read, and have been a lurker on here for a while.
I'm not going to play your game because I do have a life outside here. I am happy to take John's advice all day long because his responses seem measured and helpful.
Yours are not. Knock yourself out with a rejoinder if you like, but I've got all the info I need from the earlier responses so I'm going to happily (and productively) ignore what you come back with and get on with said life, enlightened by the helpful responses of John et al.

 

[ban-all-sheds]

Clown.

 

[ban-all-sheds]

Oh - and look, JohnW2 agrees with and approves of a post accusing me of writing paranoid nonsense when it is blindingly obvious that I said the same things as John D.

More indulgence of a pathetic desire to have a pop at me no matter how unjustified.

Your moral compass is broken, John - you need a new one.

 

[Steven Prentice]

I can see how you get confused, no help at all from ban-all-sheds. Would of course be more helpful to know how and why you think things are not cirrect. Its easy to sit behind a screen and say "thats not right" but much harder to suggest a workable solution.


So two devices rated the same (32A MCB feeding a 32A MCB ) is not the best. In the case of a fault, you never know which one will trip... and it might be better to put in a smaller MCB (25A maybe, but would this be OK for the welder?)) intio the garage.. and that way of course if it trips the lights in the garage will stay on (guessing the garage lights are fed from its CU somewhere)

Like John says, check that the ring curcuits wirig is OK and increase that to a larger MCB for the compressor.

However I would agree with John and Ban-All-Sheds and I think your thinking the same, to get an electrician to look at it and do the work Far better than us sitting behnd our keyboards guessing whats going on

 

[ban-all-sheds]

So two devices rated the same (32A MCB feeding a 32A MCB ) is not the best. In the case of a fault, you never know which one will trip... and it might be better to put in a smaller MCB (25A maybe, but would this be OK for the welder?)) intio the garage.. and that way of course if it trips the lights in the garage will stay on

Please show how much discrimination there is between a 25A and a 32A MCB.

 

[JohnW2]

So two devices rated the same (32A MCB feeding a 32A MCB ) is not the best. In the case of a fault, you never know which one will trip... and it might be better to put in a smaller MCB (25A maybe, but would this be OK for the welder?)) intio the garage.. and that way of course if it trips the lights in the garage will stay on (guessing the garage lights are fed from its CU somewhere) ...

It's actually far 'worse' than you think as regards having two MCBs on the same circuit. Even if you have, say, a 16A (or perhaps even 10A) one in series with a 32A one, there is no guarantee that the 16A (or 10A) one will trip before the 32a one in the event of a fault. Don't forget that until something trips and stops the current, the current due to a full-blown fault (i.e. a 'short-circuit') could easily be 'hundreds of amps' - which is almost as far above the trip threshold of a 32A MCB as it is above the trip threshold of a 16A or 10A one.

The more different are the ratings of the two MCBs, the more likely it is that the lower-rated one will trip first, but there are very few guarantees. With 32A and 25A, as you suggested, it would be almost down to 'tossing a coin' to determine which (or both) would trip in response to a fault.

Kind Regards, John