Garage fed by 4mm SWA

[SarahB]

Hi all, I hope you're all well and looking forward to the weekend ! Can I ask a quick one please? I've been asked to put a 16 Amp MCB on to a garage Distribution Board, but its full so will obviously need changing. However, it is being fed by 4mm SWA. I thought it had to be 25mm tails, or have I misunderstood? I don't want to do it if it's wrong from the start. It's already running some sockets and lighting. Thanks for any advice on this

 

[Spoon]

Usually the garage consumer unit is fed from the consumer unit in the house. If you look at it you should see the 4mm cable going into it. Also if you are changing the garage CU or adding extra circuits to it, then this falls under Part P.

 

[SarahB]

Hi Spoon, and thanks for the reply. It certainly is fed from the main consumer unit, so does this mean it would be OK to go ahead? The Part P issue is fine, I'm registered to do the work. I really appreciate the help.

 

[Hawk81]

I don't mean to seem unhelpful but if you really need to ask these questions are you really sure you can be doing any of this work? It's very simple and basic questions. My first year apprentice can answer your questions.

 

[Spoon]

I have to agree with Hawk on his comment, but as you have stated that you are Part P registered then I will take your word for it, seeing that its nearly xmas and im in a happy mood.
Now you have to start doing all the calcs to see if you can add the 16A MCB. What is it for? What rating of MCB is the 4mm cable wired to in the house CU? How is the cable installed?

 

[Amp David]

Yes, you will need to install new 25mm SWA, i'd choose 3 core, the 4mm is no good imo:santa_smiley:

Take the 4mm an weigh it in:willy_nilly:

 

[ab1978]

first of all how far is the garage from the c/u in house what other mcbs are in the c/u in garage what size mcb is the 4 swa on? what circuits are in garage

 

[micknew]

Another DIYer, obviously!!

 

[seb77]

you dont need 25mm2 SWA to supply a garage with only 6amp lighting and 2 x 16amp circuits!!!!

 

[SarahB]

Right, thanks for the replies. I just want to clarify something, I was of the opinion that the 4mm was fine and was happy to do the cable calcs. This isn't a job I have been to, but was asked about by one of the lads who works for the same company. Have you ever given an answer to someone, and they are so sure that you were wrong that you have even started to doubt yourself? That is why I asked. I'm a bit upset by the response, if I'm being totally honest. Is it a sexism thing? "It's just a stupid woman." Fair enough, I'm fairly newly qualified but I always thought this was a great place to ask a question. Sorry, but I really am genuinely upset now.

 

[topquark]

The 4mm is probably ok, if it's xlpe sheathing (that would take up to around 42Amps total). You should also look at the earthing arrangements in the garage (and whether any bonding is needed).

 

[DurhamSparky]

Sarah, ignore some of the idiots on this forum! they like to lurk about and jump out every so often. ironically they are the same people who when a technical question is asked they shy away and don't say boo to a goose! they may have the qualifications but they are a breed from the 2.5 for sockets and 1.5 for lights school... or monkey see monkey do...

any way moving on 4mm is good up to 32A MCB installed in certain situation but anything below that is fine.

Check the Bonding and Earthing as usual and just swap the bloody box to a larger one.

Is the SWA using the 3[SUP]rd[/SUP] core as earth or the sheath!??

We all have to start from somewhere but people forget where they come from.

 

[Octopus]

Have I missed something but what is at the "house" end? If the client wants another 16A mcb have they said what they want to do with the circuit?

Sorry if this has been covered but that's where I'd be starting from.

 

[telectrix]

agree with both the last 2 posts. as long as your 4mm is protected by the correct fuse/MCB for the method of installation, then it will be fine, as long as you know the limitation of what you can load it with.

 

[Andyfm]

I don`t think it was a "sexism" thing, its just sounds like a very basic question from someone who is allowed to "sign off" their own work.