out house

[dingdonger1]

Hello all.
I have recently bought a house that has a small brick out house attached to the back of property which has power.

This is supplied via 16A mcb at main consumer unit with a 4mm twin and earth cable running to out house. ( cable run approx 10 meters from C/U - up through internal walls/ceiling then out through external wall in plastic conduit to junction box) The out house has 2 x 2 gang sockets fitted.

I was wondering if I would be ok to change mcb to a 20A to allow me to put more sockets in? i don't know what the rating of a 4mm cable is?
i would like to put fridge, washing machine, tumble drier and a few other smaller powered units in this out house but am unsure of loading etc

any help/advice greatly appreciated

 

[Iggifer]

You would be fine to uprate the MCB to 20a, the worst case for 4mm is 22a but I think you'll find, even if you add two more 2g sockets (i.e. to give you 8 sockets total) you still won't trip the mcb

You may get close to tripping it if you run the w/m t/d at the same time as the fridge compressor kicks in, but unlikely.

So long as you're smart about it, you will be fine.

 

[JohnW2]

Are you certain that it's 4mm² cable? It just seems a little odd that (unless they were being kind and thinking of 'future-proofing' for you!) anyone would install cable that large with a 16A MCB.

Kind Regards, John

 

[dingdonger1]

Yes it's def a 4mm cable as its stamped on cable. I was unsure of current rating of this cable and whats the max size of breaker i could utilise for this type of cable?

 

[Taylortwocities]

The size of the cores is actually 4mm² - that is the cross sectional area of the copper itself.

The size of teh cores is usually embossed on the outer sheath of SWA cables.

Please check for sure its 4mm². It will say something like 4mm x 3 or similar.

If it is 4mm² XLPE insulated cable then you could use a 32A MCB, subject to the usual installation tests of course!

 

[JohnW2]

The size of teh cores is usually embossed on the outer sheath of SWA cables. ... Please check for sure its 4mm². It will say something like 4mm x 3 or similar. ... !

... a 4mm twin and earth cable running to out house.

Kind Regards, John

 

[Taylortwocities]

Doh Doh Doh

 

[ban-all-sheds]

i would like to put fridge .. in this out house

Is it heated?

 

[ericmark]

I will try to tell you what should be done.
1) Find size of cable (seems you have done this)
2) Inspect the route and decide which reference method is appropriate. i.e. Reference Method A (enclosed in conduit in an insulated wall)
3) Look up on the tables to see the maximum current. (in example above it's 26A)
4) Measure or calculate the loop impedance.
5) From the above decide on protective devices required.

One would whoever selected a 16A protective device did all of the above however rules have changed and to add extra sockets it would need to comply with current rules. So first question is it RCD protected and if not what will be the method used to add this protection?

There are a number of ways to add RCD protection starting at a consumer unit with twin RCD's fitted moving to consumer unit with RCBO's fitted then an extra box with either a RCBO or RCD to using RCD fuse connection units (FCU) to RCD sockets.

RCD sockets are expensive and if your just adding one OK but if adding 3 or 4 then you may want one of the other options.

You state "up through internal walls/ceiling" and what is important is what thermal insulation is in those walls? If for example Reference Method 103 (in a stud wall with thermal insulation with cable not touching the inner wall surface) was the worst case on the run then maximum current for 70C thermoplastic insulated and sheathed flat cable is 17.5 amp.

So question has to be does it really need to carry more? Having 8 sockets is not really a problem if they exceed 16A it trips then you switch some thing off and reset. Then you look at if you can fit a larger MCB why worry until tried as it may just not be needed. Only if you were swapping MCB for a RCBO would you what to know first.

I worry at saying uprate MCB as I have done it in the past then visited the house and realised there was some thing missed out like going through a cavity wall now filled with insulating material.

It's not one size fits all Batt Cables like many other manufacturers publish the tables as linked here and you must decide which one of the insulation methods fits what you are doing. At the end of the job you will be testing and inspecting (well you should at least) and you will be completing the minor works certificate and signing to say all is correct (well you should). So it's up to you to decide if all complies and is safe. We can tell you to stick your hand in the fire and I would hope you would ignore it. It is the same with any other advise you have to decide and to do that you need facts not guess work so first work out what is the worse installation method used en-route then base your maximum size MCB on that not just guess work.