Shed Electrics.

[SlipperySid]

A couple of question. Electrician has run swa down to shed and is terminated in a metal box that will be connected to a garage consumer unit similar to this set up.

What size if cable will be used from the box to CU?

If I want an external socket I can switch off so no one can use it when I'm not around what's the best way to do this? Add it via a switched FCU?

Thanks.

 

[ban-all-sheds]

What size if cable will be used from the box to CU?

The size chosen by the person who installs the CU, designs and installs the final circuits, and who carries out all the necessary tests on them and the sub-main, and then signs this declaration:

I being the person responsible for the design, construction, inspection & testing of the electrical installation (as indicated by my signature below), particulars of which are described above, having exercised reasonable skill and care when carrying out the design, construction, inspection & testing hereby CERTIFY that the said work for which I have been responsible is to the best of my knowledge and belief in accordance with BS 7671:2008, amended to 2015 except for the departures, if any, detailed as follows:

Somehow I don't think that can be you.

If I want an external socket I can switch off so no one can use it when I'm not around what's the best way to do this? Add it via a switched FCU?

Sounds as good a way as most.

 

[JohnW2]

If I want an external socket I can switch off so no one can use it when I'm not around what's the best way to do this? Add it via a switched FCU?

.. or maybe just a suitable switch - the plugs that going into the socket will have fuses.

Kind Regards, John

 

[bubachuba]

If I want an external socket I can switch off so no one can use it when I'm not around what's the best way to do this? Add it via a switched FCU?

.. or maybe just a suitable switch - the plugs that going into the socket will have fuses.

Kind Regards, John

hey john.
although would need to be suitable for the protection. lighting switches are rated at 10A are they not?
best
buba

 

[SlipperySid]

The size chosen by the person who installs the CU, designs and installs the final circuits, and who carries out all the necessary tests on them and the sub-main, and then signs this declaration:

Ok, I'll ask it another way.

What size will it need to be, 2.5mm or larger?

 

[SlipperySid]

If I want an external socket I can switch off so no one can use it when I'm not around what's the best way to do this? Add it via a switched FCU?

.. or maybe just a suitable switch - the plugs that going into the socket will have fuses.

Kind Regards, John

hey john.
although would need to be suitable for the protection. lighting switches are rated at 10A are they not?
best
buba

One of these would do it then?

http://www.toolstation.com/shop/Ele...sd3354/Crabtree+20A+Double+Pole+Switch/p61802

 

[ericmark]

If you need a consumer unit I would consider you would have a larger than 20A supply so it would exceed 2.5mm² for my shed with socket and lights I could likely get away with a 10A supply and the 2.5mm² is only to guard against volt drop.

All that is needed is a switched fuse connection unit for the lights there is no need for a full consumer unit unless you are wiring the shed like a mini-house. Even a caravan normally only has a 16A supply.

Only when you want to use major heating appliances is a consumer unit required in the shed.

 

[JohnW2]

.. or maybe just a suitable switch - the plugs that going into the socket will have fuses.

hey john. although would need to be suitable for the protection. lighting switches are rated at 10A are they not?

That's why I said a suitable switch (probably a 20A one for one socket) - a light switch (as you say, probably 10A max) would not be suitable.

Kind Regards, John

 

[ericmark]

I being the person responsible for the design, construction, inspection & testing of the electrical installation (as indicated by my signature below), particulars of which are described above, having exercised reasonable skill and care when carrying out the design, construction, inspection & testing hereby CERTIFY that the said work for which I have been responsible is to the best of my knowledge and belief in accordance with BS 7671:2008, amended to 2015 except for the departures, if any, detailed as follows:

This is neither funny or helpful. I agree the poster does not seem to realise without giving the facts like what size protective device is used and length of cable no one can answer his question as to cable size.

However using a switch suitably rated to isolate a socket he has already answered his own question using a switched FCU you know the switch is suitable for the load. You could also use a grid switch face plate with a keyed switch next to socket.

I would have thought the picture actually shows a supply out of a consumer unit not a supply into a consumer unit. I see no point in supplying a large consumer unit with a small supply.

The only case where the supply and the unit being supplied have duplicate MCB and RCD protection is with caravans and boats where it would seem we don't trust the supplier to protect so we do it twice. I still think with a caravan a duel pole 16A RCBO (30 mA) as main isolator would be better with a smaller MCB for lighting. i.e. total limited to 16A not 16 + 6 amp.

From a 16A supply there is some sense in 10 + 6 as then overload on sockets will not trip lights. However since the RCD will not discriminate why bother with MCB?

I see nothing wrong with asking questions about something one knows nothing about. It would really help if a customer knew the difference between a RCD for all and RCBO's when asking for a consumer unit change. We see again and again how people have no conception on how using a fan heater, hot tub or electric patio heater will make on the supply required to a shed.

Small heaters with flues are made but in the main they are 12 or 24 volt DC motors with 25 sec or 35 sec gas oil or LPG I have not seen any 230 Vac direct powered. This is where the garden shed is different from a caravan with a caravan we have 12 volt and gas as well as 230 Vac so 16A is ample.

Once the poster says exactly what he has and wants I am sure we can help. As a guide a caravan works with 16A supply which is normally connected with 2.5mm² cable no longer than 25 meters so you should be able to supply a shed with 2.5mm² cable if it is supplied in a similar way. But as yet you have not said how the cable is protected.

 

[SlipperySid]

Thanks ericmark, at least someone can be adult about it.

There are two 20 amp mcb's in the consumer unit. One to the garage the second to the shed. From the cu to the shed there is already a swa cable which is approximately 25 metres long.

If one were to measure the swa I guess it would be a case of using the same size twin and earth to the cu?

 

[bernardgreen]

similar to this set up.

When fixing the front cover ensure the screws are NOT long enough to cut into the cables.

The "electrician" should have used the knock outs in the other walls of the box.
Connecting the banjo direct to the Earth in the terminal block would have been better than taking via two screwed terminals.

Even better to have stripped the SWA back so that the cores and inner sheath of the SWA could go straight through to neutral bar and MCB in the consumer unit

 

[SlipperySid]

similar to this set up.

View attachment 86107

When fixing the front cover ensure the screws are NOT long enough to cut into the cables.

The "electrician" should have used the knock outs in the other walls of the box.
Connecting the banjo direct to the Earth in the terminal block would have been better than taking via two screwed terminals.

Even better to have stripped the SWA back so that the cores and inner sheath of the SWA could go straight through to neutral bar and MCB in the consumer unit

That's not my set up.

 

[bernardgreen]

That's not my set up.

That is good.

Your set up will be better having seen how not to do it.

 

[ericmark]

Quick calculation I get volt drop to around 8.6 volt with 2.5mm² cable so it is a little high for lighting, but you are unlikely to draw full 20A anyway so I would say that is within limits. With an income of 0.35Ω you should expect an earth loop impedance at the shed of around 0.78Ω well within the limits. So it would seem there are no likely problems.

What we are worry about is the jobs worth electricians who unless spot on will not pass it. Your allowed a 6.9 volt drop for lighting and 11.5 for power. To my mind using LED lights often they will work 150 ~ 250 volt so the extra volt drop in real terms is only a problem with fluorescent lighting so I would not worry. However if one was to nit pick it will exceed the volt drop limit. Using a 16A MCB instead of 20A it will fall within the limits with a 6.7 volt drop I personally would only swap if caught out I some how do not think most electricians even work out the volt drop so likely they would not even know.

 

[SlipperySid]

Quick calculation I get volt drop to around 8.6 volt with 2.5mm² cable so it is a little high for lighting, but you are unlikely to draw full 20A anyway so I would say that is within limits. With an income of 0.35Ω you should expect an earth loop impedance at the shed of around 0.78Ω well within the limits. So it would seem there are no likely problems.

What we are worry about is the jobs worth electricians who unless spot on will not pass it. Your allowed a 6.9 volt drop for lighting and 11.5 for power. To my mind using LED lights often they will work 150 ~ 250 volt so the extra volt drop in real terms is only a problem with fluorescent lighting so I would not worry. However if one was to nit pick it will exceed the volt drop limit. Using a 16A MCB instead of 20A it will fall within the limits with a 6.7 volt drop I personally would only swap if caught out I some how do not think most electricians even work out the volt drop so likely they would not even know.

Thanks for that, the swa has already been fitted. Just not sure of the size. It's the run from the junction box to shed cu that's not there at the minute. That would only be about 300mm, I take it this run would need to match the swa in size?

This bit