RADIAL SOCKET SPURS. How to install them correctly and safely.
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SPURS ON RADIAL SOCKET CIRCUITS may look the same as any other spur but they must be treated differently to those on ring circuits. This is one of the often asked questions and is an often misunderstood issue.
Why should radial sockets be treated any differently?
Are sockets allowed on radial circuits?
What size breaker must it be? Is it always 32 amps?
Here, in this video, we will show you several different scenarios and give you the information that you need to be able to install spurs on to radial circuits efficiently and safely.
A correctly installed spur will help to protect the users from the dangers of electricity and reduce the risk of fires in buildings.
In the video we will also explain the requirements of the Wiring Regulations in relation to radial spurs so that you are able to carry out the work with confidence.
Electricity is dangerous. Always work within your capabilities and seek competent advice if required.
This video is for general guidance and education only, every electrical situation is different and you must ensure that you have taken appropriate steps to ensure your safety and understanding of the particular circuit that you are working on. Not every electrical situation can be covered in this video.
SEE ALL - To view a list of all our LearnElectrics videos, click on the link below. There are many videos on many electrical topics including Installation, Part P, 18th Edition, Testing, Certification, Lighting, Sockets, Ring Circuits and much more. kzhead.info/tools/YaJQnpO4XAp0yCgqzMkmfA.html
This is a fabulous channel for anyone wanting common sense and clarity. Please keep making more videos as you just have a gift in being able to transfer your knowledge so easily. So glad I found it!
Thank you! Will do. There are over 200 videos on the channel and new ones every week. Thanks for watching.
Thankyou. We try our best.
Top notch channel. Thank you for your work. Your teaching is so valuable.
I appreciate that, thank you. Dave.
Really good tutorial. Answered all my questions. Many thanks
Happy to help. Dave.
Excellent explanation. Thank you
You are very welcome and thanks for the positive feedback. Lots more videos on the way.
Doing my house extension electrics, following your instructional videos has helped me no end and saved me £££, thank you!
Thanks for the comments, appreciated. Glad the videos have helped. Dave.
Honestly this channel should be up there with 100k subscribers very informative and clears a lot if doubts ... one request could you do a video on kitchen wiring design using just a 6/4 mm cable spuring off for cookers,sockets etc I know the ring design with 32 amps and cooker with 20 amps but I'm really interested in how electricians use just the one radial circuit with fuse spurs using 4/6mm cable
Thanks Allah. Certainly a video to consider. Thanks. Dave.
Just about to wire my shed. This video is like gold dust,! A rare but valuable explanation which I’ve been looking for, for ages. Thank you, I will follow these rules to the letter.
What excellent feedback and great to know it has helped. Good luck with the shed. thanks for watching and lots more to come. Dave.
Love it confirms my understanding of a radial
Thanks for watching, glad it helped. You may find this video on ring and radial differences useful. Dave. kzhead.info/sun/aauHkpWLineghJ8/bejne.html
Nice explanation, thanks.
Glad you enjoyed it. Always trying our best. Thanks, Dave.
This is very clear and helpful, i am a lot clearer now on radial circuits.
Great to hear that and thanks for watching. Lots more to come.
Wow! This is very informative, thanks for sharing it with us Dave. It worth it and the best tutorial on the topic for me...dl
Glad you enjoyed it Daniel. thanks for watching.
@@learnelectrics4402 You are welcome
Good explanation 👍
Thankyou very much. Dave
Perfectly informative and helpful. It’s given me valuable information to add additional sockets in my garage. Really appreciate your effort
Thank you Jamie. Great feedback, glad it helped. Dave.
very good explanation, better than at college
Excellent, just what we want to hear. Thanks. Dave.
At 5:48. The two spurs with only two single sockets on each. These two spurs off the 4mm radial can be in 2.5mm cable. The maximum current the two sockets on each spur draws is 26A (13A for each socket). The fuses in the plugs limit the current draw on this spur, not the 32A MCB at the consumer unit. 2.5mm cable is rated at approx 27A maximum current draw, so 2.5mm is suitable. If the 2.5mm cable is seriously derated because of being surrounded by insulation, etc, it can draw a max of 25A, then 4mm cable has to be used. No need for an FCU in the spur as the fuses in the two plugs will allow only a max 26A to run in that spur, below the 2.5mm cable's current rating.
Thanks for the info John.
thank you
You are very welcome Jimmy, thank you.
Hi buddy, great video as usual. But quick question. For 32amps radial circuit in the osg the only reference method where the cable current carrying capacity is more than 32amps is clipped direct i think without it having it front of me. Would you not go 6mm just to be safe? Im still learning so just asking mate.
For a 32A radial socket circuit, use 4mm. Take a look at the video on the link below, it will explain all. kzhead.info/sun/qq98qMt9jp6be6M/bejne.html
Can you connect 5 different kitchen appliances on a radial on 4mm cable or is it best to add it to ring
Have a look at this video on ring and radial circuit differences. Hope it helps. kzhead.info/sun/aauHkpWLineghJ8/bejne.html
I have just started my kitchen unit refurb, and have found just 1 twin socket wired to a radial circuit The radial is the old cooker circuit, now on a 16A MCB, in CU. 2.5mm cable to the socket, from junction box fed with 6mm (original cable). Pretty sure i can have a few more sockets & extractor feed from this circuit ??
With a 16A breaker and 2.5 T/E on a radial circuit, you can add sockets etc. as you wish as per the video. Dave.
Hi there! I've got a 1 socket spur at the moment under my kitchen cabinets. Can I change it to a double socket outlet and connect my dishwasher and washing machine on it pls? thanks
A spur can be one single socket or one double socket. Thanks for watching. Dave.
Hi Dave, just seen your Radial socket spurs video. Can you comment please. Re: My integral garage. My main fuse box inside the house has a single 16A Breaker marked garage socket only which serves a single 13amp socket in the garage. The wiring is 2.5mm and is a single twin and earth cable. Does this arrangement tick the box as a true radial circuit as I thought initially it was a spur coming down the wall from upstairs in 20mm white upvc conduit. I want to increase the number of sockets by a factor of 4 making 5 double sockets suitably arranged around the garage walls. Your diagram around 5.28 minutes into your video seems to fit perfectly which suggests it's ok for a circuit to use a 16A or 20A Breaker. I do also want to use a FCU switch either side of the original double 13amp socket so I can isolate the 4 new double sockets either side of the original socket fitted by the builder. Like a U shaped configuration of sockets, 2 down the left wall, 2 down the right wall and the original socket on the back wall. So my question is, if the builder's electrician used a radial circuit from the main fuse board to the garage and marked the 16A Breaker as Garage Sockets does your diagram at 5.28 minutes fit my understanding that I can extend this radial circuit the way your diagram suggests and extend either side of the original socket. Finally given the fact the fuse board 16 A Breaker is clearly marked garage sockets and is a single length of 2.5mm twin and earth can I be sure this is not a spur from the upstairs ring main. Cheers Steve
Steve, only you can be certain it is a single cable from the 16A breaker. Plug something into the garage socket and turn off the 16 A breaker, if it loses power then the 16A breaker is on that cable. You can also do the same with the ring that you suspect. Turn the ring off and see what happens in the garage. Yes, you can extend a radial circuit as you suggest, remember not to overload by plugging too much into the sockets. 16 amps is still your total load shared between the sockets.
Thanks Dave, appreciate the prompt feedback. I did turn off the 16A Breaker marked garage socket at the fuse board and the power was turned off at the garage wall socket. I will do the same with the Breaker that controls the upstairs ring main wall sockets just to be sure that power is still ON in the garage. Pretty sure this will confirm the garage power supply is a radial circuit. Your KZhead channel was the only one I understood because it dealt specifically with Radial circuits and additional power sockets. Great video and what I took from it was the importance of protecting the cable at all times. I have fitted two fused switches, one either side of the original 13amp double wall socket as I want to isolate the extra sockets when not in use and only turn either of them on when I need power to various power tools. The wiring to these 2 fused switches was also taken off another KZheadr due to the switch needing a Supply in and a Load out. I hadn't appreciated that a fused switch requires a power in and power out configuration. Thanks again Dave @@learnelectrics4402
Hi Dave, may I share a current challenge (no pun intended) ? I am refreshing some garage electrics and can not locate the source of the spur that feeds the single 2.5mm T&E entering the garage from an underground conduit. I do know (by electrical isolation) the spur comes off the only ring final in the main house but can find no fused connection unit. I was proposing my best compromise to fit a 13A FCU as the first item on the garage circuit. This clearly leaves the 2.5mm spur from the house vulnerable to a short circuit fault as the ring is on a 32A MCB with RCD upstream, but it would limit the current drawn in non-fault conditions. Any thoughts?
Mike, refusing at 13 amps will certainly make that part of the circuit safe. Another option I have done in the past is to rewire the whole circuit from either the CU or a point at which I know where the cables are coming from. Even though you do not know where the connection is made, the 13A FCU in the garage will disconnect at 15 to 17 amps and stop any flow along that leg from the house so it is theoretically still protected. Not the test book answer but you are making it safer which is important. Good luck. Dave.
@@learnelectrics4402 Thanks for sharing your thoughts.
My pleasure Mike. good luck.
I am trying to work out how to do a radial run from a 32amp breaker that needs 4 FCUs for washing machine, dishwasher, extractor hood and built in microwave. Your video says that it needs to be run with 4mm cable but as I understand it the FCUs must be spurred off sockets meaning that 3 cables need to go into each terminal on the socket. But three 4mm cables don’t fit. Can you advise me please on what to do? There are no free 20amp breakers available in the consumer unit. Thank you for your time. These videos are excellent.
No John. Wire the FCUs just as you would sockets. Run 4mm to the first FCU and back out to the next FCU and so on. Just think of it as one long line of cable 1 cable in, 1 cable out. You can even go socket, FCU, FCU, socket. Its a radial circuit so just daisy chain it. The loadside cable from the FCU to a single appliance can be in 1.5mm cable. The 3 cable ideas are only if you spur off after you have all the sockets in and no room for manouver on cable positions.
@@learnelectrics4402 thank you so much for replying. So the in and out to the next FCU is only 2 cables....feed in and feed out to next FCU. And because the FCU has two sets of entry points I’m only cramming 2 cables into the in....and then out....bit and one from the separate load terminal to the plug socket for each appliance? If I’ve got that right? I’ve been watching all your videos on lighting, ring and radial circuits and they are so well presented and understandable. Just needed to get this clarified. Hope I’ve got it right this time, thanks to your advice which is much appreciated.
My pleasure John. Yes, you've got it now, two cables for the supply side, and one for the load.. Good luck with the project. Dave.
Hi, Thanks for the video... Why do you need to put thicker 4mm cable just before FCU, but OK to do 2.5mm after... Will this bit of cable just before FCU be ever overloaded as it only will ever drain on this cable as much as the FCU allows? Hope this makes sense
Good question. Until the conductor has passed through the FCU it is not protected by the FCU and so must have the same rating and size as the rest of the circuit before the FCU. Hope this helps. Dave.
@LEARN ELECTRICS Thank You for your reply. I just cannot get in my head, even if its not protected by FCU, how could possibly be this cable overloaded if this only be drawing power required by devices behind FCU... If its legal requirement then so be it I just cant get my curious head around this...
Its not just a little bit of cable. It actually goes all the way back to the CU before it meets a fuse to protect it. Fortunately, we don't make the rules. Sometimes we just have to go with the flow. Good questions though and thanks for viewing. Lots more to come. Dave.
Mr Gresso, a cable can be protected by a fuse downstream or upstream - nothing wrong with that. So effectively you are correct. Convention is that a cable is best protected by a fuse downstream - so everything _after_ the fuse is protected. For tidiness the 4mm is run to the FCU.
How do you know/work out the design current demand, does it go off the number of outlets?
The anticipated loads on the circuit. Difficult with sockets I know. But ... think about it. Which circuit is likely to be heavily loaded, the kitchen where the kettle, washing machine, toaster, dishwasher are, and the food mixer and anything else. Perhaps over 20 amps at times so you might need a 32 amp breaker Then you have the bedrooms, a TV, a computer and a bedside light. 5 amps if you are lucky, so a 16amp breaker may easily be big enough. Good question, thanks for watching.
Hi Dave I have a question How many sockets can we put on a 32A ring main ? Can you explain please
That's always a difficult one Emi. Theoretically as many as you want because the 32 amp breaker will stop you overloading the circuit. In practice just be sensible, what do you use the room for. In the lounge you might need 4 behind the TV and 2 doubles at different places in the same room. In a bedroom, perhaps only two in each room. A kitchen - well, loads but will you have everything plugged in at the same time, they are usually placed for convenience. There are suggested numbers by some organisations but they are all slightly different. I might put together a list of sensible quantities. Thanks for watching.
I have a 9 kva generator rated 220 volts 30 A. Can it start and run two hairdryers rated 2000 watts 220 volts each at the same time simultaneously? Another question if i connect two of them, which mm cable can i use and the socket should be rated how many A?
Take a look at this video on the power matrix. It will help you to calculate all the loads you want to run off the generator. kzhead.info/sun/mcyBocOOh5iNm2w/bejne.html
You dont mention what the round white boxes are on your circuit diagrams? Presumably they are junction boxes to aid the extension of the circuit? Example at 05:42 into the video. Thanks
Spot on, JBs. Thanks for watching.
Could you answer this for me I run a radial in 2.5 mm armoured from the fuse board in garage on 16 amp breaker, to a summer house I have just four sockets I have 6 led spotlights inside with its own switch and 4 outside it with its own ip rated switch but I just wondered I’m taking two fused from the radial to provide power to the light switches is it ok to have them in the radial or should I spur off the radial you know what I mean ?
It is recommended that you use a 3A fused spur for the lighting. some sparks use a 3A switched fused spur as the light switch. Take a look at these two videos. I don't know the length to your summer hoiuse but make sure that the voltage drop is ok when lots of things are switched on. The videos will show you how to do it. Dave. kzhead.info/sun/obqTla1-nHetn2g/bejne.html kzhead.info/sun/aauHkpWLineghJ8/bejne.html
@@learnelectrics4402 cheers it’s from the garage fused board it’s only 27 metres I think I will use two fused spurs to feed each switch. I’m a JIB electrician but not done it like this before thanks will watch. It going to be a very low wattage heater and tv on occasion and the lights which are nothing down there it’s on a 16 amp breaker in 2.5 armoured down never put a fused spur within a radial like this it’s fine isn’t cause you don’t want to spur of a spur it’s just wants to be part of the radial doesn’t it ?
at 7:51 why is the bottom left socket ok using a 2.5mm cable? theres no fuse between the socket and the break unlike the FCU on the right
Its a radial circuit and the cable is the same size as the cable coming out of the breaker. Have another look at the video, you will pick it up on the next viewing. Thanks for watching. Dave.
27 A for 2.5 mm² sounds much. In Finland max allowed is 16 A (theoretically 19 A). On surface mount one could use 25 A.
Many countries have their own rules. Thanks for watching, very much appreciated. Dave.
+LEARN ELECTRICS Why is the secondary-side of FCU shown as needing 2.5mm cable, surely this can be reduced to 1.5mm, in the same way as FCUs attached to Ring-Circuits ?
The slide is showing just one example of a reduction in size from 4mm to 2.5mm. This is qualified 2 slides later where it states the secondary side can be 2.5 or 1.5. Hope this helps.
@@learnelectrics4402 Oh you are right, apologies!. In which case, I have a different inconsistency to raise!. I'm covinced the unfused-spur cable going TO that FCU could be 2.5mm for the same reasons that the double-socket could be an unfused-spur of 2.5mm ... so long as the input-side of the FCU is not extended further.
Not according to the Wiring Regulations, until it has actually gone through the 13A fuse it is still being protected by a 32A breaker. What if there is a short circuit in the FCU on the input side. The 13A fuse will not be in circuit to give protection. Remember, the fuse or breaker is there to protect the cable. Thanks for taking the time to view the video. Hope you enjoyed it.
@@learnelectrics4402 The same applies to double-socket as unfused-spur you show on same diagram, (and similarly for 2.5mm spur on a ring circuit ), in either case it is accepted the shorter bit of 2.5mm is not resistive enough to prevent MCB tripping in 0.4sec even with 32A breaker, and is accepted the downstream pair of 13A fuses limits the current you can take from the spur. The FCU has the same property and should be no different in accepting 2.5mm as the unfused part of the spur and then 2.5mm or 1.5mm beyond it.
Thanks for your useful input, great stuff. Dave
I thought you are unable to spur on another spur ? Without a fused socket added ?
A lot of people think that Joshua. This video is about RADIAL circuits which are different to RING circuits. If you follow the rules regarding cable sizes and breaker sizes it is permitted in the Wiring Regulations. Hope this helps. Dave.
We have a maximum number of 12 for sockets in every circuit, but unfortunately I don't know from which standard they have translated it 🙂
We are only using UK standards here Sajid. Any maximum number is either custom and practice or just a recommendation. Hope this helps. Dave.
isn't it 27A in air? and 21A when in the walls, due to insulation?
For 2.5 and ref method C it is 27A. Ref method C includes clipped direct to the wall and skimmed over. Hope this helps. Thanks for watching. Dave.
There's no such thing as a spur on a Radial
Take a look at the Wiring Regulations page 556 where it talks about spurs on radial circuits. Thanks for watching,
@@learnelectrics4402 if it's the same size cable/correct size it's not a spur on a radial it's extending the leg.
Hi Dave,in a radial 32A breaker size and 4mm square cable ,why is it safe to add one spur socket using 2.5 mm square cable? Sorry to trouble you but I will be very grateful for your answer.Thank you.
One spur socket will have a maximum load of 13A on the circuit. 2.5mm cable has a capacity of 27A, so the load is not going to overheat the spur cables. Have a look at this video, EXTENDING SOCKET CIRCUITS, click on the link below kzhead.info/sun/ZtF7iLJ6rqKui6c/bejne.html
thank you
Thanks you. Glad that you find them useful. Dave.