New Shed Supply

Hmmmmm at shed/outhouse end you have around 6kW to work with (non XLPE)

Hmmmmmmmmmmm dont know what to say about that really.

 

Mind you, it may only be 200volts by the time the lekky crawls all the way up the garden.

 

The calculator is showing a vd of 7.9 volts Bazz - all calcs @ 230v.

 

In that case, JP, you are the only person who has actually calculated the volt drop.
Our esteemed original poster certainly has not. He's just installed some cable on the basis that it can be changed if the electrician thinks it isn't enough.


Not what i would call designing an installation.

 

The chap is going to break it at 32 amps Bazz - I dont know what to say about that now. Is it ok? Doesn't seem to cut the ice?

20 amp should be used? Not sure myself now

 

Start here
https://www.tlc-direct.co.uk/Book/4.3.9.htm

actually, start here
Requirements for Electrical Installations, Iet Wiring Regulations, BS 7671:2008+A3:2015 (Electrical Regulations)

 

Ok so here is the thing, SWA cable does not need RCD protection because it has adequate mechanical protection but because you are running a length of T&E before connecting it to the SWA you need RCD protection for that run of T&E which could be considered a silly design.

Furthermore you need to satisfy the complete mode of isolation at the source with a double pole isolator and as mentioned the length of the cable could well be extensive and require you to use a larger cross sectional area to overcome cable loss for use with a 30+Amp circuit.

You are talking about feeding a split load consumer unit from one 4mm2 long run of SWA cable from a single pole 32Amp RCBO which all be it if you had done this before 2015 it would not be such an issue but due to Amendment 3 it is now an issue.

Regardless of the consumer unit on the shed side and cable length, lets deal with the supply side.

If you look at XLPE Armoured cable table on page 8 for reference method D(in ground) you will see that you need for a 4mm2 cable and 32Amp MCB with of course a Double pole isolator. You can also see the Voltage drop constant per mV/A/m that is the loss in Millivolts per Amp flow for each metre to calculate your loss and it is sometimes good to add and assume an extra 10% to be safe as each connection also causes a resistance.

http://www.aeicables.co.uk/literature/CurrentRatings.pdf

Now you could make an isolated suply using a mini consumer unit with a double pole isolation switch and a 32Amp MCB feeding directly into the SWA cable and not going into some T&E chase connecting to the SWA in some strange location elsewhere. This design would be fed from the incomer tails by splitting them with a service block:

http://www.screwfix.com/p/2-x-5-way-dp-100a-service-connector-block-25mm/48024



Of course this would require isolation of the incoming supply to do this and by no means am i advising you to attempt this. It is a professional installation that is needed but for educational purposes only i have provided you with this information.

http://www.screwfix.com/p/wylex-63a-2-way-metal-consumer-unit/3056j



And all this work is required to be notified with building control as you are installing a new consumer unit.

You may be asking allot from a small 32Amp 4mm2 circuit to power an entire split load consumer unit but hey as long as you have a double pole isolation switch and a 32Amp overload protection for the SWA cable then it is ok. If your XLPE SWA cable is not long enough then buy some more SWA cable and extend it with the appropriate connector for use with Armoured XLPE cable. It could be done through a metal clad junction box but this will require periodic inspection as the screw terminals do come loose over time so you can't hide it, plaster over it or box it in somewhere which can't be seen. We always find it out and point the finger...

Furthermore you could get all fancy and use a rotary isolator. This would be powered from the RCBO in your consumer unit and the Live and Neutral would go into this rotary switch and then your SWA cable would be connected to the isolated side of the switch. Just remember anything that leaves the consumer unit in cable that is NOT mechanically protected such as SWA cable MUST be RCD protected. That means if you use T&E to hookup to a isolator it will need RCD protection.

http://www.screwfix.com/p/bg-4-pole-rotary-isolator-switch-63a-230-400v/8536r



NOTE: I am only providing you with this information so you can educate yourself(for educational purposes only), by no means am i saying you should do this and you use this information at your own risk. All electrical work now must be carried out by a Qualified person with at least a bare minimum qualification in a Electrical related subject so a GCSE life skills on how to wire a 3 pin plug is not considered an electrical qualification lol.

You must pay close attention to inspection and testing, any circuit must be tested before energising to be sure it is safe and sound and it requires labelling so people know what it is powering.

Hope this gives you an insight into just the scratching the surface as we say of what the job entails, food for thought maybe...

 

Sorry to pick, Fire but

and

You wrong there. That only applies if the cable(s) are concealed in walls etc at a depth less than 50mm from the surface. If its on surface/in conduit then RCD protection is not required. Unless the destination location or equipment requires RCD protection.

Again, sorry but that is total horse poo.
Anybody can do electrical work, but they must comply with Part P wrt electrical safety. If the person doing the work and it is notifiable (like this) then the DIYer must raise a Building Notice with the Local Authority and pay their fee BEFORE THE WORK STARTS and subject themselves to regular inspections. Usually the LABC will expect the DIYer to demonstrate compliance with BS7671 in the Design, Installation and testing of the installation. So the DIYer would need a set of calibrated test equipment (hireable) and also the ability to drive it and interpret the results.

When Part P started, many LABCs had electrical bods who tested notifiable DIY installations, but this service has all but disappeared. The LABC will expect out poster to test the installation and generate an Installation Certificate confirming compliance with BS7671. otherwise the Building Notice will not get completed.

 

I've an ongoing house refurb under a building notice. I'm doing some work and a builder has built the extension. Recently phoned my tame BC officer who has overseen the first phases of the work to see at what stage he wanted to do the next inspection, and informed him just starting first fix services. "You doing electrics yourself he asked"? "No, I said have a sparky coming in". His reply was (surprisingly) "you can do it yourself you know, you just need to get it signed off at the end" !! This from LABC!!

 

I am certain when i looked at it last year it mentioned the change from Competent to Qualified under Amend 3 but hey i stand corrected if this was another section in the IET guides instead of the BS7671.

Hey don't go spreading the surface mounted cables not requiring RCD many may get that confused and run a non RCD protected ring final in trunking. It is easy to neglect to read the final part of the sentence.

As far as i am concerned and yes this is my opinion is that anything leaving the consumer unit in regard to DIY should be RCD protected. You can't expect a DIYer to correctly perform a full risk assessment for a non RCD protected circuit. Unless of course it is SWA cable which is simply, very well mechanically protected.

 

Changed from Competent person to Skilled electrically.

Yes the wording had changed as i thought, qualified is used in the manufacturers guides and the BS7671 has changed from Competent to Skilled electrically.

http://electrical.theiet.org/wiring-matters/50/amendment-no-3/

 

Just your opinion. But let's think about your assertion. If the cabling has to be RCD protected, how on earth will the not-very-skilled DIYer know that the RCD works? Just press the test button? Or do all DIYers come equipped with a RCD tester?
Get real. Most of them only have a neon screwdriver.

Anyways, let's stick to what the regs say. Surface clipped cables, or wiring in trunking or conduit does not require RCD protection. Nor does SWA cable.

 

Me, obviously
Anyway, its beer o'clock.

 

Well yes of course, everyone does things differently.

Me I try to avoid using the rear entry points when fitting a consumer unit and use trunking above and bellow with steel or brass glands and nuts fastening the trunking to the metal clad consumer unit. Is this wrong to do it like this, NO are those that route the cables from the rear wrong, NO it is just that each person has his or her way of preference in doing things.

The regs are but guidelines to make sure we learn from our mistakes of the past and make sure we do not repeat them going forward and hence we follow these guidelines. As the saying goes there is more than one way to skin a cat.

So who is right... Well the person who puts the preservation of life and safety first, even if it costs a little more to do it.
So for the example you made about the extra sensor, well he was right because them sensors save life, what do you value more the £1000 or your life? You cant take the money with you when you are dead can you. Even if that extra cost saved someone else's life other than your own then you can feel proud of it.

As i have said many times on this forum i would like to see split load consumer units removed from the market, i think they are outdated and have overstayed their welcome. A fully populated RCBO consumer unit provides far more safety and versatility than a split load and yes they maybe double the price but again you can't put a price on safety.

Take a look at what you want achieve in your shed, if you installed a consumer unit with a main switch and then 6 RCBOS for each individual circuit instead of a split load it would be a far better option would you not say?

 

Beer O'Clock it is, well called..

 

I've seen DIY'rs hire, borrow and buy a multifunction tester before, just saying. lol

There are less expensive RCD testers on the market, you don't need buy a multifunction tester.
Whats wrong with calling in an electrician to do the test?