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Hi all, getting some electrical work done on the house, including installing a power supply for lights, sockets and a powered rollor door to a detached garage. The garage currently has no power supply at all, and they will be installing armoured cable under the back garden patio. What size of cable would they normally use and would this be suitable to install an charge point at some later date ? If not, what size of cable should I ask them to install ? I don't currently have an EV but I am aiming to get one later in the year and I'm not getting a charge point installed until I have at least ordered the car as the supplier might even have some sort of offer on one.. For now, I just want the option. Presumably the extra cost of specifying a thicker cable now would be less than the cost of replacing the thinner one later !
 

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Hi all, getting some electrical work done on the house, including installing a power supply for lights, sockets and a powered rollor door to a detached garage. The garage currently has no power supply at all, and they will be installing armoured cable under the back garden patio. What size of cable would they normally use and would this be suitable to install an charge point at some later date ? If not, what size of cable should I ask them to install ? I don't currently have an EV but I am aiming to get one later in the year and I'm not getting a charge point installed until I have at least ordered the car as the supplier might even have some sort of offer on one.. For now, I just want the option. Presumably the extra cost of specifying a thicker cable now would be less than the cost of replacing the thinner one later !
if the distance isnt to great, 10mm should be more than adequate, just dont go plugging a hot tub in at the same time.. it happens..
gary
 

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. . . Presumably the extra cost of specifying a thicker cable now would be less than the cost of replacing the thinner one later !
Left alone, a general builder would probably go for a cable that would just support one 13A socket and a few lights - perhaps as small as 2.5 sq mm.

6 sq mm ought to be enough (unless it's a long way from house) for an EV supply and a small surplus but would need to be bigger if you plan on multiple sockets for a lot of heavt using equipment.

But if you run your cable through a large enough ducting (and leave a pull through rope in it) you can always uprate the supply at a later date without incurring much extra cost.
 

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I could very easily be wrong about this, but doesn't a charge point have to be on a completely separate circuit? If that's the case then you'd need a separate cable to be run through the ducting at the same time as your general supply, or just leave a draw cord for it to be added later as long as there is good access especially at the house end (and the ducting is a generous size), as Eric suggested.
 

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32A plus any other load - lights, sockets, etc.

Worth considering if there's anything more you might add in the future - solar, battery storage, etc. Upsizing the cable is pretty cheap in material cost, the total bill is mostly labour.
 

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I could very easily be wrong about this, but doesn't a charge point have to be on a completely separate circuit? If that's the case then you'd need a separate cable to be run through the ducting at the same time as your general supply, or just leave a draw cord for it to be added later as long as there is good access especially at the house end (and the ducting is a generous size), as Eric suggested.
Separate FINAL CIRCUIT.
 

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A lot of ifs and buts, but why not just tell your electrician that you want to be able to add a 32A load in addition to the lights and sockets. Or even go slightly further and get him to install a 32A Commando socket - that way the cable and consumer unit will be big enough for the job.

You can still get the OZEV grant, I believe, for swapping out the Commando socket for a chargepoint.
 

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I'd run a 16mm 3c XLPE/SWA and install an additional CU... 1nr EVCP may quickly turn into the need for 2nr EVCPs.. the Mrs may want you to chuck the tumble dryer outside to save some room in the kitchen.. you may chuck the kids or granny out there and convert to a room with electric heating... you may feel that your bills are high and want solar on the roof of your garage, etc, etc.. 6mm is enough for sockets and lights...
 

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It almost always comes down to voltage drop when sizing cable for a long run on any domestic job as the current rating really isn't an issue. 4mm² three core SWA is rated at 55A when buried, 6mm² three core SWA is rated at 69A, 10mm² three core SWA is rated at 92A and 16mm² three core SWA is rated at a ludicrous 119A, more than any domestic single phase supply can safely provide. Although is is generally good to oversize a bit if you can, it is worth remembering that copper prices have risen sharply lately and cable prices have risen in the same way, and there is no point at all in running cable that is massively oversized for the requirement, unless it is a very long run and there is a need to keep Zs low enough to meet the trip time of whatever over-current device is being used (MCBs are slower than BS88 fuses, for example). It's also a pig to manhandle hefty armoured cable, 10mm² is hard work and 16mm² and over is absolute swine to work with.

There is a useful calculator on the TLC site that gives a good idea of cable sizing and voltage drop and often gives a surprisingly small cable size for a given job, although it uses the tables from BS7671 so is compliant with the regs: Voltage Drop Calculator | TLC Electrical

For example, for a 20m run of armoured cable, run underground, then it's technically OK to use 4mm² for a load of 9.1 kW, although that is right at the limit and anyway charge points are all type approved for use with 6mm² cable, so although using 4mm² would be OK as far as the regs go it would probably be against the MIs, and MIs always trump the regs. Perhaps worth also remembering that ground temperature 600mm down in the UK is usually around 8°C, so it's fine to use the 10°C setting on the TLC calculator for buried cable, the default 30°C setting is really for cable that's clipped direct inside a building.
 

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It almost always comes down to voltage drop when sizing cable for a long run on any domestic job as the current rating really isn't an issue. 4mm² three core SWA is rated at 55A when buried, 6mm² three core SWA is rated at 69A, 10mm² three core SWA is rated at 92A and 16mm² three core SWA is rated at a ludicrous 119A, more than any domestic single phase supply can safely provide. Although is is generally good to oversize a bit if you can, it is worth remembering that copper prices have risen sharply lately and cable prices have risen in the same way, and there is no point at all in running cable that is massively oversized for the requirement, unless it is a very long run and there is a need to keep Zs low enough to meet the trip time of whatever over-current device is being used (MCBs are slower than BS88 fuses, for example). It's also a pig to manhandle hefty armoured cable, 10mm² is hard work and 16mm² and over is absolute swine to work with.

There is a useful calculator on the TLC site that gives a good idea of cable sizing and voltage drop and often gives a surprisingly small cable size for a given job, although it uses the tables from BS7671 so is compliant with the regs: Voltage Drop Calculator | TLC Electrical

For example, for a 20m run of armoured cable, run underground, then it's technically OK to use 4mm² for a load of 9.1 kW, although that is right at the limit and anyway charge points are all type approved for use with 6mm² cable, so although using 4mm² would be OK as far as the regs go it would probably be against the MIs, and MIs always trump the regs. Perhaps worth also remembering that ground temperature 600mm down in the UK is usually around 8°C, so it's fine to use the 10°C setting on the TLC calculator for buried cable, the default 30°C setting is really for cable that's clipped direct inside a building.
Where'd you get your figures from Jeremy? Isnt XLPE reference D 91A?

Add in few rating factors for temp/thermal resistivity/depth and we are probs down to around 75A no? Supplied from a 63A MCB, enough for 2nr 7kw chargers... say 58A on current UK voltage?... utilisie Zappis & harvis on octopus, you have full capacity between 0030-0430 when everyone is asleep.

10mm XLPE at 71A would be fine, but not alot of wriggle room in terms of rating factors.

Yeah VD prob wouldnt come into it unless the OP has a massive walk to the garage each day!

Copper is expensive, but so is doing it twice.
 

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Yep fair play, i just go with the big blue book.

There's always been a disparity between the current ratings for SWA in the regs and that from the manufacturers, for as long as I can remember. I remember having a heated debate with an IET bloke back when I was a Notified Body for the LV and EMC Directives and never getting a decent answer, and that was around 20 years ago. There are a lot of things in the regs that have been dreamt up by people that have zero experience of the real world, and who seem to focus on effects rather than causes. A good example would be fire resistant CU enclosures to fix the problem of crap terminations. The IET should have insisted that all terminations are made foolproof (the old two screw ones were pretty damned good) and condemned the crappy steel rising gate ones, but instead they chose to ignore the cause of the fires and instead try and stop the inevitable fires from leaving the enclosure. They are a bunch of muppets in my considered opinion (and that includes having spent several years teaching electrician apprentices in college . . . ).
 

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There's always been a disparity between the current ratings for SWA in the regs and that from the manufacturers, for as long as I can remember. I remember having a heated debate with an IET bloke back when I was a Notified Body for the LV and EMC Directives and never getting a decent answer, and that was around 20 years ago. There are a lot of things in the regs that have been dreamt up by people that have zero experience of the real world, and who seem to focus on effects rather than causes. A good example would be fire resistant CU enclosures to fix the problem of crap terminations. The IET should have insisted that all terminations are made foolproof (the old two screw ones were pretty damned good) and condemned the crappy steel rising gate ones, but instead they chose to ignore the cause of the fires and instead try and stop the inevitable fires from leaving the enclosure. They are a bunch of muppets in my considered opinion (and that includes having spent several years teaching electrician apprentices in college . . . ).
Yep, agreed, i like to work on the principal that Id rather loose the job by over spec and sleep easier at night.
 

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When I got my garage electrified I used 16mm SWA
The cost of the cable wasn't that significant against the cost of the job - and it only needs to be done once.
I now have a 7kWh EVSE
I also have about 7kWh of battery inverters for the house
Along with the usual lights, doors and other garage stuff
 

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Probably worth remembering that there are still a very large number of houses in the UK that only have 16mm² tails from the meter. Until about 20 or so years ago this was the standard sized used for every new installation and was considered fine to run a whole house. The regs upped this to 25mm² a while ago, but that only applies to new installations and there is no requirement to update any existing installation unless it gets replaced.

BATT 16mm² three core buried SWA is rated at 119 A maximum, 96 A if in a duct and 107 A if in air, which, even for someone being a bit conservative is overkill (unless it is a very long run and either the voltage drop or the need to keep Zs down to ensure a quick trip is an issue), given that most UK supplies are fused at either 80 A or 100 A. 10mm² three core SWA is rated at 92 A buried, 82 A in air or 75 A in a duct, and would be more than enough to run two 32 A charge points simultaneously with 4 or 5 kW of spare capacity at the same time.

Given that the total house maximum demand has to be measured/assessed before any installation of equipment drawing this sort of power, and given that a lot of houses may not have enough spare supply capacity to allow two charge points to be installed without some form of load sharing/load limiting system (either built in or via something like a Garo priority box), then it is hard to see the merit in going massively overboard with cable sizing. It is worth remembering that the almost standard supply cable to most UK homes is an AL/Cu concentric that is only rated at 100 A maximum anyway, so it is arguable that there is not much point in making any cabling downstream from that any more capable.
 

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Hi all, getting some electrical work done on the house, including installing a power supply for lights, sockets and a powered rollor door to a detached garage. The garage currently has no power supply at all, and they will be installing armoured cable under the back garden patio. What size of cable would they normally use and would this be suitable to install an charge point at some later date ? If not, what size of cable should I ask them to install ? I don't currently have an EV but I am aiming to get one later in the year and I'm not getting a charge point installed until I have at least ordered the car as the supplier might even have some sort of offer on one.. For now, I just want the option. Presumably the extra cost of specifying a thicker cable now would be less than the cost of replacing the thinner one later !
In this discussion, did the OP ever mention an estimated cable run length ( not the direct line distance)?
 

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Probably worth remembering that there are still a very large number of houses in the UK that only have 16mm² tails from the meter. Until about 20 or so years ago this was the standard sized used for every new installation and was considered fine to run a whole house. The regs upped this to 25mm² a while ago, but that only applies to new installations and there is no requirement to update any existing installation unless it gets replaced.

BATT 16mm² three core buried SWA is rated at 119 A maximum, 96 A if in a duct and 107 A if in air, which, even for someone being a bit conservative is overkill (unless it is a very long run and either the voltage drop or the need to keep Zs down to ensure a quick trip is an issue), given that most UK supplies are fused at either 80 A or 100 A. 10mm² three core SWA is rated at 92 A buried, 82 A in air or 75 A in a duct, and would be more than enough to run two 32 A charge points simultaneously with 4 or 5 kW of spare capacity at the same time.

Given that the total house maximum demand has to be measured/assessed before any installation of equipment drawing this sort of power, and given that a lot of houses may not have enough spare supply capacity to allow two charge points to be installed without some form of load sharing/load limiting system (either built in or via something like a Garo priority box), then it is hard to see the merit in going massively overboard with cable sizing. It is worth remembering that the almost standard supply cable to most UK homes is an AL/Cu concentric that is only rated at 100 A maximum anyway, so it is arguable that there is not much point in making any cabling downstream from that any more capable.
Jeremy, if you were to carry out a survey with regards to increasing additional loads on an existing install.. would you consult the manufacturers spec or bs7671?.. i feel that the manufacturers spec would only be applicable when guarantreeing where and when the cable was supplied from.
 

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Jeremy, if you were to carry out a survey with regards to increasing additional loads on an existing install.. would you consult the manufacturers spec or bs7671?.. i feel that the manufacturers spec would only be applicable when guarantreeing where and when the cable was supplied from.

You've hit the nail on the head here. I used to always teach apprentices to think, use their judgement, learn all they could from their apprentice masters and never, ever, get caught by the trap of thinking that the regs cover every use case. Sadly things have changed, and now someone can do a 16 week course and leave college with the misguided view that they are a "fully qualified electrician".

Good experience is worth a million times more than anything I ever taught an apprentice at college, and the same goes when using the guidance in BS7671 (and it is really mainly guidance, it is perfectly acceptable to do something not within the blue book if you can show, with evidence, that it is no less safe).

When it comes to MIs, then the same judgement is needed, along with some common sense that takes into account the circumstances of the installation. Sometimes MI's can be a bit suss, and might lead me to ignore the normal rule that the trump the regs, other times they will make far more sense than the regs. Take the cable sizing specced in most charge point MIs. 6mm is overkill in terms of both current rating and VD for most domestic installations, 4mm would usually be OK, and what would be used for many other similar domestic loads. However, most charge point manufacturers have taken the heat transfer at terminations into account and decided, very wisely, to specify 6mm mainly to reduce the possible temperature rise at the termination, and allow more heat to flow back and be dissipated by the cable.
 

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You've hit the nail on the head here. I used to always teach apprentices to think, use their judgement, learn all they could from their apprentice masters and never, ever, get caught by the trap of thinking that the regs cover every use case. Sadly things have changed, and now someone can do a 16 week course and leave college with the misguided view that they are a "fully qualified electrician".

Good experience is worth a million times more than anything I ever taught an apprentice at college, and the same goes when using the guidance in BS7671 (and it is really mainly guidance, it is perfectly acceptable to do something not within the blue book if you can show, with evidence, that it is no less safe).

When it comes to MIs, then the same judgement is needed, along with some common sense that takes into account the circumstances of the installation. Sometimes MI's can be a bit suss, and might lead me to ignore the normal rule that the trump the regs, other times they will make far more sense than the regs. Take the cable sizing specced in most charge point MIs. 6mm is overkill in terms of both current rating and VD for most domestic installations, 4mm would usually be OK, and what would be used for many other similar domestic loads. However, most charge point manufacturers have taken the heat transfer at terminations into account and decided, very wisely, to specify 6mm mainly to reduce the possible temperature rise at the termination, and allow more heat to flow back and be dissipated by the cable.
Too true. My own CP includes the final run through 400mm of foamed in-situ wall installation. By calculation, 6mm2 too small to conduct the ohmic heat. Used 10mm2 just for the through wall cable, rotary isolator on the inside, chargepoint on the outside.
 
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