We are doing a full house renovation. The electrician put in two external 6mm cables to run lights and sockets to an outdoor office, lights and sockets to a garage, 2 x air conditioning units, external lights, an electric gate and an EV charger. I now find out the builder has only used one of these external cables. The electrician is telling me this is OK but I have my concerns. When I mention buying the EV charger he told me I could only get a 20A one however when I pulled a face, he said I could get a 32A one. I'm now worried. Am I going to run into problems?
External Electrics
- Thread starter Whoops330
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I have no idea why he unilaterally decided to do this. The problem is that the cables were supposed to be put underneath the new patio yet only one was put down. To use the other cable he would now need to pull up the patio!
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If it was in a written spec that there were to be 2 cables and they only fitted one, make them lift the patio, lay the second cable and re lay the patio at their expense.
Thats where ducting comes in handy for. Pulling additional. Cables into a area
Why was the builder fiddling with the electrics
Alarm bells
Alarm bells
6mm is good for upto 45Amps max, dependedent on length of cable run and a few other factors, so you could probably use it for a 40Amp supply with no issues, good enough for a faster EV charger. You can get good deals on charging on off-peak, so you are not likley to be using the office an charger at the same time, giving more 'head room' for the charger.
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How far away is this outdoor office?
As cable length has a significant impact as well as the load (Amps/Watts), upon selecting the correct cable size to meet the volt drop requirement of regs 525.1 to 525.203?
My gut feeling is as you say that 2x 6.0mm would have been a much better solution..
and a single 6.0mm could be pushing things a bit, unless the cable length is just a relatively short run?
If you are doing a house renovation without any written work schedule specifications then you may well have shot yourself in the foot... Whereas as ProDave said.. if the work was not done to the correct original specification then it should be rectified at no further cost to you!
I've been self employed for over 25years..
And I have come across loads of builders who claim to know "how to do electrics"..
But so far I have never actually seen one that does...!
I have however done numerous remedial jobs, rectifying builder ****-ups!
Some builders may know how to join two cables together; Live to Live, Neutral to Neutral, Earth to Earth. And are Ok at digging trenches to lay cables into.. Other than that they are generally out of their depth with anything electrical and should never be trusted!
Builders are normally good at mixing mortar and sticking bricks together to build walls.. Cutting timbers to make floors and stud-walls.. Leaving holes for windows & doors.. Drinking Tea and eating bacon sandwiches... Putting Acrow props in place ready for fitting an RSJ etc... BUT never trust them with cables OR pipes!!
As Binky said a 6.0mm cable is good for carrying 40amps.. but if the cable gets too long volt drop becomes a problem..
Plus considerations about what loads are actually in use simultaneously needs to be evaluated..
A 40amp load over 6.0mm cable supplying both sockets and lights would need to meet the 6.9v (3%) volt drop..
Which would start to exceed the 3% once you get to around 24meters in length.
e.g.
6.0mm CSA cable is 7.3mv/A/m.. and (7.3x40x24)/1000 = 7.01volts!
If just running 32A you start having trouble at 30m (7.3x32x30)/1000 = 7.01v
Or if your electrician was suggesting 20A, then maybe you cable is more like 47m long?
(7.3x20x47)/1000 = 6.86volts.. which is within the 3% 6.9v limit.
Basically we need a bit more information about the installation to comment on what potential problems you may or may not have!
As cable length has a significant impact as well as the load (Amps/Watts), upon selecting the correct cable size to meet the volt drop requirement of regs 525.1 to 525.203?
My gut feeling is as you say that 2x 6.0mm would have been a much better solution..
and a single 6.0mm could be pushing things a bit, unless the cable length is just a relatively short run?
If you are doing a house renovation without any written work schedule specifications then you may well have shot yourself in the foot... Whereas as ProDave said.. if the work was not done to the correct original specification then it should be rectified at no further cost to you!
I've been self employed for over 25years..
And I have come across loads of builders who claim to know "how to do electrics"..
But so far I have never actually seen one that does...!
I have however done numerous remedial jobs, rectifying builder ****-ups!
Some builders may know how to join two cables together; Live to Live, Neutral to Neutral, Earth to Earth. And are Ok at digging trenches to lay cables into.. Other than that they are generally out of their depth with anything electrical and should never be trusted!
Builders are normally good at mixing mortar and sticking bricks together to build walls.. Cutting timbers to make floors and stud-walls.. Leaving holes for windows & doors.. Drinking Tea and eating bacon sandwiches... Putting Acrow props in place ready for fitting an RSJ etc... BUT never trust them with cables OR pipes!!
As Binky said a 6.0mm cable is good for carrying 40amps.. but if the cable gets too long volt drop becomes a problem..
Plus considerations about what loads are actually in use simultaneously needs to be evaluated..
A 40amp load over 6.0mm cable supplying both sockets and lights would need to meet the 6.9v (3%) volt drop..
Which would start to exceed the 3% once you get to around 24meters in length.
e.g.
6.0mm CSA cable is 7.3mv/A/m.. and (7.3x40x24)/1000 = 7.01volts!
If just running 32A you start having trouble at 30m (7.3x32x30)/1000 = 7.01v
Or if your electrician was suggesting 20A, then maybe you cable is more like 47m long?
(7.3x20x47)/1000 = 6.86volts.. which is within the 3% 6.9v limit.
Basically we need a bit more information about the installation to comment on what potential problems you may or may not have!
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your builder is when he needs to put the 2nd cable under the patio
if only they had used duct, then they could have pulled in the 2nd cable with minimal effort...
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So who was 'project managing' this job?
Thanks for the replies. The builder was project managing the job and the electrician had followed the schedule in supplying the two cables. It is the builders fault that the second cable wasn't placed under the patio. The builder has agreed to do this now rather than not get paid!
Best you get the spark to do this, not the builder
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