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Discussion Starter · #1 ·
I know this has been asked before but I believe it was a fair time back. I'm laying undeerground SWA cable around the side of the house to the front for a kitchen (we have a large B&B and room for a self catering unit, no way through the house). While I'm at it I'd like to lay cable for electric charging points. I'll be laying to depth/spec and taking into account voltage drop for length (inc photo's so end fit can sign off on).
I would like to know more on the cable spec required, or a good company to work with (Scottish Highlands). I've just started this research so am brand new to the EV scene (without having an EV car). The charging could be for ourselves or two to three cars. What threw me a little was the mention of an initial demand on certain Tesla's and also mention of laying two cables. Not even got to the charger unit ot if our house has the required input (which I'll find out in the next few days), including if grants are available.
I don't mind going overspec, like 10mm SWA XLPE (or is this even overspec?).
Thanks in advance
 

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You should probably lay an Ethernet cable or two in the trench too. Say if you get a proper smart charger such as Zappi and one for a wireless access point for general use/smart devices.

Cheers

EDIT cross post, lol
 

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What is your incoming supply rated at? Is this 10mm just supplying charge points?

It really depends how much power your wanting available for charging... A 10mm single phase cable can handle around 70A, so roughly two cars charging at 32A.

Clearly you might want more than this available if your wanting to give three cars the full 32A rating. Conversely if its a standard domestic supply rated 80 or 100A total, with all your B&B loads, you might not even comfortably have 32A total spare.

So a lot will depend on your incoming supply. A heavy consumer like a B&B might go three phase, and a 10mm three phase cable is likely plenty.
 

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If the cable run is less than 30 metres 6mm is enough, you can buy the ev cable with cat 5 or 6 in it.

If your planning on having 2 or 3 chargers I'd run 16mm 3 core to a dedicated ev db and a separate cat 6
 

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For full future-proof (nearly) 16mm 4-core. Covers the 3-phase possibility.
From TLC assuming 20m run:
10mm² 3-core - £5.14/m = £102.80
16mm² 4-core - £9.67/m = £193.40
Against the other costs of trenching, extra electrical work, actual charging equipment, or having to dig it all up again in the future because it wasn't enough £90 is small beer.

Or put a smaller cable in a duct, so you can pull extra cables in as needed ... Cost ??
 

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I used 16mm to get to my garage - about 10-15m or so. No regrets and for the price of the cable a no brainer .
Other are suggesting running a Cat5. Run several, even if you don't terminate them - if you need em and they ain't there it will cost you loads, but doing it at the same time with cost peanuts.
I have 8 between the garage and the house of which I currently use either 3 or 4 (I can't remember)
 

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You can set up Tesla chargers in pairs to load balance, which would allow you to fit 4 as 2 pairs load sharing, so you get the benefit of 32A charging when low demand, along with the capacity of 4 cars charging at up to 16A for volume.

You cannot mix and match but you could have 2x Tesla for load balancing along with another single 32A sockected unit to allow for Type 1 connectors to charge. That way you are pretty much covered for everything.
 

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Congratulations that you are thinking of this. It will make your accommodation desirable for booking. If the supply to the building is restricted to 100 amps you might just think of multiple 3.6 kw chargers. I am guessing that you might want to offer charging to 4 or more guests and that will be a challenge. However if you have 3 phase supply you can offer some 3.6 which would offer 40 kWh of charge overnight, or about 120 miles of driving and some at 7.2. Does not the Scottish tourist board offer advice on this?
 

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I know this has been asked before but I believe it was a fair time back. I'm laying undeerground SWA cable around the side of the house to the front for a kitchen (we have a large B&B and room for a self catering unit, no way through the house). While I'm at it I'd like to lay cable for electric charging points. I'll be laying to depth/spec and taking into account voltage drop for length (inc photo's so end fit can sign off on).
I would like to know more on the cable spec required, or a good company to work with (Scottish Highlands). I've just started this research so am brand new to the EV scene (without having an EV car). The charging could be for ourselves or two to three cars. What threw me a little was the mention of an initial demand on certain Tesla's and also mention of laying two cables. Not even got to the charger unit ot if our house has the required input (which I'll find out in the next few days), including if grants are available.
I don't mind going overspec, like 10mm SWA XLPE (or is this even overspec?).
Thanks in advance
10mm SWA XLPE is along the right lines. What is the approximate end to end length?

You want to consider how much spare end cable to leave to minimise future cable joints.

There is no initial demand for Teslas or any other BEV.
 

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You must take into account the end to end cable length. I had PodPoint install in my garage but it required a 70m run around the property from the meter. It included me needing to prepare the groundwork which involved 15m under the driveway and another 15m along a hedge. Luckily I used ducting (38mm flexible).

However, the electrician specced 10mm SWA which they supplied together with the data cable. They fitted it all but the charger kept dropping out after a few minutes. The supplied 10mm SWA cable wasn’t able to carry the voltage.

Our property was at the low end of the voltage limits at 223v. The voltage drop over the cable length at 32amp was 20v and the allowed limit was down to 217v but we were only getting 203v which was why it was tripping out.

They temporarily downgraded to 16amo which gave 3.5kW but they had to come back a few weeks later and replace the whole 70m run with 16mm SWA cable. Luckily the ducting made it relatively easy to replace the cable and all is now operating normally.

You will definitely need to accurately measure the cable length from end to end and also check the incoming voltage to your property if you are on single phase. The lower the voltage to begin with will need to be considered as there will be a drop depending on how many amps you need.
 

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The voltage drop over the cable length at 32amp was 20v
This was a grossly miscalculated (mis-assumed is probably nearer) cable size.
The regs specify a maximum permitted volt drop on a (non-lighting) cable run of 5% from the origin of supply, so 3 or 4% - about 9V - for the cable is a sensible target.
Length of cable run is a crucial number which even some electrical installers don't seem to understand.
 

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Discussion Starter · #17 ·
Thank you all! This information is proving invaluable. Especially tips on Cat cable (never knew I needed this), and stuff like surplus length for final fit, volt drop and trip, 3 phase, ducting with a pull through cable etc.
Will start digging soon in conjuction with input from an electrician to keep me right on regs. I'll also have a chat to some folk on what Strath Lodge is on at the moment (80/100amps etc).
Laurence
 

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I specified thicker than needed power cabling for our exterior 7kW charger (thinking one day it might be replaced with a dual socket model), but running some ethernet at the time didn't occur to me. In hindsight that would have been a good idea.
 

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Thank you all! This information is proving invaluable. Especially tips on Cat cable (never knew I needed this), and stuff like surplus length for final fit, volt drop and trip, 3 phase, ducting with a pull through cable etc.
Will start digging soon in conjuction with input from an electrician to keep me right on regs. I'll also have a chat to some folk on what Strath Lodge is on at the moment (80/100amps etc).
Laurence
Check any TT earth rod requirements too, given you're digging things up anyway.
 
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