[LaurenceC]

Hi
I'd previously posted a query on underground cable size. I've dug the ditch for the kitchen cable and while I'm at it lay the EV cable (25mtr total inc terminations). House is 100A and TN-C-S. This is where I'm at....
For 3 cars at most on overnight charging 30A each I'm planning on laying 16mm 4 core.
The idea being if I need to go 3 phase I can, but can the 4 core be used in single phase applications...I'm not shooting myself in the foot? Also laying Cat 6 cable so thats covered. I was going to go 10mm but can go the extra cost for peace of mind.
Adequate?
TIA
Laurence

 

[Tandy0]

I believe I saw a single phase circuit using 4 core where two were used for live & two for neutral.

 

[LaurenceC]

I believe I saw a single phase circuit using 4 core where two were used for live & two for neutral.

Yeah I'm pretty sure it's possible, or unused cores are tied up to earth. End terminals are sleeved up appropriately...I believe

 

[freddym]

Hi
I'd previously posted a query on underground cable size. I've dug the ditch for the kitchen cable and while I'm at it lay the EV cable (25mtr total inc terminations). House is 100A and TN-C-S. This is where I'm at....
For 3 cars at most on overnight charging 30A each I'm planning on laying 16mm 4 core.
The idea being if I need to go 3 phase I can, but can the 4 core be used in single phase applications...I'm not shooting myself in the foot? Also laying Cat 6 cable so thats covered. I was going to go 10mm but can go the extra cost for peace of mind.
Adequate?
TIA
Laurence

Yes, 2 cores can be twinned up for single phase. Still need to consider earth faults.

 

[freddym]

I believe I saw a single phase circuit using 4 core where two were used for live & two for neutral.

Whilst you are digging, put in earthing.

 

[LaurenceC]

Whilst you are digging, put in earthing.

I thought earth was derived from neutral anyway. In a TT-C-S house the earth is taken from the supply neutral and sent out separately. I could be wrong in assuming it can be done again at terminal since the neutral would be armoured and a separate earth more prone to failure?

 

[Tandy0]

Use the armouring for an earth if necessary, surely?

Though I believe with detached garages, it is sometimes necessary to have an independant earth rod, as it is considered the house earth potential may be different.

 

[freddym]

I thought earth was derived from neutral anyway. In a TT-C-S house the earth is taken from the supply neutral and sent out separately. I could be wrong in assuming it can be done again at terminal since the neutral would be armoured and a separate earth more prone to failure?

Might be best to consult a sparky NOW,

 

[LaurenceC]

Might be best to consult a sparky NOW,

I have one in mind already, he just wouldn't be up to spead on the EV leccy regs but certainly for earth queries.

 

[Asparagus next left]

I to have been out of the game for a while but:-

1) The earthing arrangement depends on the type of wall charges used ie do they include the necessary trips & sensors within the electronics. The cheaper ones require a separate earth rod.

2)The steel armour is definitely to be earthed but depending on its electrical resistance it may not be suitable for conducting any potential earth fault (depending on 1 above) and the garage installation in general.

3) You are sailing close to the wind on the loadings for 3 chargers with no diversity on the circuit, your 100a fuse is not going to hold for long. (I hope your neighbours aren't watching TV)

4) Pairing cable cores used to be fround on, but as in this case the cores will be the same length, this view may have changed.

5) The network earthing arrangements are bound by different regulations, you shouldn't combine earthing and neutral cores within an installation.

 

[ChrisCross123]

I to have been out of the game for a while but:-

1) The earthing arrangement depends on the type of wall charges used ie do they include the necessary trips & sensors within the electronics. The cheaper ones require a separate earth rod.

2)The steel armour is definitely to be earthed but depending on its electrical resistance it may not be suitable for conducting any potential earth fault (depending on 1 above) and the garage installation in general.

3) You are sailing close to the wind on the loadings for 3 chargers with no diversity on the circuit, your 100a fuse is not going to hold for long. (I hope your neighbours aren't watching TV)

4) Pairing cable cores used to be fround on, but as in this case the cores will be the same length, this view may have changed.

5) The network earthing arrangements are bound by different regulations, you shouldn't combine earthing and neutral cores within an installation.

The biggest issue with doubling up cores is that the terminals of the equipment being connected may not be sized / designed to take multiple conductors. Some terminals specifically state only a single conductor should be installed.

Best practice would be to earth unused cores, although it is arguably sufficient to seal off the unused conductors at both ends so there is no possibility of them coming into contact with live parts.

If the cross sectional area of the armour is insufficient to meet the regs / get the earth resistance low enough you could run a separate earth, but then you would also need to consider protecting it. Better option would be a five core XLPE under these circumstances (armour still needs to be earthed regardless).

 

[ChrisCross123]

I have one in mind already, he just wouldn't be up to spead on the EV leccy regs but certainly for earth queries.

The latest regs contain new information about supply and earthing arrangements for EVSEs, so I would be wary.

Whilst the worst thing that can happen is you end up with an unsafe installation you also don't want to end up with a supply arrangement that your EVSE installer refuses to connect.

 

[LaurenceC]

I to have been out of the game for a while but:-

1) The earthing arrangement depends on the type of wall charges used ie do they include the necessary trips & sensors within the electronics. The cheaper ones require a separate earth rod.

2)The steel armour is definitely to be earthed but depending on its electrical resistance it may not be suitable for conducting any potential earth fault (depending on 1 above) and the garage installation in general.

3) You are sailing close to the wind on the loadings for 3 chargers with no diversity on the circuit, your 100a fuse is not going to hold for long. (I hope your neighbours aren't watching TV)

4) Pairing cable cores used to be fround on, but as in this case the cores will be the same length, this view may have changed.

5) The network earthing arrangements are bound by different regulations, you shouldn't combine earthing and neutral cores within an installation.

Thanks for you input.
I'll definately stay within a safe loading, even if this means dropping down to 2 chargers.
I forgot to add I will be looking at installations that have their own electronic safety systems in the regs just in case the earthing potential isn't enough (I wonder if I can even check that myself). Just trying to get to some ideal cable ordered and layed before I shortly start filling in.
At what point is diversity controlled? Am I even best laying separate cable for each charger?
TIA

 

[Asparagus next left]

The things you will need to know when sizing the cable:-

Is the cross section of the core 1 large enough to carry the current (60amp) 2 Where its run, so as not to over heat (buried, clipped direct or under insulation etc 3 To ensure that the volt drop is within limits when carrying said load so that it functions safely and correctly. According to Google for a 25m run swa if you want 5% drop you need 10mm2 or 3% 16mm2

Added to this is the question of earth fault path. As someone already suggests normal practice is to use one of the spare cores if there's any doubt. This can be calculated & is normally measured after installation (it's a costly bit of kit)

Diversity is down to experience I'm afraid, but I would suggest that in this case no allowance at all can be assumed. There will be a very high probability of both on together and for a very long time. Further I would suggest when using that you stagger switching by a few seconds to avoid high in rush currents

Separate cables will not help & only increase cost

Good luck and don't forget the yellow notification tape

 

[LaurenceC]

The things you will need to know when sizing the cable:-

Is the cross section of the core 1 large enough to carry the current (60amp) 2 Where its run, so as not to over heat (buried, clipped direct or under insulation etc 3 To ensure that the volt drop is within limits when carrying said load so that it functions safely and correctly. According to Google for a 25m run swa if you want 5% drop you need 10mm2 or 3% 16mm2

Added to this is the question of earth fault path. As someone already suggests normal practice is to use one of the spare cores if there's any doubt. This can be calculated & is normally measured after installation (it's a costly bit of kit)

Diversity is down to experience I'm afraid, but I would suggest that in this case no allowance at all can be assumed. There will be a very high probability of both on together and for a very long time. Further I would suggest when using that you stagger switching by a few seconds to avoid high in rush currents

Separate cables will not help & only increase cost

Good luck and don't forget the yellow notification tape

Brill, great info thanks. I've loads of tape....left me an entire reel when laying the kitchen cable

 

[curl666]

You can't use the armouring as your main earth, as you are planning on extending a TNCS (PME) supply.

 

[LaurenceC]

There

You can't use the armouring as your main earth, as you are planning on extending a TNCS (PME) supply.

Thanks

 

[LaurenceC]

Going to do a little more research in connecting with an installer here on the West Coast Scotland. I'd like to engage with them if possible. Its obvious I'm speculating too much on core quantity and earth specs. I might get a cold shoulder if installing the cable but there's no way i'm digging that up again...and it needs filling in within the next few weeks. I have thought about ducting but there's a tight bend round the house. Anyone pulled a 16mm round a 90°?

 

[curl666]

What’s the likely the hood of a future 3phase supply?

Are you certain on your incoming fuse being 100amp, rather than a 100amp holder which could be de-rated to 63/80amp?

 

[LaurenceC]

What’s the likely the hood of a future 3phase supply?

Are you certain on your incoming fuse being 100amp, rather than a 100amp holder which could be de-rated to 63/80amp?

On the phase front I don't think there is ever a chance it will become 3 phase...and I'll need to check on the amp rating in reality. I managed to touch base with a certified installer out here on the West Coast (there aren't many) and he said 16mm 3 core would do me. I could get a 3 phase unit specifically for the EV's but they are expensive. He also liked the Easee Home Chargepoint. Awaiting him coming back to me about a site visit.