[bounce2020]

Hi, I'm looking for advice before booking an installation.

My subboard (rated 40A max and has 40A RCD) runs from 20A MCB on main board.

Garage has two circuits:

• Lights (6A MCB)
• Sockets (16A MCB, I have a treadmill and 2kW heater on sometimes)

One remaining space on the subboard where I'd like to install Wallbox Pulsar Plus (7.4kW)

The flex from main board to subboard is chunky, not sure what thickness.

Specs say 32A max current for the EV charger. If the MCB on main board is upgraded does this sound like it should work? Or is a subboard rated 40A max a bit low?

If we have to run off the main board it's no big deal, just a bit more work for the installer to fish cables across ceiling, and a few metres more flex but well within budget for cabling allowed for on the quote.

Thanks for any help.

 

[mikeselectricstuff]

First thing you need to establish is the rating of the feed to the subboard. if it's "flex" as you mention it's unlikely to be sufficient. cable often has the rating or size printed along its length

 

[Jrtev]

You've got a 20amp mcb in your house dB feeding the garage?

 

[mikegs]

You've got a 20amp mcb in your house dB feeding the garage?

The arrangement he has is very common - mine is like that and others on here have it too. A 'builder's standard' if you like.

The snag for an EVSE is that the cable is probably only 2.5mm2 so can only do what it was originally intended for - lights and a socket.

 

[gary wyatt-williams]

yes, im afraid 6mm supply is the min required for a 7kw charger, if yours is fed by a 20a mcb it is most likely only 2.5mm..
gary

 

[freddym]

Is the cable to the garage underground? In conduit? Long shot but worth seeing if it can be replaced by a bigger X section cable.

Overall though sounds like don't waste time and money going via the garage.

 

[mikegs]

Is the cable to the garage underground? In conduit?

From the OP's penultimate paragraph it sounds like running another cable isn't that big a deal.

Though the electrician may have other ideas on that

 

[freddym]

From the OP's penultimate paragraph it sounds like running another cable isn't that big a deal.

Though the electrician may have other ideas on that

Spot on😁

 

[bounce2020]

I think I might have told the electrician that put the subboard in that I might want to install a charging point at some point in the future, as it looks like 10mm twin core has been used.

My concern is whether the sub board (with a bigger MCB swapped in at the main board) can safely handle the load if a 7kW charger is added - is 40A RCD ok there? I can avoid using electric heater/treadmill/EV charger all at same time but it feels like it should be left idiot proof for future owners.

 

[mikeselectricstuff]

No harm in putting a bigger RCD in while you're at it - only about £20.

 

[freddym]

I think I might have told the electrician that put the subboard in that I might want to install a charging point at some point in the future, as it looks like 10mm twin core has been used.

My concern is whether the sub board (with a bigger MCB swapped in at the main board) can safely handle the load if a 7kW charger is added - is 40A RCD ok there? I can avoid using electric heater/treadmill/EV charger all at same time but it feels like it should be left idiot proof for future owners.

There are a few things that suggest best to forget above this forum and go direct to you sparky. If you can't determine the spec and cross sectional area of the cable, no one here can really help.

 

[freddym]

I think I might have told the electrician that put the subboard in that I might want to install a charging point at some point in the future, as it looks like 10mm twin core has been used.

My concern is whether the sub board (with a bigger MCB swapped in at the main board) can safely handle the load if a 7kW charger is added - is 40A RCD ok there? I can avoid using electric heater/treadmill/EV charger all at same time but it feels like it should be left idiot proof for future owners.

Did your sparky really install twincore?

Best get a sparky in site😦😦😦😦

 

[gary wyatt-williams]

Did your sparky really install twincore?

Best get a sparky in site😦😦😦😦

correct, you cannot export PME, live & neutral out to the outbuilding, then an earth spike to make it TT, the steel wire will be earthed at the main board then isolated at the garage board.. his electrician knew what he was doing...
gary

 

[Aragorn]

The cable should have the size printed on the side, can you find this designation?

Twin core SWA is not uncommon, the armour can be used as the earth conductor, subject to some calculations.

 

[Aragorn]

correct, you cannot export PME, live & neutral out to the outbuilding, then an earth spike to make it TT, the steel wire will be earthed at the main board then isolated at the garage board.. his electrician knew what he was doing...

Or he was just trying to save a buck and use the cheaper cable...

You also dont know if its a detatched garage. If its part of the house its perfectly fine to keep it inside the equipotential zone. You can even export the equipotential zone to an outbuilding if you follow certain rules. Its not a "cannot" at all.

 

[freddym]

correct, you cannot export PME, live & neutral out to the outbuilding, then an earth spike to make it TT, the steel wire will be earthed at the main board then isolated at the garage board.. his electrician knew what he was doing...
gary

I'm not sure the OP has a clue as to the cable type. So all advice from the forum is potentially very misleading😗