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2 electricity supplies to one building

Former Community Member
Former Community Member
Hello, I am a not an engineer but need some advice on uk wiring regulations please. 

A national utility company is fitting a 32A charger in my garage for an electric vehicle. 

The garage is detached from my house but there is an existing circuit from the house consumer unit to the garage for lighting and a power socket. The cable runs along a garden wall. 

The new charger will have its own cable run from the same consumer unit in the house down to the garage. 

My problem is that the engineer who came to do the installation refused to do it as he said the garage is a building in its own right and regulations do not allow 2 supplies to one building.

My question is: Do 2 wiring circuits from the same consumer unit constitute 2 supplies If the consumer unit is located in an adjacent building? 

I would have thought that this was still a single supply and to have 2 supplies you need 2 separate meters with 2 consumer units which is not the case here but then, as I said, I’m no engineer. 

Edit.....The engineer stated that the regulation related to avoiding the risk of a voltage between 2 different earths. To me this again only makes sense if you were talking about 2 totally different supplies from different meters and therefore possibly different sub stations etc.
  • 0
    I’d have say that of course you can have two supplies to your garage.

    Wether from the same DB or from different DBs or even different transformers. 


    a warning label of multiple points of isolation might be wise. 


    Get him to show you which regulation this contravenes? 


    it would, however, I feel be a better design to have a DB in the garage and is how I’d prefer to do the job.
  • 0
    It seems to me that this is like saying can I have one circuit for my lights upstairs and another one for the sockets.


    At one point I had two separate supplies into my own garage, but that was until the old circuits were transferred to the new distribution board. AFAIK, nothing wrong with the arrangement.


    If the EVCP is in the garage as opposed to on an external wall, I do not see any problem at all.
  • 0
    Nothing wrong with two or more distinct circuits feeding an outbuilding - commonly done. An extreme example might be where the outbuilding contains a boiler serving the main house and so has control circuits linking the two, in addition to power/lighting. The earthing system does need to be common - but that's easily achived just by linking all the c.p.c.s together in the outbuilding.

       - Andy.
  • 0
    Get a real engineer, rather than a technician,  would be my slightly flippant advice.

    There may be good reasons for what is proposed but the explanation given does not match.

    It is quite common to have multiple supplies to one building if large amounts of power are in use.

    In this case there are not even multiple supplies, just multiple final circuits from the same distribution point.

    What does need care, is how the earthing is arranged - especially for car chargers where special rules apply.

    If the plan is to make the charger supply 'TT' - that is to say that there is an electrode and no connection to the company supplied earth. (and if the car may be outdoors on charge this is likely to be required), then this needs to be out of simultaneous reach of circuits that use the company supplied earth terminal. (or they may need to be converted to use the same TT electrode as well.)

    Regards

    Mike

  • Former Community Member
    0 Former Community Member
    I think this may well be the real issue then.

    The charger will be inside the garage as I have no drive (the garage is at the bottom of the back garden and  opens directly onto a back lane). The garage  light switch and 13A socket are near to where the unit needs to be mounted. 

    Putting everything on one circuit creates another problem though as there was to be a device fitted to monitor total load at the meter and to throttle back the supply to the charger if it got close to the 100A max available but clearly I would not want the garage lights dimming too. 

    Having said that I plan to charge the car on economy 7 so it would not be an issue in real life.
  • 0
    Two seperate DNO supplies into the same building is considered poor practice and best avoided, though it is not totally prohibited.


    Two consumers circuits derived from the same incoming DNO supply should present no problem at all.
  • 0
    Apparently Zappi E.V. chargers do not need to be TT supplied. They have an inbuilt R.C.D. AND a circuit to detect TN-C-S neutral loss as well. Also the Zappi E.V. charger can be set to a maximum current consumption to prevent main fuse overloading.


    Z.
  • 0
    MHowell:

    . . . Putting everything on one circuit creates another problem though as there was to be a device fitted to monitor total load at the meter and to throttle back the supply to the charger if it got close to the 100A max available but clearly I would not want the garage lights dimming too. . . 


    The charge rate is set by the car, not the charger or the installation. The charger you are talking about does have a connection to monitor the current drawn by your installation, but this is connected to the charger and used to negotiate a different charging current with the vehicle, based on the load being drawn from the DNO supply. The charger will be configured with the maximum available. 


    As others have said, several cables from the same supply point feeding your garage is not an issue. As Broadgage has pointed out, the issue is two DNO supplies into the same property. 


    Regards,


    Alan. 


  • 0
    MHowell, your lights will not be affected! If the supply to your garage was suitable then the charge point could be lifted from there. The load adjustment instruction applies only to the charge point. Likely a CT at your intake position with a separate CAT 5E or wireless connection to the charger. 

  • Former Community Member
    0 Former Community Member
    The charger will be an ABB one as there is a deal between the utility company doing the installation and my employer as this is for their company car. I don’t know how the ABB unit works but the supply monitoring unit (not ABB I think) is a separate box that will go next to the consumer unit. Both have wifi.

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