Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Helpful Answer
  • Locked Locked
  • Replies 8 replies
  • Subscribers 33 subscribers
  • Views 888 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

House supply TT and loadings

DAVID MCNAUGHTON

Is there a limit to what an overhead supply can handle, loading wise?

Sorry if that sounds daft, I haven't worked with TT much in the past.

Existing house has an oven supply, no electric shower, and just your average size place with normal amount of circuits for a 3 bedroom house.

Fuse is 60/80A

A double garage is being built for a car enthusiast, he is requesting the following.

An electric garage door. ( no details as of yet )

Car Stacker Lift ( no details as of yet )

2 HP compressor

AC unit ( external condenser with one cassette inside ) ( around 4 amps )

General sockets and LED lighting.

Submain length is 45 meters.

My initial thoughts was to install a 10mm 2 core to a new DB which will be staked  SPD and RCBO's 

I can't see that the equipment will be used at the same time, at the most maybe the AC will be on while he is lifting a car in the air with a few general things plugged in and the lights on.

Compressor won't be used at the same time the door is being opened or a car is being lifted in the air for example.

I thought the 10mm will be ok on a 32A MCB protected by the 100ma main switch.

Now is is asking for a car charger. I have suggested a Zappy which is 7kw

So now I'm thinking of a 16mm 2 core on a 40A MCB

Your thoughts would be apreciated.

  • +1

    Relatively small and short term loads such as power operated garage doors or vehicle lifts can generally be ignored when considering if the incoming supply is sufficient.

    An air compressor is more of a concern due to inrush or starting currents resulting in lamp flicker. A small air conditioing unit is unlikely to much matter as will be used only in hot weather when electric space heating is not used.

    A 7kw EV charger is more of a concern as it is a long hour load. I would be very doubtful about a 7kw charger on a service of less than 100 amps.

  • +1

    Is there a limit to what an overhead supply can handle, loading wise?

    In principle the earthing system (or cables being overhead rather than underground) makes no difference to the power availability - entire villages can be supplied by overheads. In practice there will be limits though - due to the size of the cables that have been previously installed and the capacity of the local transformer - which may well have less spare capacity in a small rural setting. Typically the limit for ordinary supplies is 100A/phase, but some DNOs prefer not to go above 80A these days and some even default to 60A. Upgrading to 3-phase (or possibly split phase) might be a possibility depending on what the local infrastructure is like, but probably isn't going to be cheap.

       - Andy.

  • 0

    Thanks for your input .

    The area isn't rural at all so was surprised to see the overhead supplies, and the cable entering the house looks tiny.

    I can't see him upgrading the supply as the car charger was an after thought just in case for the future.

    Do you think the owner should notify the DNO before connection as the maximum demand is likely to exceed 60A?

    Do people do that or just connect and notify?

    If I advise car charging should only be done at night when demand is low it doesn't actually stop him from charging at anytime  

  • 0 in reply to DAVID MCNAUGHTON

    You should notify the DNO of the charger.  Many will do a free fuse upgrade to facilitate EV connection.  Is the meter rated at 80/100A or smaller?  There are still plenty of 40A and 60A rated meters around.

  • 0 in reply to statter

    Hi Statter Fuse carrier says 60/80

  • 0

    Householder needs to find out what supply has been agreed with the DNO.

  • +1

    There is nothing magic about overhead lines - the maximum supply is  determined by the cable size and the transformer load. Some underground cables are pretty thin too .  Properly only the DNO can advise on what loads can be connected, and should be advised if large loads are being added. Strictly this need to notify applies to showers, cookers etc as well, but in practice no-one does.
    you may be able to follow the lines to the transformer with a pair of binoculars, and you can estimate what the Trx size is and how may properties it serves but that may not be the full story

    Find your DNO here https://www.energybrokers.co.uk/electricity/pes-areas/search

  • 0 in reply to mapj1
    mapj1 said:
    you may be able to follow the lines to the transformer with a pair of binoculars, and you can estimate what the Trx size is

    Or if they are powerful enough, read the plate.

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines