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Extending semi-redundant 30 amp circuit

Discussion in 'Electrics UK' started by jso, 14 Nov 2017.

  1. jso

    jso

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    We have a 30 amp circuit serving a pottery kiln housed in the attached garage. It is currently used very infrequently. We also have a need to run electricity to a couple of workshops in the garden. Could we extend that circuit to the workshops, and promise ourselves never to fire the kiln whilst using the workshops, or, if not, is there a neat way to utilise the circuit serving the kiln to take power to the workshops, in such a way that should we ever need to use the kiln, we could disconnect the workshops and reconnect the kiln? Currently the kiln is hard wired into a big switch on the wall in the garage.
     
  2. ban-all-sheds

    ban-all-sheds

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    Changeover switch.

    Sorted.

    Or get rid of the kiln.


    Why doesn't your electrician have any ideas?
     
  3. jso

    jso

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    I'd like to come across as knowing what I'm after, when I engage one.

    And I can't get rid of the kiln, as my wife would like to keep it for the time being.
     
  4. JohnW2

    JohnW2

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    You certainly could, in principle, just extend the circuit.

    As BAS has said, if you don't trust yourselves not to use the kiln and workshop power at the same time, you could get a changeover switch fitted - so that the power went either to the kiln or two the workshops, according to what you did with that switch, and that is probably the correct way to do it. However, even if you did not do that, the worse that would be likely to happen (if you did use power in both locations) would be that the breaker supplying the circuit would trip (or the fuse protecting the circuit would blow) - in effect, it would be no different from plugging too many loads into a standard sockets circuits.

    How much current/power does the kiln use, and how much do you envisage using in the workshop(s)?

    Kind Regards, John
     
  5. jso

    jso

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    Kiln: 6Kw

    Workshop 1: fluorescent light fittings; 100w worklight; 2 2Kw heaters; sewing machine.
    Workshop 2: fluorescent light fittings; 150w worklight; 2 kw heater; 1500w mitre saw; other power tools (but nothing used simultaneously)
     
  6. JohnW2

    JohnW2

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    Do I take it that it's thermostatically controlled? If so, then I imagine that the average power consumption over a reasonable period of time (after it had initially heated up) would be a lot less than 6kW.
    Would both workshops ever be heated simultaneously?

    Does this circuit originate from your house's main consumer unit / fuse box? Do you happen to know what size cable it is wired in?

    Kind Regards, John
     
  7. jso

    jso

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    Not sure. It's an old kiln. We turn it up manually - medium - high - then knock it down again after a certain amount of time.

    Yes

    Yes; it's governed by a 30 amp fuse

    I don't know the actual square mm, but the cable itself seems substantial - 12mm across - similar to what I've seen used for cooker connections.
    We very much trusted the electrician who wired that in for us when we moved here and wanted to install the kiln in the garage.
     
  8. JohnW2

    JohnW2

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    Thanks.

    I think it's worth your talking to your electrician about this. It sounds as if the maximum total load (assuming everything 'on' and running full belt) would amount to 45A or so, and it's possible that you could have tour present (garage) supply upgraded to that level. The existing cable between CU and garage might be large enough to cope with that current but, even if it's not, replacing it might not be a big deal in terms of the 'big picture'. My greatest uncertainty, given that you talk about a 30A fuse, is that you may have an old CU/fuse box which cannot have circuits greater than 30A. If that is the case, an alternative to having the whole CU replaced would be for the electrician to arrange a separate supply (separate from the house CU) for the garage+workshops.

    Having said all that, and particularly if the kiln is only going to be required rarely, BAS's original suggestion of having a changeover switch in the garage would be the simplest and cheapest. That way you could have electricity going to the kiln OR workshops (but not both) according to the position of the switch.

    Kind Regards, John
     
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  9. ban-all-sheds

    ban-all-sheds

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    A 6kW kiln doesn't need 30A, so if you didn't mind more cabling twixt garage and sheds you could at least have the lighting in those permanently powered, i.e. not via the C/O switch, if that would be of use.
     
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