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Posted to uk.d-i-y
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Consumer Unit and high current draw 46A.
wrote:
Hi group,
I am considering installing two 12kw air source heat pumps to replace
my old oil fired boiler.
The trianco activair units quote a start up current of 23amps which
then drops to 17.7amps for normal operation.
Question.
Will a modern 100amp consumer unit be able to handle this?
Yes, it's only the same as a smallish electric shower.
Will it be simply a case of having two 32amp mcb in the consumer unit
and feed each air pump with a cable from
each?
You could do it that way, yes.
For the coldest periods I would expect both units to be
operating most of the time therefore drawing 36amps.
You need to assess existing maximum demand and diversity and see if
there is scope for adding this extra load.
How much current can you draw from a domestic supply cable?
This is the $64,000 question.
You consumer unit may well be rated at 100A. You may well have an
electricity board cut-out with a fuse holder that's rated at 100A.
However, the fuse in the cut-out may be 40A, 60A, 80A or 100A. You will
only know this by removing the fuse and having a look, which most likely
will involve cutting off the electricity board seal.
Also, the rating of the fuse may not reflect the capacity of the supply
cable (i.e. it may be a 60A fuse on a supply that's good for 80A or it
may be an 80A fuse on a supply that's barely adequate for 80A, or 80A
fuse on a supply that's good for 100A, etc). You can only tell by having
someone experienced to assess the size of your supply cable and
measuring the source impedance of your supply. This will inform whether
the existing fuse (a) is correct and (b) can be safely upgraded to the
next size.
In my limited experience, most houses have a 60A or 80A fuse.
If one
consumer unit would be possibly overloaded could I simply have 2
100amp consumer units? One for the house and one for the air pumps.
Unlikely to overload the consumer unit, but yes in principle you could
have two consumer units on the same supply cable.
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