Splitting one house into two

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sulli_21
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Splitting one house into two

Post by sulli_21 »

Im trying to wrap my head around a job im approaching where an existing single storey house is adding an extra storey.
The goal is to have two separate apartments each with their own electricity metering. Ideally, the existing 16mm underground cable is re-used, taken to a meter box with the two meters, and then split off to the relevant submains. I haven't approached the network yet but cant see a problem with this unless someone here can tell me otherwise. The two apartments would be considered one installation? The meter box would be the distribution and MEN point.
My other query though is maximum demand. Do the two apartments have to be fused to a total of less than the 63a supply? ie two 32a (which is actually 64), or one 40 and one 20?
Ideally I would like one at 32a and one at more like 50a.
However going by maximum demand calculations using multiple units, demand is pretty low except for an EV charger in one of the apartments pushing it up. Hope that all makes sense and any guidance appreciated. Thanks!
AlecK
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Re: Splitting one house into two

Post by AlecK »

Where an installation is set up with multiple occupancies. Not difficult.
Setting up a single installation with multiple occupancies is relatively straightforward; but needs care when converting an existing installation that wasn't originally designed & installed for this arrangement.

Setting up two separate installations is trickier; as they can't share any cable in common [3.9.8.2].
Which involves moving the POS to where they split; and the existing mains from street becoming private works.

Location of POS is the key to whether a particular arrangement is a single installation ,or several separate installations in a common structure.

If the occupancies are to be separately metered; networks / retailers will have requirements relating to location, space required, layout, etc.
This may include a requirement for a means of isolation upstream of all metering.
Probably simplest to have both lots of metering at a common location.

As you've noted, the existing supply capacity is likely to be under-sized for the additional load.
Same applies for the existing mains cable from POS to meterbox; as it's unlikely to have much "spare" CCC.
Any added load will also affect volt drop calculations for both the existing and new parts of the installation.

There's no absolute requirement to ensure that ratings of submain protection don't add up to more that rating of supply fuse.
But you do need to avoid operation of overcurrent protection in normal use.
The general rule is to establish what load is to be carried, choose cable(s) to carry it, then protect the cable(s) [2.5.3.1]

Remember that EV charging is rated 100% for calculating max demand.
Also that networks are not required to provide overload protection for mains; so you may have to provide this.

The existing meterbox may well not be a switchboard, so may need to be converted to become the MSB for the enlarged installation.
Including setting up the MEN link there, and running new MEC to electrode.
Also overcurrent protection for each outgoing circuit of submains.
The main switch(es) for the entire installation must be located at MSB.
In addition; each occupancy must have access to a main switch that controls their portion of the installation [2.3.3.3(b)]
(this could be at their own DB)

Then the existing PEN mains to existing swbd for ground floor will need to be converted to be submains, complete with PEC;
and that swbd (currently the MSB) needs to be converted to be a DB (no MEN link ).
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