For installations of energy storage systems in dwellings, I would recommend that a set of monoblocs or cells is housed in a non-combustible (metal) enclosure which also contains the overcurrent protection for that battery array.

That may well mean you you may not need to worry about the plastic enclosure that the overcurrent protection is housed in, see Regulation 421.1.201 (ii).

Akbar Ramzan said:

Many installers are using plastic enclosures however to house a double pole MCB which acts as a means of isolation as well as overload and short circuit protection. This seems wrong, especially when dealing with a DC source with high energy withstand requirements. They are using this in escape routes within the house.

The batteries should not be in escape routes, to be honest. Consideration of not impeding escape routes (that would include in case the battery has a fire or fault) is in IET Code of Practice for Electrical Energy Storage Systems, 2nd Edition, Section 11.2.3, Table 11.1.

Ok, yes that is ideal but what about the majority of existing batteries which require external overcurrent protection as per manufacturers instructions?

Akbar Ramzan said:

Ok, yes that is ideal but what about the majority of existing batteries which require external overcurrent protection as per manufacturers instructions?

Also a thought ... I can buy an mcb separately, but that doesn't mean it's correct to install it on a din-rail simply screwed to the wall. I know I need an enclosure for that ... same goes for monoblocs?

So you’re implying that these “monoblocs” should be installed into another enclosure which prevents the user from being able to access the battery connectors without a tool and ensure the cable between the battery and the MCB is inaccessible and protected.

that seems sensible but I don’t think I have seen many installs which do that. I have seen rack mount batteries with a lockable door though.

Akbar Ramzan said:

So you’re implying that these “monoblocs” should be installed into another enclosure which prevents the user from being able to access the battery connectors without a tool and ensure the cable between the battery and the MCB is inaccessible and protected.

That's my feeling. Ordinary persons and children should not have access to DC connectors for the levels of current we are talking about, that can be removed on-load without a tool, unless of course we are talking about a plug and socket-outlet combination to an appropriate standard for use by ordinary persons, specifically made to be capable of being disconnected safely on-load.

Akbar Ramzan said:

don’t think I have seen many installs which do that. I have seen rack mount batteries with a lockable door though.

There are alternative solutions, sometimes even from the same battery manufacturer. I have definitely seen solutions available with batteries in a metal enclosure that also contain the overcurrent protection, provided as a complete package. One manufacturer of a popular "monobloc" solution with rack, also has the "complete package" option, available as a "bolt-together" expandable set with inbuilt overcurrent protection.

Akbar Ramzan said:

So you’re implying that these “monoblocs” should be installed into another enclosure which prevents the user from being able to access the battery connectors without a tool and ensure the cable between the battery and the MCB is inaccessible and protected.

That's my feeling. Ordinary persons and children should not have access to DC connectors for the levels of current we are talking about, that can be removed on-load without a tool, unless of course we are talking about a plug and socket-outlet combination to an appropriate standard for use by ordinary persons, specifically made to be capable of being disconnected safely on-load.

Akbar Ramzan said:

don’t think I have seen many installs which do that. I have seen rack mount batteries with a lockable door though.

There are alternative solutions, sometimes even from the same battery manufacturer. I have definitely seen solutions available with batteries in a metal enclosure that also contain the overcurrent protection, provided as a complete package. One manufacturer of a popular "monobloc" solution with rack, also has the "complete package" option, available as a "bolt-together" expandable set with inbuilt overcurrent protection.