Split load has one RCD covering only one of two groups of MCBs.
Dual RCD has two RCDs which cover one group each.
Split load is just the name given to this arrangement as obviously both are split load.
The electrical trade is full of such inappropriate names and terms.
I have often wondered where the names come from, we also have high integrity which means the board is split into three sections, two with a RCD and one with no RCD.
Not worked out what name is given to my consumer unit with no RCD?
When I say RCD I mean a stand alone device, you can get combined RCD and MCB called a RCBO, so technically speaking my board does have 14 RCD's as 14 RCBO's but that is not what I was counting.
Likely the split load is a good compromise with a group of MCB's with a single RCD for all, and a group of RCBO's.
The major problem is what will fit the board. The early boards were not tall enough to take the early single module width RCBO, we now have shorter versions, but consumer unit means a type tested distribution unit and if you fit items not included in the type testing it ceases to be a consumer unit.
I know technically I should not fit wrong make, but the German Institute of Standards in German the acronym DIN stipulate a rail (DIN rail) which is reasonably standard, it can result in terminals not lining up, or the bit that sticks through lid not lining up, but it does mean often the wrong make will fit, but even if they fit spot on, it means not type tested.
I am told some where there is a rule that where an ordinary person is in charge only type tested items should be used, not sure if IET/BSi or HSE rules, but if your living in the home and you can change them then your not an ordinary person, so it is rather muddy as to what can and can't be done.
But if we assume with split RCBO's are used, then the comparison split to duel must show split as better option.
But this house the sockets were split front/back and the lights split up/down, so it would be impossible to arrange so if a fault in any room trips the RCD it will not trip the lights in that room. I know we can loose all power at any time, but it is assumed a RCD will trip when some thing has gone wrong, like an electric shock, it is bad enough when you get a shock without being also plunged into darkness as well.
So we have sockets which are more likely to trip to any other circuit so you could say sockets on their own RCBO, but lights are more essential so could say they need own RCBO, and freezer not working could mean dangerous food, so do you put freezer on its own RCBO so less likely to trip, or with something which is likely to alert you that it has tripped? Rechargeable torch that auto switches on will power failure is favourite.
But where you group MCB's together you must assess the risk, I considered my consumer unit is in the old garage now classed as annex under the main house, and to reset any trip, I need to go outside on an unlit path and down steps to access the CU to turn them back on. So if I have all RCBO then less likely to trip, and if it does trip more likely outside lights will still work, and also unless freezer likely I can wait until morning to reset. I assessed the risk, and decided risk of falling while going to reset them too high, so have done all I can to reduce risk.
Mothers house the CU was assessable without need to get dressed. My old house was in garage, but no steps, so each house different.
