Hi,
I'm planning my installation of a Multiplus-II 5000/70/50 in my home in the UK along with ESS and later solar. I will be splitting my existing consumer unit into essential and non-essential loads to enable UPS mode in the event of a grid outage.
My question is whether the circuit protection device fitted inside the non-essential loads consumer unit which feeds the Multiplus-II AC-In input needs to have RCD protection or if an MCB can be used. Of course I will have a full set of RCBOs on the various other circuits on both essential and non-essential consumer units but I'm concerned about discrimination if I was to also use an RCBO to feed the Multiplus-II input. I could probably get a time-delayed RCBO but I wonder if this is really needed.
The Multiplus-II installation manual simply states that
The AC input must be protected by a fuse or magnetic circuit breaker rated at 32 A (for 3 kVA model), 50 A (for 5 kVA model) and 100 A (for 8 kVA and 10 kVA model) or less, and cable cross-section must be sized accordingly.
so my guess is that this might not be so much an inverter product question but more of a UK wiring regs question.
I have the regs and on-site guide so can read up on that but just wondering what others have done? The cable feeding Ac-In will be 10mm2 (singles ideally but T&E possibly) and will be running a short distance through 75x75mm trunking to the AC isolator and then again in the same trunking to the Multiplus-II so risk of damage to the cable is minimal. I could use SWA but that would be cumbersome and probably overkill.
Any thoughts? My feeling is that using a 50A MCB is the pragmatic choice but I'll need to check the regs to see if the short run of non RCD protected cables in trunking is a problem.
Thanks, Craig.
Update: Checked the OSG in section 7.2.5 and as far as understand it, as long as the cables are not “installed in walls or partitions”, which surface mounted trunking isn’t, there is no requirement for RCD protection. The prospective fault current in a fault condition inside the Multiplus would easily cause disconnection of the 50A MCB inside the allowed time so I think an MCB is appropriate. Anyone aware of any other regs which contradict this or am I misunderstanding anything?
