Background: Offgrid place in dorset, 3.6kW inverter providing all the power. Landlord wants me to partially rewire the supply and CU. I've agreed with his electrician that I'll do the work and he'll sign off.. I've got a copy of the latest site guide and I know I'm not brown/blue colourblind so we're good to go.

 

Question: SP Inverter output breaker (MCB) as specified by the inverter manufacturer (25a) feeding ?mm2 3-core NYY-J, 10m or so to the new consumer unit. Does this length of NYY-J, which is basically acting as the meter tails, need double pole switch-fuse isolation, or can I rely on the SP breaker at the inverter output for this?

 

No issue to fit a switch fuse, I just need to know...

As this is an inverter supply, not a DNO head, I can’t see anything wrong with just breaking the single inverter supply. A DP switch would be “nicer” straight after the SP breaker but can’t really see it makes much difference in an off grid situation.

Thanks for the input... I'm going to be running some 100x100 trunking underneath the inverter to help with the layout, should be easy enough to add a DP switch there.

44 minutes ago, HughF said:

Question: SP Inverter output breaker (MCB) as specified by the inverter manufacturer (25a) feeding ?mm2 3-core NYY-J, 10m or so to the new consumer unit. Does this length of NYY-J, which is basically acting as the meter tails, need double pole switch-fuse isolation, or can I rely on the SP breaker at the inverter output for this?

Not sure how being grid makes any real difference to wiring regs.

Inverters are usually isolated on both the DC and AC side with DP switching.

When disconnecting a PV system it is normal to AC isolate first then the inverter shuts down properly.  I have seen an electrician twist the DC isolation on a sunny day, it arced badly.

My current inverter has single pole switching on the AC in and AC out (manufacturers instructions), and the DC side is completely separate. Separate enclosure, separate breakers for the inverter and MPPT in/out.

 

The new inverter (I'm installing a SunSynk 3.6kW into the house, and moving the AC supply over to that from the existing inverter that is currently in an outbuilding), has a built in MPPT with double pole isolation, but the MIs simply state 'provide a breaker if x amps on the AC input and AC output.

 

I'll get what you mean about treating the supply to the CU as a standard install, and hence the >3m rule applies.

 

One of these:

 

https://www.tlc-direct.co.uk/Main_Index/Distribution_and_Switchgear_Index/Hager_SP_1/index.html

 

Would do the job of the AC output protection, overcurrent protection for the meter tails to the CU, and a double pole isolation - provided I replaced the fuse with a 32a, to suit the supply cable to the CU.

 

Or one of these, which seems far too cheap:

 

https://www.directtradesupplies.co.uk/product.php/202439/fusebox-100a-fused-switch--63-80-100a-fuses---white-?gad_source=1&gclid=Cj0KCQiAwP6sBhDAARIsAPfK_wYt1JfB81akm_12qjDSLn3fpF8pvs4PSzmRgggHVlRRcM04sWMQmlEaAp_sEALw_wcB

Edited January 11, 20242 yr by HughF

Went with a pair of rotary isolators, one for AC in and one for AC out. Also went for a 2 module enclosure that can house a pair of MCBs to provide inverter input and output overcurrent protection.

 

Decided to put the consumer unit <3m away from the inverter so no need for a switchfuse on the supply cable.