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16mm tails 100A fuse - EV & ESS

vantech

Hi all,

Just looking for a quick sense check.

I currently have job with a 100A DNO fuse with 25mm meter tails feeding the main consumer unit. I’m planning to install an additional external consumer unit via a Henley block to supply:

  • 7kW EV charger
  • 5kW battery storage system (charging) plus 5kW backup circuit (discharge capability) - total 10kW. 

Due to routing constraints, installing 25mm tails to the external CU will be very difficult, so I’m considering using 16mm² tails instead.

The maximum potential simultaneous load on these tails would be approximately 74A (5kW charge + 5kW discharge + 7kW EV). The EV has a 60A load curtailment so the maximum is likely never going to be this high, and the backup circuit on the ESS is supplying sockets (excluding kitchen) and lights, so unlikely ever going to be more than 2-3kW. 

Given that the load is effectively limited by the connected equipment, would 16mm² tails be acceptable on a 100A supply in this scenario, or would 25mm tails be required?

Appreciate any guidance or references to regs / best practice.

Thanks.

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  • 0
    vantech said:
    I’m planning to install an additional external consumer unit via a Henley block

    I am not sure that I understand the proposal.

    Presumably the battery and backup circuits are there in case of grid failure. So what prevents the battery supply going to the main CU? Is the output of the battery limited to 5 kW?

  • 0 in reply to Chris Pearson

    I assume the ESS function has an output which remains live on grid failure and a contactor on the input which disconnects the inverter from the grid (and creates the N-E link) in the event of grid failure (a bit like  a computer UPS).  It is one of the two "normal" arrangements for such things, the other is a separately controlled contactor disconnecting the whole house on grid fail leaving the ESS running but that suffers from being a two box solution and something needs to detect restoration of the grid, either electronics with the contactor or an unswitched feed from before the contactor to the ESS electronics.

    I assume the ESS is something like https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-II-inverter-charger-EN.pdf which is generally intended to support through connection of loads although it can operate with an external contactor (transfer switch) if required.

  • 0 in reply to Chris Pearson

    The current install: 

    DNO fuse = 100A 

    Meter > 100A isolator > internal CU 

    New install: 

    Meter > 100A isolator > Henley blocks > internal CU (25mm) and new CU (16mm) 

    New CU: 

    40A EV charger (max 7kW) 

    63A ESS (max 10kW)

    The ESS can charge and discharge at 5kW, and also has a backup circuit (that is a true UPS) that can also supply 5kW. If the charger and backup supplies are both at their maximum, the total demand from the ESS is 10kW. 

    The maximum load on the 16mm tails is therefore 74A max (it’s impossible for for this to be higher, the EV is single phase, 7kW max. The UPS output on the ESS shuts down if the load goes beyond 5kW). 

    The UPS output is TN-S in backup operation (grid disconnect, N-E link, and earth rod supplement). 

    Thanks. 

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  • 0 in reply to Chris Pearson

    The current install: 

    DNO fuse = 100A 

    Meter > 100A isolator > internal CU 

    New install: 

    Meter > 100A isolator > Henley blocks > internal CU (25mm) and new CU (16mm) 

    New CU: 

    40A EV charger (max 7kW) 

    63A ESS (max 10kW)

    The ESS can charge and discharge at 5kW, and also has a backup circuit (that is a true UPS) that can also supply 5kW. If the charger and backup supplies are both at their maximum, the total demand from the ESS is 10kW. 

    The maximum load on the 16mm tails is therefore 74A max (it’s impossible for for this to be higher, the EV is single phase, 7kW max. The UPS output on the ESS shuts down if the load goes beyond 5kW). 

    The UPS output is TN-S in backup operation (grid disconnect, N-E link, and earth rod supplement). 

    Thanks. 

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