Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Replies 26 replies
  • Subscribers 38 subscribers
  • Views 834 views
  • Users 0 members are here
Options
You may also be interested in

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.

Parents Reply Children
  • 0 in reply to gkenyon

    Hi, 

    It’s a single phase install. 100A cut out, residential supply. 

    DNO has approved a 5kW feed-in. 

    The ESS has a 5kW inverter, and a backup circuit (creates a N-E bond during backup, supplemented by an Earth rod). If the ESS is charging its batteries at 5kW, there is also a possibility that the backup (essential loads) output can also pull 5kW so the total demand from the ESS has a theoretical maximum of 10kW (with the obvious lower loading noted above, socket circuits etc, not the kitchen - gas heating, no large loads, plus lighting). 

    This new ESS combined with a 7kW EV charger, will connect into a new dedicated external CU. The plan is for the ESS to sit on a 63A MCB, and the EV a 32A RCBO (2 pole). This new CU is then connected via 16mm tails to a Henley block. 

    The Henley block is fed from a DP isolator (from the back of the meter). The main house CU (25mm tails) are connected back in, with the new 16mm tails connected to the new CU. 

  • 0 in reply to vantech

    The current-carrying capacity of 16 mm2 single-core PVC 'tails' using Ref Method C is 87 A single-phase, or 79 A three-phase, according to Table 4D1A of BS 7671.

    Therefore, there is no protection provided against overload (if you think you need that) from the 100 A fuse.

    Alan B said:
    There's a regulation that says anything under 3 meters can be protected by a downstream device.

    Yes, overload protection can be omitted provided the risk of faults is minimised ... that is why we use insulated and sheathed tails.

    In terms of fault protection provided by the distributor's service fuse (cut-out):

    • If the service fuse is assumed to be 100 A BS 88-3 16 mm2 conductors are protected for prospective fault currents exceeding approximately 450 A, and 25 mm2 conductors are protected for prospective fault currents exceeding approximately 340 A

    • If the service fuse is a 100 A BS 1361 fuse, 16 mm2 conductors are protected for prospective fault currents exceeding approximately 520 A, and 25 mm2 conductors are protected for prospective fault currents exceeding approximately 400 A
  • 0 in reply to gkenyon

    Thanks 

Community Rules & Guidelines