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
  • Locked Locked
  • Replies 33 replies
  • Subscribers 32 subscribers
  • Views 3064 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

Very long run of LV Cabling

fiftyhertz

Hi all,

 

im looking at a project where the landlords LV cut out is approx 850 metres from the proposed tenants installation. The earthing arrangement is TT and protected by a time delayed 300ma RCD and a 63A MCCB.

 

The landlords sub main is going to be 2 x 4C 95mm2 in parallel buried in the ground to supply 20KVA worth of power. This achieved a volt drop of 1.6% which leaves 1.9% VD for lighting. From my Amtech calcs I also get about 1ka at the load Dis board (Phase fault)

 

im not worried about Earth Loop because of the RCD, but i am thinking about the adibatic of the phase conductors. If the tenant puts a long run of cabling in, this will comply from a Zs perspective, but could there be issues with the line under a phase to neutral /phase to phase fault as the cable could slowly cook under a lowish load without tripping the breaker. Is this a valid concern? Amtech isn’t throwing up any faults, but just wanted your thoughts.

 

thanks in advance

Parents
  • 0

    A pair of transformers is certainly an option, but remember that the customer will be paying forever for the iron losses, and also paying for the copper losses when loaded.

    If going down this route, select the transformer taps to give about 250 volts at the load end, NOT 230 volts. This will give more leeway for voltage dropping under load. If a voltage regulator is installed at the load end then this will help with proper equipment operation but it adds another layer of cost, complexity, and another single point of failure. Remember that a voltage regulator compensates for voltage drop, but that the losses still exist and are being  paid for.

    The simplest option is almost certainly either three phase 400 volt or split phase 460 volts if available at the supply end.

Reply
  • 0

    A pair of transformers is certainly an option, but remember that the customer will be paying forever for the iron losses, and also paying for the copper losses when loaded.

    If going down this route, select the transformer taps to give about 250 volts at the load end, NOT 230 volts. This will give more leeway for voltage dropping under load. If a voltage regulator is installed at the load end then this will help with proper equipment operation but it adds another layer of cost, complexity, and another single point of failure. Remember that a voltage regulator compensates for voltage drop, but that the losses still exist and are being  paid for.

    The simplest option is almost certainly either three phase 400 volt or split phase 460 volts if available at the supply end.

Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines