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

  • State Helpful Answer
  • Replies 15 replies
  • Helpful Answers 1 Helpful answer
  • Subscribers 39 subscribers
  • Views 393 views
  • Users 0 members are here
Options
You may also be interested in

230V Supply from 400V Line to Line in a Control panel

Pabindu Gamage

Hi, 


I have a situation where I need to install a 230V control system which draws about Max 5A ( at230V) inside a existing Dinrail enclosure. 
However, the incoming (feeder) cable of this enclosure is a 3 Core + Earth and doesn't have a Neutral, as the load is 3 phase with no neutral.

My task is to provide a 230V supply for a control equipment that we are going to install inside this enclosure. I am struggling as there is no neutral available. 
feeder is very long hence we cannot afford to run a neutral from the SDB to this enclosure.  either. 

1) Would it be possible to mount a small control transformer and feed this with 400V supply and then generate a 230V supply ? (below link)

https://www.yesss.co.uk/eris-400va-panel-transformer-230400v-primary-122448110240v-secondary?srsltid=AfmBOoq0MCaJYskcQovSxGEfzGITtVWGUpqrmsWnTT7WLwGIsOa1xMz0


2) and if so, will this be a floating neutral ? and how do I make the neutral 0V then if required? from a practical point of view.

Thank you in advance for your support. 

  • 0 in reply to Sergio Fernandez

    Its quite often not all that practical to retrofit that over a long distance, especially for a small load increment, and also means that if there is RCD cover it needs to be changed for 4 pole sensing instead of 3. The 400:230 transformers, and their bigger cousins 690:400 exist for a reason, and delta (no neutral) distro is quite common in large factory settings.

    Even a star delta motor starter does not actually need the star point to be neutralled....

    Occasionally one comes across 230V loads connected between 1 phase and CPC which is very naughty and relies on the TNC-S supply NE  bond. 

    Mike

  • 0 in reply to Sergio Fernandez
    Pabindu Gamage said:
    feeder is very long hence we cannot afford to run a neutral from the SDB to this enclosure.  either. 

    Not quite sure how a neutral could be added, especially if the cable is SWA; but if that has been ruled out on the basis of cost, replacing the whole cable is also excluded.

  • 0

    It's not uncommon to see a 400V AC input, 230 V AC output, transformer used for single-phase control circuits in machinery and control installations.

    Simply connect one of the output lines to incoming cpc to earth the output, and it makes 230 V TN-S supply.

    For a maximum 5 A output at 230 V, the transformer will need to be at least 1.2 kVA (1200 VA), but it's quite common to use a higher rating of transformer to address volt-drop issues at maximum current.

    If there are high "earth leakage" currents expected from class Y capacitors on the output of the transformer, it's also possible to reduce these using a a 400 V input, 115-0-115 V output, and instead of earthing one of the output lines, earth the output centre-tap to make it 'split-phase'. However, in this case, you will have to use full 2-pole protective devices so that a fault to PE, regardless of which line, the fault occurs from.

  • 0 in reply to gkenyon

    Thank you very much for your support. This is very helpful and reassuring. 

  • 0 in reply to Pabindu Gamage

    Just make sure you order a transformer with at least simple separation between input and output, and not a lower cost autotransformer.

Community Rules & Guidelines