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

Question

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.

gkenyon · Accepted Answer

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 .

AJJewsbury · Answer

Yes, a 400 to 230V transformer is a common solution to this sort of problem. Just connect one pole of the output to the supply circuit c.p.c. to make it N (and hence a small TN-S system). (Depending on the situation, other options might also be considered - e.g. a separated (floating) system). 
 - Andy.

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

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