Control Transformers in a Control Panel

[Bruno1]

I have a question regarding the need for a control power transformer in a control panel. I have a 230VAC 3 phase control panel that I'm designing. I need 110VAC in that panel for various items. Is there any reason why I can't pull the 110VAC directly from one of phases on the distribution block (fuse it of course) and the neutral side from the neutral distribution block rather than installing a control power transformer? I've seen other designs where  in  similar cases a control transformer (230VAC to 110VAC) was used. Does it have to do with separately derived neutrals or is the transformer not even necessary? Thanks  

Edited November 24, 2017 by Bruno1

[Mendon Systems]

If it was powered by 208Y then no problem, but 230 comes in various flavors depending on where you are located. Some 230 sources have a neutral reference that provides 115 volts and others don't. There is also the infamous "wild leg" 230 that has one phase which is at 284 volts to the neutral. It is a whole lot safer to use a 230/120 control transformer.

[Bruno1]

The project is in the Northeast. I was mistaken on my original post, the supply is 230 VAC single phase.  So I can easily get 110VAC from that. What are the rules as to when a control transformer is required? Thanks again for the help. 

[nehpets]

Personally, I would go for 230v to 110v centre tapped to earth, this would reduce the touch voltage to 55v (unless of course you are dull enough to touch the two legs at the same time ), this is a much safer option.

 

Steve

[IO_Rack]

If the main breaker is a GFI then using the neutral will cause it to trip.

[nehpets]

Oops I didn't make it very clear that the 110v would be derived from an isolating transformer 230v primary / 110v secondary centre tapped to earth.

 

Steve

[IO_Rack]

You were clear enough. I was responding to Bruno1 with a situation were a control transformer would be required.

[cHud]

We often supply cabinets where our supply is prone for spikes. Using a control transformer reduces the damage that can be caused to the control side ( power supply or coil etc side). That is our main reason for installing them. If history is a yard stick then I wouldnt go without them in a 3 phase to single phase or 24vdc control cabinet. 

Even when supplied by single phase. Might be an overkill but doing things proper results in less problems. Often don't know the state of customers electical supply until there is a fault in your cabinet

Edited November 28, 2017 by cHud