220VAC Control Circuitry in Control Panel

[XL Automation]

Hello;

I design automation and control panels for manufacturing plants. I am designing a piece of equipment that will be portable, and could end up either in Europe or the US. The control panel is fed by 480 or 400VAC 50/60HZ 3 phase power. The panel contains some variable frequency drives, programmable controller, etc. The majority on control/logic voltage in the panel is 24VDC, generated from a power supply in the panel. The variable frequency drives will operate at either 400 or 480VAC. There is a control transformer in the panel that is rated at 50/60HZ and has 400 and 480VAC primary taps for US/European use. The secondary is 240x120 The question I have revolves around the few devices in the panel that operate at 220-230VAC single phase.

If I were designing this panel for US only use, I would wire the transformer for 240/120 such that I have two 120v to neutral phases and 240 between the phases. Then I would use either 120 or 240VAC power as needed. Anything being fed via 240VAC would have a two-pole breaker, obviously. Since this panel is for potential European use, I don't want to use the 120VAC at all. My initial thought (and how I originally designed the panel) was that I wire the transformer the same, but I just didn't use the neutral for anything. All 240VAC circuits would of course be 120VAC to ground and would be feed from two pole circuit breakers.

I believe in Europe, 220-240VAC circuits have 240VAC to ground and the second conductor is 0V to ground (i.e. a neutral). If I were building this panel for strictly European use, I would ground one of the 240VAC secondary legs on the transformer instead of the center tap and all of my 240VAC control circuits would require single pole breakers.

My question is that would this be acceptable to do this in the U.S.? On first glance, I don't see anywhere in the code that this would be disallowed. I simply have a 240VAC control circuit voltage with one hot conductor and one neutral. For U.S. use, I would have a placard that alerts any technician that control voltage is 240VAC.

I appreciate any help or suggestions. I don't want to seem like an idiot, but I simply have never come across this before, having always built panels with 120VAC control power.

Thanks,
Michael
XL Automation, Inc.

 

[petersonra]

As a practical matter IEC uses different color codes for wires and has a number of other issues that would generally prohibit the use of the same control panel for both markets.

 

[pfalcon]

... If I were designing this panel for US only use, I would wire the transformer for 240/120 such that ...

Why? There's no US prohibition I'm aware of against using 240V single phase control circuits, just unusual in the US. Grounding at center is done to provide small appliance power for things like laptops. It's not necessary for machine control. Ground one leg and use a single pole breaker. Label and document accordingly.

 

[eric9822]

Another consideration if you are trying to comply with NFPA79 or wish to sell to companies that want machines that comply with NFPA79.

From 2007 NFPA79 (Latest one I can find)

9.1.2.1 AC Control Circuit Voltages. The ac voltage for control circuits shall not exceed 120 volts, ac single phase.

Exception #1: Other voltages shall be permitted, where necessary, for the operation of electronic, precision, static, or similar devices used in the control circuit.

Exception #2: Any electromechanical magnetic device having an inrush current exceeding 20 amperes at 120 volts shall be permitted to be energized above control voltage through contactor or relay contacts. The contactor or relay contacts shall break both sides of the circuit powering the magnetic device. The relay coil shall be connected to the control circuit.

 

[XL Automation]

Well Cool

Well Cool

Thanks for the good advice so far. I have a CE expert that is looking at the European specifications. I am hoping that for industrial controls, I can use appropriately labeled black wiring for hot and white or lt. blue for neutral.

It just seemed odd to have 240VAC in the panel without a center tapped neutral.

 

[Besoeker]

Thanks for the good advice so far. I have a CE expert that is looking at the European specifications. I am hoping that for industrial controls, I can use appropriately labeled black wiring for hot and white or lt. blue for neutral.

It just seemed odd to have 240VAC in the panel without a center tapped neutral.

A couple of points.
In Europe the three phase LV is nominally 400V line to line and 230V line to neutral. You wouldn't actually need to use a control transformer if you used one phase and neutral.

The "harmonised" colours for the three phases are brown, black and grey for L1, L2, and L3. Neutral is blue.
For small power and control we use wire of the appropriate colour. For power cabling we mostly use black with coloured heat shrink sleeving at the terminals for identification.

 

[petersonra]

A couple of points.
In Europe the three phase LV is nominally 400V line to line and 230V line to neutral. You wouldn't actually need to use a control transformer if you used one phase and neutral.

The "harmonised" colours for the three phases are brown, black and grey for L1, L2, and L3. Neutral is blue.
For small power and control we use wire of the appropriate colour. For power cabling we mostly use black with coloured heat shrink sleeving at the terminals for identification.

interesting way of hooking up to the Cb there.

 

[Jraef]

What are the devices that can't be run from 24VDC?

The problem you will have is that if they are coils, your users anywhere outside of North America will be hard pressed to find replacement 120V coils for anything. They are available to sevice OEMs sending machnes to NA, but they are not common off-the-shelf items.

Then you have almost the revers here in the US, you will be hard pressed (especially now days) to find a 230V coil on the shelf of any distributor in NA. Used to be more common, it just isn't any longer.

But if your loads are not coil driven, i.e. power supplies, heaters etc., then I would opt for using 230V for everything. That way you standardize on a 2 pole breaker for them and just provide a TB that the IEC users can bond to Neutral for one side if necessary. They usually switch the Neutral conductor with the breaker anyway, something we are not allowed to do here (barring exceptions).

 

[Besoeker]

interesting way of hooking up to the Cb there.

It was not possible to connect the four conductors for each phase directly to the CB terminals. I think it's a fairly common limitation is as much as it was raised in another thread here recently.

 

[mm11]

Thanks for the good advice so far. I have a CE expert that is looking at the European specifications. I am hoping that for industrial controls, I can use appropriately labeled black wiring for hot and white or lt. blue for neutral.

It just seemed odd to have 240VAC in the panel without a center tapped neutral.

Using light blue wiring could pose a problem. NEC Art. 504, Intrinsically Safe Systems, designates light blue for conductors, raceway, etc, to identify intrinsically safe wiring. [(504.80(C)]

 

[petersonra]

It was not possible to connect the four conductors for each phase directly to the CB terminals. I think it's a fairly common limitation is as much as it was raised in another thread here recently.

I can't say I have ever seen it done quite like that.

sometimes you can get 4 hole lugs for the breaker either with it, or as add ons.

I wonder if I could get UL to approve something like that for our 508a panels.