480VAC question 2

[xyzz]

Our canadian OEM company starts selling packaging machinery to US.
Currently the standard input power is 3PH 208VAC, but we want to offer 3PH 480VAC option as well.
The question: according to the US codes, is it acceptable to feed a control panel with 480VAC, assuming that there is only one enclosure for both power and 24VDC logic circuits?
If yes, what are the specific requirements in such case?

 

[mpparent]

Just a question, why would you want 480V? Wouldn't it be simpler to design around 120V for your incoming control power?

Mike

 

[busbar]

Machine-tool control power transformers are available with 480, 240 and 208V-tapped primaries and 120V secondaries, and [correctly fused] have close to universal application in US industrial control.

Use of greater than grounded 120V for control circuits is {thankfully} rare, more time consuming to troubleshoot and requires oddball replacement parts.

 

[xyzz]

I have to clarify my question.
The typical machine has ~1HP AC inverter + hot melt glue application system.
Powering it with 120VAC single phase means too high currents and the machine will still require special power line, not a regular wall outlet.
The price becomes higher also.
On another hand, both inverter and glue applicator are easy available in 480VAC input power version.

Control circuits are 24VDC only.
Control power supply is transformer+rectifier+capacitor.

My question is: is it legal in US to have control circuits in the same enclosure with 480V power circuits?
For canadian 600VAC it may be not.

 

[CHDean]

Yes,you can do it. There is no real difference between using a 480-120VAC control power transformer or a DC power supply in an enclosure with a power device such as starters and drives. What you will normally see is that both power and control circuit are disconnected through a common means ( disconnect or breaker ) similar to a combination motor starter.

 

[sloop]

CHDean is right. I have engineered many control panels and
480VAC was always stepped down to 120VAC(Trans) to feed the 24vdc power supply for PLC controls. The 24vdc should be isolated with an isolation contactor arrangment as part of the control circut. all this is provided in the same enclosure. Each power source should be isolated on seperate terminal strip.

 

[xyzz]

Sloop? what do you mean by "isolation contactor arrangment as part of the control circut"?
Please, explain.
Does it mean that the logic power supply cannot be under power all the time while the main power switch is on? (the AC executables are fed via contactor).

 

[buzzp]

Yes you can do it. Higher control voltages are very common in Canada. I am not sure why. We used to sell products with up 575V control capability, generally only Canadian customers.

 

[xyzz]

Sorry, guys, but you are talking of high CONTROL voltages, while I clearly stated that the control is 24VDC only.
480VAC or 575(600)VAC is NOT a control voltage, this is the main power voltage used only for powering executable devices.
Can anybody answer my question as it was put?

 

[buzzp]

I am not sure of any specific requirements, although there are likely some. Sometimes the control section is seperated from the so called high voltage section with another internal door/lexan cover/ etc.
If they wanted them seperate how would this be accomplished say with a 480V contactor with a 24VDC coil?

 

[xyzz]

This is a good question, since we use exactly 24V coil contactors.
But still unclear whether such separation is required.

 

[buzzp]

I have never heard of any requirements inside the panel just familiar with general practices. I am sure there are no requirements. There may be requirements as far as conduit runs and the like but none for within the panel that I have ever heard of.

 

[DHHall]

Be aware of what the National Electrical Code says in 300.3 Conductors.
(C) Conductors of Different Systems.
(1) 600 Volts, Nominal, or Less. Conductors of circuits rated 600 volts, nominal, or less, ac circuits, and dc circuits shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. All conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway.

The NEC futher discusses remote-control. signaling,and power limiting circuits:
Article 725.55 Separation from Electric Light, Power, Class 1, Non–Power-Limited Fire Alarm Circuit Conductors, and Medium Power Network-Powered Broadband Communications Cables.
(A) General. Cables and conductors of Class 2 and Class 3 circuits shall not be placed in any cable, cable tray, compartment, enclosure, manhole, outlet box, device box, raceway, or similar fitting with conductors of electric light, power, Class 1, non–power-limited fire alarm circuits, and medium power network-powered broadband communications circuits unless permitted by 725.55(B) through (J).

 

[xyzz]

DHHall,
Thank you for your reply.
The first part is simple, clear and logical on the common sense level.
The second part, unfortunately, includes so many external links, that is hard to be understood without them.

 

[rbulsara]

Firstly, using a control transformer with 480V primary and low voltage (as required) seconday is a common practice. Preferably the control transformer should be located in Power secton and control wires carried to a control cabinet or section or keep 480V leads as short and away from easy reach in the control cabinet/section as possible.

Meeting Code is one thing, making an equipemnt safe for common end users is another. Avoiding lawsuits in the USA is even more important. Also any listing agencies such as UL, CSA, ETL will have their own requirement.

A good design to keep control cabinet and power cabinet separate, even by using a barrier in one enclosure. Only controls circuit related to control the power/starter contactor should be in the power compartment.

 

[advidana]

Contact NEMA and UL for requirements, because without them your equipment will usually not be acceptable in the USA.