480VAC question
480VAC question
(OP)
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?
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?






RE: 480VAC question
Mike
RE: 480VAC question
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.
RE: 480VAC 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.
RE: 480VAC question
RE: 480VAC question
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.
RE: 480VAC question
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).
RE: 480VAC question
RE: 480VAC question
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?
RE: 480VAC question
If they wanted them seperate how would this be accomplished say with a 480V contactor with a 24VDC coil?
RE: 480VAC question
But still unclear whether such separation is required.
RE: 480VAC question
RE: 480VAC question
(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).
RE: 480VAC question
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.
RE: 480VAC question
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.
RE: 480VAC question