Primary and Secondary System in Single Electrical Enclosure

[fifty60]

I have machinery that will have a primary system, and an identical system as a secondary system. Both systems will be powered by 460Y/277 VAC. The primary electrical enclosure will be located outside in the Northern US.

The enclosures will contain Circuit breakers, distribution blocks, contactors, relays and Soft Starters.

The soft starters are the only component that contain electronics.

My primary concerns, especially for the soft starters are the heat/condensation in the summer and cold temperatures in the winter. For example, it is -10 C outside, the primary system fails and the secondary system powers up. The secondary system's soft starters may fail if started below freezing.

It is hard to make the enclosure suitable for both winter and summer. Heaters don't like ventilation, for example. So I think the best solution is to use an air conditioning system coupled with a heater.

The AC system is expensive, so i would like to, if possible, place both sytems inside the same enclosure. Is this even possible? One enclosure, but with 2 disconnects for two seperate power drops? Would all the wiring inside the enclosure have to be orange? Is there any way to access a single cabinet with two disconnects? Can I use a dual cabinet, with seperate doors, but somehow share a refrigeration system?

 

[fifty60]

To try and simplify the question, is it common to find electronics such as Soft Starters outside in winter and summer conditions? If it were just summer, I would put a ventilation fan. But since it is winter, I definitely do not want the ventilation fan on while I am trying to heat the cabinet.

The AC solution would work, but is expensive and could require periodic maintenance. I do not want to do this unless it is absolutely necessary...

 

[fifty60]

The title for this post is now not very relevant. I am no longer considering a single enclosure.

I am still struggling with the heating/cooling of the enclosure. I have certainly seen enclosure that have ventilation fans for summer and thermostat controlled heaters for winter. Is this a correct way to approach this?

Even with the ventilation fans off, how do you overcome the vents in the winter time to heat the enclosure?

 

[GoldDigger]

One way is to use a motorized damper to close the vent either on low temp or when the heater is on.

 

[fifty60]

Interesting, I did think of that. It is probably best not to compromise the nema 4 rating of the enclosure...

Leaning towards the closed loop AC system. My concern now is, what happens when the panel needs serviced for some reason in the middle of winter?

The panel is fine while the enclosure is closed, but what if it needs opened? I am relying on the AC to dehumidify the enclosure...this would not be in play in the winter....if it was opened in the winter wouldn't component condensation happen while the enclosure heated back up?

I have a PLC, and my initial thoughts were to keep this inside and run the control wiring to the outside panel. Since I have to condition the outside panel anyway, why not put the PLC outside in the outside enclosure, and just run a single RS485 wire to the PLC. It would reduce a lot of wiring....

But, if the enclosure AC system fails in winter, or if the enclosure needs to be opened in winter for servicing... it create a situation where the PLC would potentially need to be replaced...it is a low cost micro plc, so maybe in the end it is worth it to reduce having to run a dozen or more control wires....

 

[Jraef]

VFDs are a problem in extreme cold because electrolytic capacitors can freeze and short if even just energized when frozen, such as after a power failure. But soft starters do not have electrolytic caps on them, maybe just a few film caps on the circuit boards that are not a problem. Many, if not most, are rated to 0 degF I believe. You should check the specs. I've put soft starters on rock crushers and mining machinery that ended up in Alaska and the Klondike, never had any issues.

 

[petersonra]

No reason you cannot put an air conditioner and a heater on the same enclosure to regulate the temperature to an acceptable range. that is what you do in your house and it works fine.

Insulation is your friend in both winter and summer.

I would not worry all that much about condensation in the winter. There is not a lot of water in cold air. If it bothers you, there are various desiccant systems you could install to remove the humidity from the inside of the cabinet that require no power.

 

[fifty60]

Jraef, Petersonra, thanks for the input. I do believe the Air conditioned approach is the way to go.

I have eliminated my control wirings between inside the building and outside to the electrical enclosure. All that I will be running is RS485 communications.

I'm not worried about the length of the run, but I am worried about the temperature gradient between the inside and outside portion of the communication cable.

Is there any issue when RS485 is ran, for example, 100 ft indoors and 100ft outdoors when it is 25 C inside and -15 C outside?

 

[petersonra]

Jraef, Petersonra, thanks for the input. I do believe the Air conditioned approach is the way to go.

I have eliminated my control wirings between inside the building and outside to the electrical enclosure. All that I will be running is RS485 communications.

I'm not worried about the length of the run, but I am worried about the temperature gradient between the inside and outside portion of the communication cable.

Is there any issue when RS485 is ran, for example, 100 ft indoors and 100ft outdoors when it is 25 C inside and -15 C outside?

The electrons do not care. the insulation on the wire might. In any case if the NEC is followed you will have to provide some means for the conduit to drain where there is likely to be condensation, and the wires within the outside conduit will have to be listed for use in wet areas.

 

[fifty60]

It is interesting that the Cold will affect the Atoms, slowing them down and decreasing resistence, but outside of that the electricity is happening at the sub-atomic level, and is not affected...