PLC installation

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zj1090

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We are looking in to installing a PLC chassi with processor and I/O modules outdoors in a NEMA 4x SS enclosure with a heat strip. The temparature in the enclosure during the summer may go up to 120F or may be more (one of the southern state of US). My concern is, eventhough they (Allen Bradely) are industrial rated, we might have intermittent problems. Has anybody done this before.
 

james_mcquade

Senior Member
zj1090,

what about the heat generated by the electrical / equipment during operation?

i have used an air conditioner made for enclosures with an internal thermostat.

regards,
james
 

hurk27

Senior Member
We are looking in to installing a PLC chassi with processor and I/O modules outdoors in a NEMA 4x SS enclosure with a heat strip. The temparature in the enclosure during the summer may go up to 120F or may be more (one of the southern state of US). My concern is, eventhough they (Allen Bradely) are industrial rated, we might have intermittent problems. Has anybody done this before.

Very common around here in lift stations, never have a problem, the cabinets do have heaters for winter and filtered cooling fans for summer.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Typically a cheap PLC is rated for 40?C operation, that's 104?F. The A-B SLC500 is rated for 60?C or 140?F, but the Micrologix is rated for 55?C or 131?F. But another problem with using a N4X box is that it's sealed, so any heat generated by the devices inside cannot escape via convection, only passive radiation (just the enclosure walls). For radiation to have any appreciable affect, you have to have a 20?C temperature delta. So to keep your internal temperature below 55?C, you will need to have a maximum ambient air temperature of 35?C, or 95?F. If your box is in direct sunlight on a day when the ambient air temp is 120?F, the internal temperature will exceed the temperature rating of the PLC. You need to provide cooling, or put it somewhere else. A Heat Exchanger will improve the cooling to needing a delta of only 10?C, but that still may not be enough, you will likely need an air conditioner.
 
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hurk27

Senior Member
Here's a lift station I did last fall.

The photo of the main control cabinet with the cooling hoods, one upper top right and intake lower bottom left, the intake hase a filter box to keep out dust, the top right has a fan on it that comes on with a thermostat:

This cabinet has the PLC, control relays, transfer switch, and a heater for winter.
They also make a micro AC unit that can mount to this cabinet.

100_5447.jpg


100_5450.jpg


While this one is in a shaded area, others I installed are not, it can get above 90 deg. here.
 
We are looking in to installing a PLC chassi with processor and I/O modules outdoors in a NEMA 4x SS enclosure with a heat strip. The temparature in the enclosure during the summer may go up to 120F or may be more (one of the southern state of US). My concern is, eventhough they (Allen Bradely) are industrial rated, we might have intermittent problems. Has anybody done this before.
Since you are choosing NEMA 4X enclosure it indicates to me that you are concerned about corrosion. So if you are protecting the outside, it seems like the PLC inside is just as vulnerable. Conformal coating of the components only goes so far, purging the enclosure or keeping the inside under s light pressure with dry air is the ultimate solution. That problem also excludes circulating outside air for cooling.
There are Vortex coolers available but their operating cost is out of sight when you look into it in detail.
The issue of air conditioning is also a tough one to solve for two reasons, one is that most of them introduce outside air, second is that they are very costly if you want to add corrosion protection to them to match the protection of your enclosure.
Stainless Steel is a very poor conductor so your heat loss through the wall itself is not so good without aid. So here are the graduated steps that I suggest to incrementally improve heat removal for your case.
? I often add a ?sunroof? over the enclosure with a 1? airgap and extending it over the sides, more on the front for service protection in inclement weather.
? Installing passive heat-sinks, with fins, on the back of the cabinet.
? Installing passive ?heat-pipe? coolers, although they only provide about 10oF cooling below ambient.
? Installing heat exchangers, if you have cooling water available, externally, again attached with heat transfer cement to the back of the enclosure.
I think installing a space heater is unnecessary; the equipment itself generates sufficient heat. That is unless you have an LCD display MMI which is sensitive to low temperature.
 

renosteinke

Senior Member
Location
NE Arkansas
Absolutely. That's why our control cabinets have air conditioners on them.

FWIW, the Allen-Bradley air conditioners are the same as the Mclean air conditioners.
 

ZinskI/E

Member
Location
New Orleans, LA
Laszlo,

I'm curious about the cost of using Vortex coolers. We routinely use them in our PLC enclosures, and honestly I've never considered the operating cost. I could see an issue if dry instrument air were of limited availability, but we don't seem to have that problem in our refinery (as evidenced by leaks, losses, etc.).

On a submarine, steam was considered a pricey commodity but is definitely not the case in any of the industrial plants I've been in since. Oftentimes the ground is soaking wet with condensate from steam leaks. Though I guess all costs are all relative.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
We have a PLC in an enclosure shaded by being on the N side of another larger enclosure. We put heaters in for condensation control mostly. Time will tell. The HMI was more of a concern for us then the PLC.

We have a an AB1500 that has been in an unconditioned space for 15 years with absolutely no failure or even a hickup. 40 below outside means 40 below in the alleyway. Sunshine is not a problem for this location.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Here's a lift station I did last fall.

The photo of the main control cabinet with the cooling hoods, one upper top right and intake lower bottom left, the intake hase a filter box to keep out dust, the top right has a fan on it that comes on with a thermostat:

This cabinet has the PLC, control relays, transfer switch, and a heater for winter.
They also make a micro AC unit that can mount to this cabinet.

100_5447.jpg



While this one is in a shaded area, others I installed are not, it can get above 90 deg. here.

Just to point out a technicality, that bigger box may have started out as a NEMA 4X, but that is now NEMA 1 Stainless Steel at best, because of the vent opening. There is a big difference.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
..and it also reduces the heat loss from the cabinet, effectively cooking the electronic components by the self-generated heat.

Not an issue in a ventilated cabinet like this one.

Most cases a cabinet in direct sunlight will need some kind of help to keep the stuff inside from being overheated. Often times just ventilation grills and insulation will do the trick. Shade helps a lot if you can arrange it. I have been known to take a bigger box and take the door off and set a smaller box inside it with air space all around. Cut some holes in the floor of the bigger box as drains and you have a decent sun shade.

Shiny aluminum boxes seem to reflect heat away pretty well. I am kind of fond of the big walk in ones like used by the railroads. Insulate them and ventilate them and you can almost live in one.

I don't like fans or AC outside. it's just something else that can fail at the worst time. Plus fans suck in a lot of dust and clog the filters so people just remove the filters. If I am forced to put a fan in I usually put it on a thermostat so it is not constantly sucking dust in and clogging the filters.

If possible, I put a high temperature switch in the box if it has AC or forced ventilation, since both inevitably fail.
 

hurk27

Senior Member
Actually that box does have a smaller box inside that houses the PLC, SCADA, and the controls, the transfer switch is located outside of that box but still in the larger cabnet, the inside box is not sealed and had openings for conductors and access to breakers, also the PLC also controls the fan, and monitors the generator and the scada sends the amount of time they run back to the main computer for preventive maintenance purposes, this site is a large very expensive subdivision (or should I say a small town) with their own utility department, there are over 40 of these lift stations.
 
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Not an issue in a ventilated cabinet like this one

Most cases a cabinet in direct sunlight will need some kind of help to keep the stuff inside from being overheated. Often times just ventilation grills and insulation will do the trick. .

If it is ventillated, then it is not a NEMA 4X is it?!


Shiny aluminum boxes seem to reflect heat away pretty well.

Aluminum - as opposed to SS - is a good conductor, so it conducts the heat gain away form the inside.
 
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