Anti-Condensation techniques

[Ken Roach]

I hope that the real-world expertise on this Forum can help out a cubicle-dweller like me.

I have a customer who has damaged two PanelView 1000 terminals because of condensation inside the cabinet. Yes, he's exceeding the specifications of the PV, because he's installing it outdoors in a NEMA 4 enclosure. In the summertime, he gets cool nights and condensation forms inside the enclosure (and inside the PV terminal) and shorts out the device.

The ambient temperature doesn't exceed what the PV is rated for, so an air conditioner doesn't seem warranted.

Will a vent fan help prevent condensation ? Could a circulating fan inside the enclosure help keep the condensation off the PanelView and in solution in the air ? Anyone know of an industrial dehumidifier ?

 

[Gerry]

It's fairly common practice to have a small strip heater with thermostat installed to prevent condensation. 75 to 100 watts can serve a fairly large enclosure. A small fan would help. Sometimes all that is required is a light bulb.

 

[Steve Bailey]

How about a small heater inside the cabinet to keep the inside tewmperature above dew point. Simply keeping the cabinet powered up ovrnight might be sufficient.

If water is condensing on some other surface and dripping onto the PV, a simple shield to direct the water away from the PV could do the trick.

 

[rsdoran]

The light bulb idea is good but if the area has constant high humidity especially if it rains a good bit then you may want to add a dessicant filter to the incoming air supply, possibly several small packets in the cabinet too.

If compressed air is available you may want to look at using air to maintain a constant pressure within the cabinet. I cant remember the company names but there are several that make devices using air to heat/cool and keep a panel clean/dry.

 

[Tom Jenkins]

In my outdoor enclosures I usually install a small heater with a fan and thermostat, usually purchased from Hoffman. I usually use about 150 to 250 watts. I set the thermostat for around 65 degrees. This keeps it warm in winter and keeps condensation out in summer.

Outdoor enclosures are usually NEMA 4 or 4X. This is great for keeping the weather out, but the panel still breathes and you can still get condensation. In some cases, such as NEMA 4 Junction Boxes, I've been known to poke a small hole in the bottom to drain condensation. It violates the NEMA 4 rating, but I've had so much condensate in some cases that the terminal strips shorted out! Definitely the lesser of two evils.

 

[ChuckM]

Sounds like there may be a need to reduce the amount of moisture in the panel to begin with. I'm suspecting that there may be water getting in from a poor or incorrect conduit connection. Once it is in there, it may just be becoming a sauna.

I can't tell you how many panels I've seen installed where the electrician penetrated the tops of the enclosure, didn't use the correct hubs or box connectors or simply didn't securely close the panel door allowing water to get in. Wait. I bet I can because I suspect everyone else has seen this happen. banghead

 

[rsdoran]

I can recall a time when the electricians on a new install had stubbed out a lot of conduit, one was a 2 inch piece that ran outside toward the silos. It was never used nor capped....rained hard one day and every thing went crazy, I freaked when I opened that cabinet with its torrential downpour on the inside covering the PLC5 chassis and cards.

 

[Tark]

I would install a small heater as others have noted.

You could also check into installing a corrosion inhibitor.
http://www.hoffmanonline.com/PDFCatalog/SpecifiersGuide/Ch12p19.pdf

 

[kellian]

Silica Gel Satchels help as well.

 

[Ken Roach]

It hasn't rained in this location for nearly two months; this is strictly condensation during a big temperature swing. It's been hitting 100 F at noon consistently for a couple of weeks, but it's barely 60 at dawn at these elevations.

I'll look into the conduit arrangement on this box to see if that could make a difference, and pick up a catalog to try to select a strip heater.

 

[rsdoran]

Silica Gel Satchels help as well.

Just to clarify, the above is a type of dessicant, which I refered to earlier.

Several years ago I played around with overclocking an Intel 300 Pentium Celeron...actually 2 in a dual cpu motherboard that I used as a server in my business. Took a little solder work to connect some pins to allow dual operation but I overclocked to almost 600MHZ. To do this I mounted the board etc in a small refrigerator, condensation was a problem UNTIL I added a small bag of dessicant. It is amazing how much that little bag could absorb.

Why would I do the above....better question is WHY NOT, I was told it couldnt be done.

 

[Tom Jenkins]

I'm back in the office, Ken, and I wanted to add a couple more things that I thought of.

First, on our outdoor panels we usually put a window door over the operator interface. Saginaw and Hoffman both have them. They are gasketed, bolt on to the outside of the front panel, and are hinged. I use them to keep the weather off the front of hte operator interface, but they would have the additional advantage in your case of keping the operator interface one layer removed from the outside temperature. That will reduce the tendency of the condensation to form first on the operator interface, since it will be slightly warmer than the rest of the exposed panel.

One other item: I have had better luck with the heaters that include a fan than with plain strip heaters. There is a cost diffeerence, but the more uniform temperature is beneficial and,particularly in your case, the air circulation will help reduce localized condensation.

 

[Terry Woods]

I agree with Gerry...

The size of the light bulb should depend on the size of the space.
Maybe a few light bulbs.
Control them with a silly little thermo-switch.

They should go off automatically as the local termperature increases and come on as the temperature cools. You might use adjustable switches and have the lights come on only as needed.

Don't need the lights in the heat of the day... do you?

 

[Colossalnut]

Tell your customer to loosen his purse-strings and relocate the panel or upgrade the enclosure. I'm sure that he intends to be in business forever so convince him to look at the long term. Personally, I don't like to be faced with the same problem again and again 'cause sooner or later it's all going to be "my fault"! Be straight-forward with the customer and you'll ultimately strengthen your integrity in his eyes. Just tell it like it is! bonkhead