Damp in External Enclosures: its Causes and How to Fix it

External enclosures and feeder pillars have to protect electric and electronic equipment from a variety of environmental stresses.  They need to provide a climate that keeps this equipment operational in environments that are often far from ideal and, if you’re in the north west of England, like we are, the main challenge is keeping the equipment dry.  Here is an overview of typical causes of damp in external enclosures and a few example of what we and our customers have done to avoid it.

First signs of water ingress in the enclosure

The first sign of water getting into your cabinet, and often the most obvious, is condensation forming on the metal surfaces and, if this is severe, it can start to create mildew on the backboard (if it is a wooden one).  Ritherdon cabinets are made with ‘marine grade’ plywood which will remain stable even in the wettest conditions.  However, this is a clear sign of damp in the cabinet and that something probably needs to be done about it.

Here are what we’ve found to be some of the most common causes of damp in external enclosures over the years:

Humid air entering via ventilation louvres

This water vapour will often condense on the cold surfaces inside the cabinet during the night; often on the sides of the cabinet itself.  This is usually very limited and tends to evaporate when the sun comes up.  However, on humid days, followed by cold nights it can cause dripping onto the backboard or the components inside the enclosure.

damp in external enclosures
Condensation forming in roof of cabinet

Severe condensation and dripping may also be a sign of water entering by one of the other mechanisms described below.  For that reason, it is important to rule these out first if you do see condensation.

How to fix it

  • A heater inside the cabinet can prevent the condensation from this source and can usually be retrofitted.
  • NB.  Adding a heater can make the condensation worse.  If a large amount of water is entering the cabinet the heater will simply evaporate more water, increasing the condensation and the rate of dripping.
  • Clever design of the cabinet and/or the layout of the components can reduce the risk of condensation droplets wetting the backboard or electrical components when they door form.

Liquid water ingress via ventilation louvres

This can create a dilemma because cabinets often need ventilation to manage heat and (ironically) moisture inside the enclosure.  Adding a standard louvre will immediately reduce the IP rating of the cabinet to IPX3 and driving rain or roadside puddle splashing can send water upwards, though a standard louvre vent.

Having said that, IPX3 is adequate for external enclosures in the majority of sites and this only tends to be a problem in the most exposed locations.

How to fix it

  • Remove ventilation louvres (if feasible) – take a cabinet without louvres to increase the IP to IPX5 or above.
  • Louvre design – we have designed louvres with internal deflectors which have been used with cabinets on harbour sides. The cabinets were occasionally hit by waves but the water was diverted back out of the vents.

Leaky cabinets

We design and fabricate our Ritherdon enclosures to a high specification and quality.  Our current designs also have a long track record in the field.  So, even though we have had the occasional teething problem with new models, we have used these to iron out issues and this is unlikely to be the cause of damp in a Ritherdon enclosure.

Removing welded joints and having more (e.g. rivetted) joints in a cabinet’s design can reduce manufacturing costs but it does create more potential pathways for water ingress with time.

Wherever possible, clever enclosure design deflects water away from openings and the seals should be fairly redundant.  Cabinets that rely only on their door seals to keep water out will tend to fail and leak a lot sooner.

How to fix it

Groundwater

This is probably the most common cause of significant damp that our customers have encountered with our external enclosures.  If the ground around the cabinet is very wet, damp will often find its way in; even through a concrete base.

avoiding damp in external enclosures
Ground water entering through the base of a cabinet.

Unsealed ducting

Large volumes of saturated air can literally blow into the cabinet via an unsealed duct.

Enclosure’s burial depth

If the cabinet-plinth joint is buried below ground level, this can be a pathway into the cabinet.  This is an example of why it is undesirable to rely on seals to keep water out of enclosures, if possible.  If the seal is damaged during installation or use, it will no longer be reliable.

avoiding damp in external enclosures
Ground level above the plinth-cabinet joint

How to fix it

  • Seal ducts – expanding PU foam seems to work well and won’t degrade too quickly inside the enclosure.
  • Mount the cabinet on a stainless steel plinth (corrosion resist and impermeable) and make sure the interface is above ground level.
  • Seal the base of the cabinet with either a resin-based product or an impermeable grout. We have a self-levelling grout that we occasionally send out to our customers which is quite easy to use on site, makes a neat job and seems to work very well.
avoiding damp in external enclosures
Impermeable grout used to seal the base of a cabinet

So, that’s a brief summary of what we’ve found to be the common causes of damp in external enclosures.  Even our cabinets occasionally have damp problems, though we’d like to think that it’s very rarely down to a fault with the cabinet.

If you are having problems with water ingress into an external enclosure, please get in touch (even if it’s not one of ours) because there’s usually something you can do to fix it, even retrospectively, and we’d be glad to help where we can.

Ben Ritherdon