Tips and tricks

This is a question often asked by machine and plant manufacturers – for example, when electrical components in the enclosure are snapped onto top hat rails attached to mounting plates.

The answer can be found in DIN EN 61439-1/-2 and DIN EN 60204-1 which states that electrically conductive parts are only admissible as part of the PE conductor connection if the basic requirements of a permanent, conductive connection with adequate current-carrying capacity have been met. Where these requirements are met, the support rail may be connected to the PE conductor with extensive contact to a bare metal mounting plate or via attachments (angle brackets, spacers etc.) when attached to the enclosure system (frame, interior installation rails etc.) Please note the following definitions:

• Permanent means that the points of contact are secured against loosening under mechanical load and protected from oxidation/corrosion
• Conductive means that the measured resistance between the component’s contact on the top hat rail and the connection point of the outer PE conductor is < 0.1 Ohm
• Adequate current-carrying capacity means that the contact/connection cross-section must be equivalent to that of a separate copper PE conductor.

Author: Hartmut Lohrey, Head of Marketing Training/Support

When considering this question, many manufacturers focus solely on a protection category of IP 55 or above, while other other key aspects may be overlooked:

Under international standard IEC 60529, IP protection categories are generally comprised of two numerals plus additional letters for electrical equipment enclosures (where applicable). However, the standard refers to laboratory testing which cannot precisely replicate every conceivable application of electrical equipment.

In particular, it does not allow for the long-term influence of weather conditions such as hail or icing. As well as protection from the ingress of dust and humidity, allowance must also be made for protection from corrosion. Special coatings or the use of stainless steel may therefore be appropriate. Another important aspect is that climate control should be designed to counteract the risk of increased condensation or direct sunlight as an additional thermal load.

Summary: Unless explicitly described as suitable for outdoor use, enclosures are generally excluded from such applications. However, the conditions under which outdoor use is possible and other appropriate upgrades – as described – should be clarified with the manufacturers.

Author: Hartmut Lohrey, Head of Marketing Training/Support

This question often arises when controllers and power distribution units in enclosures are configured with multiple different devices and components.

Low-voltage switchgear assemblies are typically assembled on mounting plates. Alongside safety aspects, functional risks such as climate control and EMC should also be considered at the planning stage. This is particularly important when using power electronics, and control/communications assemblies which are supplied by a busbar system via protective gear and switchgear.

The manufacturers of these types of assemblies often define very precise requirements with regard to positioning and distance from other assemblies in their assembly and operating instructions. These instructions must be observed, otherwise the warranty may be voided in the event of a malfunction or damage.

Particularly in confined spaces in compact machines, for example, it is therefore all the more important to make the best possible use of the enclosure interior with a broad range of accessories and system parts.

Static or hinged installation of 19 inch-based devices must also be supported, along with the assembly of additional mounting levels using partial mounting plates. These may be arranged at the side of the enclosure or in front of the main mounting plate, either vertically hinged or tiltable.

In this way, the required spacing to prevent hot spots or reduce electromagnetic interference is easily achieved. What is more, bare metal, corrosion-proof and conductive accessory parts for EMC provide excellent potential equalisation of device housings, cable shields and, where applicable, EMC fan-and-filter cases via direct contact with the attachment.

Heavy installed equipment that cannot be secured to the mounting plate should be easily and safely supported by corresponding load-bearing parts on the enclosure base or on the horizontal frame section in the case of frame enclosures.

Author: Hartmut Lohrey, Head of Marketing Training/Support

This is a frequently asked question at Rittal when siting enclosures for many different applications. To answer correctly, we must distinguish between three key scenarios: firstly, transporting the enclosure to its installation site; secondly, ensuring its security and attachment once in situ; and thirdly, feeding cables into the enclosure. These three scenarios have a direct influence on the selection of accessory parts. Clearly, a wide range of assembly tools are needed to cover most applications.

First, let’s consider transportation

If an enclosure needs to be lifted and moved by crane, a base/plinth is not required. If an enclosure needs to be moved by forklift or truck, a base/plinth is appropriate, provided it is of a modular design with load-bearing corner pieces and separate trim panels and the enclosure frame is capable of supporting the load.

Secondly, let’s consider stability

For a rigid attachment to the floor in order to securely withstand vibrations and shocks, we advise against using a base/plinth and screw-fastening or even welding the enclosure frame directly to the floor. Alternatively, there are special designs for mechanical decoupling (vibration dampers and shock absorbers) or for an exceptionally rigid connection to the substructure (such as an earthquake-resistant base/plinth) .

Finally, let’s look at “cable infeed”

If cables are to be inserted without floor ducting, a base/plinth is essential. The modular design of the base/plinth plus suitable accessories supports cable routing underneath bayed enclosure suites and mechanical strain relief outside of the protected room. The base/plinth also provides space for storing surplus cable lengths where necessary. Incidentally, these should be stored in a meandering, rather than circular, pattern for EMC reasons. As well as a solid base/plinth (with perforated trim panels to support enclosure ventilation in clean environments), levelling feet may also be a useful addition for uneven floors, either alone or combined with the base/plinth.

Author: Hartmut Lohrey, Head of Marketing Training/Support

We often hear these and similar questions during the hot summer months or for enclosures sited in tropical countries. There are generally concerns about condensation inside the enclosure and the related consequences.

To answer this question, we must consider three key aspects: the temperature difference between the target internal temperature and the maximum ambient temperature (does it need to be cooled below the ambient temperature), the operating period of the electrical system inside the enclosure (are there periods when the electrical system is switched off completely?) and protection of the electrical system from ambient conditions (is a high protection category required?)

The answer to these types of questions usually begins with “Yes, but ...".

If the target enclosure internal temperature is significantly below that of the environment, cooling will be required. When the enclosure is opened, condensation can form immediately on individual assemblies or components, for example if they are directly in the flow of cold air from a cooling unit.

When the electrical system is completely switched off, if the enclosure system is well-sealed (IP 55) the rapid temperature drop in the environment may cause condensation to form on the internal surfaces of the enclosure and collect in the base area.

There are a range of different strategies available to prevent condensation problems in the enclosure:

• Heat dissipation by means of active ventilation while accepting an interior temperature that is at least 5°C higher.
• Allowing adequate “warm-up time” before opening the door after active cooling has been deactivated
• Use of a “standstill heater” to maintain an internal temperature adequately above the ambient temperature and prevent dew formation on the walls.

Another aspect is condensation on external surfaces with excessive cooling of the internal temperature and the associated risk of corrosion on damaged coatings.

A precise analysis of the relevant requirements is needed to identify the best solution.

Author: Hartmut Lohrey, Head of Marketing Training/Support

This is a less common question at Rittal, but it does crop up occasionally in connection with power distributors with conductor currents of > 200 A.

There are various reasons why certain items of equipment in the enclosure gets hot. For current-carrying components such as conductors, terminals, protective gear and switchgear etc., poor contact, dense packaging inside the enclosure, inadequate heat dissipation surfaces or simply incorrect dimensioning (at the load capacity limit) may explain why heat losses create hot spots, which in turn cause insulation damage with short-circuits or fires.

But why do passive mechanical components such as gland plates in a compact enclosure or fastening cross-members in a busbar system exhibit excessively high temperatures during an infrared inspection?

DIN EN 61439-1, a crucial standard for enclosure manufacturers, contains an important piece of information in sub-section 10.10.4 "Verification of temperature rise ... using assessment".

In this regard, it is important to ensure that conductors carrying currents of more than 200A and adjacent structures must be arranged in a way that minimises eddy currents and hysteresis losses. This addresses the effects of the magnetic field surrounding any flowing current. This magnetic field is perpendicular to the direction of current and may cause eddy currents and remagnetisation in conductive materials, which in turn can generate significant local heat.

In practice, this means that when outward and inward conductors are routed separately (not as cables), for example in the form of basic insulated individual conductors or busbars, the spacing between them should be kept to a minimum. Furthermore, mounting parts and metallic surfaces with conductors passing through them perpendicular to the surface should be as thin as possible and made from poorly conductive or even insulated material.

Cables where the conductors are routed very compactly together do not generally exhibit magnetic effects because at any given time, the sum total of outward and inward currents is identical. Because the magnetic fields of these partial currents run in opposite directions, they largely cancel one another out. As a result, temperature rise due to eddy currents and remagnetisation does not occur, or is minimal.

Author: Hartmut Lohrey, Head of Marketing Training/Support

Cable shield contacting or “earthing” is a very common question relating to EMC-compatible enclosures. Today, the use of shielded cables both inside the enclosure and externally to operating equipment is essential for ensuring the availability of a powerful control and communications system in an electromagnetically charged environment.

Put simply, the cable shield is intended to prevent unwanted radiant emittance from the system and irradiation into the system. However, it can only perform this task if there is an optimum conductive connection at the enclosure entry and exit points (provided the enclosures are made from electrically conductive materials). The aim is to create a fully shielded structure comprised of the enclosure, cable shield and component housing.

For example, if the component is enclosed in a motor connector housing made from insulating material, the cable shield should be connected to the motor housing at this end (via the clamping strip). If the enclosure is made from insulating material (such as a sensor), where possible the cable shield should be connected to the reference potential on a conductive structure of the installation.

On the enclosure side, all shielded cables should be conductively connected to the installation surface on one side of the enclosure using EMC cable glands; this also ensures optimum potential equalisation between the cable shields.

If suitable EMC cable glands cannot be used, the cable shields should be connected as closely as possible to the entry/exit point using a suitable combination of shield bus and contact clips. It is important to ensure a conductive connection with maximum contact surface using a short braided earthing strap from the bar to the mounting plate. It is also important to keep shield contacting separate from the mechanical strain relief of the cable.

Because the system design generates large currents on the cable shield, adequate current-carrying capacity must be provided. Metallic contact systems are preferable to conductively coated plastic systems in such cases.

Author: Hartmut Lohrey, Head of Marketing Training/Support