Control cabinet

01

Choose the IP rating for the site

The IEC explains that an IP code has two numerals: the first, from 0 to 6, grades protection against solid objects up to no ingress of dust; the second, from 0 to 9, grades protection against liquids up to high-pressure hot water from different angles. The tests behind each numeral are in IEC 60529. [1]

Ask for the IP rating of the assembled cabinet with its cable entries, fans and filters fitted, not only of the empty enclosure.

Give the supplier the site (indoor, outdoor, washdown, dusty), ambient temperature range, supply voltage and prospective short-circuit current, and the loads to be controlled.

02

Check internal temperature rise and cooling

In an article supplied by Rittal, Wiring Harness News explains that heat is the main enemy of electronics in enclosures: a 10 K rise above a component's maximum permitted temperature can halve its service life. A sealed cabinet loses heat only through its walls; the temperature rise is the heat loss divided by k × A, with k = 5.5 W/m²K for sheet steel and A the enclosure surface area per DIN 57 660 part 500. [2]

Editorial calculation with that formula: 400 W of losses in a 600 × 2000 × 600 mm cabinet with 5.16 m² effective surface gives 400 / (5.5 × 5.16) ≈ 14 K, so about 36 °C inside at 22 °C ambient.

If the result is too high, ask the supplier which cooling it proposes (ventilation where the IP rating allows air exchange, a heat exchanger or a cooling unit) and for its heat-loss calculation from the component losses. [2]

03

Set the short-circuit current rating

Siemens explains that under NEC Article 409 an industrial control panel must not be connected to a supply whose available short-circuit current exceeds the panel's short-circuit current rating (SCCR), and that the user is responsible for calculating and documenting that available current. UL 508A, covering panels up to 1000 V and 40 °C ambient, gives the calculation method in Supplement SB4. [3]

All power-circuit components count: busbars, breakers, fuses and holders, overload relays, switching devices, terminal blocks and plug connectors; control-circuit components, transformers and field loads do not. The panel rating is set by the power-circuit component with the lowest SCCR that is not protected by a current-limiting component in the feeder circuit; tested high-capacity combinations or current-limiting devices in the feeder can raise it. [3]

Outside North America, ask which assembly standard and verification the supplier applies for short-circuit withstand, and for the rated values on the nameplate.

04

MCC, PLC, stainless and IP66 cabinets, ATS panels and low-voltage switchgear

SKYT lists MCC, PLC, stainless and IP66 electrical cabinets; Huaquan lists ATS control cabinets and low-voltage switchgear alongside generators; CNC Electric shows motor control cabinet and distribution cabinet projects and lists low-voltage circuit breakers; CNKEEYA lists low-voltage switchgear. Ask each for the cabinet's IP rating, heat calculation and short-circuit rating. [4] [5]

05

Enclosure, power-circuit components, control devices, busbars and wiring, cooling and cable entry

Two rows set the ratings the order must state: the enclosure fixes the IP code and the heat-dissipating surface, and the power-circuit components, not the control devices, set the panel's short-circuit current rating. [1] [2] [3]

06

Dimensions, IP rating, voltage, ambient, rated current and short-circuit rating for a cabinet order

The dimensions row feeds the heat check: with Rittal's k = 5.5 W/m²K for sheet steel, 400 W in a cabinet of 5.16 m² effective surface gives about 14 K rise (editorial calculation). [2]

07

Send the site, electrical and control data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Site: [indoor or outdoor; washdown; dust; ambient temperature range; altitude]
Supply: [voltage; frequency; earthing system; available short-circuit current]
Loads: [motors and drives with ratings; heaters; other outputs]
Control: [PLC and HMI brand; I/O list; network; safety functions]
Enclosure: [IP rating; material; size limits; mounting; cable entry]
Thermal: [component losses; cooling method]
Documents: [single-line and wiring diagrams; heat calculation; SCCR or short-circuit verification; test reports]

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