1. The regulatory definition and functional basis of ShchM and RUSP
ShchM and RUSP solve different tasks on the same site. A mechanization panel (ShchM) is a stationary or semi-stationary intake, metering and distribution unit for the whole section: it is installed once at the connection point and is not moved. A portable distribution unit (RUSP) is a mobile panel with 3 to 8 sockets that is carried along with the work front. Requirements for assemblies intended for construction sites are set by GOST IEC 61439-4; the GOST R 51321 series has been superseded by the GOST IEC 61439 series.
The RUSP, in turn, is a mobile electrical product, structurally optimized for frequent spatial relocation (carrying) directly to the work area. If the ShchM acts as a local transformer or low-level feeder substation, then the RUSP is the terminal distribution node, providing the direct connection interface for the end power tool.
2. Structural differences and enclosure materials
The architecture of the ShchM and RUSP housings is dictated by the conditions of their spatial placement. ShchM mechanization panels are made predominantly in metal welded or knock-down housings of sheet steel from 1.5 to 2.0 mm thick. This approach is driven by the need to house inside the enclosure not only switching automation but also bulky electricity metering devices (current transformers, meters) as well as busbar assemblies. A stationary ShchM weighs from 30 to 80 kg and more – it cannot be carried by hand.
By contrast, mobile RUSP panels are designed for maximum compactness and minimum mass. The main materials for their enclosures are high-tech polymers: impact-resistant ABS plastic, self-extinguishing polycarbonate, or specialized dense rubber (thermoplastic elastomer). The use of plastic and rubber housings solves two crucial engineering tasks at once:
- Ensuring Class II electrical safety (double or reinforced insulation per GOST IEC 61140-2012), which eliminates the risk of electric shock in the event of an insulation breakdown to the housing, since the housing itself is a dielectric.
- Reducing the product weight to 5–15 kg, which allows a single worker to move the device around the construction site without using lifting equipment.
3. Comparative analysis of the internal circuitry and component composition
The switching topology of the ShchM is oriented toward high input currents (usually from 100 A to 400 A) and includes commercial or technical metering blocks. Inside the ShchM, PEN busbars or separate N and PE busbars of considerable cross-section are mounted. The output lines of the ShchM are often stationary terminal blocks or high-power connectors for feeding other panels (including RUSP), tower cranes, concrete-mixing units and pumping stations.
The internal circuit of the RUSP is laid out differently. The range of rated input currents is limited to values of 16 A, 32 A, 63 A and, less commonly, 100 A. The main feature of the RUSP is the high density of integration of plug connectors directly into the external panels of the housing. All sockets are fitted with spring-loaded protective covers. The circuit breakers and RCDs (UZO) inside the RUSP are protected by transparent polycarbonate inspection windows, which allows the state of the breakers to be monitored and their switching on/off to be performed without disturbing the overall tightness of the housing.
| Comparison criterion | Mechanization panel (ShchM) | Portable distribution unit (RUSP) |
|---|---|---|
| Type of installation | Stationary, floor-standing or wall-mounted on anchors/supports | Mobile, portable (on a frame, handle or legs) |
| Housing material | Sheet steel with anti-corrosion coating | Impact-resistant polymer, polycarbonate or rigid rubber |
| Rated input current | From 100 A to 400 A (typical solutions) | From 16 A to 100 A |
| Connection interfaces | Terminal clamps, main busbars, power connectors | Built-in plug sockets to the IEC 60309 standard |
| Electricity metering | Mandatory integration of a metering unit (meter + CT) | Usually absent (optional for local monitoring) |
| Electrical safety class | Class I (requires mandatory grounding of the housing) | Class I for a steel housing – PE is mandatory; Class II only for panels with a polymer housing without accessible metal parts |
4. Areas of application and coordination in the power grid hierarchy
The interaction of ShchM and RUSP on a site is built on a strict hierarchical principle in accordance with the requirements of SNiP 12-03-2001 (Occupational Safety in Construction). The construction mechanization panel is installed directly at the boundary of balance-sheet ownership or near the main intake distribution unit (VRU) of the facility. A main armored cable from the transformer substation is connected to it. Radial cable lines run from the ShchM, feeding the portable RUSP units dispersed around the facility.
The RUSP is placed directly in the work production zone: in rooms where interior finishing is carried out, on the floors of monolithic buildings under construction, in technological trenches. To the RUSP, workers connect the final mobile mechanisms: rotary hammers, grinding machines, portable lighting, low-power submersible pumps. ShchM and RUSP do not replace each other: the ShchM takes the incoming supply, handles metering and distributes power around the site, while the RUSP carries it further – to the floors and working zones.
5. Economic and operational aspects of the choice
When justifying the budget for an electrical equipment procurement project, it is important to consider the total cost of ownership. The capital expenditure on acquiring a ShchM is higher due to the material intensity of the metal housing and the cost of the metering devices. However, the ShchM is designed for a service life of many years in one place. An attempt to use a ShchM as a portable device leads to rapid wear of its structure, deformation of the cable entries and violation of safety requirements.
The RUSP, having a lower initial cost per unit of equipment, requires strict control of the mechanical loads on the flexible feeding cable. The operational flexibility of the RUSP makes it possible to minimize the costs of laying hundreds of meters of small cables from a remote panel to each tool – it is enough to run a single powerful power line to the RUSP and perform the distribution locally.
6. Grounding system topology and the organization of commercial metering
The fundamental structural differences between a stationary mechanization panel (ShchM) and a portable distribution unit (RUSP) entail completely different approaches to organizing grounding systems. In accordance with the requirements of Chapter 1.7 of the PUE-7 (Rules for Electrical Installations), construction and production sites use a protective grounding system of the TN-C-S or TN-S type. To correctly understand the difference in connecting the ShchM and the RUSP, one must examine in detail the physics of current distribution along the protective conductors.
The mechanization panel (ShchM) is in most cases the point of separation of the combined PEN conductor arriving from the transformer substation. Inside the metal ShchM housing, a Main Grounding Busbar (GZSh) is installed. The combined conductor is rigidly fastened to the GZSh, after which it is electrically split into a working neutral conductor (N) and a protective neutral (PE). Re-earthing of the PEN at the incomer is required by clause 1.7.61 of the PUE, while the resistance standard is set by clause 1.7.103. The resistance of the re-grounding loop to which the GZSh of the mechanization panel is connected is calculated and verified instrumentally. A step-by-step calculation of the required loop resistance for a three-phase 380 V network:
Step 1: Determining the standard resistance. Per clause 1.7.103 of the PUE, at a line voltage of 380 V the resistance of each re-earthing electrode of the PEN conductor must be no more than 30 Ω, and the total resistance of all re-earthings of the line's PEN conductor no more than 10 Ω. The value of 4 Ω applies to the earthing arrangement to which the source neutral is connected (clause 1.7.101) and does not apply to a re-earthing electrode at the facility.
Step 2: Calculating a single vertical electrode. The resistance of a single rod R1 of length L (m) and diameter d (m), driven into soil with a resistivity ρ (Ω·m), is calculated by the formula: R1 = (ρ / (2 · π · L)) · ln(2 · L / d). For loam, ρ is taken as 100 Ω·m. With a rod length of 3 m and a diameter of 0.016 m:
Step 3: Determining the number of electrodes. The required number of rods (n), taking into account the utilization factor (Ku ≈ 0.8 for a loop), is calculated as n = R1 / (R_required · Ku). Against the 30 Ω standard for a single re-earthing electrode: 31.4 / (30 · 0.8) = 31.4 / 24 = 1.3, so two electrodes are enough. Against the total standard of 10 Ω: 31.4 / (10 · 0.8) = 31.4 / 8 = 3.9, so four electrodes. The rods are joined with a steel strip and connected to the ShchM housing.
Unlike the ShchM, the portable RUSP panel is connected via a five-wire scheme (L1, L2, L3, N, PE). Inside the RUSP, the N and PE busbars are insulated from each other, and re-joining them is strictly prohibited. Factory-built RUSP units come in steel enclosures: such an enclosure is Class I and is connected to the PE conductor of the supply cable. A separate local earthing loop is not needed for it – protection is provided by the PE of the supply line. Class II with no housing connection occurs only in panels with a polymer enclosure without accessible metal parts.
Another fundamental difference is the integration of measuring current transformers (CTs) for commercial or technical electricity metering, which are mounted exclusively in the ShchM. Current transformers convert high primary currents (for example, 200 A) into secondary currents (5 A) that are safe for the metering devices. The calculation of the secondary load of a current transformer is performed to verify its accuracy class (usually 0.5S for commercial metering). The power of the secondary circuit is calculated as: S = I² · R, where I = 5 A, R is the resistance of the copper wire and the meter contacts. Step 1: The resistance of a wire with a cross-section of 2.5 mm² and a length of 1 meter is 0.007 Ω. Step 2: The power loss in the wire S = 5² · 0.007 = 25 · 0.007 = 0.175 VA. Step 3: The total load is checked against the rated power of the CT (for example, 5 VA).
View in catalog: Construction Site Distribution Board, Complete Switchboard Equipment, Panel and Cabinet Enclosures, Compact Distribution Board.