Power Supply and Voltage for Block Machines in Iraq: Read the Site Before You Wire the Panel

Power supply and voltage for block machines in Iraq is settled at the site, not on the quotation. Every machine we build is designed for 380 V, 50 Hz, three phase, and the installed capacity is fixed before shipment: 104 kW on a QST1800, 57.6 kW on a QST1200, 34.4 kW on a QST6-15, 34.15 kW on a QS-1200A cuber. What the site delivers at the panel terminals is a different number, and it decides cable size, breaker rating and whether the line finishes a shift without tripping.

What does 380 V / 50 Hz mean at the machine terminals?

The nameplate value describes the panel, not the street. Vibration exciters, the hydraulic pump motor, the PLC supply and the stacker all assume 380 V at 50 Hz, and the rating is the same on a QST1800 at 104 kW as on a QST6-15 at 34.4 kW. Voltage does not tell you the load; installed capacity does.

Those loads do not peak together, because the pump, the vibration cycle and the stacker work in sequence, but the incoming feed has to carry the sum when the sequence overlaps. A plant ordering a 104 kW machine asks its site for that capacity before the batching plant and the curing area are counted. Size the feed on installed capacity, then clamp the running current after the first week and keep the reading.

How do you read the site before the panel is wired?

Three readings decide the job, and all three are taken where the panel will stand, not at the transformer gate. Measure phase to phase and phase to neutral on all three phases. A supply that reads 380 V on two phases and less on the third is telling you a joint or the neutral is suspect, and no breaker setting repairs that.

Check phase sequence with a meter before the first start. A reversed order turns the hydraulic pump backwards and the conveyor the wrong way, and the machine runs for a few minutes before anything sounds wrong.

Then log one full working day, first start to last stop, and write down the lowest reading. The evening hours matter most, when the same feeder carries every house on the street. A site that holds its voltage at noon and loses it after sunset needs a different under-voltage setting from one that is steady all day.

Cable section follows the distance from the transformer

The cross section of the incoming cable is set by three inputs together: the load in kW, the one way length from the transformer to the panel, and the drop you accept at the terminals. A 34.4 kW machine close to the transformer and a 104 kW machine at the far end of the yard do not take the same conductor, and the second case is where most site trouble starts, because the cable was bought for the machine and not for the run.

Drop is cumulative. Every extra metre of undersized conductor takes voltage off the motor terminals, and the motor answers by drawing more current for the same torque, which puts heat into the winding and into the cable. Derate for the ambient temperature of the yard and for the number of cables sharing a tray, and agree in writing where our scope ends and the site cable begins.

Breakers and thermal relays follow installed capacity

The main breaker sits above the total running load and below the continuous current of the incoming cable, so the cable is protected before the machine is. That window is narrow on a 104 kW machine and wide on a 34.4 kW one, which is why a breaker frame cannot be picked from the model name.

Each motor takes its own thermal relay, set on the current stamped on that motor rather than on the machine total. A relay set to the total never trips on one overloaded motor, and a relay set too tight trips on every start. On a QST1800 the stacker is 3.7 kW against 104 kW installed, and the two settings are not in the same range.

Why does a vibration motor pull harder at start than at run?

An exciter motor drives an eccentric mass, so it draws a starting current well above its running current and keeps drawing it until the rotor reaches speed. The breaker has to ride that start without tripping and the thermal relay has to ignore it, which is why the two devices are set from different numbers.

Head size changes the problem. A QST1800 carries 280 kN of vibration force and a QST1200 carries 150 kN, both at 3,800 to 4,500 vibrations per minute, so the larger head accelerates more mass and takes longer to reach speed. Set the relay on the nameplate current, the magnetic trip high enough to clear the start, and test with an empty mould before the first production shift.

Phase loss, under-voltage and phase sequence: where to set the trip

Three protections, three different jobs. Phase loss trips the moment one of the three phases disappears, and it should trip fast, because a motor running on two phases overheats in minutes. Phase sequence blocks the first start if the incoming order is reversed, and stays in service after that as a guard against a later reconnection.

Under-voltage is set from the site log, below the lowest reading recorded under normal load, with a time delay long enough to ride through the dip caused by starting the largest motor. Set it at nominal and the machine trips on every start; set it too low and the contactors chatter with the controller resetting in the middle of a cycle.

When the mains drops completely, one step stops: the moulding cycle. Do not let the press finish a cycle on a supply that returns in steps, and do not restart with a mould full of half pressed concrete. Empty the mould, then restart in sequence. Generator sizing is a separate calculation from panel protection and starts from the same site log.

Five electrical details to confirm before shipment

Panel drawings are made to order, and five answers from the site remove most of the rework.

• Measured voltage and frequency at the panel position, on all three phases, with the lowest reading of a full working day beside it.
• One way length and route from the transformer to the panel, and whether the cable is already laid or still to be bought.
• Transformer rating, and the other loads that share it, including the batching plant and the curing area.
• Phase sequence at the site, the earthing arrangement, and who witnesses the first start.
• Which machines run together and the shift pattern, since a QST1800 at 104 kW and a QST6-15 at 34.4 kW ask a site for very different capacity.

Send those five and the panel leaves the works matched to the machine and to the site.