Change Over Power Contactors

...especially if the contactor sees the starting current for the motor(s) for the pump(s) when changing over. GA

Maximum current is when the supply voltage is lowest (within the allowable range). Maybe voltage is down.

I stand corrected.

It exceeds the 400A only during starting of the motor. At normal conditions the current is around 380A per phase at full load.

Is the 380 FLC a nameplate motor value, or is it the actual current being drawn?

Load 380 amps and contactor rating is 400 amps; Please note that contactor rating normally mentioned at 25' C. Consider increasing contactor rating using "De-rating factor" using manufacturer's "de-rating curves".

25ºC sounds too low as a default value, especially in India.

GA, though at the moment, the forum does not know where Anonymous Poster #1 is located; were it to be Iceland, for example, then the temperature de-rating protocol might not be applicable.

High Voltage Relay & Contactor Selection Details by GIGAVAC

The Basics of Contactors - Electrical Construction & Maintenance

पैसा बुद्धिमान और पौंड मूर्ख

When your contactors all burn out, buy the correct size!

Being cheap never pays.

In the absence of details we can only speculate, but there is a REASON why contactors have an inductive motor FLA rating that is significantly lower than the simple amp rating.

Is it rated at 400A for switching motor loads or only 400A for switching resistive loads?

Regardless the current is way too close to the contactors maximum rating. If When the supply voltage sags below the normal expected motor voltage the motor current will go up. This is likely almost certain to happen and will very likely push the current above the 400A rating of the contactor causing overheating problems.

Increase the size of the contactor or spread the motor load across other contactors to reduce the contactor current.

Ho about providing the cable size for these motors as heat can be generated from ill sized conductors, causing heat at the contactor. But agree the contactor is slighty underrated for start up currents.

What other components are heating up in the panel as ventilation can be an issue. Loose connections. Undersized cable. Undersized contactor. Poor ventilation. High ambient air temperature.

So the cable is rated at 350 Amps in ground and 430 Amps in free air, 300 Amps ducted, on a 400 amp contactor with a full load of 380 Amps and not allowing for peak load on start up. Pretty much instantaneous heating on start up and relying on natural air cooling.

4 c 185 sq.mm cable may be external to the panel.

What is the size of interconnecting cable terminating in the contactor.

check the size and termination at the contactor.

There could be a difference in contactor ratings between NEMA and IEC contactors. NEMA is usually more conservative, while IEC uses a number of factors (often overlooked) to come to a smaller "right-sized" contactor. If you have an IEC rated device, it might be under-rated for pump starting due to mis-applying one of the sizing factors.

Frequent operation of a marginally sized contactor can cause it to overheat.

You should check the torque on the cables at the contactor terminals. Have you taken an IR camera to the contactors to see where the source of heat is from?

Can you please check on (a) busbar / cable sizing used with recommended termination sizing as per Copper / Aluminium (b) tightness of termination (c) IP of panel is what? as higher IP would lead to higher temperature in panel as air circulation would be restricted. (d) Is there high inrush current during starting?

Thanks