MCE contactors

[ians]

Ok i know i should have stuck to better quality ... but i thought how bad could it be ... half the price half the quality ... i have been using a lot of onesto circuit breakers ... supplied from the same supplier and havent had any issues.

I built a control panel and finished installing it last week ... did the commisioning over the weekend and everything seemed fine.

Monday morning i go to site to check everything is ok ... i see the side of the overload relay is swollen ... i thought that is a bit strange ... so i investigate further ... i see the bottom middle terminal plate is loose ... I thought no it cant be ... I checked and re checked the terminals like i always do ... then one last random spot check while commisioning.

Anyway i shoot off to the wholesaler and get a replacement contactor and overload relay (just in case) arrange a shutdown and do a quick replacement .. to find the new overload relay norally open contact is not normally open but closed ...no time to fuss with it during a shut down ... will investigate further ... bypassed the circuit got the system up and running.

I take the damaged contactor and overload relay to the workshop to do an inspection ... to find the middle terminal is actually broken off ... not loose... i have to say that is a first ... all the years and hundreds of control panels i have built ... i have never had a terminal screw on a contactor break ...not while tightening nor during operation.

[ians]

I have been informed that the contactor and overload will be replaced ... I cannot replace the entire control panel components ... so the plan is to purchase a few spare contactors and overloads ... relays ... etc ... because it is an essential part of the production line.

Part of my commissioning sheet ...includes checking every single terminal ... and as each terminal is checked a red dot is marked next to the terminal ... when the panel is complete every terminal has a red dot.

Normally i would trust my wrist with the tension (been doing it for 38 years ... but hey I could have been wrong all that time) ... if i look at videos of people tightening terminals to 1.7 Nm (generally for neutral and earth bars) and 2.3 Nm for circuit breakers ...earth leakage and mains switches ... i would guest the tension i apply is about right ... but in future ... i would like to make sure there is no confusion.

Why suddenly now do i feel the need to invest in a torque scredriver ... it is simple ... take note of the new terminals compared to the older ones ... they seem to be manufactured with alluminum ... even wiring ... you need to check with lighter ... if it glows red ... a good chance it is pure of a good grade of copper ... the the wire melts take it back ... it is a low grade copper tinned wire.

[ians]

Some feedback ... everything was replaced and all working 100 %.

We did find a few other issues ...not with the control gear ... but with the water ...drain and pressure ...without getting too technical ... if the pressure increases the current decreases ... if the pressure is decresed the current increases ... I would have thought it works the other way ... all to do with pump curves ... I learnt a few things.

We also found another glitch in the sytem ... the dosing system has a solenoid and releases the water at a specific time ... which causes the water level to drop rapidly ... some fine tuning was required

[Justloadit]

We did find a few other issues ...not with the control gear ... but with the water ...drain and pressure ...without getting too technical ... if the pressure increases the current decreases ... if the pressure is decresed the current increases ... I would have thought it works the other way ... all to do with pump curves ... I learnt a few things.

This is synonymous with many makes of centrifugal pumps and pumps that have worn with years of service.
The way the pump works is by forcing the water against the outer casing of the pump as it rotates, and thereby forces the water to be pushed out of the pump. If you block the flow of the pump, theoretically if it is a good quality pump, then the blockage would cause a reverse force on the rotor blades, however, if the gap between the rotor blades and the casing is a little greater than specifications, then you get the pressure being released backwards and the motor load reduces as is noted by the drop in current.
Another issue may be that the pump cavitates, where the water heats up due to the forces involved, and changes state from liquid to gas. Prolonged running under these conditions causes damage to the pump blades and pump stator.

There is some interesting videos an explanations about this. If you interested simply google Cavitation