Manual Operation of Contactor, oops!

[newbie guy 0]

Hey guys. I had this happen to me 30 years ago and again just recently. We were troubleshooting a contactor that was not pulling in for a motor. While looking, one of the Electricians in training, pushed in the contactor to manually make it. The contactor sparked and let out magic smoke. It didn't blow any fuses, and after the contactor was replaced, and the subsequent fault corrected on why the coil on the contactor wouldn't energize, the motor started fine. The contactor worked as expected. This happened again the other night. I wasn't there, but it sounds like the same type of issue happened. The Contracting Engineer said it was because of an arc flash condition caused by manually making the contactor. What say anyone else please?

[GT6Steve 4]

Absolutely agree. This is a very common and relatively dangerous practice. I've done it since 1973 but have been getting more wary as I become aware of my mortality. Like what if the motor is shorted and the fuses were oversized by the previous shift? I stll do it but I'm sure to ram it home hard with a long screwdriver and wear PPE. Not a recommended practice as I've seen too much that goes wrong over the years....

[newbie guy 0]

[newbie guy 0]

Assuming there's nothing wrong downstream, what would cause the Contactor to fail if you simply push in the the contactor bar? Again, I agree this is not safe practice, but curious why a contactor would fail under "normal" circumstances.

[GT6Steve 4]

Because if you're not adequately committed the contactor may not make full contact across all three phases which will single phase the motor, draw high currents and generate a lot of heat. Throughout this I've been picturing the NEMA contactors I've grown up with which are very robust and can tolerate this kind of abuse. Nowadays we're all faced with these toy IEC crap which will not forgive a mistake. Your newage electrician needs to be VERY aware of the protections the IEC assumes will be built into an application using their standard. Mixing old school NEMA and IEC creates a very dangerous condition when it's not fully understood. Hmmm, rereading your post I want to expand a bit. When there's an arc of any kind it ionizes the air making it conducive to conduction. If perhaps, one leg of the contactor lags it will draw an arc and cause ionization. Now this ionized air supports if not encourages conduction making it easier to arc across barriers to another phase. IEC equipment is much smaller than NEMA so the barriers are much smaller reducing the safety factor for this arcover. Often, IEC contactors are replaced into panels because they're available, they fit or just because. That panel has not been designed to IEC specs and now that toy contactor is a bomb. It is nowhere near as forgiving as the old NEMA giant was. Just saying, take care and pay attention to how things are changing.... Edited 4 Nov 2013 by GT6Steve

[RussB 22]

When you operate a large contractor in by hand and one is not "fast and hard" on the push, there is a good possibility of "single phasing" the circuit for a fraction of a second, which can do harm and cause big sparks.

[BobB 58]

Never without a really good reason. See below. And as for IEC contactors vs the US NEMA monsters, we use IEC contactors in Oz and I have very rarely had to replace one. The only time it has happened is when a motor blew up and even a NEMA contactor will not survive that! Another issue along the same lines, I refuse to use relays with test buttons or manually latched mechanisms - the PLC does not know Bubba has pushed the test button or latched the mechanism! More common cause for a big bang than most things I can think of. I have, at times, pushed a contactor in - usually because a coil or circuit has failed in a critical situation. Had an issue at a children's hospital some years ago. The mains and generator HV switching was 240VAC so a couple of UPSs had been installed and a simple ATS logic as well. The mains latch and had opened the HV, the generator contact is held on. While on generator the ATS logic failed (both timers) - the hospital lost all essential power as the PLC could not keep the generator on or latch the mains. Both UPSs were fully charged. Nothing like a nice hard broomstick handle, a knife to cut off a sliver and a pair of pliers to use as a hamer to wedge the sliver of broomstick handle into the contactor! Ran that way for months until they would allow me to repair the simple ATS! That had to be done live as well. Been doing live work since the sixties - all depends if you are trained properly to do it or not.