[unsaint32]

Today I took an online class about motor circuit troubleshooting. It said never to press the manual coil pickup button of the starter while the circuit is energized. It didn't explain why.

As long as I made sure that it is safe for the motor to be turned on, I don't see why I cannot press the manual coil pickup button in order to know that the starter contacts are working right. I guess I could have easily used a meter.

Am I just not seeing some inherent danger of pressing the manual pickup button while the circuit is energized?

Thanks.

 

[fanelle]

Well if there is a fault on the load side of the contactor you are potentially creating an arc flash right in your face.

 

[ScooterMcGavin]

If its a very large starter you wouldn't be able to hold it in. You wouldn't be able to overcome the magnetic forces trying to repel the contractor when starting and could cause some serious arcing.

 

[JRaef]

I think I have posted this in here before, but here goes again (possibly). The reason(s) it is a bad idea:

1) As per fanelle's post. Major safety hazard. When contacts close into a fault, they can vaporize, spraying molten silver alloy all around. Trust me, it hurts, A LOT. I have a chest scar from where some from a Size 6 contactor burned through to my breast bone, took almost a year to fully heal.

2) When a contactor coil pulls in the armature, there must be sufficient mechanical force not just to overcome the springs (or in the case of A-B, gravity) and make it move. The MUCH WORSE problem occurs when the contacts hit and current flows. Current flow creates a very strong magnetic field around the conductors in the contactor. The current paths are purposely arranged in a horseshoe fashion so that when you drop OUT the coil, the magnetic forces in that shape are opposing each other and force the contacts open quickly, extinguishing the arc as fast as possible. But when you first close the contactor and the current jumps to 600% of the normal current at that moment, the coil magnet must be strong enough to resist that impulse of magnetic force trying to force them open again. That's why when you get low voltage to a coil, it chatters loudly and destroys the contacts in a matter of seconds. Your finger CANNOT possibly exert that much force on anything above maybe a 20A contactor. That means that what is happening, at a microscopic level, is that when you manually push that "Go" button, the contacts are actually opening and closing 120 times per second. It's only a tiny amount, maybe it only feels like a vibration, but that tiny amount is enough to make the contact material melt and either vaporize, in which case you are killing the contactor life, or cause them to weld, which can be a very bad thing for the machinery.

Whenever someone doubts me, I tell them to disassemble a Size 3 contactor to remove the contacts and covers, put your fingers around the armature, energize the coil and try to hold it from smashing your fingers. Nobody so far has taken me up on that.

 

[unsaint32]

So, essentially I am using the manual button as a momentary push button right?

If so, how can there be a momentary push button with 240v 16Amp rated?

What do you think would be the safe maximum current rating of a momentary PB?

Thanks.

 

[fanelle]

That manual push button that you keep referring to is not actually a push button. It is simply a visual point on the relay so you can verify that the contacts pulled in. The only time I have ever know that it was acceptable to push it in manually is in a de-energized state with it disconnected from all writing so you can check resistance across the contacts on the relay.

 

[theloop82]

Plus manually engaging the contactor defeats all the safety interlocks installed in the coil circuit such as limit switches and whatnot. Most often the reason your contactor wont suck in is that one of the interlocks is activated or malfunctioning so it does you good to troubleshoot that part of the circuit first anyways so you can energize the coil properly.

I have seen someone run a huge factory door off the end of the rail by pushing the contactor manually in. I would never do it unless the mains are de-energized and i am only testing to make sure it isnt bound up. I never got what exactly you are proving by pushing it in manually while energized anyways that you cant prove by testing the line side for voltage.

 

[JRaef]

So, essentially I am using the manual button as a momentary push button right?

If so, how can there be a momentary push button with 240v 16Amp rated?

What do you think would be the safe maximum current rating of a momentary PB?

Thanks.

The push button has no magnetic blowout design in the current carrying components like the contactor does. Apples and oranges.

 

[Jlarson]

Get a couple flat heads, wedge that ****er in.

Actually no, don't do that :laughing:

 

[triden]

I did it today on a nema 2 starter. Still alive phew!

 

[bobelectric]

On a job where the a/c tech? used toothpicks to jam a contactor on.

 

[unsaint32]

I forgot about the coil. I realize now the manual coil button is not same a PB.
BTW, do you guys think that a contactor/starter manufacturer should make some safety provision to prevent people from pushing that button while the circuit is energized? At least a plastic see through guard with a warning or something?

Thanks for all of your replies. You guys potentially saved my life. Now I will never manually energize a starter coil when energized, especially I can do the same troubleshooting task with a meter.

 

[McClary’s Electrical]

And if the holding contacts are energized the starter will pull in and stay in. You may be trying to bump it to check rotation and end up with an full speed motor and engaged starter.

 

[JRaef]

... BTW, do you guys think that a contactor/starter manufacturer should make some safety provision to prevent people from pushing that button while the circuit is energized? At least a plastic see through guard with a warning or something?

The answer to that question has always bothered me. When I worked for Siemens, an old Furnas guy who worked on their NEMA contactor designs agreed with me that it was foolish. But the Germans had told him it was because people need to be able to check, with power OFF, that the contactor can move freely and is not jammed. Their point was that common sense (and strict rules in Germany) would dictate that nobody would ever even CONSIDER pushing the plunger in on an energized starter. Lol... Oblivious engineering arrogance from guys who had obviously never been in the field working on real stuff. I noticed that the new ABB "block contactors" no longer have that big orange Go Button in their design, you need two flat blade screwdrivers to push the plunger in from both sides at the same time. When I got splattered and burned, it was from an older ABB contactor, they must have noticed the problem and decided to make it more difficult to do dumb things...

Old Furnas and Allen Bradley NEMA design contactors that use gravity dropout instead of springs and cranks do not have "Go Buttons" by the way, you have to work at lifting the armature bar from the sides. But Sq D, CH and most of the others had a front-facing mechanism, partly because for Fire Pump Starters, you are required to be able to manually engage the contactor if the coil circuit fails. Thats why Siemens and AB cannot sell their NEMA contactors to Fire Pump starter mfrs. But if you look at a Fire Pump starter, there is a heavy duty lever mechanism with a snap-over knee lock that does this, it's not done with just human muscle force.

 

[dogleg]

That has been the way I check rotation on a pump motor replacements,after verifying no phase to ground.However phase to phase is such a low reading in the windings that one could be fooled on a phase to phase fault.I check it that way because it is a little quicker to release the contactor versus the manual switch.But a phase to phase with the door open and your face staring at it is not safe,so maybe I'll re-consider pushing the button in with a screwdriver and use the manual button.:thumbsup:

 

[pudge565]

That has been the way I check rotation on a pump motor replacements,after verifying no phase to ground.However phase to phase is such a low reading in the windings that one could be fooled on a phase to phase fault.I check it that way because it is a little quicker to release the contactor versus the manual switch.But a phase to phase with the door open and your face staring at it is not safe,so maybe I'll re-consider pushing the button in with a screwdriver and use the manual button.:thumbsup:

Why not buy a rotation meter?

 

[dogleg]

I've got one and use one when replacing the same pump motor,but how can you be sure the new pump motor will react the same as the replaced one?

 

[pudge565]

I've got one and use one when replacing the same pump motor,but how can you be sure the new pump motor will react the same as the replaced one?

There are rotation meters that you spin the motor shaft and it shows rotation of the particular phases you have connected. You match that with the rotation of either the old pump or the lines.