Do You Trip Contactors?

[Rubycon]

I have many such as:

Allen Bradley, Potter & Brumfield, ITT, AEG, ABB, and others.

Nothing like feeling the power sizzling below a large Klein screwdriver pushing the plunger down keeping over 600 Amperes at 690VAC 50Hz rolling off those silver contacts the size of Eisenhower dollars!

 

[renz20003]

I have actually

 

[Rubycon]

It's not safe as anyone that knows what this about will tell you!
But high current from a locked rotor makes long runs of THHN inside conduit dance all around making the sound as if the tube was filled with Mexican jumping beans on a warm day!

 

[renz20003]

It's not safe as anyone that knows what this about will tell you!
But high current from a locked rotor makes long runs of THHN inside conduit dance all around making the sound as if the tube was filled with Mexican jumping beans on a warm day!

I thought you meant like tripping the dry wall guy or the framer

 

[Perknose]

I thought you meant like tripping the dry wall guy or the framer

Title Edited For Coherence.

Perknose
Forum Director

 

[Rubycon]

Title Edited For Coherence.

Perknose
Forum Director

Coherence with what?
If you trip over a cord and knock a heater over, its tip sensor will trip out causing its element to become de-energized. This avoids a hazardous condition and a trip to the hospital. Often this is a tip supplied by your local electrical utility company safety division when the weather turns cooler. And people get trippy.

 

[Perknose]

Coherence with what?
If you trip over a cord and knock a heater over, its tip sensor will trip out causing its element to become de-energized. This avoids a hazardous condition and a trip to the hospital. Often this is a tip supplied by your local electrical utility company safety division when the weather turns cooler. And people get trippy.

Mind, like an old-time fuse, blown.

 

[Red Squirrel]

Speaking of contactors, there's a 60a one at my church that keeps blowing up in the AC unit. Even the stall draw of the compressor is less than what they figure is going through that contactor. It just vaporizes the contacts. I'm thinking a dead short situation, but even then I would expect the breaker to trip before it actually blows up the contactor to that point.

 

[Rubycon]

Speaking of contactors, there's a 60a one at my church that keeps blowing up in the AC unit. Even the stall draw of the compressor is less than what they figure is going through that contactor. It just vaporizes the contacts. I'm thinking a dead short situation, but even then I would expect the breaker to trip before it actually blows up the contactor to that point.

If it's a 60A contactor feeding the unit then the compressor LRA is probably way over that. Even so, the wiring should be inspected. It could be a momentary connection to chassis ground or a malfunctioning control that's short cycling/jogging the compressor. Chattering contacts with a high load will produce a lot of arcing. If it welds closed that could be real bad as the only thing left to kill power to the compressor is disconnect fuses opening or the feed CB.

 

[master_shake_]

i am out of it.

thought the title was tip contractors.

 

[zinfamous]

I feel that I have stumbled into a pun thread that I simply don't understand.


AH! The r's are reversed!

 

[Red Squirrel]

If it's a 60A contactor feeding the unit then the compressor LRA is probably way over that. Even so, the wiring should be inspected. It could be a momentary connection to chassis ground or a malfunctioning control that's short cycling/jogging the compressor. Chattering contacts with a high load will produce a lot of arcing. If it welds closed that could be real bad as the only thing left to kill power to the compressor is disconnect fuses opening or the feed CB.

Yeah quite an odd issue, the contactor just vaporizes pretty much, so more than just welding shut. The first time it happened they assumed it was lightening or something because the damage just seemed too catastrophic to be some kind of short. Will be interesting to hear what they find.

 

[BoomerD]

Squirrel...the problem is obvious...

Your church has sinned...

 

[skyking]

speaking of tripped contactors, my remote location had a power outage and does not have full automatic generator backup. There are two buildings, some long runs of Cat5e, several switches. A handful of APC ups's.
I had an ssh session open to server in building A, and I had sshed over from that to a server in building B.
This melange of UPS's and crap held together for a 10 minute outage, I did not loose the tunnels! I was doing other things and just noticed I had UPS messages from apcupsd from both servers. I need to go get lotto tickets

 

[OutHouse]

I thought you meant like tripping the dry wall guy or the framer

lol funny, with the updated title i still read it as tip.

i had a drywall guy remudding 2 rooms last week, and no I did not tip him.

 

[John Connor]

I've tripped contactors before. Looks something like this.

 

[shortylickens]

 

[pcgeek11]

Yes, but Arc Flash is no fun.

 

[BUTCH1]

If it's a 60A contactor feeding the unit then the compressor LRA is probably way over that. Even so, the wiring should be inspected. It could be a momentary connection to chassis ground or a malfunctioning control that's short cycling/jogging the compressor. Chattering contacts with a high load will produce a lot of arcing. If it welds closed that could be real bad as the only thing left to kill power to the compressor is disconnect fuses opening or the feed CB.

Anything pulling LRA (locked rotor amps) needs to be shut down ASAP once the situation is known, the compressor needs replacement, no sense putting the wiring system feeding that condensing unit through a torture-test.

 

[Rubycon]

Yes, but Arc Flash is no fun.

Especially in Russia!

Love the 50Hz growl...

Anything pulling LRA (locked rotor amps) needs to be shut down ASAP once the situation is known, the compressor needs replacement, no sense putting the wiring system feeding that condensing unit through a torture-test.

Actually all motors indeed pull LRA, albeit shortly, when starting. This is why in residential (single phase) setting one notices dimming of lights when there is a call for cooling. (heating too with heat pump system when outdoor temp is above lock out temp)

Longer runs, bad terminal connections, etc. create excessive voltage drop making the time to start longer. Sometimes it takes too long causing the thermal protection (Klixon) to engage. Adding a hard start kit (cap) can help but isn't the cure.

With 3 phase systems starting is typically faster. But it's still fun manually starting large centrifugal systems seeing a 1000A ammeter pegged for a good 10 seconds - and that's at 4,160V!

And before the days of most systems having time delay relays AND incandescent lighting in homes, the dimming was quite noticeable. Especially during a thunderstorm when the power was interrupted briefly and the unit re-started only to have its hermetic compressor stay stalled due to the high pressure between suction and discharge. Heat pumps with reversing valves designed with "fail to heat" had the advantage here since loss of power also meant they would disengage when the power cut out occurred instantly equalizing sides. These could restart immediately. No waiting for equalization and dealing with two (or more) Klixon bounces...

 

[Red Squirrel]

Speaking of startup draw, laserjet printers are actually quite notorious for it. When they first start up they use a lot of power, I'm not sure why because the fuser is just a resistive load and the motors are pretty small, but I guess the fuser + all the motors starting is a big draw. I've measured voltage drops as low as 90. Problem with that is that it is sometimes not quite within the trip threshold of UPSes, but low enough that computers don't like it. My parents have that problem with the printer, randomly if they try to print it causes the computer to reboot due to the brownout. I've instructed them to unplug the UPS before they print, so it forces the computer to run on UPS power and it won't be affected by the brownout. Though something is weird at their house because I used to have the same issue in my room when I lived there, I had to plug the printer in the hallway plug, as that one was on the other AC leg.

 

[John Connor]

So why did these arc flashes occur?

 

[pcgeek11]

So why did these arc flashes occur?

An arc flash happens when electric current flows through an air gap between conductors.

Accidents caused by touching a test probe to the wrong surface or slipped tool are the most common cause of an arcing fault. Arc flashes can also be caused by: Sparks due to breaks or gaps in the insulation.

Electrical safety hazards such as exposure to shock and Arc-Flash can be caused by:

1. Carelessness
2. Worn or broken conductor insulation
3. Exposed live parts
4. Loose wire connections
5. Improperly maintained switches and circuit breakers
6. Obstructed disconnect panels
7. Water or liquid near electrical equipment
8. High voltage cables
9. Static electricity
10. Damaged tools and equipment

The severity and causes of electrical hazards are varied, but the best protection is to deenergize equipment before working on it.

 

[John Connor]

Thanks for the answer.

 

[CraKaJaX]

Anything pulling LRA (locked rotor amps) needs to be shut down ASAP once the situation is known, the compressor needs replacement, no sense putting the wiring system feeding that condensing unit through a torture-test.

We use starters for (almost) all of our 4kV motors. Depending on the curves and associated relays, a simple device like this saves a LOT of money vs a straight contactor.