Contactor buzzing like crazy

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tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
Dear all
I installed two 4 pole Bulletin 400 Allen Bradley contactors today each with a 120V coil.
Upon energizing the contactors for a quick test before quitting time I noticed they were buzzing like crazy.
Ridiculously loud.
Upon testing coil voltage I get a reading of 130V. I imagine the "120V" coil is not happy with the 130V.
or i am missing something?
or the contactors are bad.

link to contactors specs:
http://ab.rockwellautomation.com/Motor-Control/NEMA-Contactors/Bulletin-400#documentation

I have herd of snubbers helping with this kind of "chatter", however i have not seen any on the manufacturers website.
Thoughts?

Thanks in advance.
 
mgookin

mgookin

Senior Member
Location
Fort Myers, FL
Golddigger:I looked at his spec sheet and don't see a DC coil option listed. Even the available modifications don't provide for a DC coil.

OP: Was there a load on it when you powered it up?

What's the part # of the contactor and what's your load?
 
mopowr steve

mopowr steve

Senior Member
Location
NW Ohio
Occupation
Electrical contractor
If you happened to install them in a box that you needed to drill KO holes in check to see if there are metal shavings in the contractor that will do it. Especially if they won't allow the plunger to seat all the way.
 
Tony S

Tony S

Senior Member
Location
Resting under the Major Oak UK
If the contactor has been in store for a while check for rust on the pole faces. Whatever it is, the coil and pole faces are the place to start looking.

That said, if it’s new I’d expect a replacement.
 
C

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
Have you tried taking your screwdriver handle and rapping on the face of the contactor when it's buzzing? Sometimes it'll help the coil seat a little better and take a lot of the buzzing away. I haven't used that style of AB contactor, is it possible to take it apart? If you can do that you might be able to verify there isn't anything lodged in the coil area and then you'd be able to blow it out with compressed air and contact cleaner. I've had to clean the coil faces with emery cloth as well to knock the rust down on older starters that buzzed pretty loud. The contactors that you can't open though, there isn't much you can do but tap on them or replace them and hope you get a couple that don't buzz.
 
tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
Thank you all for your ideas.
I am testing them with just the coil voltages, the actual load breakers were off so no no short circuit possibility.
I tried just powering up one or the other contactor since I thought unlikely to get two bad ones.
Both were new in box from reputable supply house. One box was even shrinkwrapped in that pallet wrap stuff.

mgookin: They are AB cat No. 400-DP30ND4, 4 pole contactors.



Cow said:
Have you tried taking your screwdriver handle and rapping on the face of the contactor when it's buzzing? Sometimes it'll help the coil seat a little better and take a lot of the buzzing away.
Click to expand...

No but i did press down with the screwdriver it stops buzzing, ill try some tapping it and compressed air thats a good idea.

If that does not work ill bring them back to she shop and test them at 120V, since I find the 130V unusual.
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
ugh, Definite Purpose... "Definite Purpose" means exactly what it says, it is intended to be in an ENGINEERED system where all issues are controlled and anticipated. DP should really stand for Don't Purchase!

No matter what brand you buy, DP is the cheapest junk made. Technically, unless you are an OEM buying them for inclusion in an assembly that you will take to UL for listing, you cannot actually install them in the field if your system is going to be inspected. They are not UL Listed, they are only UL Recognized, meaning they MUST be engineered into a system and tested with the entire assembly.
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
tortuga said:
No but i did press down with the screwdriver it stops buzzing, ill try some tapping it and compressed air thats a good idea.

If that does not work ill bring them back to she shop and test them at 120V, since I find the 130V unusual.
Click to expand...

If anything they are less likely to buzz when driven with a higher voltage. And 130 is well within the tolerance band for nominal 120V.
The problem seems to be that for some reason the armature is not being pulled completely into the actuated position and the pole faces are buzzing as the 60Hz goes through zero current. There should be some feature, such as a pole shading coil, which is intended to keep the armature in position as the 60Hz current goes through zero, but that is a relatively weak holding force which will not work if there is any space between the parts.
 
tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
Well I brought out some spare contactors from the shop that I knew did not buzz swapped them in and they buzzed just as bad.
One of my old shop contactors actually smoked but it was really old 1960's era.
I recehcked coil voltages with a true rms meter and still get 130V or slightly over which should be fine. Its a 3 phase 240/120V delta system.

Jraef said:
ugh, Definite Purpose... "Definite Purpose" means exactly what it says, it is intended to be in an ENGINEERED system where all issues are controlled and anticipated. DP should really stand for Don't Purchase!
Click to expand...
Uh o... I too have a yuckey feeling about that.
Jraef said:
No matter what brand you buy, DP is the cheapest junk made. Technically, unless you are an OEM buying them for inclusion in an assembly that you will take to UL for listing, you cannot actually install them in the field if your system is going to be inspected. They are not UL Listed, they are only UL Recognized, meaning they MUST be engineered into a system and tested with the entire assembly.
Click to expand...
I too have always wondered about 'Definite Purpose', I don't see a clear code reference requiring contactors to be listed under 110, 430.8 or 409.110.
I do see examples of requirements for listing such as luminaires 410.6 or receptacles 406.3(A) and the only switches I see a requirement for listing on is 404.14 (C) CO/ALR (D) 347 volt switches, 404.8(C) muiti pole snap switches,404(C)tub or shower switches, so I would expect something similar.
GoldDigger said:
If anything they are less likely to buzz when driven with a higher voltage. And 130 is well within the tolerance band for nominal 120V.
The problem seems to be that for some reason the armature is not being pulled completely into the actuated position and the pole faces are buzzing as the 60Hz goes through zero current. There should be some feature, such as a pole shading coil, which is intended to keep the armature in position as the 60Hz current goes through zero, but that is a relatively weak holding force which will not work if there is any space between the parts.
Click to expand...
Fascinating, thanks. I took them apart. Once I removed all the black metal dust they had gathered where the C shaped steel plates come together i am guessing you call this the 'pole faces' I got the chatter too stop temporarily. The culprit might be a minute amount of self tapping screw or K/O hole saw dust in the box as I believe its a NEMA 3 or 4 sealed enclosure. I did not see "shavings" in the contactor but some black powdery dust.
Ill take some photos next week and post back.
Thank you all
Happy T day !
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
If your "known good" contactors chartered too, I see only two strong possibilities:
1. There is something wrong with the AC waveform, not just the voltage, or
2. There is something about the way the relays are mounted that is causing the problem. (Twisting the frame, forming a magnetic short, etc.)
 
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