IEC overloads

Thread Starter

reyamkram

Joined Dec 1, 2013
1
I have a situation the other day, I have 2 motors that burnt out from single phasing. Also burnt out the contactor and overload. The overload that was in the circuit was an IEC brand adjustable current. I was told that IEC overloads will not open a power circuit when the contact is welded together. Will only open when normally closed so the contacts in the control circuit. And will not open the power circuit.

In my experience, every overload that I have ran into during single phasing the power and the control circuit will open and protect the motor. Is it true that IEC overloads that do not open a power circuit and cause the motor to burn out when you have a welded contact and do not open a power circuit during single phasing. What good are they if they do not open a power circuit?

can you please help or advise me on this? Thank you very much.
 

strantor

Joined Oct 3, 2010
5,177
ANY overload will continue applying power if the contacts are welded shut. Nothing special about IEC. Nothing is perfect; how many times did the overload work correctly before it failed? If you want to prevent this in the future, use slow blow FUSES.
 

mcgyvr

Joined Oct 15, 2009
5,394
There must be something "lost in translation" here.. OBVIOUSLY if a contact has "welded" it won't open properly...

You MUST determine why the contacts welded in the first place.. excessive overloads? high breaking current? high vibration?
 

MaxHeadRoom

Joined Jul 18, 2013
19,394
For a replacement you may want to look at what is known as a Special Purpose Contactor rating, this is a type used on welders, plasma supplies, HVAC etc, these have extra features that stand up to high cycling rates.
The majority of contactor O/L's have a N.C. contact to open the coil supply.
If the contactor has welded shut then the OL is ineffective.
Max.
 
Last edited:

#12

Joined Nov 30, 2010
18,167
Welded contacts are about as useful as a blown fuse. Neither of them will do their job.

About the, "Special Purpose" contactors, I have seen a contactor so worn that one of the contact buttons was completely gone. Only the flat spring remained, and the contactor was still controlling the compressor correctly. That is amazing performance!
 

strantor

Joined Oct 3, 2010
5,177
Welded contacts are about as useful as a blown fuse. Neither of them will do their job.

About the, "Special Purpose" contactors, I have seen a contactor so worn that one of the contact buttons was completely gone. Only the flat spring remained, and the contactor was still controlling the compressor correctly. That is amazing performance!
Seen that too. Amazing!
 

GetDeviceInfo

Joined Jun 7, 2009
1,646
ANY overload will continue applying power if the contacts are welded shut. Nothing special about IEC. Nothing is perfect; how many times did the overload work correctly before it failed? If you want to prevent this in the future, use slow blow FUSES.
How would slow blows prevent this?

I personally have never seen an overload that disconnects power, but rather breaks control, which subsequently drops the main contactor.. Multiple hard starts are a good way to splash contacts, as are dirty armatures, shorted motor circuits, etc..
 

inwo

Joined Nov 7, 2013
2,419
How would slow blows prevent this?

I personally have never seen an overload that disconnects power, but rather breaks control, which subsequently drops the main contactor.. Multiple hard starts are a good way to splash contacts, as are dirty armatures, shorted motor circuits, etc..
Agree, op may be under the impression that an overload device opens the power circuit.
 

MaxHeadRoom

Joined Jul 18, 2013
19,394
It can under some circumstances where the O/L detection will trip the 3ph NFB, (Non Fused Breaker) used as the enclosure disconnect, some have either a coil trip or a N.C. sense contact, or both.
Max.
 
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