wiring concern_(off topic here)

sheryl86_ann

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Greetings!

Pardon if i used the circulation for this kind of question.

In a 3 phase wye- delta motor wiring, it is normally wired this way..From main power source to magnetic contactor followed after with an overload relay then to the motor load.

Is it possible to wire this way.. From main power line next is overload relay followed with magnetic contactor then last is motor.

There is a bimetal strip which will bend when it received excessive amount of heat when the motor is overloaded that will open the contacts, that's how overload relay behaves. Is my question on its motor wiring possible?

Hope to hear any in this circulation.
Thank you very much.

Sincerely,

Sheryl Caño
Philippines
 
Of course it is possible to connect the overload relay before the contactor. But it is stupid! The overload relay is always live, connected this way and it would be difficult to change it, should it become neccessary.
 
electrical_geek said:
Of course it is possible to connect the overload relay before the contactor. But it is stupid! The overload relay is always live, connected this way and it would be difficult to change it, should it become neccessary.
Click to expand...

Thank you very much for the inputs. I just need to give a supporting details why not do that way. I am thinking of looking into an electrical standards if I could find some supporting files. Lets say someone suggested we will wire it that way (OL before contactor).

Thank you once again.

Sincerely,

Sheryl Caño
Philippines
 
electrical_geek said:
Of course it is possible to connect the overload relay before the contactor. But it is stupid! The overload relay is always live, connected this way and it would be difficult to change it, should it become neccessary.
Click to expand...

Wouldn't changing the overload without proper lock-out / de-energizing be just as stupid?
 
sheryl86_ann said:
In a 3 phase wye- delta motor wiring, it is normally wired this way..From main power source to magnetic contactor followed after with an overload relay then to the motor load.


The answer to your question has two answers.
#1 yes, you can wire the system this way.
#2 if you take into account everything, we (as in the compaines i work for)wire motors this way. 1) the main power source, 2)fusing to protect the wire going to the motor contactor/overloads, 3) motor contactor with overloads, 4)motor disconnect, 5) the motor.

NFPA 70 - National Electric Code is adopted here in the US and there is also an international version. Article 430 covers motors, motor circuits, and controllers.
I personally buy the hardbound version with illustrations and index tabs.

NFPA 79 - Electrical Standard for Industrial Machinery
is a good source for information.

You can also check out www.mikeholt.com (electrical website).

Hope this helps.
James
Click to expand...
 
The overload can be before or after the contactor,
It really is just a matter of choice.

It is mainly that most people now expect to find the overload wired after the contactor, to the extent that from a SAFETY point of view I would never wire an overload before a contactor now.

The exception being where the overload is incorporated into a motor curcuit breaker that acts as isolator and overload in one unit, then onto a contactor.

A bit of history now
When Star Delta (Wye Delta) starters were very common, it was not unusual to find the overload before the contactors, as this way it was possible to set the overload to the full load of the motor, where as an overload after the contactors needed to be set to 58% of motor full load as it was only in three of the six motor leads.
 
Gil47 said:
The overload can be before or after the contactor,
It really is just a matter of choice.

It is mainly that most people now expect to find the overload wired after the contactor, to the extent that from a SAFETY point of view I would never wire an overload before a contactor now.

The exception being where the overload is incorporated into a motor curcuit breaker that acts as isolator and overload in one unit, then onto a contactor.

A bit of history now
When Star Delta (Wye Delta) starters were very common, it was not unusual to find the overload before the contactors, as this way it was possible to set the overload to the full load of the motor, where as an overload after the contactors needed to be set to 58% of motor full load as it was only in three of the six motor leads.
Click to expand...


Yes - but if you do this, then the overload has to cope with the full start current ( X3 FLC)for the duration of the start. Dependent on the application, if you fit the overload below the delta contactor, you do not have issues when starting large fans, for example.

Wouldn't changing the overload without proper lock-out / de-energizing be just as stupid?
Click to expand...
Not if the equipment is constructed to the required standard.
 
Last edited:
One question that no one has asked so far.
Is it a "Manual" motor starter with build-in overload protection?
If it is it is acceptable in the US.
These things can be used as branch protection as well as per UL
(consider it as a Supllemental Circuit Protection or SP).
 
Most modern wiring techniques utilise type two co-ordination whereby the circuit breaker incorporates overload and short circuit protection, it is the easiest wirirng method, so yes to your answer
 
markie said:
Yes - but if you do this, then the overload has to cope with the full start current ( X3 FLC)for the duration of the start. Dependent on the application, if you fit the overload below the delta contactor, you do not have issues when starting large fans, for example.


Not if the equipment is constructed to the required standard.
Click to expand...

Disagree, depending on lots of variables not stated :p
 
Just had a look through the first electrical catalogue on the shelf at work which has "Sprecher schuh" type two motor protection circuit breakers up to 400 Amps, even using standard overloads after the main contactor, the swtichboard fuses or circuit breakers have to handle the full current which is why manufacturers make motor start fuses/circuit breakers, I guess the same idea follows over to type two breakers.
 

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