Using Magnetic Contactors in Residential Application

Thread Starter

Sp@ceR

Joined Mar 11, 2018
50
Hi guys. As far as I know, contactors are mostly used in industrial motor controls. In my breaker box, after the main switch (3 pole 63A MCB) I thought to wire a contactor beside it, and a 2 way selector to control the coil opening and closing. (Practically pointless because I could trip the whole circuit by the 3 pole MCB, but wiring a contactor is new thing to learn). I cannot wire the selector directly to the main switch since the contacts are only rated for 10A. I have a few questions:

1. What AC type should I pick in residential use? From what I read here: http://www.eecontrols.com/documents/Pages21-30.pdf the appropriate one should be AC-7a? It's hard to anticipate what electronics are coming in the future so I assume of what I have now: oven, ceiling fans, 1.5hp A/Cs, TVs, charger, laptop etc.

2. Is AC3 contactor able to handle AC1 specification? For example if an AC3 contactor is not used with squirrel cage motor, instead with regular lighting circuits, it can handle larger currents? I see many AC3 have 'Ith=AC1=?A' written on them.

My house is running 380V 3ph 50Hz.

Has anyone done this to the house?
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
20,695
A contactor is basically just a relay on steroids. :p
You mean your residential wiring is powered with 380V?
Or is this one phase to the star neutral?
The contactor has a coil like any relay and can be ordered with a voltage rating suited to the voltage being used in the control system from low voltage DC or AC up to 250v is usually the range.
The contacts are just heavy duty rated, Also the contactor can be Definate Purpose rated, i.e. HVAC use etc.
Another feature is low current aux contacts can be added, if needed.
What do you intend controlling?
Max.
 

Thread Starter

Sp@ceR

Joined Mar 11, 2018
50
A contactor is basically just a relay on steroids. :p
You mean your residential wiring is powered with 380V?
Or is this one phase to the star neutral?
The contactor has a coil like any relay and can be ordered with a voltage rating suited to the voltage being used in the control system from low voltage DC or AC up to 250v is usually the range.
The contacts are just heavy duty rated, Also the contactor can be Definate Purpose rated, i.e. HVAC use etc.
Another feature is low current aux contacts can be added, if needed.
What do you intend controlling?
Max.
Incoming is 380V 3ph. Refer main post, wiring diagram here: https://forum.allaboutcircuits.com/threads/residential-3-phase-wiring-help.167540/
I just thought to use a contactor as an alternative main switch to control the electricity to the whole house. Imagine as if I can trip/ reconnect the power without having to open up the breaker cover with a 2 way selector switch mounted outside ;)

I have added another question to the main post in case if you missed it:
2. Is AC3 contactor able to handle AC1 specification? For example if an AC3 contactor is not used with squirrel cage motor, instead with regular lighting circuits, it can handle larger currents? I see many AC3 have 'Ith=AC1=?A' written on them.
 

BillB3857

Joined Feb 28, 2009
2,533
If you were to use an aux contact, it could be configured so that in the event of a power failure, power would stay off until manually reset. Most damaging voltage transitions occur when power is restored by the utility. A manual reset through your contactor would be cleaner.
 

MaxHeadRoom

Joined Jul 18, 2013
20,695
I would obtain the Definate Purpose rated contactor for this application,
Where are you located, what is the 1ph rated circuits in your residence? Voltage?
I would assume they are 230v with a star grounded neutral?
Max.
 

Thread Starter

Sp@ceR

Joined Mar 11, 2018
50
I would obtain the Definate Purpose rated contactor for this application,
Where are you located, what is the 1ph rated circuits in your residence? Voltage?
I would assume they are 230v with a star grounded neutral?
Max.
Definite Purpose Contactors. From what I read, these are for HVACR applications or more like general purpose without AC(1/2/3 etc) rated?

I live in Malaysia. On older houses are single phase 230V. Latest built houses mostly equipped with 3 phase 380V which will get the same 230V from each phase. Not sure about the star grounded neutral tho.
 

MisterBill2

Joined Jan 23, 2018
6,067
What has not yet been mentioned is that the coil that makes that contactor close the circuit requires a fair amount of power to operate, and so it is going to be getting warm.
Incoming is 380V 3ph. Refer main post, wiring diagram here: https://forum.allaboutcircuits.com/threads/residential-3-phase-wiring-help.167540/
I just thought to use a contactor as an alternative main switch to control the electricity to the whole house. Imagine as if I can trip/ reconnect the power without having to open up the breaker cover with a 2 way selector switch mounted outside ;)

I have added another question to the main post in case if you missed it:
2. Is AC3 contactor able to handle AC1 specification? For example if an AC3 contactor is not used with squirrel cage motor, instead with regular lighting circuits, it can handle larger currents? I see many AC3 have 'Ith=AC1=?A' written on them.
An "AC3" rated contactor means that it has three sets of contacts. So you can use one set or two sets or all three.
 

MisterBill2

Joined Jan 23, 2018
6,067
What has not yet been mentioned is that the coil that makes that contactor close the circuit requires a fair amount of power to operate, and so it is going to be getting warm. And I am really wondering why you would be choosing to switch the power in the breaker box, using a contactor. That is a very uncommon way of controlling anything.

An "AC3" rated contactor means that it has three sets of contacts. So you can use one set or two sets or all three.
 

MaxHeadRoom

Joined Jul 18, 2013
20,695
Definite Purpose Contactors. From what I read, these are for HVACR applications or more like general purpose without AC(1/2/3 etc) rated?
I live in Malaysia. On older houses are single phase 230V. Latest built houses mostly equipped with 3 phase 380V which will get the same 230V from each phase. Not sure about the star grounded neutral tho.
Definate purpose take a higher repeated operation than the standard version, also generally have arc quench contacts.
You can use a 230vac coil version.
So the supply is similar to Europe/Australia etc, except you have all three 380v phases, normally the neutral 230v (star point) is earth grounded.
The neutral is Not switched.
Max.
 

Thread Starter

Sp@ceR

Joined Mar 11, 2018
50
So the supply is similar to Europe/Australia etc, except you have all three 380v phases, normally the neutral 230v (star point) is earth grounded.
Yes, or you can refer to British Standards. That is what most of our electrical system is referenced closely to. I really don't quite see much benefit of 3 phase installed in residential actually...except it can cater more electricity and prevent frequent tripping. Mansions and fully/ semi-detached houses and such like...

If you were to use an aux contact, it could be configured so that in the event of a power failure, power would stay off until manually reset. Most damaging voltage transitions occur when power is restored by the utility. A manual reset through your contactor would be cleaner.
Bill, do you have a wiring diagram to show?
 

MaxHeadRoom

Joined Jul 18, 2013
20,695
Yes, or you can refer to British Standards. That is what most of our electrical system is referenced closely to. I really don't quite see much benefit of 3 phase installed in residential actually...except it can cater more electricity and prevent frequent tripping. Mansions and fully/ semi-detached houses and such like...
I personally have never heard or 3 phase in a residence apart from special circumstances.
I once was required to wire for 3ph in a (UK) residence uing a large heating load, they ran the 3 phase in for it specially.
Here is a contactor diag.
Ignore the O/L's they are not required in your application, besides they show them on the wrong side of the coil.
Notice the use of the fourth (aux) contact in order to retain the coil.
Also as to the diagram, it shows the coil controlled across 2 phases, in your case i would use one phase and the star neutral (230v) for the coil circuit.
Max.
 

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MisterBill2

Joined Jan 23, 2018
6,067
I personally have never heard or 3 phase in a residence apart from special circumstances.
I once was required to wire for 3ph in a (UK) residence uing a large heating load, they ran the 3 phase in for it specially.
Here is a contactor diag.
Ignore the O/L's they are not required in your application, besides they show them on the wrong side of the coil.
Notice the use of the fourth (aux) contact in order to retain the coil.
Also as to the diagram, it shows the coil controlled across 2 phases, in your case i would use one phase and the star neutral (230v) for the coil circuit.
Max.
Actually 3-phase Y tied has become common for the bigger all electric homes in some areas. It is 120V to neutral and 208 between phases and it supports those larger AC compressors very well.
 

MaxHeadRoom

Joined Jul 18, 2013
20,695
Actually 3-phase Y tied has become common for the bigger all electric homes in some areas. It is 120V to neutral and 208 between phases and it supports those larger AC compressors very well.
I have only ever seen 208v used in small factories that have a lot of lighting.
I don't think i would favour that with residential with 230 appliances, just squeaks in the -10% tolerance.
Max.
 

MisterBill2

Joined Jan 23, 2018
6,067
I have only ever seen 208v used in small factories that have a lot of lighting.
I don't think i would favour that with residential with 230 appliances, just squeaks in the -10% tolerance.
Max.
Check the Grainger catalog and see all of the 208/230 volt motors listed. And it is quite reasonable to use for residential applications. It just means selecting replacement motors a bit more carefully. And aside from AC compressors the rest of the 220-230 volt appliances use it for heating, which 208 is a better choice. In electric dryers the motor is a 120 volt device, mostly. Likewise, electric water heaters and electric stoves.
 

MaxHeadRoom

Joined Jul 18, 2013
20,695
Check the Grainger catalog and see all of the 208/230 volt motors listed. And it is quite reasonable to use for residential applications. It just means selecting replacement motors a bit more carefully. And aside from AC compressors the rest of the 220-230 volt appliances use it for heating, which 208 is a better choice. In electric dryers the motor is a 120 volt device, mostly. Likewise, electric water heaters and electric stoves.
Doesn't allow any error in order to satisfy the ±10% guaranteed or recommended supply tolerance for residential service standards. When running the higher voltage appliances etc.
This is the standard here, and AFAIK most of N.A.
In the event of a 10% drop you would end up with 187v! :rolleyes:
Max.
 

BillB3857

Joined Feb 28, 2009
2,533
This is a ladder diagram of a start-stop system. The contact across the start switch (normally open) is the seal contact that will keep the relay picked up as long as power is applied and the stop button (normally closed) is not pressed. It is usually an auxiliary contact since it isn't required to carry any of the normal load current, like the main contacts.
 

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BillB3857

Joined Feb 28, 2009
2,533
The advantage of a relay, when properly set up, is that in the event of a power failure, even wnen power is restored, the load isn't activated until commanded to do so by the push of a button.
 

MaxHeadRoom

Joined Jul 18, 2013
20,695
This is a ladder diagram of a start-stop system. The contact across the start switch (normally open) is the seal contact that will keep the relay picked up as long as power is applied and the stop button (normally closed) is not pressed. It is usually an auxiliary contact since it isn't required to carry any of the normal load current, like the main contacts.
And as I pointed out in my diagram, it may be better (safer?) to use the N in place of L2.
Max.
 
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