Help with Sourcing Right Relay - Remote Control Via Low Voltage of Higher Voltage/Amp Load

Thread Starter

JHMarshIII

Joined Oct 27, 2023
7
Hiya, newbie here. My use case is to build a switch to remotely controls three, 30 amp, 240VAC circuits and one 15 amp 120VAC circuit. I've identified an IP based controller (uSwitch), which uses 12VDC to power two relays.

But I'm having trouble identifying the four relays I would need. Do I choose solid state or electromechanical? Also, the high voltage side has 10 gauge wire the load side of the relay would need sit in between. Additionally, my project box enclosure would need to support high voltage.

The controller (uSwitch) has two 12 VDC relays. I envision using the first relay to control the three 240VAC, 30 amp relays, and the second to control the 120VAC 15 amp relay. So far I've only been able to find 24vdc to 240vac (40amp) relays. I'm having trouble visualizing if the relay can support 10 gauge wire.

The loads I'm trying to control are three individual electrical resistance coils in an electrical heating furnace and one fan and logic board circuit. The unit has it's own 200 amp service panel and four breakers. This relay box would sit between the four circuit breakers and the electric furnace.

Can anyone suggest the best relay for this project and where I can source it? Thanks much.
 

eetech00

Joined Jun 8, 2013
3,820
1. The 3 external relays should be power relays and each have 12vdc coils with contacts rated at the minimum current of 30A@240VAC.
2. The 1 external relay should also be a power relay and have a 12vdc coil with contacts rated at the minimum current of 15A@120VAC. This relay could be the same type as above.

The coils would be driven by the same 12VDC power source as the uSwitch device and would be controlled/wired via the uSwitch internal relay contacts.

The external relays should all be UL certified for safety. All related wiring should follow electrical standards.
If your not an electrician, you should probably consult one.
 

Ian0

Joined Aug 7, 2020
9,499
You need a contactor.
https://chint.co.uk/product/nc1-4pole-ac/
but you are unlikely to find one with a 12V coil.
I would suggest using an opto-triac/triac combination to switch the power to a contactor with a 230V coil.

If you use a solid-state relay, don't forget that it will dissipate 1 Watt for every amp.
 

MisterBill2

Joined Jan 23, 2018
17,794
This is an interesting challenge. You will find relays, or contactors, with 24 volt AC coils are very common with 30 amp contact arrangements rated for 240 volt service. They will be entirely suitable for 120 volts AC switching as well. SOME of those devices may also operate acceptably well on 12 volts DC, although some might tend to overheat.
I recommend "Automation Direct" as a resource for such devices.
You will need to avoid the cute little circuit board assemblies because they appear to be much more hobby application types and not rated for the higher power applications.
 

MaxHeadRoom

Joined Jul 18, 2013
28,513
Hiya, newbie here. My use case is to build a switch to remotely controls three, 30 amp, 240VAC circuits and one 15 amp 120VAC circuit.
3 x 30amp Heating loads? It is customary with this arrangement to bring heating elements on line sequentially to avoid a 90amp+ load, which is higher when the elements are in the cold condition.
You do not say whether the loads are to be sequenced or you had switch all 3 simultaneously?
Personally I never use AC coil contactors or relays, the DC are more reliable in the long run.
Schneider or Square-D have 12v coil contactors.
 
Last edited:

Thread Starter

JHMarshIII

Joined Oct 27, 2023
7
A good 40 amp relay should be able to easily handle 10 gauge wire and possibly even 8.

Are you currently controlling anything with your existing relays? If not I would do something like this https://mccombssupply.com/c240c-dou...LKlZViLD31pklgFQbPDYyON3WI3hYhuRoCDQ0QAvD_BwE
and use the existing relays to control the coil power (240 VAC).
Thank you GeekOfTheWeek. Nothing would be controlled other than the group of three relays and other one relay. I'm faced with a 12vdc controller limitation if I want to use the off the self uSwitch. However, since my application is control of an HVAC class system, perhaps I need to find a different IP based controller that supports 24vdc.
 

Thread Starter

JHMarshIII

Joined Oct 27, 2023
7
This is an interesting challenge. You will find relays, or contactors, with 24 volt AC coils are very common with 30 amp contact arrangements rated for 240 volt service. They will be entirely suitable for 120 volts AC switching as well. SOME of those devices may also operate acceptably well on 12 volts DC, although some might tend to overheat.
I recommend "Automation Direct" as a resource for such devices.
You will need to avoid the cute little circuit board assemblies because they appear to be much more hobby application types and not rated for the higher power applications.
Trust me if I could find an off-the-self solution I'd buy it! So it seems my limitation is in the IP based controller. Which only offers 12vdc switching. I will need to look for another.
 

Thread Starter

JHMarshIII

Joined Oct 27, 2023
7
3 x 30amp Heating loads? It is customary with this arrangement to bring heating elements on line sequentially to avoid a 90amp+ load, which is higher when the elements are in the cold condition.
You do not say whether the loads are to be sequenced or you had switch all 3 simultaneously?
Personally I never use AC coil contactors or relays, the DC are more reliable in the long run.
Schneider or Square-D have 12v coil contactors.
So let me expound on my application. I just had installed a duct based, forced hot air, Electric Thermal Storage (ETS) system. It is designed for steady heat, not on-demand heat. It works by storing electric resistance heat in an insulated box of thermal ceramic bricks (the Core). You buy the electricity off-peak (about 5¢ a KwH) which makes it less expensive or competitive with oil or gas.
Hiya, newbie here. My use case is to build a switch to remotely controls three, 30 amp, 240VAC circuits and one 15 amp 120VAC circuit. I've identified an IP based controller (uSwitch), which uses 12VDC to power two relays.

But I'm having trouble identifying the four relays I would need. Do I choose solid state or electromechanical? Also, the high voltage side has 10 gauge wire the load side of the relay would need sit in between. Additionally, my project box enclosure would need to support high voltage.

The controller (uSwitch) has two 12 VDC relays. I envision using the first relay to control the three 240VAC, 30 amp relays, and the second to control the 120VAC 15 amp relay. So far I've only been able to find 24vdc to 240vac (40amp) relays. I'm having trouble visualizing if the relay can support 10 gauge wire.

The loads I'm trying to control are three individual electrical resistance coils in an electrical heating furnace and one fan and logic board circuit. The unit has it's own 200 amp service panel and four breakers. This relay box would sit between the four circuit breakers and the electric furnace.

Can anyone suggest the best relay for this project and where I can source it? Thanks much.
Yikes, I specified the wrong load numbers. These are 60 amp 240 vac breakers on the supply side with #6 awg wire. However the true load is 40 amps on circuit #1, and 50 amps each on circuit #2 and circuit #3. The fourth is the same at 15 amp (120v).
 

Thread Starter

JHMarshIII

Joined Oct 27, 2023
7
3 x 30amp Heating loads? It is customary with this arrangement to bring heating elements on line sequentially to avoid a 90amp+ load, which is higher when the elements are in the cold condition.
You do not say whether the loads are to be sequenced or you had switch all 3 simultaneously?
Personally I never use AC coil contactors or relays, the DC are more reliable in the long run.
Schneider or Square-D have 12v coil contactors.
Yikes, I specified the wrong load numbers. These are 60 amp 240VAC breakers on the supply side with #6 awg wire. However the true load is 40 amps on circuit #1, and 50 amps each on circuit #2 and circuit #3. The fourth is the same at 15 amp (120v). For ease of planning and safety (since the breakers can pass upto 60amps) I should probably stick with 60 amps for the first three relays.

So let me expound on my application. I just had installed a duct based, forced hot air, Electric Thermal Storage (ETS) system. It is designed for steady heat, not on-demand heat. It works by storing electric resistance heat in an insulated box of thermal ceramic bricks (the Core). You buy the electricity off-peak (about 5¢ a KwH) which makes it less expensive or competitive with oil or gas.

ETS is designed for dwellings that are occupied year round. I'm occupying the dwelling part-time and never on any sort of schedule. So I want to remotely control the overall supply to the ETS. The ETS has its own load panel (200 amp) with three 60 amp two pole breakers with #6 wire to the ETS which also has for safety it's own breakers (one for each heating resistance coil. To address MaxHeadRoom's question, I don't think the internal control board will allow the unit to activate unless the load is present at all three heating resistance coils.). I'm essentially trying to throw the breakers remotely. So I can charge the Core a day in advance of occupying the dwelling.

Hiya, newbie here. My use case is to build a switch to remotely controls three, 30 amp, 240VAC circuits three 60 amp 240VAC and one 15 amp 120VAC circuit. I've identified an IP based controller (uSwitch), which uses 12VDC to power two relays.

But I'm having trouble identifying the four relays I would need. Do I choose solid state or electromechanical? Also, the high voltage side has 10 6 gauge wire the load side of the relay would need sit in between. Additionally, my project box enclosure would need to support high voltage.

The controller (uSwitch) has two 12 VDC relays. I envision using the first relay to control the three 240VAC, 30 60 amp relays, and the second to control the 120VAC 15 amp relay. So far I've only been able to find 24vdc to 240vac (40amp) relays. I'm having trouble visualizing if the relay can support 10 gauge wire.

The loads I'm trying to control are three individual electrical resistance coils in an electrical heating furnace and one fan and logic board circuit. The unit has it's own 200 amp service panel and four breakers. This relay box would sit between the four circuit breakers and the electric furnace.

Can anyone suggest the best relay for this project and where I can source it? Thanks much.
 

MaxHeadRoom

Joined Jul 18, 2013
28,513

Thread Starter

JHMarshIII

Joined Oct 27, 2023
7
Appears to be your typical HVAC compressor motor relay.!
Are you in the UK by any chance, I used to install off-peak storage units, they used off peak power to store heat over night and used thermal blocks to store the heat.
The down side was you had to predict the next days weather! o_O
I'm in the states. Interesting that you did ETS installs in the UK. In my system an outdoor sensor has been incorporated that informs the controller board of temperature trends. This system is 24.8 kWH.

I think I've found the solution using 65 amp contactors. I will post back my project outcome and pictures.
 
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