Load Switching

[JFowler]

Hi,
I’m having trouble finding a relay that I’m looking for to switch between loads in a residential application. I was looking for a 50amp DPDT relay with 120VAC coil and planned to install a set of 3 way switches so the coil could be switched from 2 locations. My question is, would there be a problem with installing a 50amp NO contractor with 120VAC coil and a 50amp NC contractor with 120VAC coil in parallel and switched in the same method? Open to alternative suggestions. TYIA!!
Jason

 

[paulengr]

Use a force guided relay. It holds state without power on it. It has two coils one for each dirrction. Use Form C contacts. This is essentially what an ATS (automatic transfer switch) is.

 

[hillbilly1]

It would be much simpler to have two N/O 50 amp contactors, drive the coils with a SPDT relay using the N/C for one contactor, and N/O for the other. The three way switches would drive the relay.

 

[JFowler]

This is what I would like to do Hillbilly but I’m having trouble finding the 50a dpdt relay with 120vac coil. Found several with dc coils but I’d prefer to not have to introduce a transformer also.

 

[JFowler]

Use a force guided relay. It holds state without power on it. It has two coils one for each dirrction. Use Form C contacts. This is essentially what an ATS (automatic transfer switch) is.

That’s not a bad idea paulengr. Thanks!

 

[texie]

This is what I would like to do Hillbilly but I’m having trouble finding the 50a dpdt relay with 120vac coil. Found several with dc coils but I’d prefer to not have to introduce a transformer also.

You are misunderstanding Hillbilly. Use 2 120 coil N.O. contactors with an SPDT interposing relay to drive the contactor coils.

 

[Todd0x1]

There used to be 50A open type DPDT relays, schneider used to have one the 199APX-14 which was 50A DPDT with 120vac coil. Now everything of this type is rated 30 or 40A. Maybe there was a UL change.

Another way to do it without the separate pilot relay would be to use two IEC contactors with a mechanical interlock and wire the coil of unit B to the aux contacts of unit A then you only need to switch the coil of A. (when A is off its NC aux contact is powering the coil of B)

 

[paulengr]

This is what I would like to do Hillbilly but I’m having trouble finding the 50a dpdt relay with 120vac coil. Found several with dc coils but I’d prefer to not have to introduce a transformer also.

Wrong term. Look for CONTACTOR, not relay. You won’t find NC main contacts but you will on auxiliaries.

 

[paulengr]

There used to be 50A open type DPDT relays, schneider used to have one the 199APX-14 which was 50A DPDT with 120vac coil. Now everything of this type is rated 30 or 40A. Maybe there was a UL change.

Another way to do it without the separate pilot relay would be to use two IEC contactors with a mechanical interlock and wire the coil of unit B to the aux contacts of unit A then you only need to switch the coil of A. (when A is off its NC aux contact is powering the coil of B)

I’ve even seen cheap ATSs built this way. They drop out on total power loss. Fancier ones have a single big custom made DPDT switch design although if you ask me it seems a lot less rugged than the contactor versions. It’s too bad ATSs are so outrageously overpriced for what they are.

The rest of the ATS is a DC power supply on both sides (dual input power supply), some fancy protection relays (voltage over/under, frequency over/under, phasing), and a control board. But for the application none of this is needed.

Maybe see if a local generator company has a scrapped out ATS with a dead control board.

 

[Jraef]

You can get lighting contactors with contacts that are NO and NC, 50A too. But you will need to know if your 50A is resistive or inductive, because a “50A” lighting contactor is based on resistive loads, to get 50A inductive you may need a larger version.

 

[Jraef]

Use a force guided relay. It holds state without power on it. It has two coils one for each dirrction. Use Form C contacts. This is essentially what an ATS (automatic transfer switch) is.

That’s not what “force guided” means. You are describing a “latching relay” or in this case, it would be a latching contactor.

Force guided simply means the contacts are directly driven by the armature and springs, not relying on levers, bell cranks or gravity for operation. It’s an issue used in Safety Relays and Safety Contactors to ensure that when commanded to open or close, the contacts are directly acted upon so that if one fails to move (welds), they all do and you don’t get a false indication that they changed state.

 

[JFowler]

Thanks everyone for your input. Let me better explain what I’m working with and exactly what I’m wanting to do.

I have a 400amp service to my home. I have no electrical panels or sub panels on the interior, they are all located at the meter. My wife recently ordered a new Tesla, so I need to install the charger. it is the gen 3 charger which can operate at a range of amperages, 60amps being the highest.

We have a guest room above our garage with a kitchenette that very rarely is used, but is used from time to time.The electrical panels are on the complete opposite side of the house. To get a circuit for the charger to the garage from the panel would be quite the undertaking as it would travel under the house to the opposite side then trench uphill to the garage. I haven’t measured it exactly, but this would make this run around 200’ long. Not to mention tearing half the yard up.

The kitchenette I mentioned has a slide in range on a 50amp circuit. Since it is rarely used, I was looking to branch off of this circuit to the charger, which will be directly beneath it in the garage, and use a DPDT contractor with a 120VAC coil operated from 3 way switches, one in the guest room and the other in the garage.

My trouble has been in finding either a 50amp AC SPDT or DPDT relay to operate the different configurations of contractors that could be made. 40amps AC is the largest I’m finding. I think someone mentioned in a comment above about this and wondering if there had been a change with something since 50amp doesn’t seem available anymore.

Anyhow, this is where I’m at. Thanks again!

 

[hillbilly1]

See post number three for your answer.

 

[hillbilly1]

Two of these.

https://www.grainger.com/search?searchBar=true&searchQuery=50+amp+contactor

 

[hillbilly1]

https://www.grainger.com/product/FU...+@+28V,+SPDT&suggestConfigId=8&searchBar=true
And one of these.

 

[kwired]

So tie both outlets directly to the supply circuit. if you use the range while charging at high rate it likely will trip the breaker. chances are that will rarely happen. If it does you will probably learn not to use that range if the vehicle hasn't been charging for very long. You weren't using both at same time anyway if you used any isolation methods.

 

[Todd0x1]

See post number three for your answer.

Do you see the idea of "use two IEC contactors with a mechanical interlock and wire the coil of unit B to the aux contacts of unit A then you only need to switch the coil of A. (when A is off its NC aux contact is powering the coil of B) " from my previous post as a viable option or is it better to use the pilot relay?

 

[hillbilly1]

Do you see the idea of "use two IEC contactors with a mechanical interlock and wire the coil of unit B to the aux contacts of unit A then you only need to switch the coil of A. (when A is off its NC aux contact is powering the coil of B) " from my previous post as a viable option or is it better to use the pilot relay?

A 50 amp mechanical interlock contactor would not work correctly in this application, let me restate that, interlocking is not required for this application. The OP is using a set of three way switches to operate the contactor this would energize only one coil, the other would need to have a 24 hour hot looped through the aux to be energized while the switch is off. Two electrically held would be much cheaper and easier to get. All that is needed is supply one load, or supply the other depending on the position of the three way switches. Only one power supply. If for some odd reason both contactors remain energized, nothing will happen other than the breaker possibly tripping on overload. Interlocking would not be necessary.

 

[JFowler]

https://www.grainger.com/product/FU...+@+28V,+SPDT&suggestConfigId=8&searchBar=true
And one of these.

Thanks hillbilly1. I believe this is the best way to go for what I’m looking to do. I was getting tripped up looking for a 50amp relay to drive the 50amp contractors. The relay you suggested is only a 10amp. By far the vast majority of electrical that I work with is strictly residential. I’ve done some light industrial but have only worked with controls a handful of times. So, I appreciate the suggestions.

 

[hillbilly1]

Do you see the idea of "use two IEC contactors with a mechanical interlock and wire the coil of unit B to the aux contacts of unit A then you only need to switch the coil of A. (when A is off its NC aux contact is powering the coil of B) " from my previous post as a viable option or is it better to use the pilot relay?

Just to be clear, yes it would work, but an expensive route to go that is not necessary in this application. Not knocking your suggestion.