Controller / Relay question

[twitch]

I'm in the process of building a controller for my Tarm to run the pump, air handler, and overheat situations (dump zone, air handler). I have a solid state relays that will basically be replacing the aquastats I have in place. Initially I want to keep the aquastats in the system in case the controller, or my programming, craps out. If I have the relay / aquastat / pump wired parallel as below, when the aquastat turns on, there will be a 'hot' wire on both sides of the relay. Will this cause a problem with the relay? I'm planning on setting the aquastat temps for overheat only situations, so the relay should be on before the aquastat, but I'm only going to run the pump if the boiler supply is a set temp above the temp coming out of the air handler, so there is a chance that the relay will be off when the aquastat is on.

 

[Dune]

Why not just run the pump right off the aquastat?

 

[stee6043]

Yes, if both your aquastat and relay are closed (contact) you will short the cirtcuit/blow the breaker/melt something...

Sure seems like perhaps you're complicating something that doesn't need to be this complicated? And for what it's worth overheat protection should rely on valves/zones that require no electricity to function properly. If your overheat protection relies on relays or aquastats you may find yourself in a pinch in a power outage....

 

[RJP Electric]

Actually it is common to see relays aquastats in parallel like that, I have a similar set up here to operate my main pump like the drawing as shown. I am assuming you are going to use the N/O contacts of the relay, in other words NOT feeding a coil or TT of the relay from the power source shown. The only time you will have problems is when you are mixing different electrical phases and voltages, but in your case you will be ok only running a single hot.

 

[Dune]

Stupid Question Department; What does the relay do that the aquastat doesn't do?

 

[kabbott]

Stupid Question Department; What does the relay do that the aquastat doesn't do?

I would assume the relay controls the pump normally and the aquastat is a fail safe for overtemp.
As RJP said you will be fine as long as your on the same circuit as in not a different leg, voltage, phase etc....

 

[jebatty]

Stupid Question Department; What does the relay do that the aquastat doesn’t do?

I'm not an electrician, so this comment is just based on my practical knowledge, whether or not I know what I am talking about. Also, my comments are unrelated to any code requirements, and following the code is important.

An aquastat opens/closes contacts for a circuit based on a temperature setting. If the intent is to control a circ, this can be done directly from an aquastat, but since the circ requires line voltage, the aquastat must have the hot wire from the line controlled by the aquastat contacts.

Or, have a low voltage control circuit (24VAC) controlled by an aquastat/thermostat, wired in series with a 24VAC relay coil, and a transformer providing 24VAC power. The aquastat/thermostat device opens/closes 24VAC power to the relay coil, which opens/closes the relay contacts. The line voltage is wired to the relay contacts to control the circ. It generally is less expensive and less line loss to use a 24VAC control circuit, and then keep the line voltage wiring limited to what it actually has to power. Possibly also some safety issues running line voltage control/load circuits, but if done properly, I'm not aware that there is a safety concern.

Depending on what is being controlled, it is possible that the contact ratings of an aquastat would not be rated for the load being controlled. In this case a relay/contactor would have to be used, with the aquastat controlling the coil, and the load served through the relay/contactor contacts rated for the load being controlled.

My system is compact and I use line voltage aquastats to control the circs. I also have a 12000W backup tankless water heater as freeze protection. The tankless water heater has a 24VAC control circuit with a contactor relay to control the 240V line feed to the heater.

 

[Dune]

Stupid Question Department; What does the relay do that the aquastat doesn’t do?

I'm not an electrician, so this comment is just based on my practical knowledge, whether or not I know what I am talking about. Also, my comments are unrelated to any code requirements, and following the code is important.

An aquastat opens/closes contacts for a circuit based on a temperature setting. If the intent is to control a circ, this can be done directly from an aquastat, but since the circ requires line voltage, the aquastat must have the hot wire from the line controlled by the aquastat contacts.

Or, have a low voltage control circuit (24VAC) controlled by an aquastat/thermostat, wired in series with a 24VAC relay coil, and a transformer providing 24VAC power. The aquastat/thermostat device opens/closes 24VAC power to the relay coil, which opens/closes the relay contacts. The line voltage is wired to the relay contacts to control the circ. It generally is less expensive and less line loss to use a 24VAC control circuit, and then keep the line voltage wiring limited to what it actually has to power. Possibly also some safety issues running line voltage control/load circuits, but if done properly, I'm not aware that there is a safety concern.

Depending on what is being controlled, it is possible that the contact ratings of an aquastat would not be rated for the load being controlled. In this case a relay/contactor would have to be used, with the aquastat controlling the coil, and the load served through the relay/contactor contacts rated for the load being controlled.

My system is compact and I use line voltage aquastats to control the circs. I also have a 12000W backup tankless water heater as freeze protection. The tankless water heater has a 24VAC control circuit with a contactor relay to control the 240V line feed to the heater.

Oh.

 

[twitch]

Thanks for the replies. Right now my pump is running of an aquastat, but once it is on it runs constantly until the boiler temp goes below the set point. I want to use the relay and a controller to only run the pump if the temp difference between the supply and return out of the air handler is say 6 degrees (need to test it).

My primary overheat dump zone is a normally opened zone valve and baseboard fin tube. If the power goes out, the valve opens. If the temp continues to climb, I turn on the air handler to dump the heat. I know this won't work in a power outage, but works great when the power is on.

The relay and aquastat would be running from a single hot lead, and the relay is NO.