Powering an external relay

The T3 controllers have relay contacts rated at 1 amp or so which is called a ‘pilot duty’ only relay and is used for powering small dampers & valves only. When you need some real power to turn on a fan or pump you need to increase the switching power by wiring in an external relay. You may also need to isolate systems of different voltages, an external relay will come in handy for these cases.

Here is how you will wire the external relay to the T3 controller, this example uses a 24VAC MRB relay board but it applies to any sort of external relay. We start off at the transformer at Tab1, this powers both the T3 controller and it also will energize the external 24vac relay. The 24vac power is also wired to one side of the T3 relay at Tab2. When the on board relay fires power is switched out to the external relay at Tab3. The current flows through the external relay coil and on through the PCB traces of the MRB at Tab4 and finally back to the transformer again at Tab5.

If you are wiring up several external loads this wiring strip will make your job a lot easier. It can be used to common up the connections on the T3 at Tab2.

Hello, at pag.31 of the T3000 manual it is described that “…There are two types of outputs, the relay outputs and analog 0 to 10V outputs. The relays are dry contacts with a UL listed rating of 120vac at 5 amps.”.
I live in Italy and our Electrical Standard is 220 Volt AC 50 Hz. I suppose I cannot connect directly relay output because 120 VAC at 5 Amps is about 60 Volt AC (120/5). So should I use a transformer and to switch a relay powered at 220 Volt?

For the USA/Canada market we have to keep all the control voltage wiring to 40V or lower so as to be classed as ‘low voltage’ wiring and avoid some heavy fees for a ‘listing’ with the various agencies involved. In fact the relays are rated to higher voltages but we don’t show it to keep our products low voltage devices. We have one item with 220V rated relays, the Tstat9. All the rest of our products use relays rated at 120VAC or so.

Thank you very much Maurice.

hi , if i am using AO to power external solid state relay or mechanical relay with coil 5 VDC ,what is max current can be supplied by AO per point and total ?

Each individual output can source up to 100ma at 10V which is enough to power most regular 12VDC ice cube relays. There is a limit for the combined total of all analog output current, going from memory it should be around 500ma total.

You can also make use of these relay modules, they plug right into the output terminals of the T3 controller and they’re high efficiency relays so you can energize more of them per controller.

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Each individual output can source up to 100ma at 10V which is enough to power most regualr 12VDC ice cube relays. There is a limit for the combined total of all analog output current, going from memory it would be around 500ma total.

You can also make use of these relay modules, they plug right into the output terminals of the T3 controller, they’re high efficiency relays so yo