Wiring Pump Overflow Switch to Zone

[paw500]

I have a condensate pump with an overflow switch. The switch has 3 leads: N.O., COM, and N.C. When the pump is normal (not overflowing), N.C. - COM is closed. When the pump is overflowing (i.e. motor died, downstream clog&hellip N.O. - COM is closed.

Typically this switch is wired directly to the HVAC air handler's shutdown circuit, so that when the pump is overflowing, the air conditioning system will be told to shut down to prevent further condensation from dripping.

Now, I want to use this switch to also alert me via an Elk zone. So I will incorporate a relay (DPDT because I have 2 air handlers draining to this pump) to signal the shut down circuits. I plan to energize the relay by taking Vaux +12VDC and wiring in the overflow switch between the Vaux COM and the relay. Then I plan to wire a zone input to the N.O. side of the overflow switch (program the zone to be N.O.), so that when the switch throws an overflow condition, the zone essentially is shorted.

Please see the attached wiring diagram.

The question here is, if I take aux power from a remote power supply such as Elk-P212S to energize the relay, do I need to splice an additional COM going back to the zone's COM (dotted line in diagram)? Or is the one COM going back to the aux power supply terminal block sufficient to make the zone (1-wire) input work?

 

[Del91574]

If the power supply is common with the panel, you don't need another common, you could jump the EOLR to the negative.

 

[jpmargis]

No EOLR is required! Your schematic (less the dotted line connection) is good to go.

 

[tmbrown97]

If there's ever an overflow and the Elk is powered off, the shutdown command will never make it to the air handler.

A safer bet would be to use a relay that's powered by the HVAC power and not just the Elk - or use some sort of fail-safe with an extra relay in the mix that the elk has to turn on to switch from default configuration to the proposed configuration; set up in a way that, should the elk not activate the relay, you still have the safety of the mechanical and fail-safe setup.

 

[paw500]

Thanks guys for clarifying the zone hookup part.

If there's ever an overflow and the Elk is powered off, the shutdown command will never make it to the air handler.

A safer bet would be to use a relay that's powered by the HVAC power and not just the Elk - or use some sort of fail-safe with an extra relay in the mix that the elk has to turn on to switch from default configuration to the proposed configuration; set up in a way that, should the elk not activate the relay, you still have the safety of the mechanical and fail-safe setup.

If the Elk power supply is dead, or somehow dies, the DPDT relay won't be energized regardless of the overflow switch position. So the shutdown circuit (R-G) will throw open in the relay, telling the air handler to shut down (or not allowed to be turned on), even if there's no actual overflow.
This gets me thinking of how to isolate the Elk in case of a faulty power supply, since in the grand scheme of things, the Elk zone alert is only secondary in importance to the proper operation and shut down of the AC in case of an overflow...

 

[KenN]

I'd go with a 3PDT relay, power the coil from your HVAC power so that as long as HVAC is powered the system works. Use the extra contact on the relay to indicate status.

EOLR can be added as desired.

 

[tmbrown97]

If the Elk power supply is dead, or somehow dies, the DPDT relay won't be energized regardless of the overflow switch position. So the shutdown circuit (R-G) will throw open in the relay, telling the air handler to shut down (or not allowed to be turned on), even if there's no actual overflow.

I can already hear the conversation with the wife:
"I'm sorry it's 95° inside the house, but that lightning storm blew the modem in the Elk and I had to send it in for repair; and without it, the A/C can't operate. We should have it back in about 2 weeks though!"

 

[KenN]

I can already hear the conversation with the wife:
"I'm sorry it's 95° inside the house, but that lightning storm blew the modem in the Elk and I had to send it in for repair; and without it, the A/C can't operate. We should have it back in about 2 weeks though!"

I believe I can come up with a schematic to solve that little problem too ...

 

[tmbrown97]

:rofl:

A/C is a sensitive issue this week - it's in the high 100's, and we got lucky - almost had to figure out where to scrape up $5K for my system, but got a good tech that was able to repair what nobody else would... wife's good friend however, heard a nasty sound around midnight and the system crapped out - they were told today they entire thing has to be replaced (compressor fried).

There are days I'd rather have water damage than a wife that's hot and uncomfortable though!

 

[paw500]

Haha... it's all about staying cool! The heck with water spillage... (a waterbug sensor on the floor will pick that up, right?). Actually with my two air handlers dumping into this pump, and the way the fans continue to run on lower speed when cooling demand is off during dehumidification mode, there's an incredible amount of condensate that gets produced! So I'm taking layered precautions to prevent a flood, which could happen if the pump is off for as little as 15 minutes!

Off to get a 3PDT relay.

However I think I'll have to tap power from the same source as the pump (transformer into the pump receptacle) instead of tapping from the HVAC, since I'd like to be able service either air handler without affecting the use of the other.

 

[kurtmccaslin]

If you use the same sensor as the pump overflow shutdown, you are not really adding a layer of protection. I would add a second float switch. In industrial applications, you would normally install the alarm float switch so that it engages before the shutdown float switch. I bet that you could find a float switch for about the same price as that relay.

 

[tmbrown97]

That is actually a good point - to know *before* it shuts off the A/C's, and adding a second layer of protection should the switch somehow fail. But at this point if we keep sending the OP in different directions he's liable to lose it!