Humdinger
Posts: 2
Joined: Fri Aug 08, 2014 10:07 am

Relay - Switching Earth

Mon May 18, 2015 12:37 am

Hey all,

I am working on a project using my Pi to act as a thermostat to control my Gas Heater. I have all the software side working well, just have a question regarding the relay.

My heater currently has a thermostat plugged in (aftermarket) which is just a remote controlled type device. The way it works is that the thermostat creates an earth bridge to 2 pins on the heaters control board (one for front burner, one for back), so basically all I will be doing is using a Relay module from the Pi to replicate this earthing.

Just wanted to double check that I can use the relay to create an earth bridge as in the picture below. I am pretty sure this should be fine but like to check!.
PiRelay.jpg
PiRelay.jpg (39.47 KiB) Viewed 702 times

ceteras
Posts: 239
Joined: Fri Jan 27, 2012 1:42 pm
Location: Romania

Re: Relay - Switching Earth

Mon May 18, 2015 8:04 am

Affirmative, that's what relays are for. As long as you use the NO connection on your board, it will have the same functionality.
Make sure your relay can withstand the maximum current required.

johndough
Posts: 254
Joined: Sun Jan 13, 2013 2:00 pm

Re: Relay - Switching Earth

Mon May 18, 2015 8:38 am

Humdinger wrote:Hey all,

I am working on a project using my Pi to act as a thermostat to control my Gas Heater. I have all the software side working well, just have a question regarding the relay.

My heater currently has a thermostat plugged in (aftermarket) which is just a remote controlled type device. The way it works is that the thermostat creates an earth bridge to 2 pins on the heaters control board (one for front burner, one for back), so basically all I will be doing is using a Relay module from the Pi to replicate this earthing.

Just wanted to double check that I can use the relay to create an earth bridge as in the picture below. I am pretty sure this should be fine but like to check!.
PiRelay.jpg
Hi

A thermostat can have a heater resistor as a compensator, this means 4 wires.
EARTH, Live, Neutral and a Switched Live.

Equally there can be just a pair of wires and an EARTH. Live and Switched Live.

#########

Using an earth as a return or putting a potential on an earth circuit is frowned upon. Also within the EU may be illegal.


~~~~~~~~~~~~~~~~~~~~~

Is Switching the Neutral OK?
In A Word, No, And It Can Be Dangerous

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Safety devices, like Current and Voltage operated Circuit Breakers to dis-connect where an earth fault is detected, use either voltage or out of balance current.

So introducing either, onto a circuit that should be at or about Zero volts, by way of a thermostat is BAAD.

#############################

Perhaps you could re-consider or post the circuit diagrams of the equipment involved.

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