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Hey all,

I just ordered this replacement electric thermostat for an electric baseboard heater at the house. After reading the reviews, it seems the accuracy of the thermostat is very low due to the unit itself heating up under a heavy load and triggering the thermostat and shutting off the heater.

One reviewer said he fixed this issue by "taking the load off" of the thermostat by adding a "solid state relay". I've googled a bit about this but have to admit that I'm totally unfamiliar with these relays.

How would I install one of these and what exactly does it do?
Can it be installed in a regular junction box?
What type of relay switch would I need?
What is a "solid state relay"?
Would this one from Home Depot be sufficient for a 30 amp circuit? Or would I be better off with a Square D one for a bit more?

Thanks in advance for any help/advice!

JC
 

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Discussion Starter #3
My apologies. The question could've been answered by those in Electrical or HVAC, so I posted it to both. Will keep it on one next time :thumbup1:
 

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The heater wattage you have may exceed the t-stats limits.

A decent electronic stat will not warm up to the point that accuracy is thrown off.

You'll be better off putting a stat that will work properly to begin with than adding a relay.
 

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Hey all,

I just ordered this replacement electric thermostat for an electric baseboard heater at the house. After reading the reviews, it seems the accuracy of the thermostat is very low due to the unit itself heating up under a heavy load and triggering the thermostat and shutting off the heater.
Yes, that's a classic problem with any line-current thermostat. Wires heat up; it's Ohm's Law. If they don't make the internal circuit pathways massively oversized, they will heat up too.

One reviewer said he fixed this issue by "taking the load off" of the thermostat by adding a "solid state relay". I've googled a bit about this but have to admit that I'm totally unfamiliar with these relays.
How would I install one of these and what exactly does it do?
A relay is a gadget which sits inline of the power feed to the heater. When it's on, it connects the heater. When it's off, it does not. You turn it on by applying 24V low-voltage. The thermostat switches that on/off.

Can it be installed in a regular junction box?
It can only be installed according to the instructions which are part of its UL Listing. Equipment only gets UL-listed when it is accompanied by instructions telling you what is allowed. You cannot deviate from those instructions (NEC 110.3b) because the relay hasn't been tested for that.

What type of relay switch would I need?
It's just called a relay, or often called a "contactor".

The type you need is is UL-Listed. You cannot use a relay which is ЯU-Recognized.
It must be listed for the purpose you are using it.
It must also have enough ampacity for the circuit breaker it is on.
Its instructions must also allow the type of mounting you want to do.

What is a "solid state relay"?
A rather bad idea. The person who proposed this was an electronics wiz, knew "just enough to be dangerous" about mains power, and ordered any-old "solid state relay" from his usual electronic component supplier. At best it was ЯU-Recognized. Right idea, wrong relay.

Further, there's no sane way to mount random components not made to go inside junction boxes, so that guy surely just left it to flop around in there. You're not allowed to do that.

Would this one from Home Depot be sufficient for a 30 amp circuit?
No. That is ЯU-Recognized, which means it's illegal to use in mains wiring. ЯU means it's approved *as a component* and you can't use it alone. When UL lists equipment, they teardown every component in it. ЯU means "no need; it's pre-approved". That component is made for repairing UL-listed equipment (like an A/C unit or heat pump).

That's why it says "Definite purpose".

Or would I be better off with a Square D one for a bit more?
Ah, there's the UL-Listed mark. However, it's the wrong voltage.

They probably make a version that is 24V. Then you just need to read the instructions to make sure they authorize a mounting method that is compatible with what's possible for you.


You want 24 volts AC.

The reason you want 24 volts is it's the standard voltage for the vast majority of furnaces, heat pumps, etc. That means you can use any thermostat on the market, including the Nest. And it means you can connect the thermostat to the relay to the transformer with common cheap #18 thermostat wiring. And everyone in HVAC will recognize your system for what it is.

This means you will need one more component, a common-as-dirt 24V transformer, but they make those in a number of form-factors for $13 or so.

Another option for relays is a RIB or Aube. The ideal relay mounts either on a junction box lid, or sticks into a knockout in a steel junction box, with the mains wiring inside the box, and the 24V wiring outside the box. These installs are best done in the basement in utility space e.g. next to the panel. Or you may be able to use a relay that mounts inside the heater itself.

The Aube's include their own onboard transformer, so you only need take 2 wires to the thermostat and yer done. However last I looked, the Aube transformers don't have enough leftover capacity to power a Nest. They may have changed that.
 

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Typical wall thermostats such as you have noted have proven dependable and operate with reasonable accuracy. They operate on air temperature at the unit. There is nothing in them that is able to determine the ampacity of the heater. Any ancillary controls are not required not recommended. Perhaps the location of the thermostat is too close to the heaters and are being influenced by the heater.
 
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