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BorisMD 09-08-2009 08:42 AM

Need a relay for off peak heat
Hi all,

First post on this site.

I'm building a garage, and have installed in-floor tubing for heating. I will be heating the water with a micro-electric heater (240v, 50A) that I plan to run only during the off peak hours (10p-630a).

The power company (Xcel), will send a signal on the order of 100mA to tell when the off peak times start and stop. The friendly fellow at the power company said one way to use this signal to operate a relay that disables the thermostat -- thereby only needing a line voltage (120v), low amperage (1amp) relay to cut out the thermostat during peak hours, thus shutting down the whole heating system during that time.

He told me that I would need a relay that is normally closed.

So my question, where does one get such a relay, and anyone have experience with such a setup?



Billy_Bob 09-08-2009 10:01 AM

Basically relays all work the same way, but they are called different things...

In the electronics world they are called "relays".

In the automotive world they are called "solenoids".

And in the electrical world they are called "contactors".

The difference is mounting and the connecting of wires as well as the voltages/amperages they are designed to be used with. Also there is a thing called "duty cycle" where some relays are designed to just be activated momentarily - say briefly on like for a doorbell. Then there is "continuous duty" rated where they are designed to be on for long periods of time - say to switch on lighting.

In the electronics world, they are designed to be mounted and soldered to a printed circuit board typically.

In the automotive world, they might be designed to plug into a fuse box or be mounted on the engine firewall or to use an electrical connector which would keep out dirt, water, and grease.

In the electrical world, they would be designed to be mounted inside an enclosed electrical box.

For the electrical use side and safely mounting inside a large electrical box so the bare wires and connections are protected from anyone accidentally touching them, search the internet for the word contactor.

Then as to your "signal" from the electric company, this is a new thing to me. If you could find technical information on this, then post the link here, that would be a big help. Or get the exact technical terms used for this.

The word "signal" is quite common and I can't search for that term. A technical term would be something like "net metering", "phase locked loop", "time of use electric meter", etc. A specific word or term to describe this signal or signaling system.

Is there a wire or wires coming from the electric meter which would have just this signal on them? Or do they connect some sort of electric box and this would have connections?

I've read a bit about this capability. Basically they can send a signal over the existing electric lines to an electric meter or the other way around. But you would need some sort of "gizmo" to separate that signal form the electric lines. ?????

Billy_Bob 09-08-2009 10:15 AM

Here is a "clue" from your electric company's web site...

"Saverís Switch is a pager-activated device that we install on your outside air conditioning units that helps reduce electric loads when price or demand for electricity peak."

Billy_Bob 09-08-2009 10:22 AM

Here is a bit more, but I can't find any technical information about the "pager" or how you would connect to it...

Billy_Bob 09-08-2009 10:27 AM

This might work for you...
(Lots of "technical" terms!)

BorisMD 09-08-2009 11:00 AM

Thanks for the responses. I think the saver switch is more for the AC. I don't think that is the same as the off-peak signal. I will call the meter guy again and put your previous questions to him.

Here's a link to Xcel's installer's PDF. About 3/4 of the way down, on page I-5.1, they have a diagram of the install.

I'll look at your other link as well.


wirenut1110 09-08-2009 11:49 AM

You can just get an "ice cube" relay with a 120 VAC coil and the coil load doesn't exceed 100ma. Which most are around 50-70ma.

It looks like you provide a 120 volt circuit, they have a relay within the meter or meter base with NO (normally open) contacts which will be used to switch your relay. Your t-stat will be switched through NC(normally closed) contacts on that relay. When their contacts close, it will energize your relay and open your thermostat.

BorisMD 09-08-2009 11:57 AM

Wirenut1110 --

I think you are correct. That's how I read the diagram also.

So, when I go to my local electrical supply house, the counter guys are not very friendly, helpful, or knowledgeable so what exactly am I asking them for when you say "Ice cube" relay?

Thanks again,


wirenut1110 09-08-2009 12:13 PM


You can get one from here or just ask for an 8-pin relay with a 120 volt coil and an 8-pin relay base.

It'll look something like this

BorisMD 09-08-2009 12:50 PM

Very helpful, thank you.

Now, not to sound like a total idiot, but according to the diagram from Xcel, that relay is the part labeled "N.C.", correct?

Also, the diagram calls for customer supplied wetting voltage not to exceed 120v, 100mA. Does that mean just run a line off one of my receptacle circuits? Those are 20A circuits, how would I limit the current to less than 100mA? Or, is this wetting voltage one of the leads that comes out of the Ice Cube relay?

On the diagram, they make it look pretty simple -- two wires from the power company hook up to two wires from the control circuit meet up in a junction box.

I wired my whole house, pool, addition, etc, but this stuff is all new to me.

wirenut1110 09-08-2009 01:08 PM

I needed to add, if your relay has to switch the 50 amps, you'll need to use a contactor instead of a relay. Relays usually are only good for 10 amps.
You can run a seperate control circuit like from a 15 amp breaker to your relay, maybe putting a small fuse in there to limit the current to .1 amps. I would think that they're just saying that whatever you're switching with their contacts, can't exceed 100ma.

BorisMD 09-08-2009 01:11 PM


I'm just switching the thermostat, so no large current load. The thermostat will be inactive during the daytime so there will be no activity at the boiler or pumps. Basically, this just interrupts the current flow to the thermostat.


wirenut1110 09-08-2009 01:16 PM

If you use a relay, run a 15 amp circuit to a box that the relay will be installed in. The hot will go to a fuse block, then out of the fuse block to their relay then, back from their relay to terminal #7 on your relay base(if you use an 8 pin octal) the neutral will go to terminal#2 on your relay base.

The switching on your relay will hook to NC terminals 1 & 4, or 8 & 5.

Again, depending on the load (amps) your relay has to switch, you may need to use a NC contactor instead of a relay.

BorisMD 09-08-2009 01:19 PM

Thanks again.

I wish I had known this _before_ I just got done with the sheetrock/taping/painting!

I may just put a box extension on one of my wall boxes and use surface conduit to the junction box.



user62257 09-13-2009 02:54 PM

wirenut1110 I am sure I miss something. Your a smart guy. But what?

Did I miss how the signal get to operate the relay.

You see where I come from, we bring a length of UF cable, 12-2 or
14-2 is okay, to the meter socket, the power company brings into the
meter socket and connect it to there signal circuit wiring,

The signal circuit wire carry voltage, usually 120 volts, that would
operate the relay coil.

Well I just wanted state something that I had seen where I live
for relay controls. This is done with what the power company
calls Rate 11. In fact I have two control panels, that I took out,
for a customer, who got rid of all his electric baseboard heat.

But even better, we have what called, Rate 3, and this meter comes
with its own clocks and relays that breaks one legs of the 240 volt
circuit, that is used to heat the water, in your electric hot water storage tank.

GOOD LUCK with your wiring. And as always, work safe.

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