Where to connect common wire


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Old 03-07-13, 10:37 AM
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Where to connect common wire

I need to run a common wire in order to install my Nest Thermostat. I have a Peerless WBV3 boiler, Aquastat L8124A1015 Relay and a Beckett Heat Manager. They only wireless I have on my system is RH and W. I originally installed my nest 3 weeks ago with just hose 2 wires and my Aquastat relay burnt out on the L2 connection. Nest paid for the replacement but they said I needed a common wire in order to install again. I ran 5 conductor thermostat wire to the boiler and replaced the RH and W wires. I have the remaining 3 wires but I would like to connect the common wire. Where would I hook up the common wire? As per nest they said any ground is fine so I hooked it up to the Ground Terminal on the aquastat relay but I do not think that is correct. Can somebody give me insight as to where the common should be connected?
 
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Old 03-07-13, 12:00 PM
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Common goes on the opposite side of the transformer, this is what will assist in powering the nest by giving it the opposite potential of an electrical circuit. R and c will power to thermostat. R will power W when there is a call for heat
 
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Old 03-07-13, 03:01 PM
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Sorry for my ignorance but where would the transformer be and what does it possibly look like? Where would you attach it on the transformer?
 
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Old 03-07-13, 03:23 PM
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James, no disrespect, but yer kinda skeerin' me a little bit.

I originally installed my nest 3 weeks ago with just hose 2 wires and my Aquastat relay burnt out on the L2 connection.
How can a thermostat connection be blamed for 'burning out' the L2 connection? L2 is the 120VAC neutral connection to the aquastat. It should have nothing at all to do with the thermostat. The two are electrically isolated via the internal transformer in your aquastat.

Remind us again what aquastat you have, and tell us again if your system is zoned, etc... I'm sorry that I've got a short memory and too lazy to look back!

Nest paid for the replacement
What 'replacement' ? The aquastat? or the NEST?

If the aquastat, how da heck did you get them to agree to that?

As per nest they said any ground is fine so I hooked it up to the Ground Terminal on the aquastat relay but I do not think that is correct.
NO NO NO... that's just wrong... what they told you, AND the fact that you did it!
 
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Old 03-07-13, 03:34 PM
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Remind us again what aquastat you have, and tell us again if your system is zoned, etc... I'm sorry that I've got a short memory and too lazy to look back!
I have an Aquastat L8124A1015 Relay

What 'replacement' ? The aquastat? or the NEST?

If the aquastat, how da heck did you get them to agree to that?
Nest replaced the Aquastat Relay, they even sent a technician out the night it blew out but they didnt have the replacement part. I ended up going to a local plumbing supply store and purchased the Aquastat L8124A1015 and replaced it myself. Since I replaced it I am using my old thermostat and I have yet to hook up the Nest.

I contacted local plumbers, electricians, Beckett and HONEYWELL to see where the common wire should connect and NOBODY knew the answer. I ended up calling Nest back to find out where I should connect it and they told me that I now do not need a common wire. I got really aggravated and spoke to tier 2 and they told me they will send a nest certified technician onsite to properly install the nest so this does not happen again (on their dime might I add ).

To be quite honest, since I have had the house the only thing I am disappointed in is the heating system and the water. It seems like a botch up job and not professionally installed. It really is so inefficient with the tankless coil and the fact that the water runs out in the shower in 3-5 minutes is really bothering me but that is another story...

I am glad Nest is going to come out and properly install it.
 
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Old 03-07-13, 03:42 PM
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With the 8124A there is no place to grab a 'common' for the thermostat wiring. It's just not desigined for that.

Can you point me to the install material on the web for the NEST? I'd like to confirm a few things.

When is this 'tech' coming?
 
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Old 03-07-13, 03:43 PM
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they told me they will send a nest certified technician onsite to properly install the nest
Still on their dime? What kinda 'connections' do you have?

Is the system zoned? How many thermostats in the home?
 
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Old 03-07-13, 03:44 PM
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Here is the NEST Manual:
http://support-assets.nest.com/image...tion_Guide.pdf

I am going to be receiving an email from the tech withing 72 hours, once I get the email we can schedule.
 
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Old 03-07-13, 03:47 PM
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Yes, everything will be on their dime. As for the connections, I ran the following wire:
Southwire 50 ft. Brown 18-5 Thermostat Wire-64169642 at The Home Depot

From the boiler to the thermostat. I have 5 wires but only 2 are being used. Rh and W and thats it.
 
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Old 03-07-13, 03:49 PM
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Here is the NEST Manual:
Seriously? That's not a manual, it's a picture book... that's all you get?
 
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Old 03-07-13, 03:50 PM
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Seriously? That's not a manual, it's a picture book... that's all you get?



Yea that is it! No other books came with it that I am aware of!
 
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Old 03-07-13, 03:53 PM
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Adding a Common C wire not required in 99% of installations.
Found this on the website... still looking for something more advanced than that picture book you linked to...

Is the system zoned? How many thermostats in the home?
 
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Old 03-07-13, 03:57 PM
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Went to 'support' page, and answered a few questions, and they say this is all you need:



I don't think the image is going to post properly, that's one messed up URL!

Nope... didn't think so.

Anyway, the pic just shows the two wires. Rh and W ... says it should work.

So, you hooked it up that way and it didn't work?

Why did you think you needed the common wire?

It's possible that you may only have to reverse the R and W ...
 
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Old 03-07-13, 04:02 PM
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Yeah that definitely did not work

I have 2 zones. My primary zone is downstairs and I have a zone for the upstairs but we are not using the upstairs at this time. What is strange is that the Thermostat contacts on the Aquastat connect to the Beckett Heat Manager and from the Beckett Heat Manager it connects to the 2 zones.

If you can see the silver boxes attached to the Copper Pires, it looks like each box signifies a "zone" but I am not 100% sure.

https://www.dropbox.com/s/kx8hom1waz...2018.54.50.jpg
 
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Old 03-07-13, 04:06 PM
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Why did you think you needed the common wire?


Only reason why I thought that was because Nest told me so. They said the reason why it happened was because I needed a common wire.
 
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Old 03-07-13, 04:21 PM
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What is strange is that the Thermostat contacts on the Aquastat connect to the Beckett Heat Manager and from the Beckett Heat Manager it connects to the 2 zones.
Say huh? I don't understand.

There shouldn't be any zones connected to the heat manager, nor should there be any wires from the T T terminals on the aquastat to the heat manager...

The T T wires on the aquastat should only be going to the ENDSWITCHES on the zone valves.

The HeatManager should only be wired to the L1, L2, B1, and B2 terminals.

I'll look at the pics again...

Since you have zones, you should be able to grab a common (if you end up needing one) from the transformer that powers the zone valves.

There's no wayinhell that the Nest could have burnt up the L2 on the thermostat... unless of course you had a wire to the Nest C terminal connected to L2 ... and I would think if you did that you would have probably toasted the Nest also in addition to the Aquastat.
 

Last edited by NJT; 03-07-13 at 04:40 PM.
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Old 03-22-13, 08:22 AM
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As you know, there is no C termonal on the L8124A. Common is neutral, it is not hot!. The problem is you cannot tie to a Ground because Honeywell uses an isolated secondary. So connecting the C terminal to ground is going to give you something other than a true Neutral or "Common" connection. If you could do that, you could connect to the nearest ground in a nearby lightswitch and be done (trust me, I tried it!) What you need to do is first download the PDF of the L8124A data sheet from Honeywell. On page 3 is the schematic of the A model. You need to locate the point on the secondary neutral side of the transformer where it connects to the relay coil. That point is "COMMON". On the schematic, it's an unmarked location just to the right of the relay coil 1K. I've been wrestling with this for several days until I had one of those Eureka! moments. My plan is to locate that point this weekend, and solder an insulatied wire that I can bring just outside of the relay. That will be my Common point. If you attach it to the other side of the of the relay coil, you will see the resistance of the coil winding. You need to tap off of it just at the neutral side of the secondary.
 
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Old 10-27-14, 05:14 PM
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Hello,

I started another thread yesterday (http://www.doityourself.com/forum/th...-smart-si.html) but I think this thread is relevant. My aquastat is even older than the L8124A, the cover says L8024F and I cannot find any information online.

Support and people who know more than me say online that it is fine to connect the hot side of a secondary transformer to Rh and the other side (of the external transformer) to C.
The two transformers are nearby but the wiring is different and the phase difference might do funny things with the voltage. Connecting transformers in parallel is seen as last effort solution under the right circumstances... What did people do here with old Honeywell aquastats?

To blow up or not to blow up the heating system is the question.

EDIT: tom_in_ma seems to have found a solution per: http://www.doityourself.com/forum/th...lay-l8124.html

Thank you tom_in_ma, I will look at TACOs or return this thermostat and get another one where it seems I can sacrifice the fan and get an external power adapter to work more easily.
 

Last edited by kinezi; 10-27-14 at 05:20 PM. Reason: Found a possible solution
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Old 10-28-14, 12:24 PM
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I was able to connect the Rh and the hot side of an external transformer that was already present so I did not have to purchase a TACO. The transformers are not in parallel and at least my thermostats supports it according to their customer service.
 
 

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