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Old 11-17-2015, 06:17 PM   #1
HT13
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Ditra Heat Wiring

Hi everyone, I have a wiring question. For 120v I use the black (power) and white (neutral) and connect them to the black wires on the thermostat. How is the connection made to 240v? The 240v wire is actually 4 wires in a residential setting: 1 ground, 1 neutral, and 2 hot/power (red and black typically) wires that are 120v each. So the question is what do I do with the two hot wires, do I connect both of the hot wires (red/black) together with one black wire on the thermostat? And the connect the neutral to the other black wire on the thermostat?

Thank you.
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Old 11-17-2015, 06:26 PM   #2
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Welcome, HT.

What you should do is read and follow the wiring instructions with your thermostat.

What you absolutely do not want to do is connect the red and black wires from your power distribution box. Those will be connected to different 120v phases of your house power and while it might be considered instructive to see what happens, it could also be very hazardous to your health.

There should be a wiring diagram with your thermostat telling you exactly how to connect it to the house wiring. If you don't understand the diagram, please find someone who does.

My opinion; worth price charged.
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Old 11-17-2015, 08:15 PM   #3
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Some answers for 240v wiring

I found another thermostat manual that is a little more clear (even though i'm confused).

Go to Page 7 of: customer.honeywell.com/resources/Techlit/TechLitDocuments/95C-00000s/400-115-051.pdf

Using this information and applying it to The Ditra Heat Thermostat:
For 120v: black (hot) and white (neutral) wires from the power source connect to the black wires on the thermostat.
For 240v: black and red (both hot) connect to the black wires on the thermostat.

For both applications the Ditra wire (underneath the tiles) is connected to the yellow wires on the thermostat.

So what I don't understand is how does this work? How do you complete a circuit with two hot wires going into your thermostat? Don't you need a neutral return? Where is the ground wired? I'm confused...

If you've ever wired a ditra heat thermostat please help and explain this to me.

I'm close to pulling a trigger on a 1000 sqft installation with 4 zones (separate ditra wires and thermostats). I'd rather use one 10 gage (30 amp) wire with 240v and wire everything from that one breaker. I need to understand the installation before I make the purchase. Again, please help.
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Old 11-17-2015, 08:53 PM   #4
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HT, let me emphasize again that you need to be referring to the wiring diagram for the thermostat you will be using. Unless you're using that particular Honeywell thermostat, don't pay any attention at all to that diagram.
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Old 11-17-2015, 11:19 PM   #5
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What most people do not understand is that the power going into a typical US household is really 240vac, not 120vac. The power coming in is coming off of the secondary of the transformer...neutral is connected half-way across the secondary. From one end to the neutral (middle) is 120vac, and from the other to the neutral it's also 120vac, but each end is out of phase of the other. From both ends, it's 240vac, with no neutral involved at all. For safety, at the power panel, neutral is connected to the safety ground, but it would work just fine without it unless there was a fault. Things like a typical stove or electric dryer need a neutral so you don't have to find a 240vac light bulb, and sometimes on a stove, provide a 120vac receptacle. Plus, sometimes they'll design the electronic controls or timers, etc., to run off 120vac verses 240vac, but it's mostly for the light bulb and on older ones, a mechanical timer. All power coming into the house returns on the other power lead (not the neutral - that is only used internal to the house). It just may only run through half of the transformer verses the whole thing when 120vac is involved.

So, unless the circuit needs 120vac in it, it has no reason to use the neutral, and all you need is the two hot leads. The safety ground wire is almost always included, but it has NO effect in normal operation, it only does something if there's an error (provide a current path to trip the breaker or blow the fuse - it normally carries NO current at all).

With that in mind, maybe the instructions will make more sense.

But, if you are not familiar with this, maybe it's best to have someone who is to finish the install for you. Plus, if you want the factory warranty, you'd also need a moderately expensive test tool that you'll probably only use once. You might be able to borrow one or rent one, but it is discussed in the installation manual. A megometer tests for leaks in the insulation. A simple ohmmeter only tests for a short from one of the power leads to ground, but a fault in the insulation may not go to ground, but could create problems down the road. That's what the megometer tests to verify the install will be reliable long-term. Schluter requires it for the warranty...other companies suggest it, but do not require it. It is prudent to do it on anything electrical being buried beneath tile.
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Old 11-18-2015, 11:22 AM   #6
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CX, thank you for your input. Of course I want to refer to the wiring diagram of the thermostat I'm going to use. The diagram from the schluter thermostat was not clear so I went to others just to get a better understanding (since they explain in detail what the 240v hookup loks like). I think schluter should provide 120v and 240v clear instructions with figures, like in the honeywell manual.

jadnashua, I understood that the residential power is supplied by two 120v cables, and when you need 240v, the breaker goes across both buses and provides 120v on each of the two hot wires in a 240v cable.

What I did not know is that the circuit can operate with just two 120v wires going into a device (thermostat in my case) and operate fine (that power can come in from one lead and thru to the other). I guess that's why the thermostat has a GFCI, if something goes wrong the GFCI will trip. I am prepared to do all the tests (even a megohmmeter) so that the installation is sound. I've wired lots of electrical around my house but to me this was considerably different so it threw me for a loop. Thank you jadnashua for your help.

Any thoughts on a cheaper megohmmeter, like this one? amazon.com/Digital-Insulation-Resistance-Tester-Megohmmeter/dp/B00KR94JRE/ref=sr_1_1?ie=UTF8&qid=1447867049&sr=8-1&keywords=megohmmeter&pebp=1447867057672&perid=11VEBX6XGENRZ5KFF9HB
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Old 11-18-2015, 07:37 PM   #7
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Again, you really don't have 120vac coming into the house...it's 240vac. The way we achieve 120vac is by the centertap on the secondary winding of the power transformer. But, think of it any way you want, but it might bite you down the road sometime.
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Old 01-29-2017, 10:42 AM   #8
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I thought I'd piggyback on this thread as I didn't really find a more appropriate one.

What are folks doing with the braid/shield wire of the heating cable?

I'm finding no mention in the manual and even the online video made by Herr Schluter omits it even though one can see it there.

Even the thermostat itself has no ground connection on it.

I guess I'm just going to tie the braid to the bare wire copper ground in the box. Laying/stuffed in there, it might be making contact with my metal box anyway, which is, of course, properly grounded.
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Old 01-29-2017, 03:20 PM   #9
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https://www.youtube.com/watch?v=ur2qaLJT7HQ

I see on this one that they do tie the braid to the bare copper wire. Works. Makes sense.
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Old 01-29-2017, 08:57 PM   #10
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You have to run the braid to copper or the GFCI won't function properly. By not function properly, I believe it might work but not be protected. The other option is that it will just throw ERR4 and not work at all. I don't know, I've never tried it. And you're right, the poorly, poorly written manual makes no mention of it. But for GFCI to work it has to be referenced to ground.
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Old 01-29-2017, 09:48 PM   #11
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Au contraire! A ground is NOT necessary for a GFCI to work! A GFCI works by comparing the power going out one lead and comparing it to the power coming back on the other side (that could be neutral or the other 120vac leg of a 240vac circuit). If they are not the same within, typically about 5ma, that means some power has found a fault path to ground, which may be through you! IOW, ground is NOT required for a GFCI to work. Now, having one gives you another layer of protection, but a GFCI will trip WAY before a CB will, and the ground is typically used as a fault path for current that can cause a CB to trip.

If the instructions don't discuss connecting the shields, it's not necessary to function...the shield can do two things: help prevent some noise propagation, or provide a ground reference (more important on audio or radio frequency stuff) to the circuit.
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Old 01-29-2017, 10:42 PM   #12
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I guess you're right. They won't trip with a standard tester though. And where I live I'm sure it's not code. If you have the copper, hook it to the braid is what I'm saying.
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Old 01-29-2017, 10:52 PM   #13
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Code allows you to put in 3-prong, grounded receptacles into a circuit without a ground if it is protected with a GFCI. It does require that you mark those receptacles as not having a ground, but it is entirely possible to do and meet code on retrofit (not new) construction. IOW, they recognize that ground is not necessary for a GFCI to work. If the installation instructions do not mention bonding the shield to ground, it is not necessary for either safety or code. Will it work if you do, probably. Will it be safer, probably not in this instance.
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Old 01-31-2017, 11:34 AM   #14
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Well, FWIW, I tied the heating cable shield to the bare copper wire. It won't make a diddley of difference since the thermostat itself has no ground connection but it felt strange just to let the braid float.

Schluter really does need to put SOME mention of this in their manual rather than ignore it altogether.
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Old 01-31-2017, 12:12 PM   #15
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https://www.youtube.com/watch?v=mpeC1ABEt9Q

Push ahead to the :25 mark. It is interesting that they did not put the temperature sensor cables inside the conduit with the heating cable. I can only think it might be to prevent electrical noise from the heating cable interfering with the sensor cable and/or to keep the heat from the heating cable (does this part get warm?! I would think not!) from damaging the sensor cables. However, they aren't separated by all that much distance so I dunno in regards to electrical noise plus they do come together at the bottom of the wall.

Now I did put all 3 cables within the conduit. My conduit was metal flex...not plastic. I had the perfect length just laying around so....

Again, there is nothing in the literature that mentions how to run these wires and it took me watching a few YouTube videos to spot this.
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