Clamping short EMT runs between boxes?

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  #1  
Old 09-24-12, 10:27 AM
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Clamping short EMT runs between boxes?

I'm going to add a 4x4 outlet box on a wall using EMT (exposed). The new box will be about 30" from an existing box. Do I need to clamp the EMT to the wall? The new conduit will make a 'L' shape. The conduit will come out horizontally about 3" from the existing box, then make a 90 turn with a EMT pull elbow, then straight up the the new box.
 
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Old 09-24-12, 12:28 PM
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I'm going to add a 4x4 outlet box on a wall using EMT (exposed)... Do I need to clamp the EMT to the wall?
Yes. I would but one support about 1/3 of the way from the pull ell to the box. IOW, if that piece was 30" long, about 10" above the ell. I would use a stand-off support unless I wanted to bend a box offset in each end of that piece of pipe just to show off.

BTW, are you using compression fittings on this run?
 
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Old 09-24-12, 03:36 PM
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I can put a stand-off clamp (mini) where you said. I can do a decent 90 with a bender, but I haven't tried an offset bend. Maybe with about a week's worth of practice I could do it.

Yes, I'd use compression fittings rather than those slip-in ones with the screw.

In place of the pull elbow, could I just use another box at the corner?


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  #4  
Old 09-24-12, 04:23 PM
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Here is a good trick for offsets:

Measure the size of your offset needed. Double that measurement and mark that on your pipe. (IE: If you need a 7" offset, make two marks 14" apart) Set your bender on the first mark. It doesn't matter which mark you use, just use the same mark for both bends. Make a 30 degree bend. Rolling the pipe over 180 degrees, put your bender on the 2nd mark facing the same way as the first bend, and using the same mark on the bender. Make the bend 30 degrees. Your offset should now be correct. I find it handy to stand up a tape measure when making the 2nd bend so I know when I should stop.
 

Last edited by Tolyn Ironhand; 09-25-12 at 03:39 PM. Reason: typo
  #5  
Old 09-24-12, 06:28 PM
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Tolyn's advice is perfect for dimensional offsets, but it isn't how you do a box offset. We can tell you how to do one of those if you're interested.

In place of the pull elbow, could I just use another box at the corner?
Sure. But rather than invest in another WP box and cover, I'd use an LR or LL conduit body, depending on which side of the lower box I was coming out of.

Ypu'll still need a clamp with that, though.
 
  #6  
Old 09-24-12, 06:38 PM
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Did the OP say whether this was outside or inside? Compression fittings are required for outside work as they are classed as raintight, but setscrew fittings are fine for inside work. I prefer steel setscrew fittings over the less expensive diecast setscrew fittings.
 
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Old 09-24-12, 08:39 PM
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It's inside, on the wall next to the furnace.

The existing set-up has a single-gang plastic box in the wall, with one of these Taymac extension rings attached:
2-Gang 6-Hole Rectangle Extension Ring-SE650S at The Home Depot
This has a combo (single outlet and toggle switch) in it. The switch controls the power for the furnace and the outlet. The wiring to the furnace is inside some Liquitite conduit attached to the top of the existing Taymac extension.

I was intending to come off the Taymac extension with conduit, and add a second 1900 box about 5 inches to the right and 20 inches above.

I have a feeling the existing box set-up is near the box fill limit. The box in the wall is probably a 18 or 20 cu.in. box but I can't find the volume of the Taymac extension. How about replacing the Taymac extension with a Raco 187 extension (22.5 cu.in.)? Then I'd use the same Liquitite conduit to the furnace, connected to one of the KOs on the top of the Raco 187. Then I could bend the 1/2" EMT for the 5" offset I need, and connect that from another KO on the top of the Raco 187 to a KO in the bottom of the 1900 box above.

This is a pic of the current setup, with the Raco 187 shown below it.
 
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  #8  
Old 09-25-12, 06:24 AM
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How about replacing the Taymac extension with a Raco 187 extension (22.5 cu.in.)? Then I'd use the same Liquitite conduit to the furnace, connected to one of the KOs on the top of the Raco 187.
I am not a fan of double-wide extension rings. Even if all of this is on a 20A circuit and requires #12, it's hard to imagine that the wall box plus a single-gang extension wouldn't have enough capacity.

Of course, you could replace the combo with a stndard switch and a GFCI receptacle...

Then I could bend the 1/2" EMT for the 5" offset I need, and connect that from another KO on the top of the Raco 187 to a KO in the bottom of the 1900 box above.
A 5" offset in a 20" run is some tight bending. I'd consider bending a tight 90 or running more liquidtite.
 
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Old 09-25-12, 07:25 AM
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If the 5" offset in 20" is tricky, it's probably better I avoid that since I don't have a lot of experience at bending. Instead of that I could come out of the side of the extension box with a 90-degree large radius EMT elbow like this:
1/2 in. 90-Degree Large Radius EMT Elbow-90281 at The Home Depot
The large radius elbow would probably allow me to go straight up from there into a KO in the bottom of the new box above.

I can run liquitite on the wall on the garage?
 
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Old 09-25-12, 11:42 AM
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I could come out of the side of the extension box with a 90-degree large radius EMT elbow like this:
1/2 in. 90-Degree Large Radius EMT Elbow-90281 at The Home Depot
What an interesting gizmo! I never saw one of those before.

The large radius elbow would probably allow me to go straight up from there into a KO in the bottom of the new box above.
OK, but you'll still have to strap it once.

I can run liquitite on the wall on the garage?
Sure, why not?
 
  #11  
Old 09-25-12, 11:49 AM
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Could also use a regular LR threaded conduit body like this:
1/2 in. Type LR Threaded Conduit Body with Cover and Gasket-58905 at The Home Depot

If I use that to make the turn, could I just use a short threaded nipple to attach it to the side of the Taymac extension ring? If so, would I use a nipple with tapered or straight threads?
 
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Old 09-25-12, 12:52 PM
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If I use that to make the turn, could I just use a short threaded nipple to attach it to the side of the Taymac extension ring? If so, would I use a nipple with tapered or straight threads?
All nipples are IPT. If you don't see the length you want in the electrical section, just wander over to plumbing and pick one up there.
 
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Old 09-25-12, 02:16 PM
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Thanks. So, it would be OK to connect an LR conduit body directly to the extension ring with the short nipple? The Taymac holes are threaded.

So, I'm leaning towards one of the following 4 solutions. All would come off the right side of the Taymac extension ring, and all EMT conduit and compression connectors are 1/2". This will connect to a 1900 box with a vertical section of EMT (about 20"). I will put a single stand-off clamp about 1/3 of the way up on the vertical section of EMT.

1. Use a short section of EMT to connect the Taymac extension to a conduit pull elbow.

2. Use a threaded coupling and two very short nipples to connect the Taymac extension to a 90-degree conduit pull elbow.

3. Using a very short nipple, connect a LR Conduit Body directly to the Taymac extension ring.

4. Connect a 90-degree large radius EMT elbow directly to the Taymac extension ring.

As an alternative, could I use a single section of EMT bent with a very tight radius (like 4" or so)?
 
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Old 09-25-12, 02:35 PM
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After I wrote the options I realized there is another simpler option. I could use nipple (about 2" or so) with a threaded pull elbow.

If I did it this way, would I need to use locknuts?
 
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Old 09-25-12, 02:41 PM
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Any of those should work.

As an alternative, could I use a single section of EMT bent with a very tight radius (like 4" or so)?
Without getting my bender out to check, I think the minimum radius for 1/2" EMT is 5".

Oh! I just checked the site. Turns out that's the radius for the one I have, but GB has a new bender out that bends 1/2' EMT to a 3.69" radius.
 
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Old 09-25-12, 03:37 PM
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To use a threaded nipple in a KO, you need to use two locknuts, one on each side of the box wall, plus a threaded plastic bushing on the end inside. To use a threaded nipple with a threaded fitting, no locknuts are needed.
 

Last edited by Nashkat1; 09-26-12 at 07:17 AM.
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Old 09-25-12, 04:29 PM
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OK, time for Pros and Cons.

1. Use a short section of EMT to connect the Taymac extension to a conduit pull elbow.
Pro: Can cut the short EMT to give the exact horizontal length I need.
Con: Requires 4 compression connectors.

2. Use a threaded coupling and two very short nipples to connect the Taymac extension to a 90-degree conduit pull elbow.
Pro: Requires only 2 compression connectors.
Con: No adjustment of the horizontal length. It's good or not.

3. Using a very short nipple, connect a LR Conduit Body directly to the Taymac extension ring.
Pro: Requires only 2 compression connectors.
Con: No adjustment of the horizontal length. It's good or not.

4. Connect a 90-degree large radius EMT elbow directly to the Taymac extension ring.
Pro: Requires only 1 compression connector (plus the one on the elbow).
Con: No adjustment of the effective horizontal length. Might be too long.

5. A single section of EMT bent with a very tight radius.
Pro: Requires only 2 compression connectors, and would look real nice.
Con: I don't have a 1/2 EMT bender that will bend that short. Probably need to get somebody to bend it for me.

6. Use a nipple (about 2" or so) with a threaded pull elbow.
Pro: Requires only 2 compression connectors. Won't need locknuts on the nipple.
Con: Can adjust the effective horizontal length by the length of nipple.
 
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Old 09-25-12, 05:58 PM
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Of course, you could replace the combo with a stndard switch and a GFCI receptacle...
In fact, the combination switch/receptacle should be changed because the receptacle would need GFCI protection. I seriously doubt the furnace is in a finished room in the basement, complete with carpeted floors.
 
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Old 09-25-12, 07:22 PM
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#5 - You can buy pre-bent 90s at most home stores and some hardware stores. You might even be able to get a full service hardware to bend you one.
 
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Old 09-25-12, 09:30 PM
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In fact, the combination switch/receptacle should be changed because the receptacle would need GFCI protection. I seriously doubt the furnace is in a finished room in the basement, complete with carpeted floors.
The contractor who put the furnace in added the combo switch/receptacle and it passed the city inspection. Of course that doesn't mean it's right. BTW, it's in the garage.

I don't mind the extra cost of a GFCI receptacle. Does a GCFI receptacle need special wiring pulled?
 
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Old 09-25-12, 09:51 PM
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I took a close look at the Taymac extension ring and there's a problem with putting a nipple into the connection on the side. With a receptacle in the box, there wouldn't be any clearace between the receptacle's connection screws and the end of the nipple, if it's screwed in 1/2 inch or so. It would be better with just a switch in there, but still tight. I could screw it in maybe 1/4 inch or so and still have enough room to get the wires around the combo switch/receptacle. How far do you need to screw a nipple into a threaded connection?

That's probably why the furnace guys connected the flex conduit at the top. The clearance is way better.

A regular 1900 4x4 box doesn't have that problem if you use a 1/2" raised exposed work cover.

See attached pic for the problem with the Taymac extension ring.
 
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Last edited by garya505; 09-25-12 at 10:12 PM.
  #22  
Old 09-25-12, 09:55 PM
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#5 - You can buy pre-bent 90s at most home stores and some hardware stores. You might even be able to get a full service hardware to bend you one.
I have one but it's about a 6 inch radius. I haven't seen any others so if I wanted a 4" radius I'd probably have to find someone to bend it for me.
 
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Old 09-26-12, 09:23 AM
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I don't mind the extra cost of a GFCI receptacle. Does a GCFI receptacle need special wiring pulled?
No. You've already got them all over your house on regular wiring. I'm surprised that the HVAC contractor didn't put one in and that his work passed without one here. All power in a garage is required to be GFCI protected. I'm also surprised that he used a weatherproof extension ring with threaded hubs here. Or liquidtight conduit. I guess that's what they keep on the truck since so much of their work is outdoors.

You can keep that x-ring and replace the combo switch/receptacle with a combo GFCI switch/receptacle if the ring is deep enough.

How far do you need to screw a nipple into a threaded connection?
Anywhere from just enough to engage the threads to as tight as you can get it. I doubt that the hubs will allow the nipple to thread end beyond the protected area they provide. If they do, you can run a lock nut into the nipple, backwards, before you thread it in, and tighten the lock nut down to secure the nipple when it gets to the depth you want.
 
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Old 09-26-12, 09:31 AM
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I have [a pre-bent 90] but it's about a 6 inch radius.
That 90 probably has a 5" radius. That's pretty much the standard for 1/2" 90s. Don't confuse radius with stub-out. My foot bender bends a 1'2" 90 with a 5" radius and a 7" minimum stub-out, to avoid deforming the end of the pipe. After it's bent, I can trim 1", maximum, off the stub end, leaving the 6" stub-out you're seeing. The remaining 1" outside the bend is needed for insertion into the coupling or connector.
 
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Old 09-26-12, 10:14 AM
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Ok, I think we're getting somewhere.

I did some measurements and I think option #5 is out. I did some more precise measuring and the vertical section of the conduit needs to be about 3" from the side of the existing extension ring, so if I'm coming off the side there just isn't enough room. I'm leaning towards option #6, since it would let me position the vertical section of the conduit exactly where I need it to hit the KO in the new box above. Horizontal positioning of the new box is not very adjustable due to space limitations.

I took another look at the garage wiring. The outlets are all on a GFCI in the first outlet box from the panel. However, as far as I can tell, the furnace outlet is on it's own dedicated circuit with NO GFCI. If I can verify that, I'd like to add the GFCI, since the box I'm adding will have a transformer in a KO, and some outlets for UV lights. I believe can just put the wiring for the added box on the Load terminals of the GFCI in the existing box, if it fits. If it doesn't fit, I'll probably use the Raco 187 extension ring I showed in the pic earlier. Nashkat1, why don't you like that kind of extension ring?

I'd like to thank you guys for all your help. I'm the sort or person that usually does a lot of homework before I attempt this sort of DIY work, and if I don't think I can do it as well as (or better than) most pros, then I don't do it myself. It usually takes me 10X longer that way, but I sleep well knowing it's done right.
 
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Old 09-26-12, 04:38 PM
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OK, here's what I'm thinking (as of today). I'd like to add a GFCI for the outlets on this circuit. The furnace itself would not be on the GFCI.

I doubt if there's enough room in the existing Taymac extension ring for a GFCI, or at least it's gonna get pretty crowded in there. So, I'm thinking I'll replace that with a Raco 187 (see pic in earlier post). Then I'll put a switch and a 2-outlet GFCI in there using a 1/2" raised square box cover (see pic). The switch will control power to the furnace and the GFCI. The new 4x4 box (downstream from the GFCI) will be connected to the load terminals of the GFCI so those outlets will be protected as well. The furnace will be connected to the circuit before the GFCI, so will not be GFCI protected.

I can use a short nipple (probably 2") to connect the new extension to a threaded pull elbow. I'll use EMT compression connectors to connect the vertical section of EMT from the elbow to the new box above. In the new box I'll put a single switch controlling a dual outlet (this is so I can switch OFF the UV lights in the winter). The new box will also get a transformer for my humidifier and ventilation.

Is it OK to have a switch controlling outlets on the GFCI load? They will be downstream from the GFCI.

I'll try to post a sketch later.

I'll use this Raco 814C cover for both the Raco 187 extension and the new 4x4 box:
 
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Old 09-26-12, 04:52 PM
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Is it OK to have a switch controlling outlets on the GFCI load? They will be downstream from the GFCI.
Yes. This is the part that doesn't sound OK:
The switch will control power to the furnace and the GFCI.
If that first switch turns the GFCI off and on, in addition to the furnace, then it also turns the downstream box with its switch and the receptacle for your grow lights off and on.

I would wire power in to the switch and to the LINE terminals on the GFCI. There's no need to switch the feed to the GFCI, and it may give the GFCI a problem.
 
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Old 09-26-12, 05:19 PM
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If that first switch turns the GFCI off and on, in addition to the furnace, then it also turns the downstream box with its switch and the receptacle for your grow lights off and on.

I would wire power in to the switch and to the LINE terminals on the GFCI. There's no need to switch the feed to the GFCI, and it may give the GFCI a problem.
It sounds like you're saying it's OK to have a switch downstream from the GFCI (on the LOAD side) but not upstream (on the LINE side). Correct?

What I wanted was to have the transformer and outlets turn off when the furnace disconnect switch was OFF, but also allow me to turn off the UVC lights independently in the winter when I don't need them. Maybe there's a different way to to that, or maybe I need to use separate switches so they are all downstream from the GFCI. How about a double switch in the new box, one for the transformer and one for the outlets? I don't want another switch in the extension box where the furnace switch is, but having two in the other box for the other stuff is OK I guess.

Anyway, when the furnace is off, 24V power to the thermostat is off, so if the humidifier/ventilation transformer is still on, it isn't doing anything.

BTW, I don't need a condensation pump, but how do you usually do it when there's one installed? Is the pump still powered when the furnace is switched off?
 
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Old 09-26-12, 06:23 PM
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Anyway, when the furnace is off, 24V power to the thermostat is off, so if the humidifier/ventilation transformer is still on, it isn't doing anything.

BTW, I don't need a condensation pump, but how do you usually do it when there's one installed? Is the pump still powered when the furnace is switched off?
These are really HVAC questions, not electrical questions. You might want to start a new thread there.

That said, everything to do with the furnace, including its controls and ancillary equipment, should be off. That's so you can safely work on it. The power for the furnace, therefore, should only be switched off when it needs to be worked on.
 
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Old 09-26-12, 06:34 PM
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No no that switch is a required disconnect for the furnace and that outlet is a service outlet for working on the furnace, the circuit shouldn't power anything but the furnace many furnaces manufactures recommend a dedicated circuit

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Old 09-26-12, 07:26 PM
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that switch is a required disconnect for the furnace and that outlet is a service outlet for working on the furnace, the circuit shouldn't power anything but the furnace many furnaces manufactures recommend a dedicated circuit
Thanks, Braether. I knew this was an HVAC question!

Are you saying that this circuit should not be extended to supply the grow lights or any other non-furnace-related load?
 
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Old 09-26-12, 07:34 PM
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No, I don't think so, grow lights can pull serious power, if the breaker was to trip the home could freeze, most furnace circuits are 15 amp.


And yes generally the condensate pump is always powered because of central air
 
  #33  
Old 09-26-12, 10:01 PM
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What's a grow light? The UVC lights I am going to use on my AC coil only draw about .5A.

I'm starting to rethink this whole plan. I can get the UVC lights in 120VAC or 24VAC. If I go with the 24VAC UVC lights instead of 120VAC, I don't need to plug anything in. I can swap out the combo switch/outlet for the combo switch/GFCI-outlet , as was suggested earlier. The switch can control the furnace and the added transformer that powers the ancillary equipment. When the switch is off, everything is off except the GFCI-protected outlet, which will be a service outlet only. No switched outlets would be required.

According to the specs, all the added equipment combined draws about 1A, so I could probably use a 24VAC 40VA transformer for all that stuff and be done with it.

And, I can add a switch on the 24VAC to the UVC lights so they can be turned off when not needed.
 
  #34  
Old 09-27-12, 04:33 AM
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We assumed grow lights when you mentioned uv

I would suggest a relay wired to the fan control wire then the light will cycle with the central air fan

Here is a lil research I did on uv lights -
"A UV light can sterilize a nearby stationary surface. Most residential systems don't need that because they dry out during the off cycle. The baddies can't grow without sustained moisture. -A UV light can't sterilize the moving air stream in an HVAC system. The baddies get less than a second of exposure as they whiz by the light.
-A UV light can and will require yearly replacement to maintain its output of UV light. The pretty blue hue is obviously not UV. The hue will stay. The UV will not. Your contractor thanks you in advance for the revenue stream.
-A UV light can also break down any plastic and other petroleum based components nearby. Luckily few people ever deal with that because they don't bother changing the lamps on a yearly basis.
-Some UV lights can also put off fancy sounding free radicals that supposedly seek and destroy baddies. They also seek and destroy lung tissue. Think ozone machines - once promoted by some as healthful, now regarded for the pollution makers that they are."

Basically giving mold spores a suntan, tho there is the potential it would keep mold off the coil a semi annual bleach solution can do the same thing
 

Last edited by Nashkat1; 09-27-12 at 06:24 AM. Reason: clarity
  #35  
Old 09-27-12, 09:05 AM
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Cycling the power to UVC lights seriously shortens the life of the lamp. It's better to leave them on for the entire cooling season (switch on in the spring, switch off on the fall). Some of the lamps are kind of pricey.
 
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Old 09-27-12, 09:08 AM
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IMO you'd be better off without
 
  #37  
Old 09-27-12, 09:12 AM
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Maybe, but for now I'm going to put them in and see how well they work. Get back to me in about a year and I'll let you know.
 
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Old 09-27-12, 01:52 PM
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Well, I'm fairly convinced that I'll go with 24VAC UVC lights, and that I need to use a separate transformer for all of the 24VAC ancillary equipment. I'd rather not run more wires in and out of the furnace just so I can put a transformer in their, so I'm thinking of using one of these for my 24VAC power:

TPB Series - Power Supplies - Air Products and Controls Inc. - You in Control

What do you think?
 
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Old 09-28-12, 04:05 PM
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What kind of connection to an enclosed transformer power supply?

I found an enclosed 24VAC power supply I like better, and I'd like to know what types of connections would be allowed for the line voltage input. OF course EMT would be OK, and I would imagine PVC is too, but what about other types of conduit like liquidtite metallic or non-metallic? I have limited options for placement of the power supply so I'd like to know my options for that. I'll be connecting to the side or top of the existing extension ring containing the main furnace switch. This will either be a KO or threaded hole, 1/2" or 3/4.

The power supply is a nice small unit (4.500˝ x 5.438˝ x 4.500˝) with a breaker, no outlet, and the low voltage connections inside. It has KOs in several locations and looks perfect for what I want to do.

This is the power supply:
Functional Devices PSH100ANWB10
 
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Old 09-28-12, 07:23 PM
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I found an enclosed 24VAC power supply I like better, and I'd like to know what types of connections would be allowed for the line voltage input. OF course EMT would be OK, and I would imagine PVC is too, but what about other types of conduit like liquidtite metallic or non-metallic?
The answer to your question is "whatever you like; whatever seems to you to offer the best outcome." Since you're doing this inside your garage, there is no code requirement for a particular type of conduit, and if the box will accept a connector for one type, it will accept a connector for any of them.

Where are you planning to mount this xfmr?
 
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