Clamping short EMT runs between boxes?

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  #41  
Old 09-29-12, 08:00 PM
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I'd probably put it on the wall near the switch. It looks like it has a KO on the left top that I might be able to connect to with a short nipple. That would put it just below and to the right of the switch, where there is plenty of free space on the wall.
 
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  #42  
Old 09-30-12, 07:09 PM
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I'd probably put it on the wall near the switch... That would put it just below and to the right of the switch, where there is plenty of free space on the wall.
Sounds like a plan to me.
 
  #43  
Old 09-30-12, 09:19 PM
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Thanks for the input. I'll post pics when I get it done. You guys here gave me the info I needed to do it the way I wanted, and also how to do it "right".

Now I just have to decide what size power supply to use. They make that unit in a 40VA, 75VA, and 100VA. The UVC light manufacturers seem to be a little ambiguous with their power requirements. I guess it's much better to go too big than to be a little too small.
 
  #44  
Old 10-01-12, 03:05 PM
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I guess it's much better to go too big than to be a little too small.
Depends on how quickly you want to have to replace those pricey lamps. I would go as exact as possible, and also keep the load minimal on a dedicated 15A circuit.
 
  #45  
Old 10-01-12, 05:18 PM
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I did some more checking on the power requirement for the lamps. Most of them are in the 16VA to 24VA range, so I need to allow for 48VA for 2 lights, or 72VA for 3 lights. I had a "brain flash" today and may put only the UVC lamps on the external Functional Devices 75VA power supply, then put the humidifier and fresh damper on a separate 20VA transformer inside the furnace.

Why, you ask?

The humidifier solenoid draws 170mA (I measured it) and the damper motors pulls something like 250mA (max) each. So a small 20VA or 40VA transformer would handle that, even if I have 2 dampers. And, I can power this transformer off the EAC terminal on the furnace board. This EAC terminal is powered any time the fan is on, which his fine for the humidifier and fresh air intake. The thermostat controls the activation of both of these, (but only when they have power). Since both the humidifier and fresh air damper will be controlled by the thermostat wiring, it sort makes sense to have the power for these in the furnace, where most of the thermostat wiring goes anyway.

Putting only the UVC lights on the external power supply gives me the independent OFF switch I want for the UVC lights in the winter. Of course being connected to the furnace switch, the power supply is always powered off when the furnace is switched off for maintenance or whatever. And, the UVC lights will not be controlled by the thermostat (at least it's not likely) so it makes sense to keep this out the furnace altogether.

The UVC lights will probably be off all summer so this means that the external power supply can be powered off for all that time. If I put everything in a single transformer, I would probably want to get a 100VA transformer, and that would be way too big for half the year.
 
  #46  
Old 10-03-12, 04:01 PM
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Sizing (and oversizing) transformers

I'm thinking of just getting a dual power supply so I don't even need the extra transformer inside the furnace.

The dual power supply I want to use is available in many configurations, from a 40VA & 40VA all the way up to a 100VA & 100VA. They also have models that have 40VA & 75VA, 40VA & 100VA, 75VA & 100VA.

So, I need to size this thing right for what I need now and possible additional loads. I understand that transformers have "no-load" current draw, which probably is proportional to the size of the transformer. Is that worth worrying about? Also, other than the additional cost of a larger transformer, is there any other reason why it's a bad idea to oversize low voltage transformers? We're talking maybe 2 times the expected load of the initial equipment, not 10 times.
 
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