What kind of relay do I need? (home HVAC/electrical) - Page 3

Brian Oshman · 20th January 2012, 08:53 PM

Since you didn't install the fan yet, install it as close to the room that you want to boost. The in duct fans don't have a lot of pushing power so you want to suck the air close to where you want it.

Netdewt · 20th January 2012, 11:56 PM

Quote:

Originally Posted by Brian Oshman

Since you didn't install the fan yet, install it as close to the room that you want to boost. The in duct fans don't have a lot of pushing power so you want to suck the air close to where you want it.

I don't have a lot of choice. The picture I posted is all I have access to. I'll do it on the left side as close as I can to where it heads into the ceiling. If this doesn't work I am SOL anyways.

EUREKA! This beautiful little tab called "EAC" is an Electrical Air Cleaner, and I don't have one. I read the installation manual where it describes the operation of the furnace in detail. EAC is always on when the fan is on, 120V!

One last question. When I plug everything in, can I just pull the breaker for the furnace (as long as it's not running when I do it, and cause ventilation issues)?

Brian Oshman · 21st January 2012, 04:42 AM

You can shut off the breaker or the service switch on the side of the unit. Either way the power will be off. Good find on that terminal. That will make it simple and you will have it for all seasons.

Netdewt · 22nd January 2012, 06:32 PM

I got the fan in, but the wiring is still in progress. Romex really isn't suited to hooking up to the control board. It's way too stiff.

I'm trying to stick with the wiring specs already inside the furnace, but that wire is really hard to find in small quantities. In the manual is says all wire inside the furnace must be rated to 105 C / 221 F, which excludes regular THHN wire. It's UL1015 PVC coated stranded stuff. Everything on the control board is between 18 and 14awg. The blower fan itself is on 18awg UL1275, but that is practically impossible to find, as far as I have seen.

What kind of fuse do I need?

Netdewt · 23rd January 2012, 04:12 AM

The booster installation manual says 14awg wire, but I would think 18awg is fine for in the furnace sine the big blower fan is 18awg and the booster only draws 0.4A.

AndrewT · 23rd January 2012, 09:25 AM

Net,
what is the total Flow and Return resistance of the 18awg cable you are thinking of using?

Now apply that 0.4Aac to determine the voltage drop in the Flow and Return wiring.

Express that voltage drop as a % of the whole 115Vac supply.
Your regulations probably state that the % lost in the cable is limited to no more than 5% (This is just a guess).
If your extra leg gives <2%, go ahead. If <1% then even better.

But do watch your cable runs. Keep them cool.

Brian Oshman · 23rd January 2012, 11:39 AM

You need to run 14 because that is code minimum for residential. Just use some THHN from the board to a j box to connect the romex to. It will work fine.

Netdewt · 23rd January 2012, 11:57 AM

Got it, I'll do 14.

Netdewt · 26th January 2012, 11:38 PM

All set up. I'll be observing everything over the next few days, but it appears to be working perfectly. I ended up putting a box in the ceiling with a switch. THHN runs from the furnace control board in flexible conduit, to that switch box, into Romex which runs through the ceiling to the fan.

Thanks all for the help.

Brian Oshman · 1st February 2012, 10:20 PM

Anytime.

23rd January 2012, 09:25 AM	#26
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Net, what is the total Flow and Return resistance of the 18awg cable you are thinking of using? Now apply that 0.4Aac to determine the voltage drop in the Flow and Return wiring. Express that voltage drop as a % of the whole 115Vac supply. Your regulations probably state that the % lost in the cable is limited to no more than 5% (This is just a guess). If your extra leg gives <2%, go ahead. If <1% then even better. But do watch your cable runs. Keep them cool. __________________ regards Andrew T.

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20th January 2012, 08:53 PM	#21
Brian Oshman diyAudio Member Join Date: Jul 2010 Location: Stewartsville, NJ	Since you didn't install the fan yet, install it as close to the room that you want to boost. The in duct fans don't have a lot of pushing power so you want to suck the air close to where you want it.

21st January 2012, 04:42 AM	#23
Brian Oshman diyAudio Member Join Date: Jul 2010 Location: Stewartsville, NJ	You can shut off the breaker or the service switch on the side of the unit. Either way the power will be off. Good find on that terminal. That will make it simple and you will have it for all seasons.

22nd January 2012, 06:32 PM	#24
Netdewt diyAudio Member Join Date: Jan 2010	I got the fan in, but the wiring is still in progress. Romex really isn't suited to hooking up to the control board. It's way too stiff. I'm trying to stick with the wiring specs already inside the furnace, but that wire is really hard to find in small quantities. In the manual is says all wire inside the furnace must be rated to 105 C / 221 F, which excludes regular THHN wire. It's UL1015 PVC coated stranded stuff. Everything on the control board is between 18 and 14awg. The blower fan itself is on 18awg UL1275, but that is practically impossible to find, as far as I have seen. What kind of fuse do I need?

23rd January 2012, 04:12 AM	#25
Netdewt diyAudio Member Join Date: Jan 2010	The booster installation manual says 14awg wire, but I would think 18awg is fine for in the furnace sine the big blower fan is 18awg and the booster only draws 0.4A.

23rd January 2012, 11:39 AM	#27
Brian Oshman diyAudio Member Join Date: Jul 2010 Location: Stewartsville, NJ	You need to run 14 because that is code minimum for residential. Just use some THHN from the board to a j box to connect the romex to. It will work fine.

23rd January 2012, 11:57 AM	#28
Netdewt diyAudio Member Join Date: Jan 2010	Got it, I'll do 14.

26th January 2012, 11:38 PM	#29
Netdewt diyAudio Member Join Date: Jan 2010	All set up. I'll be observing everything over the next few days, but it appears to be working perfectly. I ended up putting a box in the ceiling with a switch. THHN runs from the furnace control board in flexible conduit, to that switch box, into Romex which runs through the ceiling to the fan. Thanks all for the help.

1st February 2012, 10:20 PM	#30
Brian Oshman diyAudio Member Join Date: Jul 2010 Location: Stewartsville, NJ	Anytime.

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