Replacing a 14/3 switched load w/ only 12/2 NMB

Reply

  #1  
Old 03-31-05, 08:52 AM
Beeek
Visiting Guest
Posts: n/a
Question Replacing a 14/3 switched load w/ only 12/2 NMB

My furnace's branch is as follows, 14/2 NMB to an emergency switch upstairs, switched on the red wire of a 14/3, and always hot on the black wire, white passes through. The 14/3 runs back downstairs to a metal (not very deep) surface mount box. One half of the box is a "singl-plex", other half is another emergency switch (both single poles). The black (14/3s always hot) goes to the outlet which feeds the condensation pump only, the switched (14/3 red) goes to the furnace feed.

My question is could I run 12/2 to my furnace area overhead, use a large ceiling octagon box over head, splice off one 12/2 run down to my outlet (always hot), run one single 12/2 up to my emergency switch upstairs, using the black as supply and white with black tape as the return to the junction box, then run a 12/2 off of the switch output return and spliced in white down to my furnace box. I'll buy a big octagon so I won't fill violate. And I'll look into the metal surface mount on the furnace, b/c there is a lot in there (14/2 and two 12/2 s).

Any better ways of doing this, I don't want to buy 12/3 just for the switch return, and would rather use 12/2 if I could (BTW no pilot lite on the emergency switch, so I don't need a neutral in the switch box?).

Once again, thank you very much (in advance),
Beeek
 
Sponsored Links
  #2  
Old 03-31-05, 09:11 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
I am confused about one issue. Please clarify the following sentence: "And I'll look into the metal surface mount on the furnace, b/c there is a lot in there (14/2 and two 12/2 s)."

Do you mean that you will be mixing 12 gauge and 14 gauge wire on the same circuit?

If you tell me that the circuit will still be 15 amp and still have 14 gauge wire on it, then I will tell you to go out any buy 14 gauge wire, or replace ALL the wire on the circuit.

To your original question...

What you are suggesting will work. What you must do is to make sure that the 12-2 leaving the box for the receptacle and the 12-2 leaving the box for the furnace remain separate. You can't cross them after they leave the box, even the neutrals, or you will have uneven current flow.

However, avoiding the purchase of a particular type of wire because you have plenty of some other type is, in my opinion, the wrong thing to do. You are almost always better off to make the run as logical and straight forward as possible even if it means buying other wire.
 
  #3  
Old 03-31-05, 09:31 AM
Beeek
Visiting Guest
Posts: n/a
Bob, thanks.

In the surface mount box you have the leads from the furnace (conduit clamp connection) which are 14 gauge stranded individual leads. So now there is 14/3 NMB in, single outlet, single pole switch, and the stranded 14 gauge feeders out. It seems a bit crowded in there when I closed it up, I was affraid with two 12/2 ins the switch, outlet, and the 14 guage stranded out, it would be a bit much.

I guess I never thought of the 14 gauge stranded feeders for the furnace. I just didn't like the current 14 gauge setup running all over creation like it does. The runs are over 150 feet total, and my furance is 9+amp plus electronics and condensation pump.

So the best way to wire it, is the /2 to swtich, then /3 to feed the furance? My description using only /2 is less straight forward? That I didn't realize.
 
  #4  
Old 03-31-05, 09:58 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Why do you want to use 12 gauge wire? With only 14 gauge wire running to the furnace you will be limited to a 15 amp breaker.

I am still confused about the last piece.

You intend to run 12/2 down to a receptacle for the pump. Is that also where the furnace connects? If so then I would use 12/3 down to that receptacle, rather than two pieces of 12/2. Other than that I see nothing wrong with your proposal.
 
  #5  
Old 03-31-05, 11:31 AM
Beeek
Visiting Guest
Posts: n/a
Bob, yes I mentioned I didn't realize about the 14g in the furnace it self. Ug, is there any benefit to using 12g? Voltage drop? Thanks for sticking with me, perhaps I should leave this untouched. Total draw is probably just over 10 amps, I haven't installed the whole house filter yet, and wanted headroom incase I did.

Current Run
SE===Switch---------Switch_____furnace
!-Neutral----------!
!-----------------Outlet+++++pump
Where
SE is the breaker box
= is 14/2
--- is 14/3
+++ is portable cord
____ is 14guage stranded in short conduit to insides of furnace
 
  #6  
Old 03-31-05, 11:44 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
12 gauge wire certainly has less of a voltage drop than 14 gauge.

If you don't have a problem I would do anything yet.
 
  #7  
Old 03-31-05, 03:02 PM
jbminyard
Visiting Guest
Posts: n/a
Clarification on mixing gauges?

Originally Posted by racraft
Do you mean that you will be mixing 12 gauge and 14 gauge wire on the same circuit?

If you tell me that the circuit will still be 15 amp and still have 14 gauge wire on it, then I will tell you to go out any buy 14 gauge wire, or replace ALL the wire on the circuit.
I've seen it mentioned many places not to mix gauges on a circuit. My question is, is there a reason to avoid this other than the possibility/risk of inadvertently putting too small wire on too big breaker?
 
  #8  
Old 03-31-05, 04:01 PM
Member
Join Date: Sep 2002
Location: welland ontario
Posts: 5,599
I'm totally confused by what you want to attemp. I will say you should not add anything to the furnace circuit that is not the furnace.
 
  #9  
Old 03-31-05, 05:05 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
The problem with mixing wire gauge on a circuit is that the breaker must be sized for the smallest wire on the circuit. Any piece of 14 gauge wire on a branch circuit means a 15 amp breaker.

If that one piece of 14 gauge wire is somewhere in the middle of a circuit where it may not be obvious, somebody later on may not know it is there and think that they can safely increase the breaker to 20 amps.

If you are going to use 12 gauge wire on this circuit, then make a note at the panel that there is 14 gauge wire downstream.
 
  #10  
Old 03-31-05, 07:16 PM
Beeek
Visiting Guest
Posts: n/a
Originally Posted by joed
I'm totally confused by what you want to attemp. I will say you should not add anything to the furnace circuit that is not the furnace.
joed, Well too late for that, my e. contractor or HVAC already added an external PC board, a condensation pump, and a whole house humidifier on the same furnace circuit. Therefore I figgured my future electronic air filter which was housed inside the furnace ductwork would therefore fall into the same catagory.

Several branches in my house go two floors out of the way to reach their destination, and the furance is one of them. I wanted to run it directly, and upgrade from 14 gauge to 12 gauge at the same time.

Clear as concrete now?

I called rheem and their max OCPD is 15 amps. Looked inside at the furnaces board, and it is wired with 18 gauge from the junction box (about 6-10 inches).

So I would be causing more trouble by changing the 14 gauge to 12 gauge? Would the suggestion be to rewire with 14 gauge (i.e. keep the same gauge?)

Thnx
 

Last edited by Beeek; 03-31-05 at 08:23 PM.
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'