Generator wiring for furnace

Reply

  #1  
Old 11-17-09, 09:24 AM
B
Member
Thread Starter
Join Date: Apr 2009
Location: Ohio
Posts: 54
Received 0 Votes on 0 Posts
Generator wiring for furnace

I have a small 2200w generator. All I really need to power is my gas furnace should we have an extended outage in the winter.

I'm thinking of removing the SP switch used as a furnace disconnect and replacing it with a single receptacle. I would then set a box and wire in a cord cord connection for the furnace. During normal operation the furnace will be powered through the cord connection. In the event of an outage, I will just unplug the furnace from the receptacle and plug it into an extension cord run through the basement window.

Does anyone see a problem with doing this?

Also, is it ok to use the existing equipment ground while on generator? If not, should I bond the furnace to a water line?
 
  #2  
Old 11-17-09, 10:08 AM
A
Member
Join Date: Sep 2009
Location: USA
Posts: 507
Received 2 Votes on 2 Posts
It's a good idea, but using a cord/plug on most furnaces is not under 4007 "Permitted Uses" of the 2008 NEC. You'll have a hard time with 400.8 "Uses not permitted" as well.

If your furnace is intended to be connected by a cord then, 400.7 (8) Appliances where the fastening means and mechanical connections are specifically designed to permit ready removal for maintenance and repair, and the appliance is intended or identified for flexible cord connection.

400.8 Unless specifically permitted in 400.7, flexible cords and cables shall not be used for the following:
(1) As a substitute for the fixed wiring of a structure.

So, ask your building department.

How about one of these instead? All approved and to Code.

TF151W Easy/Tran TF Furnace Transfer Switch
 
  #3  
Old 11-17-09, 10:10 AM
Andrew's Avatar
Member
Join Date: Apr 2003
Location: USA
Posts: 1,017
Received 14 Votes on 10 Posts
  #4  
Old 11-17-09, 10:27 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,942
Received 44 Votes on 42 Posts
Code usually forbids a furnace from operating on a flexible cord under normal circumstances. Instead, I recommend a single circuit transfer switch with a 15A inlet. You can buy these pre-made or make one yourself using a large junction box ($10), NEMA 5-15 inlet ($20), and a 15A heavy-duty SPDT three-position rocker/toggle switch ($10). You should also use a protected wiring method such as conduit or metallic cable down to the transfer box and then into the furnace.

The grounds from the line, furnace and generator inlet are all connected. The furnace is not bonded to the water lines.
 
  #5  
Old 11-17-09, 11:09 AM
B
Member
Thread Starter
Join Date: Apr 2009
Location: Ohio
Posts: 54
Received 0 Votes on 0 Posts
Originally Posted by ibpooks View Post
Code usually forbids a furnace from operating on a flexible cord under normal circumstances. Instead, I recommend a single circuit transfer switch with a 15A inlet. You can buy these pre-made or make one yourself using a large junction box ($10), NEMA 5-15 inlet ($20), and a 15A heavy-duty SPDT three-position rocker/toggle switch ($10). You should also use a protected wiring method such as conduit or metallic cable down to the transfer box and then into the furnace.

The grounds from the line, furnace and generator inlet are all connected. The furnace is not bonded to the water lines.
Thanks for everyone's input. You've been quite helpful.

Why a three position rocker. Is this for disconnecting means? If I understand this right, the neutral does not need to be disconnected. Can I just use a 3 way switch (or DPDT if needed) feeding the existing disconnect?
 
  #6  
Old 11-17-09, 12:17 PM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,942
Received 44 Votes on 42 Posts
You can use a three-way (SPDT) switch if the furnace already has a disconnecting means. If you want to combine the disconnecting means into the transfer switch then you need a three-position switch (GEN - OFF - LINE). Only the hots need to be switched.
 
  #7  
Old 11-17-09, 12:35 PM
B
Member
Thread Starter
Join Date: Apr 2009
Location: Ohio
Posts: 54
Received 0 Votes on 0 Posts
Originally Posted by ibpooks View Post
You can use a three-way (SPDT) switch if the furnace already has a disconnecting means. If you want to combine the disconnecting means into the transfer switch then you need a three-position switch (GEN - OFF - LINE). Only the hots need to be switched.
Great. This looks like a cheap and easy way to go. Just to be clear. I'm going to install a 15A inlet in a w/p box on the outside of the house. Inside will be a three way switch with one pole hooked to the utility power and one pole hooked to the generator power. All neutrals will be wired together and all grounds will be hooked together. The common pole will feed the furnace disconnect (along with the ground and neutral) - correct?
 
  #8  
Old 11-17-09, 01:01 PM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,942
Received 44 Votes on 42 Posts
Your plan sounds correct.
 
  #9  
Old 11-17-09, 01:09 PM
B
Member
Thread Starter
Join Date: Apr 2009
Location: Ohio
Posts: 54
Received 0 Votes on 0 Posts
Originally Posted by ibpooks View Post
Your plan sounds correct.
Thank you for your help. Should be quick and easy.
 
  #10  
Old 11-19-09, 07:34 PM
Andrew's Avatar
Member
Join Date: Apr 2003
Location: USA
Posts: 1,017
Received 14 Votes on 10 Posts
I noticed that the commercially available single circuit transfer switches have overcurrent protection. Would it be necessary to install a 15A breaker or fuseholder into the homemade version? Not a code expert, but it seems to me that the generator's 15A breaker would suffice while on generator current, but would like to hear your opinions.
Thanks,
Andy
 
  #11  
Old 11-20-09, 09:17 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,942
Received 44 Votes on 42 Posts
It is also my opinion that the generator breaker is sufficient for an OCPD.
 
  #12  
Old 11-20-09, 09:46 AM
D
Member
Join Date: Nov 2009
Location: USA - VA
Posts: 4
Received 0 Votes on 0 Posts
Furnace

Just remember, if you are going to use a 3 position switch so the center position is off as your disconnecting means, it needs to be located in a readily accessable place and be painted red and labled as a furnace cutoff.

Dan
 
  #13  
Old 11-20-09, 09:47 AM
B
Member
Thread Starter
Join Date: Apr 2009
Location: Ohio
Posts: 54
Received 0 Votes on 0 Posts
Originally Posted by Andrew View Post
I noticed that the commercially available single circuit transfer switches have overcurrent protection. Would it be necessary to install a 15A breaker or fuseholder into the homemade version? Not a code expert, but it seems to me that the generator's 15A breaker would suffice while on generator current, but would like to hear your opinions.
Thanks,
Andy
You bring up a good point. I just looked at the generator, and the circuit breaker is 20A, which is too large for the 15A circuit. I already ordered the inlet, which is rated for 15A. So I'll need to fuse it down before the inlet.
 
  #14  
Old 11-20-09, 09:50 AM
B
Member
Thread Starter
Join Date: Apr 2009
Location: Ohio
Posts: 54
Received 0 Votes on 0 Posts
Originally Posted by DSmitts34 View Post
Just remember, if you are going to use a 3 position switch so the center position is off as your disconnecting means, it needs to be located in a readily accessable place and be painted red and labled as a furnace cutoff.

Dan
I'm going to use the existing SP switch that is currently being used as the furnace disconnect. I'll paint the cover red and label it to bring it up to code.
 
  #15  
Old 11-20-09, 09:53 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,942
Received 44 Votes on 42 Posts
Originally Posted by bobbsledd View Post
You bring up a good point. I just looked at the generator, and the circuit breaker is 20A, which is too large for the 15A circuit. I already ordered the inlet, which is rated for 15A. So I'll need to fuse it down before the inlet.
Sounds like tossing in a 15A fuse holder would be a good idea too.
 
  #16  
Old 11-20-09, 10:02 AM
B
Member
Thread Starter
Join Date: Apr 2009
Location: Ohio
Posts: 54
Received 0 Votes on 0 Posts
Originally Posted by ibpooks View Post
Sounds like tossing in a 15A fuse holder would be a good idea too.
I'm thinking of putting a fuse holder in a WP box that I can plug into the generator. That way, I can protect anything that I use the generator for that's a 15A circuit.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: