Utility power to a Generac transfer switch

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  #1  
Old 12-22-10, 10:14 AM
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Utility power to a Generac transfer switch

I have a 70 amp breaker protecting the transfer switch panel on the utility power side and a 65 amps breaker protecting the generator from the transfer switch panel. The 70 amp breaker has been occasionaly tripping during the last two years (always during the winter) and I know it is being caused by the emergency heat for the heat pump (40 plus amp draw alone). My question is would be be easier/cheaper to up the utility breaker/wiring to 100 amps or just move the emergency heat circuit from the generator panel into the main panel? This was happened a few times during the day when I was away and the generator ran all day because the tripped breaker cuts off the utility power. I understand the work is basically the same put I am not sure if upping the breaker to 100 will mess with any of the generator warranties.

Sorry about the long response.

Leslie
 
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  #2  
Old 12-22-10, 12:34 PM
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Is the 70A breaker protecting your entire service or just a subpanel with a portion of your loads on it?
 
  #3  
Old 12-23-10, 05:55 AM
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The 70 amp breaker is in the main panel and protects/feeds the generator transfer switch/panel from the utility side. The majority of the house's "normal" circuits are in the generator panel except the large draw things like the elect oven, elect stove, shed subpanels, septic system, and the larger of the two heat pumps.

Leslie
 
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Old 12-23-10, 08:34 AM
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Ahh okay I understand. Is the aux heat on a separate circuit from the heat pump compressor? Would it be possible to just move the aux heat circuit back to the main panel? It does seem like you want at least some heating on the generator panel in case you need it in an emergency.

You can't increase the 70A breaker unless the panel and conductors are rated for higher. If the panel can do up to 100A, you can increase the feeder conductors to #3 copper/#8 ground and switch to 100A breaker. The max rating of the Generac panel should be printed on the panel label.
 
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Old 12-26-10, 05:03 AM
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You may have rectified this situation already however, your transfer switch is rated at 100 amps and the pre-wired feeders (#4 copper) are rated for 100 amps. so you may upgrade the breaker from 70-100 amps.
 
  #6  
Old 12-26-10, 06:28 AM
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your transfer switch is rated at 100 amps and the pre-wired feeders (#4 copper) are rated for 100 amps
I disagree. #4 copper is approved for residential 100 amp service entrance wiring, but this is a branch feeder. I, like ibpooks, suggest #3 copper for this application.
 
  #7  
Old 12-26-10, 07:29 AM
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310.15 B(6) says residential services and feeders. If you have a 100 amp disconnect and feed a subpanel, you won't have to use #4 for one and 3 for the other.
 
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Old 12-26-10, 07:30 PM
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Originally Posted by wirenut1110 View Post
310.15 B(6) says residential services and feeders. If you have a 100 amp disconnect and feed a subpanel, you won't have to use #4 for one and 3 for the other.
Well......you are right. There is no better way than to see what the NEC actually says. The keyword here is residential.
 

Last edited by CasualJoe; 12-26-10 at 07:31 PM. Reason: added comment
  #9  
Old 12-26-10, 10:45 PM
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Yes, but only if the feeder carries the full load of the dwelling. I think the wording of that table was altered between 2005 and 2008 to make it more clear. I do not believe that 310.15b6 applies in this case as this is not the main service and it does not carry the full load of the dwelling.
 
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Old 12-27-10, 07:47 AM
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310.15B states:
(B) Tables. Ampacities for conductors rated 0 to 2000
volts shall be as specified in the Allowable Ampacity Table

Conductor (AWG or kcmil)
Service or Feeder
Rating (Amperes) Copper
Aluminum or
Copper-Clad
Aluminum
100 4 2
110 3 1
125 2 1/0
150 1 2/0
175 1/0 3/0
200 2/0 4/0
225 3/0 250
250 4/0 300
300 250 350
350 350 500
400 400 600
 
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Old 12-28-10, 01:23 AM
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Originally Posted by Justin Smith View Post
310.15B states:
(B) Tables. Ampacities for conductors rated 0 to 2000
volts shall be as specified in the Allowable Ampacity Table

Conductor (AWG or kcmil)
Service or Feeder
Rating (Amperes) Copper
Aluminum or
Copper-Clad
Aluminum
100 4 2
110 3 1
125 2 1/0
150 1 2/0
175 1/0 3/0
200 2/0 4/0
225 3/0 250
250 4/0 300
300 250 350
350 350 500
400 400 600
If that based on 75C rated conductor like THHN/THWN sound proper but if you used SE or SER cable then the bet is off due they only still have 60C rating so just becarefull when you post this chart and make sure you mention what tempture rating of conductors that will change a bit if not pay attetion with it.

Merci.
Marc
 
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Old 12-28-10, 06:37 AM
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Seems like it may just be easier to move the aux heat circuit from the generator subpanel back into the main and fill the empty spot in the sub with the sewage pump circuit thats currently on the main (50A v 20A). This will lower the demand on the subpanel and still leave a heat pump unit covered by the generator.

Thanks guys.

Leslie
 
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