Protecting both legs in 240v circuit

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  #1  
Old 09-29-13, 07:43 AM
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Protecting both legs in 240v circuit

Hi,I know that two breakers are ganged together in a 240v circuit so that both legs are disconnected if there is a short in either leg. I have an older service panel that has a pullout block for a range that has a shotgun-type fuse in each leg. How does this work then? Just one fuse blows? Thank you.
 
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  #2  
Old 09-29-13, 08:15 AM
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You are correct. The one leg would continue to supply power. The appliance performance would be greatly reduced, if it worked at all.
 
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Old 09-29-13, 10:01 AM
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I do not have an electric range hooked up to it. Can I hook up it up to a subpanel with a 20 amp breaker to it to provide 240v to a submersible well pump?
 
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Old 09-29-13, 11:11 AM
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Can I hook up it up to a subpanel with a 20 amp breaker to it to provide 240v to a submersible well pump?
Yes. You will need to add a bonded ground bar to the subpanel. The neutral bar will not be used but should not be bonded to the case. The panel should be labeled 240 volts only.
 
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Old 09-29-13, 11:16 AM
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The subpanel would be in the same structure (in the basement)as the fuse panel. Then I shouldn't need a separate ground bar?
 
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Old 09-29-13, 11:26 AM
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Oh, OK I was thinking ground rod. I don't need a separate ground rod but I must add a ground bar.
 
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Old 09-29-13, 11:39 AM
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If the 240 volt pump(around 6 amps) was the only thing I would be running off this subpanel then could I feed it with NMB 12-2 with ground. Or do I need to run 3 wires with ground?
 
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Old 09-29-13, 11:50 AM
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A straight 240 pump can run on xx-2 cable. The white will be reidentified as a hot with black or red tape or magic marker.
 
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Old 09-29-13, 11:59 AM
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OK, so if I wanted to add a 120v circuit(along with the 240v) to the subpanel, would I then have to feed the subpanel with 3 wires plus ground?
 
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Old 09-29-13, 12:45 PM
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so if I wanted to add a 120v circuit(along with the 240v) to the subpanel, would I then have to feed the subpanel with 3 wires plus ground?
Yes.

I feed it with NMB 12-2 with ground.
Probably not. The wire much be sized to the fuses. I doubt you could get 20 amp cartridge fuses to fit your holder. Maybe go with 40a fuses and use 8-2 for 240 only or 8-3 for 120/240.
 
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Old 09-29-13, 01:05 PM
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Or, if I use a 30 amp fuse, I could run 10-3 plus ground for 120/240? Also, I've read that I should use a slow-blow fuse if it's feeding a motor. Is this true even if it's running through a 20 amp breaker in the subpanel?
 

Last edited by brucers; 09-29-13 at 01:43 PM.
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Old 09-29-13, 03:06 PM
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Or, if I use a 30 amp fuse, I could run 10-3 plus ground for 120/240? Also, I've read that I should use a slow-blow fuse if it's feeding a motor.
A time delay or slow blow fuse is OK, that's what I'd use. You'll probably have to also buy a set of fuse reducers to fit the range pull-out of your panel if you go with 30 amp fuses.
 
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Old 09-29-13, 03:06 PM
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Or, if I use a 30 amp fuse, I could run 10-3 plus ground for 120/240?
Yes.

I've read that I should use a slow-blow fuse if it's feeding a motor.
I would regardless of what is being fed. Note standard breakers mimic the action of a slow blow fuse for the most part so it would be no different than using a standard breaker.

Is this true even if it's running through a 20 amp breaker in the subpanel?
Yes.
 
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Old 09-30-13, 09:31 AM
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What amp rating size of subpanel would I need? Say I'm going to use a 40 amp fuse and 8-3 wire, is there a maximum amp rating of the subpanel. Can I put in a 100 amp 6 slot as long as my total current figures less than say 80% of 40 amps?
 
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Old 09-30-13, 09:47 AM
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It doesn't matter what the rating of the subpanel is so long as it is large enough to handle the total load. Just size the overcurrent protection in the panel you're feeding from to protect the feeder conductors.

Can I hook up it up to a subpanel with a 20 amp breaker to it to provide 240v to a submersible well pump?
How far away is the well pump? How long will the conductors be from the subpanel to the pump? Will they be individual conductors in conduit?
 
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Old 09-30-13, 09:59 AM
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"How far away is the well pump? How long will the conductors be from the subpanel to the pump? Will they be individual conductors in conduit?"

The well will be drilled about 20 ft from the house and the wells in this area are around 200 ft deep. So, about 220 ft from the pump to the subpanel. Not sure what size 240v pump they will put in, but the driller told me the pumps draw around 6 amps. The wires are not in conduit.
 
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Old 09-30-13, 12:29 PM
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about 220 ft from the pump to the subpanel. Not sure what size 240v pump they will put in, but the driller told me the pumps draw around 6 amps.
OK, you should be good - in fact more than good - for 6A at 220' on a 20A 240V circuit run in cable.
 
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Old 09-30-13, 01:41 PM
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Do you think you may need a light or receptacle at the pump? if so run 12-3 to a small subpanel.
 
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Old 10-01-13, 11:25 AM
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Because fuses are not ganged together , if short is only on one leg, that legs fuse will blow not both fuses. I hope this will clear up any confusion with our moderators.
 
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Old 10-01-13, 11:56 AM
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Because fuses are not ganged together , if short is only on one leg, that legs fuse will blow not both fuses. I hope this will clear up any confusion with our moderators.
Thank you for a clarification.
 
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Old 10-01-13, 09:00 PM
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Because fuses are not ganged together , if short is only on one leg, that legs fuse will blow not both fuses. I hope this will clear up any confusion with our moderators.
No, not really, because what's confusing me is why you're insisting on answering this question from the original post:
Originally Posted by brucers, in post #1
I have an older service panel that has a pullout block for a range that has a shotgun-type fuse in each leg. How does this work then? Just one fuse blows?
when it was answered in the second post:
Originally Posted by pcboss, in post #2
You are correct. The one leg would continue to supply power.
 
  #22  
Old 10-01-13, 11:43 PM
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"A time delay or slow blow fuse is OK, that's what I'd use. You'll probably have to also buy a set of fuse reducers to fit the range pull-out of your panel if you go with 30 amp fuses. "
OK, I'm going to use time-delay 40 amp fuses(with 8-3 wire) in the Range block. Do I need time-delay in the Main block too(50 or 60 amp)?
 

Last edited by brucers; 10-02-13 at 12:47 AM.
  #23  
Old 10-02-13, 04:04 AM
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Do I need time-delay in the Main block too(50 or 60 amp)?J
Best to use them. As I wrote earlier most homes now use breakers and the common residential breaker is "slow blow" allowing for momentary overload.
 

Last edited by ray2047; 10-02-13 at 06:21 AM.
  #24  
Old 10-02-13, 05:32 AM
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Best to use them. As I wrote earlier most homes now use breakers and the common residential breaker is slow blow allowing for momentary overload.
If the pump normally draws 6 amps, what is the maximum surge/startup current one would expect?
 
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Old 10-02-13, 06:20 AM
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If the pump normally draws 6 amps, what is the maximum surge/startup current one would expect?
You would have to check the name plate for locked rotor amps but rough rule of thumb 18 amps.
 
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