Yet another subpanel question


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Old 05-23-14, 11:30 AM
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Yet another subpanel question

Hello I was trying to figure out if the following wiring would work safely. I am planning to instal a sub panel about 40 feet away from the current panel. The main breaker 200amp is located outside the house in the meter box just one two pole breaker. I know the standard would be to tap off a two pole breaker in the house panel however its fully loaded already most are now double 20's in the single spots. I would like to feed the subpanel right from the main lug connections. I have read this is bad on this site but couldn't find a reason why but would guess as those who do it usually put either 2 wires into a single lug or that it creates an unprotected line to the subpanel. In this case I plan to remove the single wire lugs replacing them with 2 wire lugs (there is plenty of room) and I would think the line would still carry the protection of the main breakers on the meter box essentially making it set up just the same as the panel I would be tapping from?

Any thoughts would be great! Thanks
 
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Old 05-23-14, 11:47 AM
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Welcome to the forums.

If you tap off the main breaker then the wiring needs to be the same as what that size breaker requires.

In other words.... you would have to run 200A cable to your sub panel.
 
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Old 05-23-14, 12:02 PM
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You could tap off the conductors but, you can't tap off the lugs.

Feeder tap rules under article 240.21 would apply.
 
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Old 05-23-14, 12:12 PM
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Thanks for the replies looks like I will have to install a small sub panel to free up some space in the main panel. And for another after I have described the setup I plan to hook up a generator to this new subpanel it is unbonded so should just be a simple hookup with no transfer switch two hots to the proper sized breaker the ground and neutral. Backfeed would be prevented by switching the outside mains off? Any no no's there?
 
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Old 05-23-14, 12:22 PM
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Backfeed would be prevented by switching the outside mains off? Any no no's there?
That is not a code approved way and is unsafe. You must use a transfer panel, transfer switch or interlock. Note though not all jurisdictions allow interlocks and many are not approved by a testing agency such as UL.
 
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Old 05-23-14, 12:31 PM
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Thanks ray2047. Is that because the neutral would still be connected? All of the box store switches I looked at just cut the two hots and left the neutral hooked up. This is basically what I have been doing currently during prolonged outages shutting of the mains hooking my generator directly the water heater breaker. Water heater disconnected of course! What are the dangers there? I forgot to add there are no codes or inspections in my area.
 
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Old 05-23-14, 12:43 PM
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What are the dangers there?
The dangers of backfeeding is that due to an inexperienced person... it is possible to have the generator running and the main get turned on accidentally.
 
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Old 05-23-14, 01:49 PM
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The code requires it to be certain that one source of power is off before another can be connected.
 
 

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