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Old 09-19-2013, 01:01 PM   #1
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Running 6/3, 50 or 60 amp breaker?


Running a 6/3 NMWU cable about 70ft from a main panel to a subpanel. I've heard mixed opinions on whether or not it should have a 50AMP or 60AMP breaker. Any thoughts?

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Old 09-19-2013, 01:22 PM   #2
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Running 6/3, 50 or 60 amp breaker?


EDIT: You're in Canada. I'll be less blind next time.

In the US, you can use 60A, NEC 240.4(B).

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Old 09-19-2013, 01:33 PM   #3
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Running 6/3, 50 or 60 amp breaker?


The amp rating of #6 copper cable is 55 amps. You are permitted to protect it with a 60 amp breaker.
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Old 09-19-2013, 01:54 PM   #4
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Running 6/3, 50 or 60 amp breaker?


If the wire is only rated at 55 why is 60 permitted? Wouldn't it be 50?
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Old 09-19-2013, 02:02 PM   #5
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Running 6/3, 50 or 60 amp breaker?


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Originally Posted by n0c7 View Post
If the wire is only rated at 55 why is 60 permitted? Wouldn't it be 50?
You can use the next common size up if the conductor ampacity doesn't match one of the common sizes.
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Old 09-19-2013, 02:08 PM   #6
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Running 6/3, 50 or 60 amp breaker?


So theoretically if you were to manage to draw lets say 59.9 amps for a prolonged period of time wouldn't that cause the wire to overheat before it would trip?
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Old 09-19-2013, 02:22 PM   #7
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Running 6/3, 50 or 60 amp breaker?


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Originally Posted by n0c7 View Post
So theoretically if you were to manage to draw lets say 59.9 amps for a prolonged period of time wouldn't that cause the wire to overheat before it would trip?
running 59.9 amps on a conductor rated for 55 amps is already a violation.

topic is referencing 240.4(B):

Overcurrent Devices Rated 800 Amperes or Less.
The next higher standard overcurrent device rating (above
the ampacity of the conductors being protected) shall be
permitted to be used, provided all of the following conditions
are met:

(1) The conductors being protected are not part of a branch circuit supplying more than one receptacle for cord and plug-connected portable loads.
(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
(3) The next higher standard rating selected does not exceed 800 amperes.
standard overcurrent device amp ratings are defined in 240.6. 55 amps is not a standard size and we are meeting all three conditions referenced above so we can 'round up' to the next standard size.
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Old 09-19-2013, 02:31 PM   #8
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Running 6/3, 50 or 60 amp breaker?


Even if its a code violation it doesn't stop someone from running a crapload of space heaters and running the load past 55 amps. Kind of struggling with this in my head. Are they assuming the size up difference is so minimal they're willing to risk it?
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Old 09-19-2013, 02:55 PM   #9
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Running 6/3, 50 or 60 amp breaker?


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Originally Posted by n0c7 View Post
Even if its a code violation it doesn't stop someone from running a crapload of space heaters and running the load past 55 amps. Kind of struggling with this in my head. Are they assuming the size up difference is so minimal they're willing to risk it?
it is a code violation for a user to overload a circuit but i know where you're coming from. practically, there isn't a problem. it isn't like there are news stories every other day about circuits installed with the round-up rule causing a bunch of fires. and also practically, there are margins built into ampacity tables. it isn't like at 56 amps the cable will explode.

so practically, it isn't a concern and code explicitly allows it. there is no risk.
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Old 09-19-2013, 03:59 PM   #10
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Running 6/3, 50 or 60 amp breaker?


In ONTARIO table 2 give us the rating of 55 amp for #6 copper wire.
Table 13 gives the " rating for setting undercurrent devices protecting conductors" with 51-60 ampacity of conductor being allowed to be protected by 60 amp.
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Old 09-19-2013, 05:21 PM   #11
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Running 6/3, 50 or 60 amp breaker?


Quote:
Originally Posted by n0c7 View Post
Even if its a code violation it doesn't stop someone from running a crapload of space heaters and running the load past 55 amps. Kind of struggling with this in my head. Are they assuming the size up difference is so minimal they're willing to risk it?
You are assuming that if the amperage is an amp or two over the rating the wire will spontaneously combust. This is simply not so.

What the professionals here from Canada are telling you is right.
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Answers based on the 2008 & 2011 NEC.
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Old 09-19-2013, 05:26 PM   #12
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Running 6/3, 50 or 60 amp breaker?


Thanks everyone!

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