Amp breaker max for AWG #8 wire

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  #1  
Old 07-26-06, 10:50 AM
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Amp breaker max for AWG #8 wire

#14 is OK for 15 amp
#12 is OK for 20 amp
#10 is OK for 30 amp

What about #8??
 
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  #2  
Old 07-26-06, 12:07 PM
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I believe it's 40A.
 
  #3  
Old 07-26-06, 12:24 PM
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The answer is not nearly that simple.

Most commonly, with copper conductors, #14 is protected by a 15A breaker, #12 by a 20 and #10 by a 30. However there are other circumstances where different values (smaller or infrequently larger) would be used.

Similarly, for #8 conductors, the conductor in most situations would be appropriately protected by a 40A or 50A breaker (with specific circumstances with 50 is permitted), less commonly smaller breakers, and still less commonly a larger breaker. The precise answer depends upon the circumstances and the load.

-Jon
 
  #4  
Old 07-26-06, 12:51 PM
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Winnie - Thanks for your response. OK - some specifics.

This was a heat pump air handler changeout. The wiring from the CB box to the disconnect by the unit is #6. (I believe the old unit had a larger heater strip and therefore required more juice.)

The manual specs say the load at 240v is 7.68 KW:
min circuit capacity = 43 amps
max overload protection = 45 amps

The #8 wire runs only from the disconnect to the unit.

This circuit has 60 amp breakers - which probably was OK for the old unit. But that seems to be too much f0r the load and for that 4 feet of #8 wire too.

I am thinking I should change to 50 amp breakers?

What do you say?

Thank you very much.
 
  #5  
Old 07-26-06, 01:17 PM
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The #8 is probably fine for the load, but the dataplate clearly states that the maximum OCPD is 45A. This means that even a 50A breaker is too large. A 45A breaker may be hard to find, but you might be able to add 45A fuses to the disconnect box.

-Jon
 
  #6  
Old 07-26-06, 01:57 PM
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Siemens does not make a 45 amp QP breaker so the best I can do is 50 amp - unless, as you suggest, I change out the disconnect box to something with a 45 in it.

Suggestion? Is it worth it?
 
  #7  
Old 07-26-06, 02:52 PM
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'Worth it' is a nearly impossible question to answer. The electrical code provides minimum requirements for safety, however this is statistical in nature. If you slightly violate the code, you increase danger, but how much? Using a 50A breaker rather than a 45A fuse? How much danger? How much cost?

There is simply not enough information to actually do a proper 'cost-benefit' analysis.

I will always recommend that you make the changes necessary to meet code. 45A fuses are common and inexpensive (they are even sold on the DIY superstore of this site). I recommend that you make the effort to add a fusible disconnect so that your heat pump is properly protected to the rating on the dataplate.

-Jon
 
  #8  
Old 07-26-06, 03:00 PM
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Winnie,
It was my understanding that all heatpump/condencers and the like must have a fused disco.For the exact reasons described. This has been common practice since I was an apprentice. Or is this another one of those MA. codes?

Almost forgot, Make sure the fuses are TIME-DELAY.
 
  #9  
Old 07-26-06, 03:11 PM
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I don't know enough to know if a fused disconnect is required, or if a simple non-fused disconnect is sufficient.

I am focusing on the original posters situation, where they have a heat pump that requires a max ocpd of 45A. A 50A breaker does not meet this requirement.

-Jon
 
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