Water Heater Sizing At Continuous?

[Little Bill]

Thank you for the feed back..

Just that I remember when the 80% and temp. ratings of wire became a concern.. and a "big deal"..

I walked away from keeping my head in the game when I joined my Onion brothers and basically just had to run pipe and pull wire..

continued with the continuing education courses to keep lic. and permit.... but well..... guess I wasn't paying attention..

Thank you.

reciprocal................... my word for the day ;- )

You can keep that word, just lose the 80% and "protecting the breaker" and FLA.
Maybe you could give them to your Onion brothers!

 

[kwired]

Ok.... guess I should pay better attention... did,t know they dropped the 80%.. or sec. 384-16(c) if that was it...

in reading..something isn't making sense.


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CB Sizing Examples

The following are examples of sizing rules.

Example 1: 50A continuous load and 125A noncontinuous load.

OCPD = 100% noncontinuous load + 125% continuous load = (1.00 x 125A) + (1.25 x 50A) = 187.5A

Therefore, a 200A OCPD is needed. If a 100%-rated CB is chosen, a 175A rating (125A + 50A) is acceptable.

Example 2: 300A noncontinuous load.

A 300A device is acceptable; a 100%-rated device is not needed since the load is noncontinuous.

Example 3: 200A continuous load.

OCPD = 100% noncontinuous load + 125% continuous load = (1.00 x 0A) + (1.25 x 200A) = 250A

Therefore, a 250A device is needed. If a 100%-rated CB is selected, a 200A rating is permitted.

Example 4: 16A continuous and 30A noncontinuous.

OCPD = 100% noncontinuous load + 125% continuous load = (1.00 x 30A) + (1.25 x 16A) = 50A

Therefore, a 50A device can be selected. Although 100%-rated devices typically are not available in sizes this small, the permitted rating would still be 50A (16A + 30A = 46A; rounded up to 50A).


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In the above examples... or in general..if you put a 50 amp continuous load on a 50 amp breaker (continuously rated) wouldn't it trip? or do they trip at like 50.0000000000000000001 ?


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http://forums.mikeholt.com/showthread.php?t=63261

I'll work on it

depends on a few things and Mark covered some of them.

You need to look at the trip curve and also apply this at whatever ambient temp the trip curve is for. In general a breaker will carry more load than it's rating, but how much and for how long all depend on the trip curve.

Main general difference between continuous load / non continuous load for both minimum conductor size as well as breaker setting selection is mostly because the non continuous breaker is dependent on the conductor to sink some heat