A/C circuit wire too small

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Notice the very LOW short circuit current ratings!

One is only 2400A. That will not be acceptable in an apartment building fed from one utility transformer. The SCC will be closer to 10,000A in many of the oness I have done!

Cheep china $rap!
 
infinity said:
I didn't see the HACR breaker mentioned.
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Most all the Installation Manuals have a "foot note" that give you a choice. If you use a HACR rated breaker you can also use a non-fusible disconnect. If you are doing a large complex ... that could add up to a lot of money !
 
Perhaps hook it up and take amp readings to see how much current it actually does draw? In any case use a fused disconnect at the machine with fuses to match your conductor rating so you don't start a fire inside the walls..............
 
Ragin Cajun said:
Notice the very LOW short circuit current ratings!

One is only 2400A. That will not be acceptable in an apartment building fed from one utility transformer. The SCC will be closer to 10,000A in many of the oness I have done!

Cheep china $rap!
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Agree that's low but with a #10 at average distances likely not a problem. Certainly something to keep an eye on.
 
macmikeman said:
Perhaps hook it up and take amp readings to see how much current it actually does draw? In any case use a fused disconnect at the machine with fuses to match your conductor rating so you don't start a fire inside the walls..............
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With HVAC it’s common for the conductor rating “MCA” to be smaller than the max OCPD listed on the name plate due to the starting current of the electric motor inside.

You can however have smaller than listed max OCPD to match the rating of the conductor but than you run the risk of nuisance trips on start ups.
 
Ragin Cajun said:
Notice the very LOW short circuit current ratings!

One is only 2400A. That will not be acceptable in an apartment building fed from one utility transformer. The SCC will be closer to 10,000A in many of the oness I have done!

Cheep china $rap!
Click to expand...
You won't find many that are rated over 5K. That because it is the default to be applied if a study wasn't done to find what it really can handle.

At same time by the time you get to the end of the branch circuit you seldom have more available current than that anyway, small conductors (in comparison to service and feeders in most cases) plus circuit length does have a limiting effect because of conductor resistance.

where you need to watch this more closely is if you have a very short run to the unit coming from a panel that does have pretty high available fault current.
 
I have heard that the power company's in many area have been using 22k trany's when they have to change them out. This is a major issue in commercial work also when there is an addition and the power company changes the transformer for a high aic. Now you have, for instance, all the existing loads on 22k equipment but the power company has now upgraded to a 42k-- not sure what sizes they use but you get the picture.
 
Dennis Alwon said:
I have heard that the power company's in many area have been using 22k trany's when they have to change them out. This is a major issue in commercial work also when there is an addition and the power company changes the transformer for a high aic. Now you have, for instance, all the existing loads on 22k equipment but the power company has now upgraded to a 42k-- not sure what sizes they use but you get the picture.
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Changing transformer just means new study might need to be done. 22k tranny is somewhat meaningless, available current at gear in question is what matters.

For lower capacity services, say 400 amp and less, often if you have at least 25 maybe up to 50 feet of service conductor, you normally will not have to look very hard at gear with over 10kA branch breaker ratings. Even if AFC is over 10k at the main, the main is probably 22-25k and series rated with 10k branches, and just a 10-20 foot branch circuit very well puts the equipment at the end under 10k being available.
 
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