new to this forum but i have trolled here forever looking for answers to situations others have encountered like this we do a lot of residential reconnects on hvac changeouts when i say a lot i am talking about 200 a year my question is this on a 10kw air handler 60 amps over current , the original equipment was fed with 6 romex which at time of install was allowable , so we are having to replace with se cable , my question is why isnt this allowed to be reconnected if equipment is like for like instead of requiring a new wire to be pulled
HVAC CHANGEOUT & RECONNECT
- Thread starter JHE4601
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- Bremerton, Washington
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- Master Electrician
That’s one long sentence and hard to follow. My experience is not dwelling units, but I seem to recall the ampacity of 10 AWG NMB has changed to 55 amps
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Was it really allowable or a mistake that was never caught? #6 NM cable has been rated at 55A for a long long time. The 10KW heat strip is not a problem for #6 NM. But if that heat strip circuit also has fan load and controls load, the sum of all that may be over 55A. Both the heater and the fan will be true amps * 125%. There should be a sticker on the unit indicating the MCA. Assuming the correct sticker was chosen (many units have multiple stickers depending on what combinations of strip heat was installed), if it says 55A or less, you should be able to use NM. Most furnaces with a fan and 10KW heat strips will be over 55A.
SE cable was sometimes rated at 60C and sometimes 75C. If you can use it at 75C, then #6 cu SE cable would be good for 65A.
SE cable was sometimes rated at 60C and sometimes 75C. If you can use it at 75C, then #6 cu SE cable would be good for 65A.
- Location
- Bremerton, Washington
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- Master Electrician
I seem to recall some furnaces were rated 9.6 kw so would be 10 kw with fan
i believe these are actually 9.6 kw with min cir of 54 max fuse 60 i will have to look at the next one we reconnect i just remember 10 years or so ago we were allowed to use 6 romex to these and now we arent allowed to reconnect same exact unit back to existing wire we either have to get hvac guys to drop back to 8kw or pull an se cable oh sorry of this is another long run on sentence
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- Tennessee NEC:2017
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- Semi-Retired Electrician
Just use some periods and maybe a comma. Periods look like the little dot between the 9 & 6 kw.
I believe #6 NM is still compliant for these numbers. The 54A MCA is key.
LBarlow
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- Location
- North Carolina
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- Inspector
It seems like what is meant here by the OP is that maybe the old unit had a MCA (minimum circuit ampacity) of less than 55 amps and the new unit may have labeling requiring more than 55 MCA. I believe that would be the reason to change the feeder size.
Also, just speculation of course, the original installation may have never been inspected to begin with.... which I run into quite a bit.
Also, just speculation of course, the original installation may have never been inspected to begin with.... which I run into quite a bit.
The way I read post 5, he is reconnecting equipment with a 54A MCA nameplate.
My experience has been that many of the older 10kw (9.6) had a Minimum Circuit Ampacity of 55 amps or less thus making a #6 NM compliant
whereas the newer"energy efficient" units have a minimum circuit amps > 55
I see a fair number of nameplates on some units that show various MCAs, some over, some under 55, dependent on what motor is installed.
When you have a nameplate that covers models A,B & C (all different motors) and 240/208 ratings the nameplates can often be a challenge to the HVAC tech (and sometimes the inspector )
whereas the newer"energy efficient" units have a minimum circuit amps > 55
I see a fair number of nameplates on some units that show various MCAs, some over, some under 55, dependent on what motor is installed.
When you have a nameplate that covers models A,B & C (all different motors) and 240/208 ratings the nameplates can often be a challenge to the HVAC tech (and sometimes the inspector
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