12/4 need to be derated?

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jjhoward

jjhoward

Senior Member
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Northern NJ
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Owner TJ Electric
Hello All;
I am installing resi 240V electric baseboards + wall tstats. If I run 4 condcutor ROMEX down the wall to the tstats (1 pair for power in and 1 pair switched power.) do I need to derate these conductors??

Table 310.15 tells me to derate these conductors, is there any exception that may apply here??

Thank you.
 
jjhoward said:
Hello All;
I am installing resi 240V electric baseboards + wall tstats. If I run 4 condcutor ROMEX down the wall to the tstats (1 pair for power in and 1 pair switched power.) do I need to derate these conductors??

Table 310.15 tells me to derate these conductors, is there any exception that may apply here??

Thank you.
Click to expand...
#10.15 tells you to derate them but it is only for 80%. #12 is rated at 30 amps and 80% of that is 24 so there is no problem unless there is more derating for temp etc, that needs to be done.
 
Ok, I was starting with 20 amps to derate the #12s.
30 amps is the 90 degree col. Even at 25 amps 80% is still OK.
Thank you!
 
jjhoward said:
Ok, I was starting with 20 amps to derate the #12s.
30 amps is the 90 degree col. Even at 25 amps 80% is still OK.
Thank you!
Click to expand...

You are welcome. If the wire is rated 90 C you can use that column for derating purposes.
 
LarryFine said:
For a 2-pole switch-loop, you still have four CCC's.
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Are you sure. I thought there was a post that said switched loops only count as one but it does make sense that both should be counted.
 
Is there something in the code that distiguishes switch legs?
When the baseboard is on, current is flowing through all 4 conductors.
 
You are required to derate switch loops.

What you do not have to count is the extra travelers in 3 and 4 way set ups.

You have to read the ROPs to see that.
 
iwire said:
You are required to derate switch loops.

What you do not have to count is the extra travelers in 3 and 4 way set ups.

You have to read the ROPs to see that.
Click to expand...

That makes sense with the 3 way and that must be what I was remembering not the switch loops.
 
iwire said:
You are required to derate switch loops.

What you do not have to count is the extra travelers in 3 and 4 way set ups.

You have to read the ROPs to see that.
Click to expand...

I wonder why it wouldn't be clear in the code and we would need the ROP to make it so?
 
Dennis Alwon said:
#10.15 tells you to derate them but it is only for 80%. #12 is rated at 30 amps and 80% of that is 24 so there is no problem unless there is more derating for temp etc, that needs to be done.
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424.3(B) says you have to go to 125% on the conductors IMHO
 
Even at 125% most space heaters ( if your thinking #12 ) are going to be 4000 watt @240 volt X 125% is still only 20.83 amp. So your still good to go.
 
Quote:
Even at 125% most space heaters ( if your thinking #12 ) are going to be 4000 watt @240 volt X 125% is still only 20.83 amp. So your still good to go.

Not so fast ! :wink:

I agree about 60* column for nm and 90* column for derating ( 334.80 ), but don't forget that pesky 240.4(D) which maxes you out at 20A for #12CU regardless of where you start derating.
 
Twoskinsoneman said:
I wonder why it wouldn't be clear in the code and we would need the ROP to make it so?
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LOL :)

It is in the code, 'only count the current carrying conductors' (my words)


BTW ... If you keep holding my feet to the fire I will have to ban you. ;) :) JK
 
acrwc10 said:
424.3(B) says you have to go to 125% on the conductors IMHO
Click to expand...

Even at 125% most space heaters ( if your thinking #12 ) are going to be 4000 watt @240 volt X 125% is still only 20.83 amp. So your still good to go.
Click to expand...

We have no idea what the heater load is. The Op never gave us that info. If the #12 is the correct size for the load, then my statement is correct. 30amps * .8 = 24 .

No , you cannot load the circuit to 20.83 amps. The load cannot be greater than 20 amps or you must use #10.
 
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