Carrier unit in attic with heat strips....

[chevyx92]

Came across a job where there had been 3 different electrical contractors on the job, why they didn't finish is beyond me. Needless to say there are a ton of things left undone. My first issue is the unit in the attic has a #2 Alum SEU cable ran to just coiled up not hooked in yet. We are under the 2008 NEC as well. I looked at the heat strips and they are 3 strip kit for a total of up to 14.8KW. The electrical connections in the unit provide L1, L2, L3, L4 (L1, L2 are fused at 60A) and (L3, L4 are fused at 30 A). the 60A fuses protect 2 of the heat strips and the 30A fuses protect the third heat strip. If you see the information label below you will see that L1/L2 MCA is 76.3 amps and L3/L4 MCA is 22.7 amps. How can they require 76.3 MCA if inside the unit they have factory 60A fuses? Also it seems to me that they should have ran a 2nd circuit for the 3rd heat strip? I don't see how the #2 SEU will suffice for all this, do you? I see the #2 SEU only good for 75 Amps. Need a little help here from all you resi guys that deal with this on a consistent basis please.

 

[augie47]

The answer to the 1st part of your question probably lies with the blower motor. You will notice L1-L2 also drop down to feed what it probably a blower motor. With 9.6 kw of heat and a decent size blower all at the required 1.25%, you may well reach your MCA.
It would sure push the 60 amp fuses, but they could be rated at 100% actual load.
The #2 AL SE under the '08 Code would indeed be a 75 amp conductor and not sufficient for the full load,in fact by actual Code it would not even be sized for your 76.3 MCA.

 

[John120/240]

Came across a job where there had been 3 different electrical contractors on the job,





View attachment 7746 View attachment 7747

Did you adress the first RED flag before the job began. Why three different contractors ?

Is the money there ? Customer attitude & expecations ? Are the man & wife both nut cases ?

There is more to this story.

 

[ceb58]

Did you adress the first RED flag before the job began. Why three different contractors ?

Is the money there ? Customer attitude & expecations ? Are the man & wife both nut cases ?

There is more to this story.

Yes, that would be the main question, Why are they walking out? As far as the heaters it looks as if they were going to hook up one set 58.5 min 60 max ocp

 

[TimK]

Resi Guys thinking wrong?

Resi Guys thinking wrong?

Just throwing darts at a wall, don't think I have ever been able to explain someone else's actions, but could they have been thinking #2, as in SER and Service Rated to panel as in Table 310.15(B)(6) would cover his 100A requirement? Although wrong, just guessing. I'm sure only one of them installed it, the question becomes was it the first or third?

 

[Dennis Alwon]

#2 seu alumin is good for 75C depending on which code cycle you use- hence 90 amps. The heaters must be broken down as art.424.22 (B) does not allow more than 60 amps for resistant heat.

 

[chevyx92]

#2 seu alumin is good for 75C depending on which code cycle you use- hence 90 amps. The heaters must be broken down as art.424.22 (B) does not allow more than 60 amps for resistant heat.

2008 NEC so its only good for 75 Amps. So thats a common thing to see then having a set of 60 amp fuses and a set of 30 amp fuses. So from the OP with picture of ratings where it says L1/L2 Dual max overcurrent protection 80/90, does that mean you can feed both sets of fuses with 1 80/90 amp circuit?

 

[Mgraw]

Yes, One circuit.

 

[chevyx92]

Yes, One circuit.

So either way the #2 Alum is too small, MCA is 76.3 amps and under the 2008 NEC the #2 is only good for 75 amps.

 

[chevyx92]

Just throwing darts at a wall, don't think I have ever been able to explain someone else's actions, but could they have been thinking #2, as in SER and Service Rated to panel as in Table 310.15(B)(6) would cover his 100A requirement? Although wrong, just guessing. I'm sure only one of them installed it, the question becomes was it the first or third?

I think it can be done, it would be a straight power panel no neutral. Then from there feed the unit properly. What you guys think?

 

[Dennis Alwon]

I think its c;ear that you can supply the unit with one or two circuits. I will usually pull one circuit however the last few I wired required 2 circuits so I ran one circuit and spli with a disco at the unit

 

[kwired]

I think you are reading the label wrong. It would help if they put a little space between each section of the label.

For a single supply circuit it is rated 54.2/59.9 amps, MCA is 76.3/83.4, MOCP is 80/90.

For dual supply circuits circuit L1/L2 is rated 36.2/40.0 amps, MCA is 53.8/58.5, MOCP is 60/60 and circuit L3/L4 is rated 18.1/20.0, MCA is 22.7/25.0, MCA is 25/25.

2 AWG aluminum SE cable is a little short of needed ampacity - because it must use the 60C ampacity column, if using say XHHW aluminum in raceway and 75C column then 2AWG would be acceptable.

 

[Cavie]

2008 NEC so its only good for 75 Amps. So thats a common thing to see then having a set of 60 amp fuses and a set of 30 amp fuses. So from the OP with picture of ratings where it says L1/L2 Dual max overcurrent protection 80/90, does that mean you can feed both sets of fuses with 1 80/90 amp circuit?

No! You can feed a fused disconect at the unit with one 90A conductor @75 degrees and install a 60 and 25 bkr/fuses with suitable sized conductors @75 degrees. Don't think of it a 3 heatstrips. It's commonly know as 15 KW. One 10 and one 5. In this case a little less.

 

[augie47]

No! You can feed a fused disconect at the unit with one 90A conductor @75 degrees and install a 60 and 25 bkr/fuses with suitable sized conductors @75 degrees. Don't think of it a 3 heatstrips. It's commonly know as 15 KW. One 10 and one 5. In this case a little less.

I respectfully disagree, somewhat.
The unit gives the option of (1) circuit with a MCA of 83.4 on a max OCP of 90.
Since the unit has internal fuses not greater than 60 amp, we have satisfied 424.22
The only possible problem I see is with termination. On a single supply you would need to jumper L1,L2 to L3L4. Some units are equipped with factory jumpers to do this. If not you would need to assure the terminals are rated for (2) conductors or make a tap to feed the two loads.