Subpanels optional??

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Copperthief

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I just got an electrical job this afternoon .... Client wants 5 circuits 3 are for hair dryers on is a convenience outlet the other for hot curlers .... This is in the attached garage which is about 50 from the panel. Should I run a subpanel?? I've got plenty of #12 if (I'd have to buy #4 and I don't wanna) or just go with the sub panel? The furthest dryer at a worst case scenario is 80 ft.
 
I would run one HR conduit and forget the subpanel. If they're all 20 amp circuits you could use the #12 if you had a few MWBC's.
 
I'd be inclined to install a panel in the garage on the grounds that they will probably want more circuits down the road. OTOH, you can come back and charge them to run more conduit and wire when they decide to add more circuits.

Having said that, it is all about money and whether you have spaces to put the new CBs in the existing panel.
 
MWBC = Multi Wire Branch Circuit. If for example you share the neutral for the three hair dryer circuits, you will only have a total of 7 CCCs. That is figured at 3 CCCs for the MWBC and 2 CCCs each for the other two circuits, for a total of 7. The neutral of the MWBC does not count, but the other two neutrals do count. Having 7 CCCs in the same conduit would require that you derate the #12 by 70%. But presuming your wire is rated for 90C (i.e., type THHN), then you start the 70% derating at the 90C value of 30 amps. Thus, your ampacity is 21 amps, and you can use the #12s with a 20 amp breaker.

Welcome to the forum.
 
One example of a MultiWire Branch Circuit (MWBC) would be when you run one black
and one red wire, one fed from L1 and one fed from L2 in a panelboard along with one neutral of the same size. Each device connected to the circuit will use 120V and will be wired from one of the hot wires to the common neutral.
At first you may think that you have gone from four CCCs to three. But the NEC recognizes that for derating calculations you only have TWO CCCs. Not bad, right?
 
Copperthief said:
Whaz a mwbc?.... And aren't my neutrals current carrying conductors... Making my ccc 10 derating my stuff? Am I over thinking this ...??
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This may help you to decipher the neutral CCC counting:

Neutral Conductors:
Here's some examples of when to count and not count the neutral as a current carrying conductor or CCC:

3?- 208Y/120 or 480Y/277 volt system-different circuit types:
A) 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
B) 3 wire circuit w/ 2 ungrounded, 1 neutral = 3 CCC's
C) 4 wire circuit w/ 3 ungrounded, 1 neutral = 3 CCC's*

Notes:
A) A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
B) In this circuit the neutral current will be nearly equal to the current in the ungrounded conductors so the neutral counts as a CCC
C) In this circuit the neutral will only carry the imbalance of the current between the three ungrounded conductors so it is not counted as a CCC, with an exception, *if the current is more than 50% nonlinear (see below for NEC article 100 definition) then the neutral would count as a CCC.

1?- 120/240 volt system-different circuit types:
D) 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
E) 3 wire circuit w/ 2 ungrounded, 1 neutral = 2 CCC's
Notes:
D) A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
E) In this circuit the neutral will only carry the imbalance between the two ungrounded conductors so the neutral is not counted as a CCC.
Nonlinear Load. A load where the wave shape of the steady-state current does not follow the wave shape of the applied voltage.
Informational Note: Electronic equipment, electronic/electric-discharge lighting, adjustable-speed drive systems, and similar equipment may be nonlinear loads.
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On the other hand, I may find out if they are allowed to run a business out of their garage, before I got to carried away. But that's just the inspector in me talking.
 
charlie b said:
MWBC = Multi Wire Branch Circuit. If for example you share the neutral for the three hair dryer circuits, you will only have a total of 7 CCCs. That is figured at 3 CCCs for the MWBC and 2 CCCs each for the other two circuits, for a total of 7. The neutral of the MWBC does not count, but the other two neutrals do count. Having 7 CCCs in the same conduit would require that you derate the #12 by 70%. But presuming your wire is rated for 90C (i.e., type THHN), then you start the 70% derating at the 90C value of 30 amps. Thus, your ampacity is 21 amps, and you can use the #12s with a 20 amp breaker.

Welcome to the forum.
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So if I did the l1 and l2 thing In a residential panel don't I have to use single throw breakers since they share a neutral? I didn't think u could share 3 circuits on a single neutral in residential but I'm kinda new at this electrical thing
 
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Copperthief said:
So if I did the l1 and l2 thing In a residential panel don't I have to use single throw breakers since they share a neutral? I didn't think u could share 3 circuits on a single neutral in residential but I'm kinda new at this electrical thing
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Check 210.4 in the NEC for detsails, but you would need to have a handle tie at a minimum on breakers for MWBC circuits. You are correct, on a single phase residential panel you can only share a neutral with L1,L2.

In your case, you could share circuits 1&3 and a neutral, 2&4 and a neutral and then have one circuit with its own neutral for 6 CCCs
 
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augie47 said:
Check 210.4 in the NEC for detsails, but you would need to have a handle tie at a minimum on breakers for MWBC circuits. You are correct, on a single phase residential panel you can only share a neutral with L1,L2.

In your case, you could share circuits 1&3 and a neutral, 2&4 and a neutral and then have one circuit with its own neutral for 6 CCCs
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Thx!!!! This was soooo helpful ... I appreciate the code reference !!! Did I say u guys are awesome and sexy !! Well u are!!! :D
 
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