Derating Woes

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jap

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Electrician
2 offices.
receptacles office 1 circuit 1
receptacles office 2 circuit 3
lighting for both circuit 5.

Single phase service all 20 amp circuits.

If I pull a neutral ro each circuit (to get away from having to use handle ties) looking at 6 #12's and 1 grnd
easily fits in 1/2" emt.

If I wire them as MWBC's and use handle ties 5 #12's and 1 grnd.

Next 2 offices #3 and #4 same way only circuit 2 and 4, but with same lighting circuit.

If I try to catch both offices with (1) 3/4" conduit (Which would hold 10 or 12 #12's easily) I've violated the derating seeing as how there would be at least 10 CCC's which would derate the thhn to 50% and drop me to 15 amp max on the circuits.

Seems Odd

JAP>
 
not a fan of 1/2" homeruns but 3/4 would be an overkill for a max of (7) wires.

JAP>
 
You have 6 circuits. For the MWBC the neutrals are not counted as CCC's so you only would have 6 CCC's.
 
jap said:
If I pull a neutral ro each circuit (to get away from having to use handle ties) looking at 6 #12's and 1 grnd
easily fits in 1/2" emt.

If I wire them as MWBC's and use handle ties 5 #12's and 1 grnd.
Click to expand...
If you wire two of the circuits as an MWBC, then you have 5 circuit conductors, but only 4 current carrying conductors for derating purposes, as the neutral of the MWBC is not counted as a current carrying conductor.

If you put two of these groups together in a single conduit, you'd have 8 current carrying conductors for derating. Or you could combine the remaining two circuits into an MWBC, to reduce the number of current carrying conductors to 6.

Cheers, Wayne
 
jumper said:
I think it would be 8 CCC. OP needs 2 noodles per office and 1 is a CCC.

OP said:
Click to expand...

If they're all going in a common raceway then there must be a junction box at the end of that raceway. His 6 circuits in that raceway, if all MWBC's, would still only be 6 CCC's.
 
5 circuits: 4 office, one lighting*.

2 MWBC for offices - 4 CCC, 2 Neutrals = 6 wires
Branch circuit for lighting - 2 CCC, neutral and hot = 2 wires
or MWBC for lighting - 2CCC, 3 wires
Shared grounds

6 CCC, 9/10 wires. No derating to 50% but I'd go 3/4" conduit.

* Unless I'm misunderstanding jap's post to use circuit #5 for all four offices' lighting.
 
You might be right that there is only one lighting circuit, five circuits total. In my previous example I assumed two lighting circuits. Either way you end up with 6 CCC's. :)
 
Dont like Handle Ties but like pulling a neutral for each circuit even less.

Forgot about cancelling out the neutral on the MWBC.

Cir 5 handles the lighting for both offices so if figured as MWBC's, I'm thinking

Cir 1,3 Neutral
Cir 2,4 Neutral
Cir 5 Neutral

So,,, CCC's=6


JAP>
 
jap said:
Dont like Handle Ties but like pulling a neutral for each circuit even less.

Forgot about cancelling out the neutral on the MWBC.

Cir 5 handles the lighting for both offices so if figured as MWBC's, I'm thinking

Cir 1,3 Neutral
Cir 2,4 Neutral
Cir 5 Neutral

So,,, CCC's=6


JAP>
Click to expand...
...and two 2P handle ties. :angel:
 
Smart $ said:
...and two 2P handle ties. :angel:
Click to expand...
PS: You can add another office receptacle set (and another 2P handle tie) or lighting circuit and still be above the 50% threshold. Size conduit accordingly, but I believe all will fit in a 3/4" EMT.

PPS: What do the plans show?
 
ActionDave said:
I never understood this. It's not hard to pull nine wires in 1/2" emt but it sure is a lot easier to bend, kick, offset and fit them into the panel.
Click to expand...

It's not so much that as it is trying to cover as much ground as possible with the fewest number of pipes coming out of the panel as possible.


JAP>
 
jap said:
It's not so much that as it is trying to cover as much ground as possible with the fewest number of pipes coming out of the panel as possible.


JAP>
Click to expand...
But you still have 5 circuits in one pipe regardless of size, if you want to go more you either need to utilize MWBC's to reduce number of CCC, or uspize conductors which may still work with 3/4" raceway if still limited to 5 circuits, but having to jump to 1" raceway presents more challenges in many cases.
 
Just run 2 pipes. Good lord.


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If this were a single phase sub panel off of a 3 phase multi gang service pack, the MWBC neutral would need to be counted correct??

I am thinking condos or other similar.
 
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