Grounding multiple circuits

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sfav8r

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San Francisco Bay Area
I need to run 6 circuits to a kitchen that is being remodeled. Rather than run 6 runs of 12/2 MC, I'd like to run all the circuits in one larger MC to a junction box (approx 50 feet from the panel) then continue from the junction box with NMC.

I would run a single ground in the MC and tie it to the 6 grounds coming from the individual circuits.


Any problem with this?

Thanks for your input.
 
Re: Grounding multiple circuits

Should not be a problem as long as you take into account all applicable Code rules. But you must always take all the rules into account.

In addition to 250.122(C) mentioned, remember the rules for more than 3 current-carrying conductors in a raceway or cable.
 
Re: Grounding multiple circuits

I'm a little confused, to get (6) 120 v 20 amp circuits to the kitchen on a single phase service (three phase too) would take in the least 7 conductors excluding an EGC.

This would even be contested by some in that we could not size one neutral to accommodate the accumulative current of one leg which would be a #6. (I say it is permitted)

This would mean that the very minimum number of conductors in this MC would be 9, once again excluding the EGC.

Does any manufacturer make 12/9 w g MC?

Roger

[ October 13, 2004, 08:50 PM: Message edited by: roger ]
 
Re: Grounding multiple circuits

I would guess this person means FMC.

Does any manufacturer make 12/9 w g MC?
Click to expand...
You can get any MC you are willing to buy enough of. :p

AFC cable systems I believe makes a 10/26 MC. :cool:

Around here I can get 12/8 or 10/8 or 10/2-10/2-10/2 MC next day.

12/8 has 6 hots, 2 Neutrals and one or two grounds. Two 3 phase multiwire circuits with or without isolated ground.

10/2-10/2-10/2 is 3 hots, 3 neutrals with or without isolated ground.
 
Re: Grounding multiple circuits

Bob, I have been educated. I have used 500/4 but never 10/2-10/2-10/2. :)

Roger
 
Re: Grounding multiple circuits

If the 6 circuits were required to be 20A rated, wouldn't the 10 or so conductors be required to be #10, due to derating(80% for the 6 current carrying)? :confused:
 
Re: Grounding multiple circuits

Originally posted by roger:
Bob, I have been educated. I have used 500/4 but never 10/2-10/2-10/2. :)

Roger
Click to expand...
We will always get it in solid getting it in a box is always tough but 500/4 would be a little harder.

AFC Cable

AFC Catalog pdf

Page 21 has the home run cable listed as in stock up to 10/16. It looks like 10/22 is available special order.

It is heavy though, the spools of 10/8 are 600 lbs + spool.
 
Re: Grounding multiple circuits

Thanks for all the input. It has been very helpful.

Regarding the derating, I am assuming the following:

There will be the appliance circuits which will be 4 conductors (2 hot, 2 neutral).

Two lighting circuits with a common neutral which therefore count as two conductors.

The EGC does not count for derating.

A dishwasher & disposal with a common neutral. And a hood, neither of which count in the conductor count because of 310.15 Exception 1 - "Where conductors of different systems, as provided in 300.3, are installed in a common raceway or cable, the derating factors shown in table 310.15 (B)(2)(a) shall apply to the number of power and lighting conductors only."

I assume this is because the lighting and power circuits are considered to more continuous whereas the the other circuits are not.

Given the above, I would derate the #12 (25 amp capacity) to 80% as the current carrying conductors will be 6. This would mean that the max is 20amp which the #12 is already derated to anyway.

Can anyone confirm or dispute this?
 
Re: Grounding multiple circuits

how many different 'systems' do you have in that raceway?
if they are all fed from the same panel, then there are only 'conductors from one system'

that exception refers to running control wiring (or something similar) with power wiring and it says you dont have to count anything but your power for purposes of derating
 
Re: Grounding multiple circuits

IMO you have 8 current carrying conductors.

The two small appliance circuits. 4

The two lighting circuits. 2

The hood, dishwasher & disposal. 2

I would suggest using 12 AWG THHN.

12 AWG THHN is rated 30 Amps Table 310.16

8 current carrying conductors get 70% Adjustment Table 310.15(B)(2)(a)

30 x .7 = 21 amps.

I assumed all 12 AWG but it will work if some are 14 AWG THHN also.
 
Re: Grounding multiple circuits

Thanks again. I misread the table at 25a instead of 30a. The #12 will do just fine even though there are 8 condctors.

Thanks again for all your input. This forum is a great tool. I hopefully can return the favor!

[ October 16, 2004, 06:30 PM: Message edited by: sfav8r ]
 
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