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# Two Circuits can the grounds be twisted together

#1
01-30-12, 06:28 AM
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Two Circuits can the grounds be twisted together

Hello,

I have two seperate circuits coming into a two gang box with two switches. Can the grounds from both circuits be twisted together? If not and I am using 14ga does the box fill for the additional ground then just add 1 to my box fill calculation?

Thanks

#2
01-30-12, 08:18 AM
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I would say that connecting the grounds of two circuits violates 250.120(C) of the NEC, which I believe states that the equipment grounding conductor must be run in the same raceway(or cable) as the circuit it is associated with for lack of better wording. There are a couple exceptions to this rule, but your situation does not appear to meet these exceptions. From a practical standpoint, a fault on one circuit may trip the breaker of the other circuit. I also believe you only have to count the largest equipment grounding conductor in the box needs to be counted.

Mod Note: Code requires all grounds in a box be tied together.

#3
01-30-12, 08:39 AM
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I would say that connecting the grounds of two circuits violates 250.120(C) of the NEC, which I believe states that the equipment grounding conductor must be run in the same raceway(or cable) as the circuit it is associated with for lack of better wording.
Actually just the opposite. All grounds must be connected together. It is conductors that normally carry a current that must be in the same raceway.

250.120(C) Equipment Grounding Conductors Smaller Than
6 AWG. Equipment grounding conductors smaller than
6 AWG shall be protected from physical damage by a race-
way or cable armor except where run in hollow spaces of
walls or partitions, where not subject to physical damage,
or where protected from physical damage.
250.148 Continuity and Attachment of Equipment
Grounding Conductors to Boxes. Where circuit conduc-
tors are spliced within a box, or terminated on equipment
within or supported by a box, any equipment grounding con-
ductor(s) associated with those circuit conductors shall be con-
nected within the box or to the box with devices suitable for
the use in accordance with 250.148(A) through (E).

Last edited by ray2047; 01-30-12 at 09:10 AM.
#4
01-30-12, 11:37 AM
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Location: Central Indiana
Posts: 191
Hmm, doesn't 250.148 refer to conductors of the same circuit that are, say, entering and leaving a box? The words "associated with those circuit conductors" has me thinking that if we are talking about two separate branch circuits that are coming into the same box, is one circuit's EGC really associated with the other circuit conductors? And if the EGC's are tied together won't a fault on one circuit have fault current on both egc's?

#5
01-30-12, 11:41 AM
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Join Date: Jul 2005
Location: Central Indiana
Posts: 191
And 250.120(C) in my 2011 NEC Handbook reads:

Where not routed with circuit conductors as permitted in 250.130(C) and 250.134(B) Exception No. 2, equipment grounding conductors smaller than 6 AWG shall be
protected from physical damage by an identified raceway or
cable armor unless installed within hollow spaces of the
framing members of buildings or structures and where not
subject to physical damage.

#6
01-30-12, 12:16 PM
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Join Date: Mar 2006
Location: USA
Posts: 33,575
Time to wait for the pros but here's some threads to read while waiting.
http://www.doityourself.com/forum/el...-same-box.html
http://www.doityourself.com/forum/el...ing-boxes.html
http://www.doityourself.com/forum/el...-gang-box.html

Last edited by ray2047; 01-30-12 at 02:44 PM.
#7
01-30-12, 01:09 PM
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Location: Central Indiana
Posts: 191
Seems like it is permitted by the Code, but maybe not required. I still think there would be an issue of multiple breakers tripping or even the wrong breaker tripping first.

#8
01-30-12, 05:42 PM
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Location: United States
Posts: 14,840
All grounds are required to be tied together. ( with the exception of isolated ground circuits) The ground wire is not required to be installed inside the raceway with the current carrying conductors.

250.120(c) talks about ground wires smaller #6 needing protection from physical damage (IE: the grounding electrode conductor)

And if the EGC's are tied together won't a fault on one circuit have fault current on both egc's?
Yes! You want as many paths back to the panel to facilitate to operation of the overcurrent device.

Best Code section I have found is 250.148 (2008)

#9
01-30-12, 05:46 PM
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Location: Milwaukee WI
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Well, let's say you've got these two (or three or four) separate circuits in one metal j-box. If you don't have a common ground, to which circuit's ground conductor would you bond the box?

I don't know all the lingo or codes, but my experience is that unless the application calls for an isolated ground, ground conductors shall be bonded together in common.

Why would that have any bearing on breakers tripping? The breakers only carry current passing through the ungrounded conductor. They don't care how the current gets back to ground.

Finally, isn't the point to get the potential down to zero? As a safety matter, if two paths are available, connecting them both together makes it safer, not more dangerous.

Edit: OK, I see Mr. Ironhand weighed in while I was composing my message. Case closed?

#10
01-30-12, 10:24 PM
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caster
Hello,

I have two seperate circuits coming into a two gang box with two switches. Can the grounds from both circuits be twisted together? If not and I am using 14ga does the box fill for the additional ground then just add 1 to my box fill calculation?
250.148 needs to be re-written. It sounds stupid. But to add my .001. In regards to the OP’s question. In your case, you will have to make the EGC permanent and electrically continuous.

In regards to your box fill: Yes, a single volume allowance shall be made for the largest equipment grounding conductor (Bare or green conductor) in your box. Based on the size conductor specified, you shall add, or subtract-depending on how you do your calculation- 2.00 cu inches.

#11
01-31-12, 04:42 AM
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Join Date: Jul 2005
Location: Central Indiana
Posts: 191
Yes, you guys are right, all grounds should be tied together. The faulted ungrounded conductor will be the only ungrounded conductor with any fault current and will only trip that breaker.