# Grounding seperate circuits together

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#### steelbuster

##### Member
I know I've seen these two topics somewhere but I can't find them now. Maybe a pointer to a thread or an answer.
1: In residential single phase service, is it good practice to pigtail the grounds from separate circuits, in the same J box, all together? Is there code or theory one way or the other?

2: Explain how overvoltage can occur on a 110v multiwire circuit if neutrals are not pigtailed through at each receptacle installation.

Thanks

#### raider1

##### Senior Member
Staff member
I know I've seen these two topics somewhere but I can't find them now. Maybe a pointer to a thread or an answer.
1: In residential single phase service, is it good practice to pigtail the grounds from separate circuits, in the same J box, all together? Is there code or theory one way or the other?

250.148 requires that where circuit conductors are spliced within a box or connected to equipment within or supported by a box the EGCs associated with those circuit conductors shall be connected within the box or to the box.

2: Explain how overvoltage can occur on a 110v multiwire circuit if neutrals are not pigtailed through at each receptacle installation.

Thanks

When a Neutral is lost in a multiwire branch circuit then the loads become in series with the ungrounded conductors. This means that we have a 230 volt series circuit and the voltage in a series circuit is additive. So the voltage at each load will depend on the resistance and the total current of the circuit.

Chris

#### augie47

##### Moderator
Staff member
I know I've seen these two topics somewhere but I can't find them now. Maybe a pointer to a thread or an answer.
1: In residential single phase service, is it good practice to pigtail the grounds from separate circuits, in the same J box, all together? Is there code or theory one way or the other?
It is good practice and a Code requirement {300.13(B)}
2: Explain how overvoltage can occur on a 110v multiwire circuit if neutrals are not pigtailed through at each receptacle installation.

Thanks
There have been some posts that explain that better than I can and I Will see if I can find one, but basically it has to do with the resistance of the load and with an open neutral, the loads are basically connected across the 240 volt source and the voltage at each is Dependant on the resistance in the circuit. An ohms' law application.

Note that Chris posted as I was typing and the two posts point out the importance of terminology. In the original post you used the word "ground". Chris correctly answered referring to an "equipment grounding conductor". I answered assuming you were speaking of the grounded conductor, or neutral.
It emphasizes how important terminology is with the Code.

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#### steelbuster

##### Member
Thanks for the quick answers. Just as soon as I posted the question I found the old Power point by 480sparky on multiwire curcuits and saved it to my desktop.
Thanks.

#### steelbuster

##### Member
In rereading the code I'm reminded of the old discussion I recall about 250.148. Is it saying to tie the ECG's from a particular circuit togeather, or ALL ECG's from ALL circuits in the box togeather?

#### jumper

##### Senior Member
In rereading the code I'm reminded of the old discussion I recall about 250.148. Is it saying to tie the ECG's from a particular circuit togeather, or ALL ECG's from ALL circuits in the box togeather?

If there are splices or connections, then yes, all EGCs are connected together, an isolated ground is an exception. Pull boxes without splices are different also.

#### jwjrw

##### Senior Member
What if its in a pvc box? I always do but I saw several on a job I went on and it passed. They had to move the panel and at least 10 cicruits were put in a 12x12 pvc jbox. Maybe the inspector didnt look.

#### raider1

##### Senior Member
Staff member
What if its in a pvc box? I always do but I saw several on a job I went on and it passed. They had to move the panel and at least 10 cicruits were put in a 12x12 pvc jbox. Maybe the inspector didnt look.

Yes, if the circuit conductors are spliced in the PVC box then all associated EGC's would need to be connected together.

This requirement is not always well known by inspectors and can be overlooked.

Chris

#### jwjrw

##### Senior Member
Yes, if the circuit conductors are spliced in the PVC box then all associated EGC's would need to be connected together.

This requirement is not always well known by inspectors and can be overlooked.

Chris

I thought so and was taught by my dad to do that but what art states this.

#### raider1

##### Senior Member
Staff member
I thought so and was taught by my dad to do that but what art states this.

250.148.

250.148 Continuity and Attachment of Equipment Grounding Conductors to Boxes.
Where circuit conductors are spliced within a box, or terminated on equipment within or supported by a box, any equipment grounding conductor(s) associated with those circuit conductors shall be connected within the box or to the box with devices suitable for the use in accordance with 250.148(A) through (E).
Exception: The equipment grounding conductor permitted in 250.146(D) shall not be required to be connected to the other equipment grounding conductors or to the box.

Chris

#### jwjrw

##### Senior Member
I read that but the phrase "to the box" made me think they meant to bond the box to all grounds. Wording is kinda confusing.

#### raider1

##### Senior Member
Staff member
I read that but the phrase "to the box" made me think they meant to bond the box to all grounds. Wording is kinda confusing.

If it is a metal box then you are correct.

"any equipment grounding conductor(s) associated with those circuit conductors shall be connected within the box or to the box"

It also says connected within the box OR to the box. So in the case of a PVC box the EGCs must be connected together within the box.

Chris

#### steelbuster

##### Member
Hmmm. I too moved a panel a while back and used a PVC Jbox for about 8 circuits. I did not tie all EGC's together and it passed, but now I believe I will do so in the future in spite of what I see as fairly ambiguous language.
My question stemmed from seeing many remodel jobs with new circuits pulled into existing boxes that do not have the ECG's tied to the old circuit. Seems like a good idea to do it and I was SURE there was some obscure bit of code that said not to do it.... wrong as usual....

#### LarryFine

##### Master Electrician Electric Contractor Richmond VA
Explain how overvoltage can occur on a 110v multiwire circuit if neutrals are not pigtailed through at each receptacle installation.
Another way to look at it is that the neutral conducts current in order to keep the load neutral point voltage at zero (relative to the supply neutral point.)

The amount of neutral current depends on the load difference on each line, which depends on what the voltage imbalance would be if the neutral was opened.

#### jwjrw

##### Senior Member
If it is a metal box then you are correct.

"any equipment grounding conductor(s) associated with those circuit conductors shall be connected within the box or to the box"

It also says connected within the box OR to the box. So in the case of a PVC box the EGCs must be connected together within the box.

Chris

I did see the or and knew deep down it was so but it could be stated better.

#### John120/240

##### Senior Member
multiple grounds ?

multiple grounds ?

Say you had a 12 X 12 metal J-box with 12ea 12-2 MC cables. Of course you bond the J-box: which method is best: to land all grounds on a ground bus
mounted to the box, or just wire nut each ground to its mate.
Thank You

#### raider1

##### Senior Member
Staff member
Say you had a 12 X 12 metal J-box with 12ea 12-2 MC cables. Of course you bond the J-box: which method is best: to land all grounds on a ground bus
mounted to the box, or just wire nut each ground to its mate.
Thank You

To comply with 250.148, the easiest way would be with a ground bus connected to the metal box.

You could not just wirenut the equipment grounding conductor to just its mate. You would need to splice ALL the equipment grounds together and then make a connection to the box.

Chris

#### RETRAINDAILY

##### Senior Member
Imo green always go green unless there is a stripe.

#### raider1

##### Senior Member
Staff member
Imo green always go green unless there is a stripe.

Are you saying that it is not OK to connect the EGC's to a ground bus attached to the 12X12 J-box?

Chris

#### SPARKS40

##### Member
This topic brings up another question. I need to run four 20 amp circuits through a 3/4 PVC conduit. I intend to pull an individual neutral for each circuit, going to a J-box in the attic, and branching out with NM from there. Is there a limit to how many circuits may share a single ground wire if i only pull one?

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