A light switch box has two circuits connected in the box - one for a light, another for switched receptacles. Do the grounds for the separate circuits have to be tied together? I think they do based on 250.148 and 250.96. The contractor says he has never connected these together in the past.
Connecting grounds - separate circuits
- Thread starter kar108
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peter d
Senior Member
- Location
- New England
Re: Connecting grounds - separate circuits
Yes.
Yes.
electricmanscott
Senior Member
- Location
- Boston, MA
- Occupation
- Massachusetts Master Electrician, one man show.
Re: Connecting grounds - separate circuits
I don't see how those two articles apply.
I always thought they must be tied together but I can't find anything to tell me this.
I don't see how those two articles apply.
I always thought they must be tied together but I can't find anything to tell me this.
peter d
Senior Member
- Location
- New England
Re: Connecting grounds - separate circuits
Scott, I think 250.148 is very poorly written, and even a bit confusing. But that is the code section that would require this.
I agree with you about 250.96. I don't see the relevance.
[ October 19, 2005, 05:06 PM: Message edited by: peter d ]
Scott, I think 250.148 is very poorly written, and even a bit confusing. But that is the code section that would require this.
I agree with you about 250.96. I don't see the relevance.
[ October 19, 2005, 05:06 PM: Message edited by: peter d ]
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: Connecting grounds - separate circuits
I agree with Scott I don't see how 250.148 would apply either. It does not say that they must be connected together.
I agree with Scott I don't see how 250.148 would apply either. It does not say that they must be connected together.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Connecting grounds - separate circuits
This is exactly the citation I would be given were I not to bond together all the EGCs present in a j-box.
The image I like that conveys the idea inherent in 250.148 is that EGCs form a web or mesh that decreases the impedance. EGCs are, if possible by the wiring layout, not to be kept as spokes on a wheel.
Edit syntax - Al
[ October 19, 2005, 06:29 PM: Message edited by: al hildenbrand ]
How does it this not apply?
This is exactly the citation I would be given were I not to bond together all the EGCs present in a j-box.
The image I like that conveys the idea inherent in 250.148 is that EGCs form a web or mesh that decreases the impedance. EGCs are, if possible by the wiring layout, not to be kept as spokes on a wheel.
Edit syntax - Al
[ October 19, 2005, 06:29 PM: Message edited by: al hildenbrand ]
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Connecting grounds - separate circuits
I think it does.
250.148 talks about circuit conductors terminating within the box. That much is clear enough. What it doesn't do is say anything about more than one circuit terminating within the same box. That is where it may get confusing.
But look at the following words from 250.148, and note my bold and all-caps emphasis:
I think it does.
250.148 talks about circuit conductors terminating within the box. That much is clear enough. What it doesn't do is say anything about more than one circuit terminating within the same box. That is where it may get confusing.
But look at the following words from 250.148, and note my bold and all-caps emphasis:
OK, so you have four circuit conductors (phase and neutral for circuit #1, phase and neutral for circuit #2). What this tells me is that ALL EGCs associated with any of the four circuit conductors must be spliced. In other words, both EGCs must be spliced.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Connecting grounds - separate circuits
Saints preserve us!
Saints preserve us!
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Connecting grounds - separate circuits
Yow!!!
Yow!!!
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: Connecting grounds - separate circuits
So if the two circuits, say a 277 volt lighting circuit and a 120 volt receptacle circuit originated from two separate panelboards you would still tie them together?
electricmanscott
Senior Member
- Location
- Boston, MA
- Occupation
- Massachusetts Master Electrician, one man show.
Re: Connecting grounds - separate circuits
Yeah guys like I said 250.148. I see it now. What helps to clarify is the exception which specifies what is not required to be connected to those grounding conductors. Thanks again NEC word smiths. :roll:
Yeah guys like I said 250.148.
I see it now. What helps to clarify is the exception which specifies what is not required to be connected to those grounding conductors. Thanks again NEC word smiths. :roll:
peter d
Senior Member
- Location
- New England
Re: Connecting grounds - separate circuits
Yes, there is no exception or distinction made for different voltages and/or different sources.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Re: Connecting grounds - separate circuits
I would, just as two circuits or voltages sharing a metal-box-and-conduit system would.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Connecting grounds - separate circuits
kar108,
Consider a simplistic example of four 12/2 NMB branch circuits running 100' from their overcurrent protective devices (OCPDs) to a 4 gang switch box. Then, another 10' to 4 different loads.
When the EGCs are kept segregated, and a ground fault at one load occurs, the return path to the panel with the OCPDs is through one #12 all the way.
When the EGCs are spliced together, and a ground fault at one load occurs, the return path to the panel with the OCPDs is through one #12 for 10' and through four paralleled #12 for 100'.
The more interconnection points between EGCs, the more likely the reduction of the overall impedance in a fault situation.
Edit syntax - Al
[ October 20, 2005, 12:07 AM: Message edited by: al hildenbrand ]
kar108,
Consider a simplistic example of four 12/2 NMB branch circuits running 100' from their overcurrent protective devices (OCPDs) to a 4 gang switch box. Then, another 10' to 4 different loads.
When the EGCs are kept segregated, and a ground fault at one load occurs, the return path to the panel with the OCPDs is through one #12 all the way.
When the EGCs are spliced together, and a ground fault at one load occurs, the return path to the panel with the OCPDs is through one #12 for 10' and through four paralleled #12 for 100'.
The more interconnection points between EGCs, the more likely the reduction of the overall impedance in a fault situation.
Edit syntax - Al
[ October 20, 2005, 12:07 AM: Message edited by: al hildenbrand ]
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Connecting grounds - separate circuits
The fact that there is a connection from the EGC splice point back to the 120 volt source does not alter the path I describe above. Nor does it create a second path for fault current. The 120 V source is not providing current to the fault point, so no fault current will flow back to the 120 V source.
Bottom line: Yes you do splice the EGCs for both systems.
To what the others have responded, I will add this: If there were a fault on a 277 volt load, there would be a path for fault current from the 277 volt source, to the fault point, via the individual 277 V load's EGC to the point at which the EGCs are spliced, and from there back to the 277 V source. That would trip the 277 V breaker.
The fact that there is a connection from the EGC splice point back to the 120 volt source does not alter the path I describe above. Nor does it create a second path for fault current. The 120 V source is not providing current to the fault point, so no fault current will flow back to the 120 V source.
Bottom line: Yes you do splice the EGCs for both systems.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Connecting grounds - separate circuits
The main bonding jumpers aren't connecting to the same GES in most buildings?
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Connecting grounds - separate circuits
Sorry, I wasn't clear. I intended that to mean that there will not be a fault current path that involves the 120 volt source. I was addressing infinity's apparent concern about an inadvertent connection of two power sources.
You are right that there will be a second fault path that involves the 120 volt panel's ground bus, GEC, the combined GES, and the 277 volt panel's GEC.
Sorry, I wasn't clear. I intended that to mean that there will not be a fault current path that involves the 120 volt source. I was addressing infinity's apparent concern about an inadvertent connection of two power sources.
You are right that there will be a second fault path that involves the 120 volt panel's ground bus, GEC, the combined GES, and the 277 volt panel's GEC.
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