grounded conductor

[Dennis Alwon]

240.4 applies to all conductors, including the grounded conductor. The real issue is if the code permits the use of a common grounded conductor outside of the two specific permissions in Articles 215 and 225. It is my opinion that there is no code rule that prohibits the use of common grounded conductors for other applications, but the code making panel does not agree.

Yeah, but we use a common grounded conductor to every sub panel without having to size the conductor on every OCPD so I am not sure why the code panel has a problem with this if the grounded conductor is sized appropriately.

Now if we had to size the ocp according to the rules from the handbook would we every have to size the grounded conductor larger than the feeder?

 

[steelersman]

Yeah, but we use a common grounded conductor to every sub panel without having to size the conductor on every OCPD so I am not sure why the code panel has a problem with this if the grounded conductor is sized appropriately.

Now if we had to size the ocp according to the rules from the handbook would we every have to size the grounded conductor larger than the feeder?

yes but your common grounded conductor in the feeder to a sub-panel is protected and sized per the size of the OCPD and would never have an additive situation on either leg. Unless you put both lines on the same line in the main panel (only giving the sub-panel 120 volts and 2 parallel feeders.

 

[iaov]

I don't believe it is a MWBC if the ungrounded conductors are on the same phase.

Its not!!!!

 

[Strahan]

So my question is what good is the formula dictated in Mike's book if it is not used in the sizing of the grounded conductor? I'm lost here

 

[don_resqcapt19]

Yeah, but we use a common grounded conductor to every sub panel without having to size the conductor on every OCPD so I am not sure why the code panel has a problem with this if the grounded conductor is sized appropriately.

Now if we had to size the ocp according to the rules from the handbook would we every have to size the grounded conductor larger than the feeder?

That feeder grounded conductor to the panel is not a common grounded conductor, it is the grounded conductor of a multiwire circuit.

 

[Dennis Alwon]

That feeder grounded conductor to the panel is not a common grounded conductor, it is the grounded conductor of a multiwire circuit.

Of course that is true...but

There is really nothing in the code, that I know of, that would help us with fixed load of 10 amps for each conductor. Why would we need to size the neutral for 120 amps if they were 20 amp circuits? Why not a 60 amp grounded conductor?

Its not!!!!

No it's not.

Here is the definition of MWBC

Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.

The Op says he has 5 circuits -- Let's assume the following config. A, B, C , A, B. Now how do all of the circuits have voltage between them to meet the definition of MWBC?

 

[Smart $]

The Op says he has 5 circuits -- Let's assume the following config. A, B, C , A, B. Now how do all of the circuits have voltage between them to meet the definition of MWBC?

voltage between conductors					
	A	B	C	A	B
A	—	208	208	0	208
B		—	208	208	0
C			—	208	208
A				—	208
B					—
N	120	120	120	120	120

 

[Smart $]

...It is my opinion that there is no code rule that prohibits the use of common grounded conductors for other applications, but the code making panel does not agree.

I agree

 

[Smart $]

So my question is what good is the formula dictated in Mike's book if it is not used in the sizing of the grounded conductor? I'm lost here

When it comes to sizing the grounded conductor, that formula AFAIK never comes into play. I could answer "what good is it...?" but that would take this thread even further off-topic. Perhaps you should ask your question in a new thread...

 

[Strahan]

If it is a multiwire branch circuit then the grounded conductor size is based on the largest device that protects any one of the phases as that is the maximum unbalanced current. Again no calculations are required to size this conductor.

Ok I'm having trouble with this one. Lets say I have a 4-wire 3phase wye config and off of L1 I have 4 circuits each seperatly protected (15Abreaker) and a load of 10amps each. Off of L2 I have 2 circuits each seperatly protected(15A brkr) and a load of 10amps each. Off of L3 I have 3 circuits each seperatly protected(15Abrkr) and a load of 10amps each.

Total load L1=40amps
Total Load L2=20amps
Total Load L3=30amps
Maximum size OCPD is 15amp Breaker because the loads are seperated on each phase.
This would be a MWBC common grounded conductor to all.
If I simply size my grounded conductor to maximum OCPD it would be sized for 15amps. After calculations I find the grounded conductor will acyually be carrying 17.33amps.

OH NO think I got the answer all loads on each phase if part of a MWBC must be protected by one OCPD not seperated as I did. If this is correct then I just got a little smarter please let me know and if this is correct your statement makes complete sense!!! Thanks

 

[Smart $]

there not all on the same phase - i would say that there will be 2 on " A " phase, 2 on " B " phase and 1 on " C " phase

Please elaborate on the details of your situation...

You said the last light is x' away from the panel. How near is the first, how many total, the distance between each, and are any branched (i.e. circuit runs in two or more directions)? This is to better determine, perhaps, the voltage drop and other possible options. Also, how likely is it that the lights of all 5 circuits will not always be on (and off) concurrently (with the exception of switching delays)?

Somewhere you said you had other conduits run as spares. Are any of these available if need be?

Is the entire circuit(s) run underground or only the home run?

 

[Smart $]

Ok I'm having trouble with this one. Lets say I have a 4-wire 3phase wye config and off of L1 I have 4 circuits each seperatly protected (15Abreaker) and a load of 10amps each. Off of L2 I have 2 circuits each seperatly protected(15A brkr) and a load of 10amps each. Off of L3 I have 3 circuits each seperatly protected(15Abrkr) and a load of 10amps each.

Total load L1=40amps
Total Load L2=20amps
Total Load L3=30amps
Maximum size OCPD is 15amp Breaker because the loads are seperated on each phase.
This would be a MWBC common grounded conductor to all.
If I simply size my grounded conductor to maximum OCPD it would be sized for 15amps. After calculations I find the grounded conductor will acyually be carrying 17.33amps.

OH NO think I got the answer all loads on each phase if part of a MWBC must be protected by one OCPD not seperated as I did. If this is correct then I just got a little smarter please let me know and if this is correct your statement makes complete sense!!! Thanks

The actual load don't matter [AFAIK except for outdoor lighting equipment?225.7(B)].

All ocpd's are 15 amp. L1 has 4. Maximum unbalanced neutral current is 4 ? 15 = 60A, the required ampacity of a common neutral.

 

[steelersman]

Ok I'm having trouble with this one. Lets say I have a 4-wire 3phase wye config and off of L1 I have 4 circuits each seperatly protected (15Abreaker) and a load of 10amps each. Off of L2 I have 2 circuits each seperatly protected(15A brkr) and a load of 10amps each. Off of L3 I have 3 circuits each seperatly protected(15Abrkr) and a load of 10amps each.

Total load L1=40amps
Total Load L2=20amps
Total Load L3=30amps
Maximum size OCPD is 15amp Breaker because the loads are seperated on each phase.
This would be a MWBC common grounded conductor to all.
If I simply size my grounded conductor to maximum OCPD it would be sized for 15amps. After calculations I find the grounded conductor will acyually be carrying 17.33amps.

OH NO think I got the answer all loads on each phase if part of a MWBC must be protected by one OCPD not seperated as I did. If this is correct then I just got a little smarter please let me know and if this is correct your statement makes complete sense!!! Thanks

I hate to say this but in this example you described you have a total of 9 circuits. In this case it would be best to split them evenly amongst the 3 phases (legs). So you would have 3 circuits on each leg. Then if only one grounded conductor (neutral) for all it would need to be rated for 45 amps (3 x 15amp OCPD) per phase (leg).

 

[Strahan]

I hate to say this but in this example you described you have a total of 9 circuits. In this case it would be best to split them evenly amongst the 3 phases (legs). So you would have 3 circuits on each leg. Then if only one grounded conductor (neutral) for all it would need to be rated for 45 amps (3 x 15amp OCPD) per phase (leg).

Yes I agree I personally would never do this I was just trying to throw a wrench into the mix. Don stated earlier size the grounded conductor to the highest OCPD and in the case I made the highest OCPD was 15amp. Now if you have to add all the OCPD's up per phase and size from there I understand but that was not the way I took Don's message. Plus I'm still sweating from Sunday night game

 

[steelersman]

Yes I agree I personally would never do this I was just trying to throw a wrench into the mix. Don stated earlier size the grounded conductor to the highest OCPD and in the case I made the highest OCPD was 15amp. Now if you have to add all the OCPD's up per phase and size from there I understand but that was not the way I took Don's message. Plus I'm still sweating from Sunday night game

no worries here. The Steelers didn't want to win because they don't want home field advantage because they play better on the road. They're happy enough having a first round bye.

 

[Strahan]

no worries here. The Steelers didn't want to win because they don't want home field advantage because they play better on the road. They're happy enough having a first round bye.

You're taking it better than most guys I work with. Good luck

 

[eager2learn]

The first light is located approximately 350' away - the last is located 575' away - there are 33 light fixtures - all conduit is underground and all the spares are being used. There are 2 branch circuits located in this area. Both circuits are 20amps and the circuits both draw approximately 7.8 amps

 

[Smart $]

The first light is located approximately 350' away - the last is located 575' away - there are 33 light fixtures - all conduit is underground and all the spares are being used. There are 2 branch circuits located in this area. Both circuits are 20amps and the circuits both draw approximately 7.8 amps

Still need some more clarification...

Are the two branch circuits included in the five you need to run (3 new + 2 existing) or are all five new circuits and the existing two individually are only representative of each new one (5 new).

How many light fixtures are connected to each circuit?

If all underground, except at the last light, is there one conduit coming up and one going down at each light fixture but the last?

Again I ask, how likely is it that the lights of all 5 circuits will always be on (and off) concurrently (with the exceptions of switching delays, expired lamps, circuit faults, etc.)?

 

[don_resqcapt19]

Yes I agree I personally would never do this I was just trying to throw a wrench into the mix. Don stated earlier size the grounded conductor to the highest OCPD and in the case I made the highest OCPD was 15amp. Now if you have to add all the OCPD's up per phase and size from there I understand but that was not the way I took Don's message. Plus I'm still sweating from Sunday night game

Maybe my post was not clear...the common grounded conductor must be sized to the highest total of the OCPDs on any single phase.

 

[tom baker]

The coloration thing is bogus. It does not exist.

For this post, yes. But 200.6(D) requires grounded conductors of different systems to be identified with a stripe, not green, if in the same raceway, cable, box, etc.