grounded conductor

[eager2learn]

so how do i calculate the feeders and branch circuits combined to equal 5% which is suitable effeciency - what i mean is it the same formula for voltage drop - right now the contractor is ready to run #8 for all homeruns and # 10 to all branch circuits - the average for all circuits to be installed as far as length is approx. 425' - i know it's crazy but i'm not an engineer you know

 

[peter d]

the total amperage of the circuit is 7.8 amps and the voltage is 120.

What type of lights are they? HID?

 

[brother]

so how do i calculate the feeders and branch circuits combined to equal 5% which is suitable effeciency - what i mean is it the same formula for voltage drop - right now the contractor is ready to run #8 for all homeruns and # 10 to all branch circuits - the average for all circuits to be installed as far as length is approx. 425' - i know it's crazy but i'm not an engineer you know

as someone stated, you might need a transformer, (ie buck boost) to get past this voltage drop if this is such an issue. Thats the only less EXPENSIVE way I can see this working.

 

[K8MHZ]

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

In a 120/240 single phase residential system a single neutral MWBC both the ungrounded conductors are on the same phase along with the grounded neutral.

If not, there would have to be some means to add a phase to a single phase system, which in most of the homes I have been in, there is not.

 

[infinity]

In a 120/240 single phase residential system a single neutral MWBC both the ungrounded conductors are on the same phase along with the grounded neutral.

If not, there would have to be some means to add a phase to a single phase system, which in most of the homes I have been in, there is not.

Here's the definition of a MWBC from Article 100:

Article 100, 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.

For this discussion the meaning the terms "on the same phase" implies that there is no voltage between the two conductors which may or may not be the case in a 120/240 volt system.

 

[ronaldrc]

You can have a neutral or grounded conductor the same size as the ungrounded conductors as long as they are on different ungrounded lines of that system.

Three phase one on line #1, one on Line #2, one on line #3 to one grounded conductor.

Single phase one on Line #1 and one on line #2 to one grounded conductor.



You can not have a common neutral of same size as the
ungrounded conductors if on the same line of a system.


Just in case someone is confusing single phase with multiphase systems.

If your talking about single phase its not Phase #1 and phase #2
its line #1 and line #2 there both the same phase.

 

[eager2learn]

so on a three phase system what you are saying is that " A " phase, " B " phase, and " C" phase all share one Neurtal = correct - so my question is can I add another hot leg to any one of the three phases putting two seperate ungrounded conductors on the same phase and the remaing two circuits each on thier own witn one grounded conductor for all. If so I presume that the grounded conductor needs to be sized accordingly. Does anyone know how to calculate load center of a circuit ?

 

[Strahan]

so on a three phase system what you are saying is that " A " phase, " B " phase, and " C" phase all share one Neurtal = correct - so my question is can I add another hot leg to any one of the three phases putting two seperate ungrounded conductors on the same phase and the remaing two circuits each on thier own witn one grounded conductor for all. If so I presume that the grounded conductor needs to be sized accordingly. Does anyone know how to calculate load center of a circuit ?

Share the same neutral as long as it is a wye configuration 4-wire. if it is if I'm following what you have just said it sounds to me like you are now making it a mwbc. What types of voltages 120/208 perhaps? Chances are you will have an unbalanced load calculate neutral(grounded conductor) current as follows: square root of (L1^2+L2^2+L3^2)-[(L1*L2)+(L2*L3)+(L1*L3)] L1,L2 and L3 representing the current through each leg.

 

[quogueelectric]

so on a three phase system what you are saying is that " A " phase, " B " phase, and " C" phase all share one Neurtal = correct - so my question is can I add another hot leg to any one of the three phases putting two seperate ungrounded conductors on the same phase and the remaing two circuits each on thier own witn one grounded conductor for all. If so I presume that the grounded conductor needs to be sized accordingly. Does anyone know how to calculate load center of a circuit ?

As long as you use DIFFERENT phases you can use the shared neutral without upsizing it.They must be together on a 2 pole breaker though. For example of 20 a lighting ckts you could not use ckt 1 and 7 without upsizing the neutral to handle 40 a of current. You could however use ckts 1 and 3 and install a 2pole breaker with a common 20 a neutral. Just change the circuit number and notify the architect to the change.

 

[Strahan]

Share the same neutral as long as it is a wye configuration 4-wire. if it is if I'm following what you have just said it sounds to me like you are now making it a mwbc. What types of voltages 120/208 perhaps? Chances are you will have an unbalanced load calculate neutral(grounded conductor) current as follows: square root of (L1^2+L2^2+L3^2)-[(L1*L2)+(L2*L3)+(L1*L3)] L1,L2 and L3 representing the current through each leg.

Sorry 208/120 my bad I don't want eaten alive

 

[eager2learn]

so lets say i have 6 ungrounded conductors that i want to share with with one grounded conductor - as long as i add the total amperage for each phase combined and size the grounded conductor to that total - i can utilize this type of installation.

 

[Strahan]

so lets say i have 6 ungrounded conductors that i want to share with with one grounded conductor - as long as i add the total amperage for each phase combined and size the grounded conductor to that total - i can utilize this type of installation.

What do you mean by 6 ungrounded would that be 2 ungrounded conductors per phase? In order to calculate the neutral that would be present on the neutral(grounded conductor) you would use the formula I put in previous post. If the loads are all equal which I highly doubt giving atleast wire length then current would be zero, but it won't be so use the formula.

 

[eager2learn]

What do you mean by 6 ungrounded would that be 2 ungrounded conductors per phase? In order to calculate the neutral that would be present on the neutral(grounded conductor) you would use the formula I put in previous post. If the loads are all equal which I highly doubt giving atleast wire length then current would be zero, but it won't be so use the formula.

so pretty much if i wanted to try to balance the phases - 3 phase 120/208 = A, B, and C phase - i need to move the branch circuit's from one phase to the other which i assume is what the formula does. so can you explain in more detail what the formula means

 

[Strahan]

so pretty much if i wanted to try to balance the phases - 3 phase 120/208 = A, B, and C phase - i need to move the branch circuit's from one phase to the other which i assume is what the formula does. so can you explain in more detail what the formula means

Yes you would want to balance the load as much as possible. Just as an example lets say I have 3 loads current on each load equalling 20amps. I would want to run one load off of L1 the other off of L2 and finnally the last load off of L3 all with a common neutral (grounded conductor) this would be your mwbc. Also this would be a 4-wire 3phase circuit. Now what really takes place (the identically balanced loads are just an imagination) is the neutral conductor will carry the unbalanced current determined by the formula : Square root of [(L1^2+L2^2+L3^2)-[(L1*L2)+(L2*L3)+(L1*L3)]] Determine what your loads are determine the current draw for each L1=Current on phaseA, L2=Current on PhaseB, L3=Current on PhaseC. Your answer will be the expected current on the neutral you would size appropriatly.

 

[infinity]

Are you trying to do something like this from the NECH and Bob:

Exhibit 225.3 A 120/240-volt, single-phase, 3-wire system (branch circuits rated at 20 amperes; maximum unbalanced current of 80 amperes).

 

[Dennis Alwon]

so lets say i have 6 ungrounded conductors that i want to share with with one grounded conductor - as long as i add the total amperage for each phase combined and size the grounded conductor to that total - i can utilize this type of installation.

If all 6 ungrounded conductors where on the same phase then yes you would need a wire capable to carry the 120 amp load. If this were a 3 phase panel with 2 ungrounded conductors per phase (a, b, c, a, b, c) then you would only need a grounded conductor with an ampacity of 40 amps.
If you had a single phase panel with 3 ungrounded conductor per phase (a,b, a,b,a,b) then you would need a grounded conductor of 60 amps.

 

[Strahan]

I guess the real question is unless I missed it is this a single phase 3-wire system or is it a 4-wire three phase system? I thought he mentioned 208V somewhere.

 

[steelersman]

As long as you use DIFFERENT phases you can use the shared neutral without upsizing it.They must be together on a 2 pole breaker though. For example of 20 a lighting ckts you could not use ckt 1 and 7 without upsizing the neutral to handle 40 a of current. You could however use ckts 1 and 3 and install a 2pole breaker with a common 20 a neutral. Just change the circuit number and notify the architect to the change.

sure you could use circuit 1 and 7 without upsizing the neutral, 1 and 7 would be on seperate legs, you just couldn't use a handle tie or a 2 pole breaker. But keep in mind he's on a 3 phase panel not a single phase.

 

[steelersman]

I guess the real question is unless I missed it is this a single phase 3-wire system or is it a 4-wire three phase system? I thought he mentioned 208V somewhere.

3 phase 120/208 panel

 

[steelersman]

Are you trying to do something like this from the NECH and Bob:

Exhibit 225.3 A 120/240-volt, single-phase, 3-wire system (branch circuits rated at 20 amperes; maximum unbalanced current of 80 amperes).

he's using 3 phase 120/208 panel