100 Branch Circuit, Multiwire.

fmtjfw

Senior Member
Section/Paragraph: 100 Branch Circuit, Multiwire.

Deleted Text

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.

Substantiation:

With the word "equal" this definition excludes a 3- or 4-wire center-grounded delta circuit as a multiwire circuit. It does not exclude a center tap grounded single phase, three phase corner grounded delta, or a two or three phase wye circuit or a center tap grounded 3 wire DC circuit. Is this omission on purpose?
 

infinity

Moderator
Staff member
Location
New Jersey
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Journeyman Electrician
Why would you want to exclude MWBC from the center tapped portion of a 3?, 4Wire Delta system?
 

fmtjfw

Senior Member
Why would you want to exclude MWBC from the center tapped portion of a 3?, 4Wire Delta system?
The definition currently does not exclude the center tapped portion of a 3?, 4Wire Delta system from being a multiwire circuits. Assume the wild leg is "B" and the legs on either side of the center tap are "A" and "C". The "equal" word causes A-B-C-N, A-B-N, and B-C-N not to be multiwire circuits. Only A-C-N is a multiwire under the current definition.

I'm suggesting deletion of the word "equal" so that all the circuits stated above are also multiwire circuits.

Sounds like I need to expand the substantiation!
 

hurk27

Senior Member
I would believe it was intentional to not include the "B" phase in a multi-wire circuit on a 4 wire high leg delta, using the "B" phase when sharing the neutral would no longer be a balanced neutral system and the current would become a vector additive to the other phase's neutral current which could lead to an over loaded neutral if the installer did not account for this, at least this is what I been told, also the "B" phase was never intended to be used for neutral loads in the design of this type of service, in most cases the transformers are sized for the single phase loads and the three phase loads by having one tank larger then the other.
 

ActionDave

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Location
Durango, CO, 10 h 20 min without traffic from wing
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wire pulling grunt
.....
I'm suggesting deletion of the word "equal" so that all the circuits stated above are also multiwire circuits.
I don't know but I have a feeling the definition is written the way for the exact reason of excluding the kind of circuits you want to include.
Sounds like I need to expand the substantiation!
Seems like you need a good reason wire up anything using one of those circuits.

Looks like Hurk agrees with me but he makes a stronger case.
 
Last edited:

fmtjfw

Senior Member
Second version of proposal

Second version of proposal

Section/Paragraph: 100 Branch Circuit, Multiwire.

Deleted Text

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.

Substantiation:

The definition as currently written defines the following to be MWBCs:

1? grounded center-tapped neutral circuits (e.g.: 120/240V)
3? 3- and 4-wire wye-connected circuits containing a neutral (A-B-N, A-C-N, B-C-N, and A-B-C-N)
a part of a 3? 4-wire delta-connected circuit corresponding to a 1? grounded center-tapped neutral circuit
DC circuits corresponding to a 1? grounded center-tapped neutral circuit (Edison circuit)

The definition currently excludes several circuits derived from a 3?, 4-Wire Delta system from being a multiwire circuit. Assume the wild leg is "B" and the legs on either side of the center tap are "A" and "C". The "equal" word causes A-B-C-N, A-B-N, and B-C-N not to be multiwire circuits. Only A-C-N is a multiwire under the current definition.

If the intention is to exclude A-B-C-N, A-B-N, and B-C-N from the definition, this proposal should be rejected.

If the intention is to include A-B-C-N, A-B-N, and B-C-N from the definition, this proposal should be accepted.
 

fmtjfw

Senior Member
second version with minor revision

second version with minor revision

Section/Paragraph: 100 Branch Circuit, Multiwire.

Deleted Text

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.
Substantiation:

The definition as currently written defines the following to be MWBCs:

1? grounded center-tapped neutral circuits (e.g.: 120/240V)
3? 3- and 4-wire wye-connected circuits containing a neutral (A-B-N, A-C-N, B-C-N, and A-B-C-N)
3? 3-wire delta-connected corner grounded circuit containing the grounded conductor
a part of a 3? 4-wire delta-connected circuit corresponding to a 1? grounded center-tapped neutral circuit
DC circuits corresponding to a 1? grounded center-tapped neutral circuit (Edison circuit)

The definition currently excludes several circuits derived from a 3?, 4-Wire Delta system from being a multiwire circuit. Assume the wild leg is "B" and the legs on either side of the center tap are "A" and "C". The "equal" word causes A-B-C-N, A-B-N, and B-C-N not to be multiwire circuits. Only A-C-N is a multiwire under the current definition.

If the intention is to exclude A-B-C-N, A-B-N, and B-C-N from the definition, this proposal should be rejected.

If the intention is to include A-B-C-N, A-B-N, and B-C-N from the definition, this proposal should be accepted.
 

charlie b

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Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
The word "equal" is there in order to prevent the use of a single neutral wire and two hot wires from the same phase (i.e., A - N - A). You would need to take that into account with your suggested wording change and your substantiation.
 

GoldDigger

Moderator
Staff member
The word "equal" is there in order to prevent the use of a single neutral wire and two hot wires from the same phase (i.e., A - N - A). You would need to take that into account with your suggested wording change and your substantiation.
Actually, the wording "ungrounded conductors that have a voltage between them" takes care of that part with or without the "equal".

Tapatalk!
 
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