6 Movement Rule
- Thread starter jap
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It first appeared in the 1931 NEC as Rule 405.b.2.
The switch (referring to a main) may be omitted in serivce conductos supplying a single-family residences having not more than six branch circuits if installation is according to sub-paragaph 3 of paragraph i of this section and if appproved circuit-breakers are used in each branch circuit and these are grouped in a single readily accessible cabinet at the point of entance.
The switch (referring to a main) may be omitted in serivce conductos supplying a single-family residences having not more than six branch circuits if installation is according to sub-paragaph 3 of paragraph i of this section and if appproved circuit-breakers are used in each branch circuit and these are grouped in a single readily accessible cabinet at the point of entance.
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- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
I don't know the answer (i.e., why the number is 6). But I can understand why there has to be a limit, and why it has to be a small number. The intent is that in an emergency, such as a raging fire, there needs to be a way to turn off all power to the building, without a great deal of trouble.
jaylectricity
Senior Member
- Location
- Massachusetts
- Occupation
- licensed journeyman electrician
The pinky is sort of weak and the thumbs oppose the rest of the fingers.
So that leaves your forefinger, middle finger, and ring finger on each hand.
That's six switches that can be flipped simultaneously.
So that leaves your forefinger, middle finger, and ring finger on each hand.
That's six switches that can be flipped simultaneously.
Jim W in Tampa
Senior Member
- Location
- Tampa Florida
Not using fingers, side of hand with a few strikes can kill 40
jaylectricity
Senior Member
- Location
- Massachusetts
- Occupation
- licensed journeyman electrician
Swing and a miss...I was making a joke.
The closest handbook I have to the '31 NEC and it's language is a 1940 by Arthur Abbott. It does not reveal any reason behind the 6 throws.
A 1929 Handbook by Terrell Croft merely reflects the 1928 NEC requirement of a disconnect for each set of service conductors. It does, however, offer a clue:
Meaning: If a meter stack does not have externally operable disconnects (i.e, you have to open a box to turn the power off) then the main must be externally operable (i.e, a handle on the side of the box). If each individual circuit (feeder in today's lingo) is externally operable, then the main does not have to be externally operable. In the language above, a 40-unit apartment building would either require an external handle on the main, or external handles for all 40 feeders.
So my guess is there was much confusion about 'externally operable', and what it would take to completely shut down the power in a building in an emergency. To simplify the process, a maximum of six disconnects was allowed. Why six? Probably just an arbitrary number.
A 1929 Handbook by Terrell Croft merely reflects the 1928 NEC requirement of a disconnect for each set of service conductors. It does, however, offer a clue:
Meaning: If a meter stack does not have externally operable disconnects (i.e, you have to open a box to turn the power off) then the main must be externally operable (i.e, a handle on the side of the box). If each individual circuit (feeder in today's lingo) is externally operable, then the main does not have to be externally operable. In the language above, a 40-unit apartment building would either require an external handle on the main, or external handles for all 40 feeders.
So my guess is there was much confusion about 'externally operable', and what it would take to completely shut down the power in a building in an emergency. To simplify the process, a maximum of six disconnects was allowed. Why six? Probably just an arbitrary number.
The power company here will not allow a Main Terminal Box in the group metering to have a Main Disconnect in it. As a matter of fact there was an installation where a Main Terminal Box had a Main Breaker in a group metering system where the Engineer knew that in the future there would be more than 6 meters in the pack. The power company had the main breaker removed in the Main Terminal Box. They consider the buss bars all the way to the back of each meter,Service Conductors,and would not allow their service conductors to be disconnected anywhere other than the Transformer. They consider each Tennant Main its own Service Disconnect. With them,You can have several meters in a Group Metering system without a Main Disconnect in the MTB.
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