3 breakers feeding receptacles with one neutral

[chiversj]

This is a transmitter installation that is about 7 years old. Three breakers are used to feed three receptacles but only one neutral is used to all three. So if I turn off one breaker and open the receptacle box, the white wire is engerized from the other circuits in use.
Is this according to the code? Thanks

 

[charlie b]

It depends on the code cycle that is in effect. But given the age of this installation, it is a good bet that this was allowed at that time. Today, the code would require a single breaker with three poles, or a handle tie that forces all three single pole breakers to be open if you manually open any one of them.

 

[raider1]

Welcome to the forum.

Prior to the 2008 NEC the installation you have is legal.

Under the 2008 NEC you are still able to run a multiwire branch circuit but you now have to provide a handle tie for the 3 single pole breakers or use a common trip 3 pole breaker. (See 210.4(B) 2008 NEC)

Chris

 

[roger]

It is called a Multi Wire Branch Circuit and yes, it is legal and in fact a very effecient wiring method from material savings, voltage drop, and power loss perspectives.

There is added danger in servicing these circuits as you have correctly questioned and in the 2008 NEC it became a requirement to use multi pole breakers or handle ties in order to open all ungrounded conductors at the same time.

See the definition of Branch Circuit Multi-Wire in article 100 and article section 210.4

Roger

 

[LarryFine]

So if I turn off one breaker and open the receptacle box, the white wire is engerized from the other circuits in use.

As long as it's intact, the shared neutral is considered not energized (being at the same potential as the service neutral), but should always be treated as energized.

If it's opened anywhere, the load side of that opening is energized through the loads, as you surmised. That's why we must pigtail it, and not depend on terminations.

 

[ptonsparky]

Many electricians, and others, find out about MWBC neutrals the hard way via a shock or damaged equipment. The quicker ones only do it once.

 

[steve66]

If the neutral is disconnected while the power to the receptacles is still on, the voltage to the recepacles can change from anything to 0 volts to the source voltage (208 or 240V, for example).

So what ever you do, don't disconnect the netural with the power on.