Wiring 120V,1PH Equipment

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noochstyle

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I have been accustom to just brining 2 wires to each 120V piece of equipment, even motor loads. Is there reasoning behind not doing this?

John
 
You might wish to expand your question a bit.

Are you asking about why it is a good idea to bring an EGC to a 120V load (thus _3_ conductors)?

Are you asking about multi-wire branch circuits, where the grounded conductor is shared between several circuits?

Are you asking about some WWII era copper saving designs where a single ungrounded conductor was carried in conduit, and the conduit itself was used as the grounded return?

My guess is that you are asking about MWBCs, and if you search this forum you will find several long discussions of the plusses and minuses of sharing the neutral. It can essentially be boiled down to: a cheaper, more efficient installation (less labor, less copper, less voltage drop) versus greater risk to equipment (risk of an open neutral condition). Many people here swear by MWBCs, others swear at them.

-Jon
 
I am really looking for what contractors really are going to do, or what is the commonly used. I specify 2#12 wires because I don't really see a problem with it for lighting circuits and small motor loads. I am new to electrical design engineering. I have only been in the industry for about one year. My mentor never explained what is the convention 2 or 3 wire. I have since moved jobs and no longer have a mentor so I am roughing it through on my own. I am trying to avoid a mistake. Can it be potentially harmful for me to specify 2 wires in 120v circuit, and what are the repercussions if any?

Thank you,
John
 
Two wire circuits are permitted when the raceway or cable is a listed EGC. I would add that in the case of a motor, if the connection method is a flexible conduit, a third conductor, an EGC is required.
 
winnie said:
Many people here swear by MWBCs, others swear at them.

-Jon
Click to expand...

Using MWBC's for residential is becoming more "swear at them" when solar retrofits are made. The shared neutral can do double duty when DC solar applications in existing general circuits are being modified. Multi-wire will not be an easy fix either for upgrades to general AFCI BC's in remod's especially after the 2008 cycle requirements become code.
I vote for swear at em. rbj
 
Hi George,

In stand-alone retrofits where DC is used on existing in-wall circuitry, Multi-wire shared neutral is a summed and not a balanced return. rbj
 
So your feeling is 'don't use MWBCs because someday the home might have a certain type of solar system added that may not be compatible with the existing wiring?'

I will keep using MWBCs and suggest better equipment selections made when retrofitting an existing electrical system.:)
 
gndrod said:
Hi George,

In stand-alone retrofits where DC is used on existing in-wall circuitry, Multi-wire shared neutral is a summed and not a balanced return. rbj
Click to expand...

If the house is already wired for AC, and is going off-grid, there are inverters that work on a stand-alone system and can output 240V ac. I don't know why one would go to a stand-alone system if they're already grid-tied.
 
neutral-inverter

neutral-inverter

PV System said:
If the house is already wired for AC, and is going off-grid, there are inverters that work on a stand-alone system and can output 240V ac. I don't know why one would go to a stand-alone system if they're already grid-tied.
Click to expand...

Hi PV

No question about it, but then, there are interactive components that are DC with battery based networks that need conversion. I am relating to older green designs that may not be line interactive. I believe the earlier single inverter outputs where there are no 240V outlets must have equipment marked for not hooking into Multi-wire branch circuits. [690.10] I still hesitate to include shared neutrals for 2008 cycle GFCI/AFCI reasons.

With new modular grid add-ons, it seems that inverter efficiencies have come a long way for sustaining a battery based backup system, so that is more a reason of interest. My experience with PV is probably outdated for sure (1976) and I could use some good inputs, especially for net metering. rbj
 
gndrod said:
Hi PV

No question about it, but then, there are interactive components that are DC with battery based networks that need conversion. I am relating to older green designs that may not be line interactive. I believe the earlier single inverter outputs where there are no 240V outlets must have equipment marked for not hooking into Multi-wire branch circuits. [690.10] I still hesitate to include shared neutrals for 2008 cycle GFCI/AFCI reasons.

With new modular grid add-ons, it seems that inverter efficiencies have come a long way for sustaining a battery based backup system, so that is more a reason of interest. My experience with PV is probably outdated for sure (1976) and I could use some good inputs, especially for net metering. rbj
Click to expand...

If you're looking at older installs, then yeah, MWBCs are a problem.

And PV's come a long way since 1976. Shoot me a PM if you have any questions. I just passed my NABCEP test.
 
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