WHEN I NEED TO BREAK THE NEUTRAL OF AN AC DISCONNECT SWITCH?

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kwired

kwired

Electron manager
Location
NE Nebraska
Sahib said:
First, what is the difference between a switch and a disconnect switch?:)
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I will take a shot at it. NEC often does use the words "disconnecing means" which can be a switch but not just any switch.

If it is a disconnecting means it must not be able to re-close via automatic means, and depending on the application may or may not require a method of locking or securing it in the open position so that it is not accidentally closed, this last part usually applies when it is not within sight of what it is disconnecting where permitted.

Many manufacturers have what they call "safety switches" which is your typical "fused disconnect" as well as non fused type of same product line. Many in the field do call these a "disconnect switch" but it is more of a generic or even somewhat of a slang term when used for this purpose.
 
V

victor.cherkashi

Senior Member
Location
NYC, NY
iwire said:
A neutral conductor can still cause a spark between it and grounded metal parts even with the branch circuit ungrounded conductor disconnected.
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Neutral terminals may has several voltage potential above ground terminal. More far you from transformer the higher the voltage, may this is reason.

Sent from my Nexus 5 using Tapatalk
 
Sahib

Sahib

Senior Member
Location
India
kwired said:
I will take a shot at it. NEC often does use the words "disconnecing means" which can be a switch but not just any switch.

If it is a disconnecting means it must not be able to re-close via automatic means, and depending on the application may or may not require a method of locking or securing it in the open position so that it is not accidentally closed, this last part usually applies when it is not within sight of what it is disconnecting where permitted.

Many manufacturers have what they call "safety switches" which is your typical "fused disconnect" as well as non fused type of same product line. Many in the field do call these a "disconnect switch" but it is more of a generic or even somewhat of a slang term when used for this purpose.
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The main difference is a switch does not isolate whereas a disconnect switch isolates so that a lightning or switching surge is not likely to pass over its isolated contacts in its open position.
 
kwired

kwired

Electron manager
Location
NE Nebraska
NEC is the code that almost always applies in the US.

IEC is not code it is design standard. IEC components are usually acceptable by NEC as long as they are listed, but still must be installed per listing and to NEC rules that apply to the situation.

NEC art 100 has the following definitions:

Disconnecting Means.
A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply.

Switch, Bypass Isolation.
A manually operated device used in conjunction with a transfer switch to provide a means of directly connecting load conductors to a power source and of disconnecting the transfer switch.


Switch, General-Use.
A switch intended for use in general distribution and branch circuits. It is rated in amperes, and it is capable of interrupting its rated current at its rated voltage.


Switch, General-Use Snap.
A form of general-use switch constructed so that it can be installed in device boxes or on box covers, or otherwise used in conjunction with wiring systems recognized by this Code.


Switch, Isolating.
A switch intended for isolating an electrical circuit from the source of power. It has no interrupting rating, and it is intended to be operated only after the circuit has been opened by some other means.


Switch, Motor-Circuit.
A switch rated in horsepower that is capable of interrupting the maximum operating overload current of a motor of the same horsepower rating as the switch at the rated voltage.


Switch, Transfer.
An automatic or nonautomatic device for transferring one or more load conductor connections from one power source to another.


NEC does not use the term "disconnect switch"
 
Sahib

Sahib

Senior Member
Location
India
kwired said:
NEC does not use the term "disconnect switch"
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Even though NEC does not use term disconnect switch, such a switch per IEC definition-a switch capable of isolating as well as operating on load is sure to be used in US. How is it called by NEC?
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Sahib said:
Even though NEC does not use term disconnect switch, such a switch per IEC definition-a switch capable of isolating as well as operating on load is sure to be used in US. How is it called by NEC?
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If you where engineering a job here you would have to specifically note you want the grounded conductor switched at each disconnecting means if that is what you desire.

Otherwise you will get a disconnecting means that only switches the the ungrounded conductors.
 
Sahib

Sahib

Senior Member
Location
India
Well,iwire,NEC does not have an answer to my question. A code proposal to include term disconnect switch in NEC per IEC definition is desirable.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Sahib said:
Well,iwire,NEC does not have an answer to my question. A code proposal to include term disconnect switch in NEC per IEC definition is desirable.
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The NEC does have the answer for those of us that work under it you are just unaware of it.

We do not need a new term, we have one. Disconnecting means.

Here is just one example of many uses of it.

210.4 Multiwire Branch Circuits.

(B) Disconnecting Means. Each multiwire branch circuit
shall be provided with a means that will simultaneously
disconnect all ungrounded conductors at the point where
the branch circuit originates.
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Very clear, it must disconnect all the ungrounded conductors. You may disconnect the grounded conductor as well but that is a choice not a requirement.

On the other hand if when we are required to disconnect all circuit conductors, including the grounded conductor they make that clear as well.

514.11 Circuit Disconnects.

(A) General. Each circuit leading to or through dispensing
equipment, including all associated power, communications,
data, and video circuits, and equipment for remote pumping
systems, shall be provided with a clearly identified and readily
accessible switch or other approved means, located remote
from the dispensing devices, to disconnect simultaneously
from the source of supply, all conductors of the circuits, including
the grounded conductor, if any
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I fully understand that in many nations it is standard practice to always disconnect all conductors. That is not the case here. Here it is standard practice to only disconnect the ungrounded conductors.

Feel free to put in a code change proposal.
 
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GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Is it completely clear by NEC definition that the EGC is not a circuit conductor?
It does not carry normal current and is not necessarily associated with a particular circuit.
 
Sahib

Sahib

Senior Member
Location
India
kwired mentioned in post # 32 various NEC definitions of a switch. A definition of isolating switch is there. A definition of load break switch is there. But a combined definition of a switch of isolating as well as load break as in IEC is not there. That appears to be a deficiency in NEC.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Sahib said:
kwired mentioned in post # 32 various NEC definitions of a switch. A definition of isolating switch is there. A definition of load break switch is there. But a combined definition of a switch of isolating as well as load break as in IEC is not there. That appears to be a deficiency in NEC.
Click to expand...

As I mentioned you are free to put in a proposal asking the CMP to call switches what you like.
 
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