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switching neutral in single phase motors?
- Thread starter dave11282
- Start date
I'm pretty sure there are no standards which mandate neutral switching for general applications. There could possibly be a requirement in specific applications where increased isolation is required, but probably not because contactors are not recognised isolation devices. If the motor was a single phase 415V machine strung across two phases then both poles would be switched.
Is this relating to a specific application?
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I don't suffer from insanity. I enjoy it...
Is this relating to a specific application?
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- Moderator
- #3
In North America, you only need to switch both poles if there is a plug connection ahead of the starter. With a plug connection, there is a possibility of reversing the Hot and neutral, so both had to be switched. The rule has been there since the days when two wire, unpolarized extension cords were common.
respectfully
respectfully
bigbillnky
Electrical
dave11282
Goodmorning
You are questioning whether or not to break the neutral conductor, yet later you refer to the voltage as 240 volt. It is a very rare motor that requires a neutral at 240 volt. Are you sure of the voltage?
One other point is that when you install a motor that requires a neutral in a hazardous location, the disconnect must open the "hot(s)" and the neutral.
Bigbillnky,C.E.F.....(Chief Electrical Flunky)
Goodmorning
You are questioning whether or not to break the neutral conductor, yet later you refer to the voltage as 240 volt. It is a very rare motor that requires a neutral at 240 volt. Are you sure of the voltage?
One other point is that when you install a motor that requires a neutral in a hazardous location, the disconnect must open the "hot(s)" and the neutral.
Bigbillnky,C.E.F.....(Chief Electrical Flunky)
Skogsgurra
Electrical
- Thread starter
- #6
Skogsgurra
Electrical
dave11282,
You ARE 230 V AC, like it or not - and even if your voltmeter says 240 V. That's why the continent changed from 220 to 230 V and you changed from 240 to 230 V. The adaption period is over.
Gunnar Englund
You ARE 230 V AC, like it or not - and even if your voltmeter says 240 V. That's why the continent changed from 220 to 230 V and you changed from 240 to 230 V. The adaption period is over.
Gunnar Englund
RRaghunath
Electrical
Panelman,
I always thought switching of neutral has to be different from phase. For safety reasons, the neutral needs to precede the phase while closing whereas open after the phase while opening.
I always thought switching of neutral has to be different from phase. For safety reasons, the neutral needs to precede the phase while closing whereas open after the phase while opening.
Skogsgurra
Electrical
I think taht you are referring to PE. It shall always be the first to make contact and the last to disconnect.
Gunnar Englund
Gunnar Englund
![[wink]](/data/assets/smilies/wink.gif "[wink] [wink]")
davidbeach
Electrical
Otherwise known to us on this side of the pond as ground.
- Moderator
- #15
The requirement in the Canadian code is that any device that switches the neutral as well as the hot lines, must disconnect the neutral simultaneously or later than the hot lines. It must connect the neutral first, or simultaneously.
The ground, earth or terre is not usually switched. If it is disconnected with a plug connection, the ground pin or stab is longer than the others to effect a late break, early make on the protective earthing terminal.
respectfully
The ground, earth or terre is not usually switched. If it is disconnected with a plug connection, the ground pin or stab is longer than the others to effect a late break, early make on the protective earthing terminal.
respectfully
Skogsgurra
Electrical
I got taht, Chuck. And a smile as well.
And, Bill. You dig up (or know) facts in an impressive manner. I did not know about that Canadian requirement. That's why I thought it was the PE Chuck was thinking of.
Gunnar Englund
And, Bill. You dig up (or know) facts in an impressive manner. I did not know about that Canadian requirement. That's why I thought it was the PE Chuck was thinking of.
Gunnar Englund
Yes Sir,after reading page after page of awesome explanations you have written in the past and you never missing a beat, this time a one liner slips through the crack and I could not resist.
Thank you ScottyUK and David I have seen reference to PE on our German equipment it was always combined with a ground symbol and connected to a green/yellow wire, I just assumed it was an abbreviation of German language for ground never giving much thought otherwise.
Chuck
Getting older is inevitable
Acting your age is optional
Thank you ScottyUK and David I have seen reference to PE on our German equipment it was always combined with a ground symbol and connected to a green/yellow wire, I just assumed it was an abbreviation of German language for ground never giving much thought otherwise.
Chuck
Getting older is inevitable
Acting your age is optional
- Moderator
- #18
Hi Folks;
I am a long way from my copy of the NEC. I have the Canadian code, and it is reasonably close to the NEC. Anyone who is motivated may search the index of the NEC for a similar rule.
In North America, the neutral is virtually always the grounded circuit conductor.
Rule 14-016 states that:
Devices (Switches, breakers, fuses) shall not be connected in any grounded conductor EXCEPT WHERE;
(a) the devices simultaneously or previously disconnect all ungrounded conductors;
(b) an overcurrent device is in a two wire circuit having one wire grounded and there is a possibility that the grounded conductor may assume a voltage difference between itself and ground due to unreliable grounding conditions of sufficient magnitude to create a dangerous condition: or
(c) overcurrent devices are located in that part of a circuit that is connected by a two pole polarized or unpolarized attachment plug provided that the circuit is rated at 15A, 125 V or less.
Personally, I don't switch neutrals under any circumstances on three wire single phase circuits or the shared neutrals of three phase circuits.
I have seen too many problems and too much expensive and needless damage caused by failures or improper action of switches in neutrals.
I have never seen damage or encountered any problems caused be a solid (unswitched) neutral.
Another interesting point re the close similarity between the Canadian and American codes is in regards to voltage drop.
The NEC RECOMENDS that the voltage drop between the consumers service and the point of utilization not exceed 5%.
The Canadian code REQUIRES that the voltage drop between the consumers service and the point of utilization not exceed 5%.
respectfully
I am a long way from my copy of the NEC. I have the Canadian code, and it is reasonably close to the NEC. Anyone who is motivated may search the index of the NEC for a similar rule.
In North America, the neutral is virtually always the grounded circuit conductor.
Rule 14-016 states that:
Devices (Switches, breakers, fuses) shall not be connected in any grounded conductor EXCEPT WHERE;
(a) the devices simultaneously or previously disconnect all ungrounded conductors;
(b) an overcurrent device is in a two wire circuit having one wire grounded and there is a possibility that the grounded conductor may assume a voltage difference between itself and ground due to unreliable grounding conditions of sufficient magnitude to create a dangerous condition: or
(c) overcurrent devices are located in that part of a circuit that is connected by a two pole polarized or unpolarized attachment plug provided that the circuit is rated at 15A, 125 V or less.
Personally, I don't switch neutrals under any circumstances on three wire single phase circuits or the shared neutrals of three phase circuits.
I have seen too many problems and too much expensive and needless damage caused by failures or improper action of switches in neutrals.
I have never seen damage or encountered any problems caused be a solid (unswitched) neutral.
Another interesting point re the close similarity between the Canadian and American codes is in regards to voltage drop.
The NEC RECOMENDS that the voltage drop between the consumers service and the point of utilization not exceed 5%.
The Canadian code REQUIRES that the voltage drop between the consumers service and the point of utilization not exceed 5%.
respectfully
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