Disconected Neutral

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xformer

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Article 404.2B Exception
Can anyone give an example where an OCPD or a disco disconnects all the ungrounded conductors and then the grounded conductor?
 
I believe there are a few cord and plug combinations where the ungrounded conductors are disconnected before the grounded and the grounding, maybe for 480 volts, or California configurations?

A transfer switch for a separately derived system would also disconnect the grounded conductor though I don't know if they do it at the same time as the grounded, before, or after
 
JFletcher said:
I believe there are a few cord and plug combinations where the ungrounded conductors are disconnected before the grounded and the grounding, maybe for 480 volts, or California configurations?

A transfer switch for a separately derived system would also disconnect the grounded conductor though I don't know if they do it at the same time as the grounded, before, or after
Click to expand...
cord and plug applications are not part of art 404 though.;)

I think there are transfer switches and larger frame molded case switches/breakers that will make the grounded conductor before ungrounded and break the ungrounded before the grounded. You won't find them in the miniature plug on style breakers.
 
You can get transfer switches that do not transfer the grounded conductor (for non-SDS systems).
And you can get transfer switches for SDS systems that disconnect all wires (nearly) simultaneously as well as ones that break the grounded conductor last and make the new grounded conductor first.
The deliberate time offset avoids exposing line to neutral loads to line to line voltages during the transfer.
I am aware of cord and plug combinations that make the EGC first, but not so sure about the grounded conductor. With line to line loads on an MWBC I would make sure all loads we're switched off before connecting or disconnecting.

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xformer said:
Article 404.2B Exception
Can anyone give an example where an OCPD or a disco disconnects all the ungrounded conductors and then the grounded conductor?
Click to expand...
514.11(A) requires the grounded conductor to be disconnected for gas pump circuits in the 2014 code. The make special breakers with an additional pole to disconnect the grounded conductor.
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. Single-pole breakers utilizing handle ties shall not be permitted.
Click to expand...
 
It's an industry requirement in many semiconductor fabrication facilities (aka "Fabs") supposedly for safety proposes. I think the practice just comes from the fact that in some types of IEC distribution systems (TN-C for example) it is a requirement, so it just became one for any facilities located here in North America order to maintain consistency around the world. But in reality, hardly anyone is building semiconductor Fabs in North America so we hardly ever see it any more. It was common for a while in the 90s though and caught a lot of people by surprise because it meant using 4 pole circuit breakers (actually 3P + SN). It wasn't an NEC thong in that case, just an internal industry standard.
 
GoldDigger said:
You can get transfer switches that do not transfer the grounded conductor (for non-SDS systems).
And you can get transfer switches for SDS systems that disconnect all wires (nearly) simultaneously as well as ones that break the grounded conductor last and make the new grounded conductor first.
The deliberate time offset avoids exposing line to neutral loads to line to line voltages during the transfer.
I am aware of cord and plug combinations that make the EGC first, but not so sure about the grounded conductor. With line to line loads on an MWBC I would make sure all loads we're switched off before connecting or disconnecting.

Sent from my XT1585 using Tapatalk
Click to expand...

sorry wrong post reply
 
Jraef said:
It's an industry requirement in many semiconductor fabrication facilities (aka "Fabs") supposedly for safety proposes. I think the practice just comes from the fact that in some types of IEC distribution systems (TN-C for example) it is a requirement, so it just became one for any facilities located here in North America order to maintain consistency around the world. But in reality, hardly anyone is building semiconductor Fabs in North America so we hardly ever see it any more. It was common for a while in the 90s though and caught a lot of people by surprise because it meant using 4 pole circuit breakers (actually 3P + SN). It wasn't an NEC thong in that case, just an internal industry standard.
Click to expand...

My guess is something to do with static charge buildup. Workstation mats and human ground straps are also usually tied to ground through a resistor of several megohms for obvious safety reasons.
 
don_resqcapt19 said:
514.11(A) requires the grounded conductor to be disconnected for gas pump circuits in the 2014 code. The make special breakers with an additional pole to disconnect the grounded conductor.
Click to expand...
I believe he was also asking for an application where the grounded conductor is made first/opened last - I don't know if those switched neutral breakers do that or that it is even required for that application.
 
kwired said:
I believe he was also asking for an application where the grounded conductor is made first/opened last - I don't know if those switched neutral breakers do that or that it is even required for that application.
Click to expand...
The grounded conductor and ungrounded conductor in a switched grounded conductor breaker open and close at the same time. I am not aware of any requirements for the grounded conductor to make first and break last. There is a requirement for plugs to do that with the grounding conductor.
 
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