Feeder Neutral Disconnection

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infinity

infinity

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I was just asked about this 4-pole disconnect switch that switched both the 3? ungrounded conductors and the neutral conductor. My comment was that as long as there was no fuse in place the neutral is permitted to be opened when opening all of the ungrounded conductors, others disagreed but could say where to find it in the NEC. Isn't this permissible? BTW an engineer designed this way (4-pole switch) for an unknown reason.

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First I would ask them if I can unplug an appliance breaking the neutral and ground.

Then you could hit them up with this.

404.2 Switch Connections.

(B) Grounded Conductors. Switches or circuit breakers
shall not disconnect the grounded conductor of a circuit.

Exception: A switch or circuit breaker shall be permitted
to disconnect a grounded circuit conductor where all circuit
conductors are disconnected simultaneously, or where
the device is arranged so that the grounded conductor cannot
be disconnected until all the ungrounded conductors of
the circuit have been disconnected.
Click to expand...
 
iwire said:
First I would ask them if I can unplug an appliance breaking the neutral and ground.

Then you could hit them up with this.
Click to expand...


The cord and plug was my exact analogy. For some reason when I looked for that code reference I couldn't find it. Merci beaucoup. :cool:
 
Appears to be a fused disconnect. Did the engineer also specify a means to not fuse the neutral?
240.22 Grounded Conductor. No overcurrent device shall
be connected in series with any conductor that is intentionally
grounded, unless one of the following two conditions is met:
(1) The overcurrent device opens all conductors of the circuit,
including the grounded conductor, and is designed
so that no pole can operate independently.
(2) Where required by 430.36 or 430.37 for motor overload
protection.
Click to expand...
 
Smart $ said:
Appears to be a fused disconnect. Did the engineer also specify a means to not fuse the neutral?
Click to expand...

This job was from a few years ago and someone found a fuse in the neutral. The spec called for a 4-pole disconnect (no one knows why and the engineer has moved on). My guess is that someone should have substituted a piece of bus in place of the fuse in the neutral conductor. Now it's been suggested that the neutrals all be removed and butt splice together by passing the switch completely. I see no code requirement to do so.
 
infinity said:
This job was from a few years ago and someone found a fuse in the neutral. The spec called for a 4-pole disconnect (no one knows why and the engineer has moved on). My guess is that someone should have substituted a piece of bus in place of the fuse in the neutral conductor. Now it's been suggested that the neutrals all be removed and butt splice together by passing the switch completely. I see no code requirement to do so.
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Installed neutral fuse was exactly my concern. I would opt for a piece of busbar rather than bypassing with butt splices. I'd also remove the "fingers" and install connecting busbar in their stead.
 
One potential reason for switching a neutral is a transfer switch where the alternate source is wired as an SDS. A neutral breaking disconnect is also required for gas dispensers.
Neither seem to apply here though.
 
Want to switch/disconnect the

Want to switch/disconnect the

Hi folks. I have a similar issue but my client wants to switch the neutral to facilitate use of some equipment he has on hand. The first picture in this thread is what I have in mind.

Here are the circumstances:
- Texas
- 2014 NEC
- 100+ yr old 2 story 2 unit duplex
- new service thru out, 2 Sq D house panels
- service disconnect after and underneath the new meter cans, required by city

Client wants to use Square D single throw 3P non-fusible HU-364-rb disconnect switches after the meter. These switches have 3 isolated legs of course for 3 phase use. Since this is residential and single phase (2 hots and a neutral) he wants to run the neutral thru one of the switched legs. I know of no reason why this would be an issue since it is not fused, mechanical and the throw is simultaneous. The ground legs of course are not switched and continuous throughout.

Can you give me NEC support for this purpose? Thanks
 

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zaford said:
Hi folks. I have a similar issue but my client wants to switch the neutral to facilitate use of some equipment he has on hand. The first picture in this thread is what I have in mind.

Here are the circumstances:
- Texas
- 2014 NEC
- 100+ yr old 2 story 2 unit duplex
- new service thru out, 2 Sq D house panels
- service disconnect after and underneath the new meter cans, required by city

Client wants to use Square D single throw 3P non-fusible HU-364-rb disconnect switches after the meter. These switches have 3 isolated legs of course for 3 phase use. Since this is residential and single phase (2 hots and a neutral) he wants to run the neutral thru one of the switched legs. I know of no reason why this would be an issue since it is not fused, mechanical and the throw is simultaneous. The ground legs of course are not switched and continuous throughout.

Can you give me NEC support for this purpose? Thanks
Click to expand...

I think this has been answered above. As long as you meet the requirements of 230.70 I don't see an issue. Art. 230.75 appears to allow the switch neutrals and in a sense requires it.

230.75 Disconnection of Grounded Conductor. Where
the service disconnecting means does not disconnect the
grounded conductor from the premises wiring, other means
shall be provided for this purpose in the service equipment.
A terminal or bus to which all grounded conductors can be
attached by means of pressure connectors shall be permitted
for this purpose. In a multisection switchboard or
switchgear, disconnects for the grounded conductor shall be
permitted to be in any section of the switchboard or switchgear,
provided that any such switchboard or switchgear section
is marked.
Click to expand...
 
zaford said:
...
Client wants to use Square D single throw 3P non-fusible HU-364-rb disconnect switches after the meter. ...
Click to expand...
What is the availble fault current at the location of the switch? Most non-fusible are only suitable for use on circuits with an available short circuit current of 10,000 amps or less. Also how are you going to comply with 230.91?

Also, the code requires a means to disconnect all of the service conductors.
230.70 General. Means shall be provided to disconnect all conductors in a building or other structure from the service-entrance conductors.
Click to expand...
 
Dennis Alwon said:
Don I don't think that is a fuseable disco
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Yes, so it will have a SCCR of 10,000. That might not be high enough, and, assuming that it is the service disconnect, the service overcurrent protective device will have to be installed next to the disconnect.
 
don_resqcapt19 said:
Yes, so it will have a SCCR of 10,000. That might not be high enough, and, assuming that it is the service disconnect, the service overcurrent protective device will have to be installed next to the disconnect.
Click to expand...

I have never seen anyone check the aic rating for a dwelling. I cannot imagine the power company would do that to us...:D
 
jim dungar said:
In Wisconsin almost every utility requires residential service entrance equipment be rated at 22kA minimum.
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Wow, have never heard of that around here. I have never checked but it seems I have heard the power company was aware of the issue of going over 10,000 on a residence so they don't
 
Dennis Alwon said:
Wow, have never heard of that around here. I have never checked but it seems I have heard the power company was aware of the issue of going over 10,000 on a residence so they don't
Click to expand...
The two biggest POCOs started requiring 22kA equipment about the same time Square D and Cutler Hammer introduced series rated "22/10" loadcenters, almost 30 years ago.
 
Though most dwellings probably don't have more then 10kA available, it really depends on size of transformer and distance/size of conductors between the transformer and the service equipment. Some "higher end" homes with larger service capacity possibly have a padmount transformer that is relatively close to the home - you especially need to pay a little closer attention when you have that situation or you could have too high available fault current. Even multifamily can sometimes have a similar situation.


I once wired a new home that was supplied by a 100 kVA transformer - we had 4 200 amp runs to that home with 4-200 amp main breaker panels as the service equipment.

Ran quick calculation on the spreadsheet Mike Holt has on his website - only thing I don't know is the impedance of the transformer but just throwing in 2.1% and 100 feet of 4/0 aluminum had me at 8000 amps. Shorten length to 50 feet and you are around 11,000. Make two 4/0 in parallel and you have around 11,000 @ 100 feet, shorten it to 50 feet and you have about 14,500.
 
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