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Safety problem with feeders and branch circuits in the same wireway.

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avargasm

avargasm

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Location
San José, Costa Rica
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Design Electrical Engineer
Patpowers said:
I wouldn’t call then earth wires, that seems to imply that they are to send faults to earth and that’s not the case. Both equipment grounds and neutrals should allow ground fault current and short circuit current to go to the same point: at the service. The only type of fault contact to earth will open is a Class A ground fault protection circuit. Even then the preferred fault path is to the service. I’m not sure of your electrical system, but there must be reasons for your concerns.
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"but there must be reasons for your concerns"

Short circuits and high load faults and arcs between conductors inside raceways are COMMON issues in electrical installations in the USA and the world. It's natural and responsible to be concerned about these kinds of faults and plan to avoid them.
 
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Patpowers

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Mississippi
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Electrician
We know faults are suppose to clear through either the neutral or the egc, why would we want to protect a neutral. If you have 20 Amp protection on the ungrounded conductor and 20 A protection on the neutral, the breakers are in series when the circuit is being utilized and your branch circuit is now protected by 40A instead of 20A. Please show me a failure that resulted in a feeder and branch circuit sharing a raceway. I would like more understanding, as something is going over my head.
 
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Patpowers

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Location
Mississippi
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avargasm said:
"but there must be reasons for your concerns"

Short circuits and high load faults and arcs between conductors inside raceways are COMMON issues in electrical installations in the USA and the world. It's natural and responsible to be concerned about these kinds of faults and planning to avoid them.
Click to expand...
Common? How common? Please point me to your statistics..
 
avargasm

avargasm

Member
Location
San José, Costa Rica
Occupation
Design Electrical Engineer
Patpowers said:
We know faults are suppose to clear through either the neutral or the egc, why would we want to protect a neutral. If you have 20 Amp protection on the ungrounded conductor and 20 A protection on the neutral, the breakers are in series when the circuit is being utilized and your branch circuit is now protected by 40A instead of 20A. Please show me a failure that resulted in a feeder and branch circuit sharing a raceway. I would like more understanding, as something is going over my head.
Click to expand...
"the breakers are in series when the circuit is being utilized and your branch circuit is now protected by 40A instead of 20A"

Wrong. But not part of the discussion. (Hint: breakers in parallel could add their currents, not in series. Remember two-pole breakers).
 
avargasm

avargasm

Member
Location
San José, Costa Rica
Occupation
Design Electrical Engineer
Patpowers said:
We know faults are suppose to clear through either the neutral or the egc, why would we want to protect a neutral. If you have 20 Amp protection on the ungrounded conductor and 20 A protection on the neutral, the breakers are in series when the circuit is being utilized and your branch circuit is now protected by 40A instead of 20A. Please show me a failure that resulted in a feeder and branch circuit sharing a raceway. I would like more understanding, as something is going over my head.
Click to expand...
You need to protect the neutral because it's a wire, and as a wire, it can catch fire, or make other things catch fire.
 
avargasm

avargasm

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Location
San José, Costa Rica
Occupation
Design Electrical Engineer
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Patpowers

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Mississippi
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Electrician
fundamental combustion phenomena in wire can happen regardless of feeders and branch circuits sharing a conduit. We do not put OCPD on neutral conductors. We do not want neutral and egc’s to open, we want them to be complete and always bonded. We do not open neutrals at light switches, it keeps the integrity of the fault path and bonding. The only circumstances where I would want a neutral conductor to open is in hazardous conditions. All Conductors servicing fuel pumps including the neutrals must be capable of being opened together. This is usually done by using a three pole contract that is mechanically held. The feeders go to the Contactor, than the panel. When the Contactor is opened all conductors open, including the neutral. Even in this situation the neutral isn’t protected by OCPD, and this is a hazardous location. The ungrounded feeders are protected, the neutral isn’t, the mechanically held Contactor opens all the conductors to the pumps.
 
avargasm

avargasm

Member
Location
San José, Costa Rica
Occupation
Design Electrical Engineer
Patpowers said:
fundamental combustion phenomena in wire can happen regardless of feeders and branch circuits sharing a conduit. We do not put OCPD on neutral conductors. We do not want neutral and egc’s to open, we want them to be complete and always bonded. We do not open neutrals at light switches, it keeps the integrity of the fault path and bonding. The only circumstances where I would want a neutral conductor to open is in hazardous conditions. All Conductors servicing fuel pumps including the neutrals must be capable of being opened together. This is usually done by using a three pole contract that is mechanically held. The feeders go to the Contactor, than the panel. When the Contactor is opened all conductors open, including the neutral. Even in this situation the neutral isn’t protected by OCPD, and this is a hazardous location. The ungrounded feeders are protected, the neutral isn’t, the mechanically held Contactor opens all the conductors to the pumps.
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I'm not talking about putting OCPDs on neutral conductors. Never said that. That's not how you protect a neutral.
 
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Patpowers

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Mississippi
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Electrician
To have a fear of fundamental combustion phenomena in wire is equivalent to having a fear of a piece of meteorite striking you. It happens, but you never know when and where and isn’t COMMON.

What are your chances of getting smacked – and killed—by a meteorite? One astronomer put the odds of death by space rock at 1 in 700,000 in a lifetime, while others say it's more like 1 in 1,600,000.

phys.org
 
avargasm

avargasm

Member
Location
San José, Costa Rica
Occupation
Design Electrical Engineer
Patpowers said:
How do you protect a neutral? I haven’t had to do that, I would like to know..
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You put an OCPD in series with the neutral, at the ungrounded conductor that feeds the neutral one. And you make sure that no other foreign power sources are going to interfere or overload the neutral.
 
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Patpowers

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Location
Mississippi
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Electrician
avargasm said:
You put an OCPD in series with the neutral, at the ungrounded conductor that feeds the neutral one. And you make sure that no other foreign power sources are going to interfere or overload the neutral.
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Umm I don’t think so, where is this allowed in code?
 
avargasm

avargasm

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Location
San José, Costa Rica
Occupation
Design Electrical Engineer
Patpowers said:
Umm I don’t think so, where is this allowed in code?
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240.4 Protection of Conductors. Conductors, other than
flexible cords, flexible cables, and fixture wires, shall be
protected against overcurrent in accordance with their ampacities
specified in 310.15, unless otherwise permitted or
required in 240.4(A) through (G).
 
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Patpowers

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Location
Mississippi
Occupation
Electrician
Best bet, use a current sensing smart monitoring system. The second you have an irregular current surge you can have it shunt trip the feeder, Boom, problem solved. Now you will even know what’s being left on and when equipment is consuming more power than necessary. Absolute Solution.

bada bing bada boom
 
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