Grounded conductor sizing over 1100 kcmils as per 250.66

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I am currently preparing to install a 4000 amp feeder to a induction furnace. It will be (5 wire system) 3 phases, ground and neutral conductor all paralleled originating from a new substation (treated like service / separately derived system). Our secondary breaker is actually a 4000 amp frame with 3000 amp rating plug installed. We will install 8 - 500 mcm's for a combined amperage of 3,040 amps.
Attempting to size the proper grounded conductor. My local JHA contends that we use 250.66 and calculate it as over 1100 kcmils copper. Which is fine I agree and generally assume 3/0 if it was in a single raceway.
My conflict / argument of this 3/0 arises from from the note 1 of table 250.66. I see this as multiple sets of conductors / paralleled. And this note states that the equivalent size shall be determined by the largest sum of the corresponding conductors of each set. (Each set being the key word) Would that not mean each paralleled set of 500 mcm would be used for the calculation. Thereby resulting in the grounded conductor being sized @ 1/0.

The bottom of that same note also states that this table also applies to separately derived conductors.Which is what we have.

Your feed back would be greatly appreciated
 
:D I have been tackling similar questions on an induction furnace install in my jurisdiction. In my situation the furnace did not required a grounded conductor,
(It was a strange configuration with 6 leads, 3 called Wye, called Delta but the 575 v transformers had no neutral terminal.)
IMHO, supply side bonding jumper would be size per 250.66 for the phase conductor in each conduit. Result 1/0
I base this on 250.30(A)(2) which directs you tom 250.102(C).

The neutral conductor would be based on load and beyond that if a system bonding jumper is not installed it would be sized per 250.30((A)(3) again based on your phase conductor in each raceway.
Your system appears to have a system bonding jumper, so IMO, your neutral would be 1/0 minimum for paralleling.
Based on my install I ask:
Does your furnace actually have a neutral load or a neutral terminal at the transformer (my furnaces did not)
As a side note: The manufacturer engineer insisted on using a bonding grid for all components. The grid was in turn bonded to the electrical system but the manufacturer did not want to install equipment grounding conductors with power conductors to any equipment.
(There a lot of input from the manufacturers rep who is also on CMP 12)
 
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As a side note: The manufacturer engineer insisted on using a bonding grid for all components. The grid was in turn bonded to the electrical system but the manufacturer did not want to install equipment grounding conductors with power conductors to any equipment.
(There a lot of input from the manufacturers rep who is also on CMP 12)
I've no experience directly with furnaces of this size and nature, but I do have experience in this type of industrial facility. Yes, everything gets bonded to a grounding grid. However, all used GRSC as the wiring method, so the conduit serves as a grounding conductor run with the circuit conductors when no wire-type grounding conductor is in the raceway. Entirely Code compliant.

That said, if a wire-type grounding conductor is contained within each raceway under 2011 NEC, the appropriate and overriding section is 250.102(C)(2)... sized per Table 250.66 based largest ungrounded in each raceway.
 
I don't want to hijack the OPs thread but will state as far as the grounding. It was GRS but much of it was open ended into bottomless control cabinets.
The cabinets were all connected to the bonding grid and the conduit was bonded on one end. The engineer did not want to bond the conduit on the open end to the control cabinets.
 
I don't want to hijack the OPs thread but will state as far as the grounding. It was GRS but much of it was open ended into bottomless control cabinets.
The cabinets were all connected to the bonding grid and the conduit was bonded on one end. The engineer did not want to bond the conduit on the open end to the control cabinets.
Would that still be compliant? I know exclusive systems supplying industrial furnaces are not required to be grounded, but don't believe that alleviates the requirement for an EGC run with circuit conductors and being bonded to the load equipment. Engineers do not have the authority to override Code unless the AHJ agrees.
 
Over 1100 kcmils according to 250.66

Over 1100 kcmils according to 250.66

:D I have been tackling similar questions on an induction furnace install in my jurisdiction. In my situation the furnace did not required a grounded conductor,
(It was a strange configuration with 6 leads, 3 called Wye, called Delta but the 575 v transformers had no neutral terminal.)
IMHO, supply side bonding jumper would be size per 250.66 for the phase conductor in each conduit. Result 1/0
I base this on 250.30(A)(2) which directs you tom 250.102(C).

The neutral conductor would be based on load and beyond that if a system bonding jumper is not installed it would be sized per 250.30((A)(3) again based on your phase conductor in each raceway.
Your system appears to have a system bonding jumper, so IMO, your neutral would be 1/0 minimum for paralleling.
Based on my install I ask:
Does your furnace actually have a neutral load or a neutral terminal at the transformer (my furnaces did not)
As a side note: The manufacturer engineer insisted on using a bonding grid for all components. The grid was in turn bonded to the electrical system but the manufacturer did not want to install equipment grounding conductors with power conductors to any equipment.
(There a lot of input from the manufacturers rep who is also on CMP 12)

My system will be grounded and bonded to the existing building system. I will have a main bonding jumper at the source of the derived system. I do not know what the load is on the grounded conductor system. Nor do I suspect there is any. I cannot get a straight answer from the manufacturer which is in Germany. The equipment is coming in November and we are in early stages of preparing for it's arrival. I suspect they do not have a load at all they are just wanting to have a wye grounded system so they insure they have a grounding reference to their system and are asking us to bring the grounded conductor to the machine to insure this is the case. I am most concerned with clarifying the 250.66 article when system conductors are required to be over 1100 kcmils and are paralleled.
 
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