Ungrounded SDS Bonding Jumper

[augie47]

I rarely have a call to inspect Ungrounded Separately Derived Systems. I presently have one for a electric furnace. 575 volt 3 phase ungrounded transformers located outside a facility with UG supply conductors in PVC to a furnace control panel inside.
The manufacturer requested the supply PVC contain the phase conductors only. The transformers and furnace equipment share a common grounding electrode system.
My first thought was that I needed equipment bonding jumpers run with the phase conductors, but it appears under the '08 Code { 250.30(B) }, that one is not required.
Am I correct that on an ungrounded SDS there is not requirement for any bonding means between the SDS and the 1st disconnecting means ?

 

[Smart $]

The system grounding requirements (or lack thereof for ungrounded systems) do not alleviate equipment grounding requirements. The non-current-carrying metal parts of the transformer must still be grounded to the secondary system grounding inside. IMO the common GES accomplishes such, but opinions may vary...

 

[augie47]

The system grounding requirements (or lack thereof for ungrounded systems) do not alleviate equipment grounding requirements. The non-current-carrying metal parts of the transformer must still be grounded to the secondary system grounding inside. IMO the common GES accomplishes such, but opinions may vary...

I agree on both counts and due to the common GES I was not too concerned, however, I do not see a NEC requirement for the GES to be common if the transformer is not located at the building nor do I see the requirement for a bonding jumper of any type. Do you know the Code reference requiring this ?

 

[don_resqcapt19]

New for 2011.

250.30(B) (3) Bonding Path and Conductor. A supply-side bonding jumper shall be installed from the source of a separately derived system to the first disconnecting means in compliance with 250.30(A)(2).

 

[Smart $]

I agree on both counts and due to the common GES I was not too concerned, however, I do not see a NEC requirement for the GES to be common if the transformer is not located at the building nor do I see the requirement for a bonding jumper of any type. Do you know the Code reference requiring this ?

None specifically regarding ungrounded systems, but 250.96 applies to essentially everything.

Don posted regarding '11 code while I was typing, so I should note I am referring to '08 code.

 

[ronmath]

Wouldn't 250.4(B) be what you are looking for?

 

[Smart $]

Wouldn't 250.4(B) be what you are looking for?

Missed that one :ashamed1:... and it is specific, though it doesn't say exactly how to accomplish its requirements (i.e. supply side vs. load side).

 

[ronmath]

IMHO,

The ground can occur anywhere from the SDS to the First disconnecting means as stated previously. If the grounding occurs at the transformer then a bonding conductor of the same size must be carried to the first disconnect and vice versa, not to mention an equipment ground from the disconnect to the equipment. If this is not done, you do not have an effective path to ground, 250.4(B)(1),(2) and (3) for induced voltage such as a lightning strike. A single ground fault will only ground the previously ungrounded system, but a second ground fault on another phase will create a line to line fault and the OCPD will trip 250.4(B)(4).

 

[augie47]

Wouldn't 250.4(B) be what you are looking for?

Excellent referene.
In your opinion, if all equipment is connected to a common Grounding Electrode System would that not accomplish the required bonding.

 

[don_resqcapt19]

Excellent referene.
In your opinion, if all equipment is connected to a common Grounding Electrode System would that not accomplish the required bonding.

300.3(B) and 300.3(B)(2) apply and would require the bonding conductor to be installed with the circuit conductors.

 

[Smart $]

300.3(B) and 300.3(B)(2) apply and would require the bonding conductor to be installed with the circuit conductors.

But that's what is being questioned. Is a non-GES bonding conductor required if the common GES establishes the required low impedance ground-fault path?

 

[don_resqcapt19]

But that's what is being questioned. Is a non-GES bonding conductor required if the common GES establishes the required low impedance ground-fault path?

You have to have an EGC or an EBC with the circuit conductors. There is no exception for this just because it is an ungrounded system. For all practical purposes the only difference between a grounded and an ungrounded system is that the ungrounded system does not have a main or system bonding jumper.

 

[Smart $]

You have to have an EGC or an EBC with the circuit conductors. There is no exception for this just because it is an ungrounded system. For all practical purposes the only difference between a grounded and an ungrounded system is that the ungrounded system does not have a main or system bonding jumper.

That's exactly what I thought. But this thread forced me to look for requirements that actually say that. I have yet to find any that actually require an EBC run with ungrounded-secondary conductors ('08 code). Perhaps you can enlighten me. I've already missed a major one today, so a second really won't make me feel much worse

 

[augie47]

You have to have an EGC or an EBC with the circuit conductors. There is no exception for this just because it is an ungrounded system. For all practical purposes the only difference between a grounded and an ungrounded system is that the ungrounded system does not have a main or system bonding jumper.

That was my original thinking, but as Smart$ notes, I'm having a difficult time providing a NEC reference to back that up.
This is an engineered design electric furnace which has a number of high-tech design features... so many pulses per cycle and phase angle calculations (the transformer actaully has two outputs to the controller), The design engineers advise that a grounding conductor of any type in the same conduit as the phase conductors somehow distorts the phase switching (their expatiation is far more technical).

 

[don_resqcapt19]

It is not very clear, but I read the combination of the rules in 250.4(B) and 300.3(B) as requiring an EGC or EBJ in the raceway.

 

[ronmath]

Sorry I'm just getting back to this.

300.3(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be installed in the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

To me, this states that you must run the EGC with the conductors and can't connect to any point on the grounding grid you want, even with an ungrounded system.

 

[augie47]

Sorry I'm just getting back to this.

300.3(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be installed in the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

To me, this states that you must run the EGC with the conductors and can't connect to any point on the grounding grid you want, even with an ungrounded system.

Not to go in circles, but that was where my argument started with the engineer. I then went to 250.30 as I was familiar with the bonding jumper requirement in part (A), however, it does not seem that Part (B) has the same requirement (in '08).
I sorta agree with don that my best bet is 250.4 but I don't truly find the wording I would like to see there.

 

[Smart $]

Sorry I'm just getting back to this.

300.3(B) Conductors of the Same Circuit. All conductors of the same circuit and, ***where used***, the grounded conductor and all equipment grounding conductors and bonding conductors shall be installed ***in*** the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

To me, this states that you must run the EGC with the conductors and can't connect to any point on the grounding grid you want, even with an ungrounded system.

There is a slight problem with grammar usage in that statement. Does the "where used" apply to only the grounded conductor or the entire underlined phrase...???

If there were a comma after "the grounded conductor" I would say "where used" only applied to the grounded conductor. But as written, I say it applies to the entire phrase.

Additionally, we know not all circuits must use a wire-type EGC. If what you are proposing is true, we would have to run a wire-type EGC with all circuits, even those run in EGC-qualifying raceways.

 

[ronmath]

Smart,

I agree with your statements and you can certainly use metal conduit for the ECG. I don't think there is any major issues with the grammer, the term "Where Used" would apply to an EGC or conduit where a conductor (I understand that the conduit can be considered a form of conductor) is not used. The original post stated that PVC was used. First was to establish that an equipment grounding conductor or equipment bonding was required (250.4(B)). Second was where this bonding could occour and the routing of the same (300.3(B)). IMO I don't see the ambiguity here, it seems straight forward. There are instances (exceptions) that possibly might qualify for the EGC to be run outside (but with) the conduit.

 

[Smart $]

... First was to establish that an equipment grounding conductor or equipment bonding was required (250.4(B)).

I agree that bonding is required per 250.4(B). However, 250.4(B)(2) does not say the bonding must be with an EBC/EGC. In fact the requirement uses the term "connected", not "bonded". And FWIW, 250.4(B)(3) is moot if (2) applies.

(B) Ungrounded Systems.

(1) Grounding Electrical Equipment. Non?current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials.

(2) Bonding of Electrical Equipment. Non?current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it.

(3) Bonding of Electrically Conductive Materials and Other Equipment. Electrically conductive materials that are likely to become energized shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it.

(4) Path for Fault Current. Electrical equipment, wiring, and other electrically conductive material likely to become energized shall be installed in a manner that creates a low impedance circuit from any point on the wiring system to the electrical supply source to facilitate the operation of overcurrent devices should a second ground fault from a different phase occur on the wiring system. The earth shall not be considered as an effective fault-current path.

As for 250.4(B)(4), if we take it literally, we would never be able to run circuit conductors in non-conductive raceways, as there is no guarantee that a faulting ungrounded circuit conductor will fault to an EBC/EGC (especially one that is insulated). It is just as likely that it would fault to another circuit conductor.


So far, what we have are two schools of thought. The following depiction shows the OP (top) and EBC required (bottom)...