208 Volts and 4160 Volt Conductors Pull Box

[jap]

If a pullbox is a raceway then whenever you had more than 3 CCC's in it you would need to apply derating.

Would that ever be an issue with 4160 volts.

JAP>

 

[JFletcher]

Why does the thought of 208 and 4160 in the same box scare the **** out of me? Would you need warning signs on such a box, reading "danger-high voltage" or "multiple sources of power" or the like?

If they are not allowed in the same raceway, why would they be allowed in the same pullbox? Why would this even be done?

 

[infinity]

Why does the thought of 208 and 4160 in the same box scare the **** out of me? Would you need warning signs on such a box, reading "danger-high voltage" or "multiple sources of power" or the like?

If they are not allowed in the same raceway, why would they be allowed in the same pullbox? Why would this even be done?

The question is not why, the question is does the NEC prohibit such an installation? I agree with you bad idea but then why does the NEC allow it?

 

[kwired]

Why does the thought of 208 and 4160 in the same box scare the **** out of me? Would you need warning signs on such a box, reading "danger-high voltage" or "multiple sources of power" or the like?

If they are not allowed in the same raceway, why would they be allowed in the same pullbox? Why would this even be done?

They are often inside same terminal cabinet on padmount transformers. Bigger three phase padmounts often have them in separate compartments, but I can't recall seeing a single phase padmount where primary and secondary were not in the same terminal compartment

 

[JFletcher]

They are often inside same terminal cabinet on padmount transformers. Bigger three phase padmounts often have them in separate compartments, but I can't recall seeing a single phase padmount where primary and secondary were not in the same terminal compartment

True, but you'd expect them there. and you're not going to open up an energized 12,470/480V xfmr like you might a pullbox.

I dont think the NEC allows it; you cant put coax in the same box as 120V unless there is a divider, 4160 and 208 in the same box? What about the fact that the 208V wiring will only be insulated to 600V?

 

[infinity]

I dont think the NEC allows it; you cant put coax in the same box as 120V unless there is a divider, 4160 and 208 in the same box? What about the fact that the 208V wiring will only be insulated to 600V?

That's what we're trying to determine. Got a code reference?

 

[Bluewyvern]

I don't think a pull box would be considered a raceway

BTW, welcome to the forum

Thank you for the welcome.

In my experience pull boxes are often used in the middle of a conduit run due to the number of bends needed. These pull boxes meet the dictionary definition of a pull box "a metal box with a blank cover that is installed in an accessible place in a run of conduit to facilitate the pulling in of wires or cables". In this case I don't think you can rationalize that this is not part of the raceway. Manholes are also used as pull boxes and the code has some leeway here as long as the cables are fixed. At the end of a duct you could try to have a pull box that pulls control and medium voltage cables into the same box; however, you would need barriers as a minimum between the cables in the box. You can rationalize that the pull box is not part of the raceway; however, then you are going to be relying on the discretion of the inspector to approve it. To avoid rework, I'd stick with multiple boxes or a barrier as a minimum.

 

[kwired]

True, but you'd expect them there. and you're not going to open up an energized 12,470/480V xfmr like you might a pullbox.

I dont think the NEC allows it; you cant put coax in the same box as 120V unless there is a divider, 4160 and 208 in the same box? What about the fact that the 208V wiring will only be insulated to 600V?

What is the danger in a true pull box when you don't even have anything terminating in there?

Individual conductor insulation level should only matter if in same raceway.

If you had relays, contactors, etc. in an enclosure you very well could have the medium voltage as the power circuit and the low voltage as a control circuit.

 

[Bluewyvern]

What is the danger in a true pull box when you don't even have anything terminating in there?

Individual conductor insulation level should only matter if in same raceway.

If you had relays, contactors, etc. in an enclosure you very well could have the medium voltage as the power circuit and the low voltage as a control circuit.

The danger is the same as when they are run in the same raceway. If insulation degrades on the medium voltage circuit's cable then there is the possibility it could short through the 600-1000V insulation on the low voltage circuit but not to ground. This can send medium voltages to numerous areas leading to possible personnel injury/death, equipment damage, arcing, and fires without ever tripping the medium voltage overcurrent protection.

 

[jap]

The danger is the same as when they are run in the same raceway. If insulation degrades on the medium voltage circuit's cable then there is the possibility it could short through the 600-1000V insulation on the low voltage circuit but not to ground. This can send medium voltages to numerous areas leading to possible personnel injury/death, equipment damage, arcing, and fires without ever tripping the medium voltage overcurrent protection.

This is one of those "What if" situations.
The same would happen when mixing 480v and 120v circuits in the same conduit, or, service entrance conductors in the same raceway as feeder conductors, but, the insulation would have to degrade on both cables at the same place and at the same time for that to happen.

Not sure if there might not be some induction issues to contend with also dealing the the High Voltage cables such as 4160 if mixed with lower voltage cables.

I wouldn't mix High and low voltage cables like this in the same raceway at all.

The lower voltages such as mixing 480 and 120v in the same raceway doesn't bother me so much.

I know what they say, and , I'll probably get criticized, but in my mind, the chances of insulation degrading on 2 different voltage cables in the same raceway at the same time where they short together and bypass the overcurrent protection ahead of it would be slim.

But that's JMHO.


JAP>

 

[Bluewyvern]

This is one of those "What if" situations.
The same would happen when mixing 480v and 120v circuits in the same conduit, or, service entrance conductors in the same raceway as feeder conductors, but, the insulation would have to degrade on both cables at the same place and at the same time for that to happen.

Not sure if there might not be some induction issues to contend with also dealing the the High Voltage cables such as 4160 if mixed with lower voltage cables.

I wouldn't mix High and low voltage cables like this in the same raceway at all.

The lower voltages such as mixing 480 and 120v in the same raceway doesn't bother me so much.

I know what they say, and , I'll probably get criticized, but in my mind, the chances of insulation degrading on 2 different voltage cables in the same raceway at the same time where they short together and bypass the overcurrent protection ahead of it would be slim.

But that's JMHO.


JAP>

This is not the same as mixing 480 and 120 v circuits because most 120 v circuits have insulation capable of handling up to 600 volts. Most low voltage cable insulation is not rated to handle medium scale voltages such as 4kv. Thus failure of just the medium voltage cable insulation is enough to cause a significant problem.

 

[ken44]

The last sentence in 300.C (2) of 2017 NEC states that "Conductors having nonshielded insulation and operating at different voltage levels shall not occupy the same enclosure, cable, or raceway." The intent of the article is clear and is in harmony with 90.1 (A) and (B).

 

[jap]

This is not the same as mixing 480 and 120 v circuits because most 120 v circuits have insulation capable of handling up to 600 volts. Most low voltage cable insulation is not rated to handle medium scale voltages such as 4kv. Thus failure of just the medium voltage cable insulation is enough to cause a significant problem.

I don't think so.
Even if the 4kv cable failed and it happened to be in the same raceway as 600v rated cable, I cant see a catastrophic event occurring unless the 600v insulation just so happened to break down and expose the conductor in that general location.

JAP>

 

[jap]

The damage will take place if the higher voltage travels down the lower voltage conductor.

JAP>

 

[Bluewyvern]

I don't think so.
Even if the 4kv cable failed and it happened to be in the same raceway as 600v rated cable, I cant see a catastrophic event occurring unless the 600v insulation just so happened to break down and expose the conductor in that general location.

JAP>

My point about the insulation capability of the low voltage circuit is that it would be degraded to failure by contact with the medium voltages in the other circuit. So, although takes both insulations to fail, the failure of the medium voltage insulation would cause failure of the low voltage insulation. Thus the failures are not independent.

 

[jap]

My point about the insulation capability of the low voltage circuit is that it would be degraded to failure by contact with the medium voltages in the other circuit. So, although takes both insulations to fail, the failure of the medium voltage insulation would cause failure of the low voltage insulation. Thus the failures are not independent.

So your saying a 600v cable will fail by the exposed conductor of a medium voltage cable simply touching it ?

JAP>

 

[JFletcher]

That's what we're trying to determine. Got a code reference?

Thank you for the welcome.

In my experience pull boxes are often used in the middle of a conduit run due to the number of bends needed. These pull boxes meet the dictionary definition of a pull box "a metal box with a blank cover that is installed in an accessible place in a run of conduit to facilitate the pulling in of wires or cables". In this case I don't think you can rationalize that this is not part of the raceway. Manholes are also used as pull boxes and the code has some leeway here as long as the cables are fixed. At the end of a duct you could try to have a pull box that pulls control and medium voltage cables into the same box; however, you would need barriers as a minimum between the cables in the box. You can rationalize that the pull box is not part of the raceway; however, then you are going to be relying on the discretion of the inspector to approve it. To avoid rework, I'd stick with multiple boxes or a barrier as a minimum.

I agree with the bolded part too... I'm going with pull boxes are part of a complete raceway system, same as a stick of EMT, elbow, or LB. 300.3(C)(2). Even if the wording somehow leaves pullboxes out of the exact language, I'm going to infer the intent of the code here is to never have conductors of systems above 600V mixed with those under, unless mentioned in one of the small letter subsections under that section, like (e) pertaining to manholes.

I know this section has already been mentioned and shot down. Meh.

 

[jap]

I'm going with pull boxes are part of a complete raceway system, same as a stick of EMT, elbow, or LB. 300.3(C)(2). Even if the wording somehow leaves pullboxes out of the exact language, I'm going to infer the intent of the code here is to never have conductors of systems above 600V mixed with those under, unless mentioned in one of the small letter subsections under that section, like (e) pertaining to manholes.

But they are not the same.
A stick of EMT, an Elbow, and an LB are generally the same trade size as the raceway they are being installed upon.
A pullbox is just that and has its own set of rules for sizing and fill requirements.

JAP>

 

[JFletcher]

Lets try this from a different angle: say you had installed conductors from 4160 and 208 in the same box, coming in from 2 different conduits/exiting 2 different conduits... simply one box was used as a dual pull point. Inspector fails it citing 300.3(C)(2). Do you think you would win an argument with him or his supervisor, or put in another pull box?

jap, I understand they have different requirements for CCC and sizing, however a pull box installed in a complete raceway has to by definition be part of that raceway - box to panel and everything in between.

Surely this question has been proposed to the CMP and a ruling has already been issued?

 

[JFletcher]

If a pullbox is a raceway then whenever you had more than 3 CCC's in it you would need to apply derating.

No more than a 8 gang switch box containing 20 or so CCC needs derating, or a 42 circuit panel needs derating. Just because certain parts of a complete raceway have different requirements... I guess I'm having a problem with this as a pull box would be somewhere in the middle rather than at the end. You're not going to find 4160 mixed with 208 in a switch box, or a panel, or a conduit... why is a pull box exempted? If it truly is, then my answer is "by mistake".

I've said my peace, win or lose. and I hope I never come across a pull box with 4160 in it if I'm working on a 208 or 480 system. I can imagine MH making a video on this and saying "No! you can't mix 4160 with 208! Anywhere!"

eta: if the conductors were fixed and there was a barrier ala the manhole requirement, I'd be okay with it. iow if pull boxes were treated the same as manholes, or (e) mentioned them specifically along with manholes.