Phases in separate pipe?

[nightmare]

I am required to mitigate what is widely thought to be an impending major electrical disaster. 4 4" PVC pipes in concrete with 4 A's in one, 4 B's in the next and so on.
They are 500's and there is one extra 500 per pipe as a spare. There was no earth ground when I arrived so I have since pulled a 1/0 through each pipe. I did this expecting to phase the work and provide ABCNG in each pipe. I have less than perfect megger results on a couple of the feeds which might cause a problem for my original plan. I am, therefore, exploring my options.

Is it bad/dangerous/code violation to put one phase per pipe and, if so, please explain? :-?

The only explanation I have gotten so far is in three parts:

1. that's the way I learned it
2. they will blow up if they ever pass through a metallic ring of any kind
3. you will really hurt someone if they ever cut into the single phase accidentally

 

[Besoeker]

I am required to mitigate what is widely thought to be an impending major electrical disaster. 4 4" PVC pipes in concrete with 4 A's in one, 4 B's in the next and so on.
They are 500's and there is one extra 500 per pipe as a spare. There was no earth ground when I arrived so I have since pulled a 1/0 through each pipe. I did this expecting to phase the work and provide ABCNG in each pipe. I have less than perfect megger results on a couple of the feeds which might cause a problem for my original plan. I am, therefore, exploring my options.

Is it bad/dangerous/code violation to put one phase per pipe and, if so, please explain? :-?

The only explanation I have gotten so far is in three parts:

1. that's the way I learned it
2. they will blow up if they ever pass through a metallic ring of any kind
3. you will really hurt someone if they ever cut into the single phase accidentally

At least it's PVC pipe and not steel. The phases not being perhaps as physically close as they would otherwise be gives the possibility of an inductive loop.
Passing through a metal ring shouldn't be a problem as long as all the phases pass through the same ring.
I can't comment on code compliance.

 

[masterinbama]

Here's a photo from another post of how it should look on both ends. Or one end can come up in a pad mount transformer.

[/QUOTE]

 

[augie47]

To my knowledge, with the PVC pipes and "open bottom" gear, it is not a Code violation. I have seen it on occasion, however, 1 of the regional POCOs will not accept it. I believe their reason was "induction" problems.

 

[nightmare]

Inductive loop?

Inductive loop?

I thought I understood inductance and magnetism very well but maybe not? Please explain what is meant by an inductive loop and how it applies to this topic. I really know that a picture should be worth a thousand words but it will not be for the other electricians I am working with on this job. help???

does the application matter?

these are feeders that emanate from an MDP that is fed by some reasonably large D/G's. 800 breaker feeding a disconnect that is 10' away and then approximately 700' of ductbank to an 800 A I-line panel.

If the phases stay individually in each pipe and the neutrals are all in one pipe, then does the earth ground stay in each pipe?

 

[Sierrasparky]

I thought I understood inductance and magnetism very well but maybe not? Please explain what is meant by an inductive loop and how it applies to this topic. I really know that a picture should be worth a thousand words but it will not be for the other electricians I am working with on this job. help???

does the application matter?

these are feeders that emanate from an MDP that is fed by some reasonably large D/G's. 800 breaker feeding a disconnect that is 10' away and then approximately 700' of ductbank to an 800 A I-line panel.

If the phases stay individually in each pipe and the neutrals are all in one pipe, then does the earth ground stay in each pipe?

If the wires are in PVC as you describe and are in close proximity and in the same trench I don't see the problem.

Now if there are metal elbows and fittings then I suppose you have a problem.

 

[Besoeker]

I thought I understood inductance and magnetism very well but maybe not? Please explain what is meant by an inductive loop and how it applies to this topic.

Puting the phases in separate pipes would increase the physical seperation between them. Increasing that increases the inductance of a pair of parallel wires.
The term on question is ln(d/a) where d is the distance between the conductors and a is the radius of the conductor.
Greater d means greater inductance, all other things being equal.

 

[Sierrasparky]

Puting the phases in separate pipes would increase the physical seperation between them. Increasing that increases the inductance of a pair of parallel wires.
The term on question is ln(d/a) where d is the distance between the conductors and a is the radius of the conductor.
Greater d means greater inductance, all other things being equal.

Code allows it if in PVC. I'm sure when they wrote the code they knew that all the conduits cannot occupy the same place. :roll:

 

[Besoeker]

Code allows it if in PVC. I'm sure when they wrote the code they knew that all the conduits cannot occupy the same place. :roll:

But the three phases could be in closer proximity if they all went down the same tube. Sure,you might need several tubes but each coud have all three phases. Loop inductance would be lower.
I don't know how much that matters.

 

[richxtlc]

If the conduit was RMC or other metal and they were physically bonded together (conduits) at each end, with one phase in each conduit, this would set up a magnetic circuit similar to that in the armature of an induction motor. it would create a tremendous amount of heat and eventually cause the failure to the equipment. I believe this is what POCO was concerned about.
As stated in one of the other threads, it does increase the inductance of the circuit as compared to one with all phases in a single conduit.
I don't see a magnetic circuit problem as you are using PVC and not metal.

 

[nightmare]

safety

safety

If there is a correctly sized earth ground in each pipe, are there any extenuating life safety issues that I might be missing?

 

[augie47]

If there is a correctly sized earth ground in each pipe, are there any extenuating life safety issues that I might be missing?

I beleive in the narrative accompanying the picture he stated "service".

 

[iwire]

FWIW the rules for isolated phase installations can be found in the exception to 300.3(B)(1).

 

[C3PO]

You might also want to look at 300.5(I)


You said in concrete??? Is this concrete underground???????

 

[roger]

If there is a correctly sized earth ground in each pipe, are there any extenuating life safety issues that I might be missing?

An "earthed" conductor plays a very small (if any) part in protecting people, we need to understand and note the difference between a Grounding conductor and an Equipment Grounding conductor. The conductor you are talking about would (should) be an EGC which terminates to the system Neutral / Grounded Conductor.

Roger

 

[CFL]

An "earthed" conductor plays a very small (if any) part in protecting people, we need to understand and note the difference between a Grounding conductor and an Equipment Grounding conductor. The conductor you are talking about would (should) be an EGC which terminates to the system Neutral / Grounded Conductor.

Roger

Did you mean to say grounded conductor and equipment grounding conductor?

 

[roger]

Did you mean to say grounded conductor and equipment grounding conductor?

No, I meant Grounding (as in earthing) and Equipment Grounding.

Roger

 

[C3PO]

I had a situation a while back on a service where I tried to run an iso phase and the POCO refused to hook it up. See this post.

http://forums.mikeholt.com/showpost.php?p=914122&postcount=24


Here is the whole thread:

http://forums.mikeholt.com/showthread.php?t=103981

 

[CFL]

No, I meant Grounding (as in earthing) and Equipment Grounding.

Roger

Thanks. I wanted to know before I put any thought into it.





O.k., I thought about it. How does this apply to this situation? Would a grounding conductor make a difference?

 

[CFL]

I'm sorry Roger, I didn't read what youy were qouting in the first place. Nevermind what I asked.