Riser Diagram, review

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Npstewart

Senior Member
Ive been revising this riser too many (see attachment) times due to new information. Usually when I revise something too much I make mistakes, anyone see an issue with this riser?

Also, im feeding panel "a" from the transformer with 500's. One time a plan review said I needed to use 600's when I did that due to a section in article 450.

I would appreciate anyones opinion.

PS. I know I need to revise the note that says "150A/3P" to "225A/3P"

THANKS AHEAD OF TIME :)
 
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somedudeindallas

Member
I would be more comfortable with a 3-1/2"C on the service entrance. Do you have a means of disconnect for the service entrance as it comes to the building? The note about the panel being within 25' for the transformer is a little open. Might want to revise to say the max feeder length is 25'. I got burned on a similiar note on one of my jobs (heigh ceiling added another 15').
 
charlie b

charlie b

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Retired Electrical Engineer
1. You said that you were going to feed panel A with 500?s. But you aren?t. You are feeding panel A with a pair of 3/0 runs. Did you really mean that you are going to feed panel C with 500?s?

2. You probably can?t feed panel C with 500?s. They have an ampacity of only 380. If you have a load calculation that shows the total load on panel C is under 380, then you can use 500?s, and you can protect them with a 400 amp main breaker on panel C. But if you can?t show that the load on panel C is under 380 amps, then you need to use a feeder that is has an ampacity at least as high as the 400 amp panel rating.

3. Your note is incorrect, and it?s not just a typo on the breaker rating. There is a 25 foot limit, but it has to do with the secondary run, not the primary feeder. Once you have a circuit breaker protecting the primary feeder, you can run as far as you like, before getting to the transformer.

4. How close is the transformer to panel A? Are you planning to use the 25 foot tap rule? If so, do you meet the requirements of 240.21(C)(3) (e.g., industrial installation, qualified access only)? If not, then the limit is 10 feet, not 25.

5. I can?t tell if you plan to use a breaker on panel A to feed the transformer. You need one, because the feeder between panel A and the 225A C/B would not be otherwise protected.

6. I don?t know why you have the 225 amp C/B anyway. Presuming that you have a breaker in panel A, the separate C/B serves no required purpose.

7. I do not know what the ?TC? box signifies.
 
augie47

augie47

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State Electrical Inspector (Retired)
similar to charlieb's comments except, you must use 600 kcmil or conductors rated at 400 amps, to feed Panel "C" (240.21)(C) and
it's panel C that must be within 25 ft of the transformer, not the 225 amp breaker. Also your feeds to the 225 amp breaker must comply the the appropriate tap rules. The #1s feeding panel B need protection.
 
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Npstewart

Senior Member
I actually confused Panel "A" & Panel "C", I typically call my panel after the Xfrmr Panel "A", and the one feeding the Xfrmer "H1"

this is applying to "charlieb"

2) I typically feed 400A panels with 500s but for some reason the NEC doesent allow it when its coming from a Xfrmr, I cant quote the article exactly. I appreciate the suggestions and I definitley will be using 600s after the reassurance.


3) I was under the impression you needed to be able to disconnect the Xfrmr within 25' from where it was being fed from. not the case?

4) The Xfrmr is sitting in the same room with Panel "C", and about 40 feet from panel "a".

5) I have a breaker in Panel "A" feeding the Xfrmr, its a 225A breaker.

6) I have the disconnect between panel and the Xfrmr because it exceeds 25'. This whole 25' thing is getting me confused lol. From what I understand you need to be able to disconnect the transformer within 25' (vertical + horizontal) of the panel its feeding

7) the T/C is a timeclock controlling the sign. Im not sure about other areas but our Energy code where im from requires that the signage and exterior lights to be controlled by a astromical time clock with a photocell over-ride

replying to augie:

Im feeding Panel "B" from Panel "C" with a 125a/3p breaker which protect it.

Replying to somedudeindallas:

The 3" conduits are actually existing which ill be notating now so I cant change to 3". Also, I wasnt going to put a main disconnect outside, im not sure where it is in the NEC but supposedly if only have to go through one door, then you dont need a disconnect, correct?

Sorry for not posting my panel schedules as well as my load calcs. I know you typically need to see whats in the panels before the riser makes sense.

I also wanted to thank everyone for replying to my post, any more suggestions would be greatly appreciated!

Nick
 
augie47

augie47

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Tennessee
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State Electrical Inspector (Retired)
Npstewart said:
I actually confused Panel "A" & Panel "C", I typically call my panel after the Xfrmr Panel "A", and the one feeding the Xfrmer "H1"

this is applying to "charlieb"

2) I typically feed 400A panels with 500s but for some reason the NEC doesent allow it when its coming from a Xfrmr, I cant quote the article exactly. I appreciate the suggestions and I definitley will be using 600s after the reassurance.
Click to expand...

240.21(C)
Npstewart said:
3) I was under the impression you needed to be able to disconnect the Xfrmr within 25' from where it was being fed from. not the case?
Click to expand...
No such requirement
Npstewart said:
4) The Xfrmr is sitting in the same room with Panel "C", and about 40 feet from panel "a".
Click to expand...
Violation 240.21(C)
Npstewart said:
5) I have a breaker in Panel "A" feeding the Xfrmr, its a 225A breaker.

6) I have the disconnect between panel and the Xfrmr because it exceeds 25'. This whole 25' thing is getting me confused lol. From what I understand you need to be able to disconnect the transformer within 25' (vertical + horizontal) of the panel its feeding
Click to expand...
On the secondary side 240.21(C) 25 ft rule
Npstewart said:
7) the T/C is a timeclock controlling the sign. Im not sure about other areas but our Energy code where im from requires that the signage and exterior lights to be controlled by a astromical time clock with a photocell over-ride

replying to augie:

Im feeding Panel "B" from Panel "C" with a 125a/3p breaker which protect it.

Replying to somedudeindallas:

The 3" conduits are actually existing which ill be notating now so I cant change to 3". Also, I wasnt going to put a main disconnect outside, im not sure where it is in the NEC but supposedly if only have to go through one door, then you dont need a disconnect, correct?

Sorry for not posting my panel schedules as well as my load calcs. I know you typically need to see whats in the panels before the riser makes sense.

I also wanted to thank everyone for replying to my post, any more suggestions would be greatly appreciated!

Nick
Click to expand...
 
charlie b

charlie b

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Lockport, IL
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Retired Electrical Engineer
I think this person needs a lesson on "Charlie's Rule." In due modesty, I think I should leave that to another member. :grin:
 
don_resqcapt19

don_resqcapt19

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Location
Illinois
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retired electrician
charlie b said:
...
2. You probably can?t feed panel C with 500?s. They have an ampacity of only 380. If you have a load calculation that shows the total load on panel C is under 380, then you can use 500?s, and you can protect them with a 400 amp main breaker on panel C. But if you can?t show that the load on panel C is under 380 amps, then you need to use a feeder that is has an ampacity at least as high as the 400 amp panel rating. ...
Click to expand...
Charlie,
These are transformer secondary conductors and the load does make any difference. These conductors must be protected at or below their ampacity. The provisions of 240.4(B) do not apply.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
augie47 said:
Npstewart said:
4) The Xfrmr is sitting in the same room with Panel "C", and about 40 feet from panel "a".
Click to expand...
Violation 240.21(C)
Click to expand...
Not a violation. There is no requirement for distance from primary OCPD to transformer.

However, there may be an issue with a disconnect not at the point of entry. Npstewart makes no mention as to whether panel A is attached to exterior of building or not, and I wouldn't call 40' away from building near the point of entry. Though distance isn't stipulated, we know for mobile homes it is limited to 30'.
 
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Mike01

Mike01

Senior Member
Location
MidWest
C/T cabinet

C/T cabinet

correct me if I am wrong but typically over 400A don't you need a C/T cabinet??

P.S. I also agree with Charlie B's comments.
If you use a 400A C/B use parallel 4/0's or could use 600's but 600's just tougher to bend..
 
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Volta

Senior Member
Location
Columbus, Ohio
I think that the GEC from the transformer to the CWP needs to be a 1/0 cu 250.30(A)(3).

I think that the EBJ from the source to the disconnect in panel C needs to be a 1/0 250.30(A)(2) > 250.102(C) > 250.66

You show six wires from C to B. Duplicate EGC?

Best location for the TVSS? Would it not be more effective at the service?
 
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