Tapped or Parallel service

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DougChris

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Rockford, IL USA
A question regarding legality of an old split bolt connection ahead of two main breakers in distribution panels.

I have come across an old 480V 3-wire service where the incoming service conductors are 'tapped' using a split bolt before the main breaker of two separate panels. The service entrance cable is 4/0 to a 325A main breaker while the 'tapped' connection is 350kcmil to a separate 200A main breaker about 15 feet away. The attached pictures show the first 480V panel where the splice or 'tapped' connection is made with taped split bolts. I would like to know if this is code compliant?
DSC04041.jpgDSC04042.jpg
 
My description may not be clear. The main service entrance cables (4/0) are routed into the panel shown. The 4/0 cables continue to the 325A main breaker in the panel shown. There is a split-bolt tap (shown taped) where the 350MCM cables then feed a 200A main breaker in another panel. In other words the 4/0 service entrance cables are tapped before the 325A main via split bolts and then run to two main breakers in separate panels.
 
I assume there is no breaker ahead of the 4/0 service conductors. If this is the case you probably have a violation of art. 230.70(A)(1) just for starters
 
Correct, the 4/0 cables are attached to the service entrance transformer terminals with no protection between the transformer terminals and mains of the two breakers.
 
Well then I see this as a violation since article 240 talks about taps but they are feeder taps. It appears to tap the se cable you would need to be sized to the overcurrent protective device. 230.90
 
Dennis Alwon said:
Well then I see this as a violation since article 240 talks about taps but they are feeder taps. It appears to tap the se cable you would need to be sized to the overcurrent protective device. 230.90
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As soon as you have more than one service OCPD, the conductors only have to be sized to the calculated load. Exception #3.
 
don_resqcapt19 said:
As soon as you have more than one service OCPD, the conductors only have to be sized to the calculated load. Exception #3.
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Yes but can they have a 350 amp overcurrent protective device protecting 4/0 wire? I thought 230.90(A) would require that the overcurrent protective device be sized for the 4/0
 
IMO, Since your service entrance conductors are supplying more than one breaker they can be sized per load without taking the breaker ratings into account.
What you show is Code compliant (as far as the taps are concerned) but dangerous as a cocked gun as the possibility of a severe overload of the conductors is possible.
 
augie47 said:
IMO, Since your service entrance conductors are supplying more than one breaker they can be sized per load without taking the breaker ratings into account.
What you show is Code compliant (as far as the taps are concerned) but dangerous as a cocked gun as the possibility of a sever overload of the conductors is possible.
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Also the distance of 15 feet between one panel and the other may violate 230.70(A)(1)
 
Dennis Alwon said:
Nevermind I see exception 3 allows it.
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Exception No. 3 allows the sum of multiple breakers to exceed the ampacity of the service conductors... but not the individual breakers to exceed the service conductors supplying it [although Exception No. 2 permits next standard size up under 240.4(B)].

For a 325A breaker, the nominal tap size would have to be 350kcmil@310A.

The 350kcmil tap to the 200A panel breaker is fine, but could have been as small as 3/0.

It appears they either got the wire sizes reversed or the panels.


One would think the main service conductors should be required to at least have an ampacity greater than the highest rated OCPD... :happyyes:
 
Smart $ said:
Exception No. 3 allows the sum of multiple breakers to exceed the ampacity of the service conductors... but not the individual breakers to exceed the service conductors supplying it [although Exception No. 2 permits next standard size up under 240.4(B)].
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Smart you always have an interesting perspective on the NEC even if I disagree with it. :D Now where does it say that one of the 2 breakers that are added together cannot be larger than the service conductors. That was my thought but I don't see except. 3 supporting that thought.

To be honest I have never seen anyone take advantage of this rule
 
Dennis Alwon said:
Also the distance of 15 feet between one panel and the other may violate 230.70(A)(1)
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Dennis, I overlooked the distance and was thinking of similar situations I have encountered over the years where the service disconnects were side by side.
I agree that the 15ft distance might well make it a violation of 230.70(A)(1),, it would here but obviously that's a allowance based on the AHJ.
 
Dennis Alwon said:
To be honest I have never seen anyone take advantage of this rule
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Very commonly used in my area when you look for it, both in commercial and in multi family dwellings.

I worked at one industrial building that had 1200 amps of service conductors with about 3600 amps of overcurrent protection. I brought it up on the forums about 12 - 14 years ago and that is when Don taught me about that exception. :)
 
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