OCPD and feeder Code violations

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WA_Sparky

Electrical Engineer
Location
Vancouver, WA, Clark
Occupation
Electrical Engineer
I have a project where there are concerning issues with the sizing of their Device and feeders.

There is a 100A service. On the service disconnect/panel there is a 200A breaker and 125A breaker, feeding downstream panels.
Technically if the overcurrent protective devices are rated for their associated existing feeders I believe it should be safe, but are there any code violations?

At the least it's a poor design because it promotes unnecessary false tripping if the total load exceed 100A.

Code articles would be awesome if you have any.

Thanks,
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Is the "100a service" a main breaker?

If so, the others will function more as switches, and each feeder should be capable of 100a.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I have a project where there are concerning issues with the sizing of their Device and feeders.

There is a 100A service. On the service disconnect/panel there is a 200A breaker and 125A breaker, feeding downstream panels.
Technically if the overcurrent protective devices are rated for their associated existing feeders I believe it should be safe, but are there any code violations?

At the least it's a poor design because it promotes unnecessary false tripping if the total load exceed 100A.

Code articles would be awesome if you have any.

Thanks,
If it is a 100 A "service", how could the load ever exceed 100 A? You can hook up as many CBs of whatever rating downstream as you want as feeders but if the service is to code, and it is a 100 A service, it has to have max 100 A OCPD.

I am not sure how it promotes "false" tripping. The CB will not trip unless it sees a short circuit or an overload. Neither of those cases is it a "false" trip.
 

WA_Sparky

Electrical Engineer
Location
Vancouver, WA, Clark
Occupation
Electrical Engineer
Sorry i was looking at an older documents.

There is a 37.5KVA 120/240 1Ø transformer on a pole. The service according to the utility was only intended for 100A.
At some point the disconnect was increased to a 200A.
Within that 200A distribution panel there is a...
200A breaker (assuming its the main disconnect), and 100A breaker
The 100A breaker feeds a sub panel containing:
(1) 40A, (1) 30A, and (1) 125A.
Also, somehow tapped of the main disconnect/distribution is a 200A/4p panel inside the building.
 

WA_Sparky

Electrical Engineer
Location
Vancouver, WA, Clark
Occupation
Electrical Engineer
If it is a 100 A "service", how could the load ever exceed 100 A? You can hook up as many CBs of whatever rating downstream as you want as feeders but if the service is to code, and it is a 100 A service, it has to have max 100 A OCPD.

I am not sure how it promotes "false" tripping. The CB will not trip unless it sees a short circuit or an overload. Neither of those cases is it a "false" trip.
False tripping of breakers meaning if the combined loads of "(1) 40A, (1) 30A, and (1) 125A." exceeds 100A, the 100A protective device will trip even if loads are operating normally.
 

WA_Sparky

Electrical Engineer
Location
Vancouver, WA, Clark
Occupation
Electrical Engineer
The big unknown being if when the service disconnect was upgraded from 100A to 200A, I do not know if the associated secondary transformer feeder was upgraded as well. To the utilities knowledge there should only be a 100A disconnect on the service. I know typically utilities may allow up to 150% of the transformer rating, allowing up to (37.5kV/240V=156.25*1.5) = 234.375A. In this case im more concerned with the feeder rather than the transformers capacity.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
False tripping of breakers meaning if the combined loads of "(1) 40A, (1) 30A, and (1) 125A." exceeds 100A, the 100A protective device will trip even if loads are operating normally.


if he has a 100 A service protected by a 100 A CB, it is not a "false" trip if it opens up if the current exceeds 100 A. That is what it is supposed to do.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
This is definitely a case of "the devil is in the details:"..wire sizes. loads, etc,
I picture (with a lot of room for error) a 200 amp M/B feed thru panel feeding and interior 200 amp panel.
The main panel also equipped with a 100 amp feeder breaker to your other panel.
IF so, and the conductors are properly sized, it may not be a problem dependent on the loads involved.
I would not be concerned about the transformer size but the service conducotr size should be verified
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
If they put in the 200A SE panel without consulting the utility, it is a violation.

If they did notify the utility, and that is ENTIRELY possible, then it's the utility's decision and concern. I have seen it time and time again that someone asks for a larger service, the utility grants their request, and does absolutely nothing different, their rules are not the same as our rules.
 

WA_Sparky

Electrical Engineer
Location
Vancouver, WA, Clark
Occupation
Electrical Engineer
I would think that a load calc would be an important part of such an assessment.
The building is expected to essentially double in size in addition to 8 new residential units, new commercial office space, small workshop, and several new RV pedestals. I anticipate the service will probably quadruple in size.
 
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