Service Question

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bphgravity

Senior Member
Location
Florida
I need some opinions on a proposed service arrangement at a daycare facility in my jurisdiction.

The plans show a 600A meter outside served with 2 sets of 350kcmil conductors from the utility transformer. From the meter, the service conductors run underground to an equipment room inside the building. The 2 sets of 350kcmil terminate in a wireway below two 400A MCB panelboards. From the wireway, one set of 300kcmil conductors are tapped to serve each of the 400A main panels. The calculated load at each main is 250A.

1. Does this arrangement violate 230.70(A)(1)? I say yes.

2. Does this arrangement violate 230.90(A)? I say yes. While Exception #3 may apply to the 800A worth of service overcurrent protection, I don't feel this exception can be used for the 300kcmil taps to the 400A mains.

Any thoughts?
 

lowryder88h

Senior Member
Location
Massachusetts
Service

Service

Bryan, in the description you have stated above, I also believe this is a clear violation of 230.70(A)(1), in which case 230.90(A) becomes a moot point.
 

tryinghard

Senior Member
Location
California
bphgravity said:
1. Does this arrangement violate 230.70(A)(1)? I say yes.

I agree with you but this room may be considered "readily accessible" & "inside the nearest point of entrance of the service conductors". I see allot of this for the utility district I work for and I think in most cases it stretches the intent, most often the disconnect simply should be outside.

bphgravity said:
2. Does this arrangement violate 230.90(A)? I say yes. While Exception #3 may apply to the 800A worth of service overcurrent protection, I don't feel this exception can be used for the 300kcmil taps to the 400A mains.

They may be trying to use the tap rule here?

If this is an active contract (or a bid) I recommend an RFI[?s], word it in such a way that it is a questing and one that demands/pins each issue to individual answers.
 

ryan_618

Senior Member
I think it is a violation of 230.90(A), but not neccassarily 230.70(A)(1). Nearest the point of entrance, as you know, is a subjective phrase. If these conductors didn't enter the wireway, they would be what...12" shorter? If that is the case, I wouldn't worry too much about it.

It sounds to me like you meet 230.40 Exception 2 for the second set of service entrance conductors (not taps), so you are covered there. I think this installation will comply if they change the breakers to 350A.
 

ryan_618

Senior Member
tryinghard said:
They may be trying to use the tap rule here?

You can't create tap condcutors from service conductors [240.2"Tap"]. This is describing a second set of service entrance conductors, meeting the rules of 230.40 via an exception.
 

bphgravity

Senior Member
Location
Florida
Thanks for the comments.

In regard to my first question, I wouldn't have a problem if the conduits extended from the ground directly to the enclosure containing the service disconnecting means. But by inserting another "enclosure" ahead of the service disconnecting means, it is causing me some concern. The use of the wireway in this example is for the purpose of making splices. These splices will require fittings and will remain accessible for the life of the equipment without any means to disconnect them. I'm still not sure on this one.

In regard to the second question, I think we all agree the set of service entrance conductors supplying the main panelboards need to be increased in size or the service overcurrent protection reduced in size.

Thanks.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Bryan
If the service conductors were increased would you need to terminated the conductors in the wireway? or could they pass thru unspliced?
 

ryan_618

Senior Member
benaround said:
That wireway would make this 6 CCC or 80% amp value, can't pipe each set of 350's right to OCPD's ?

True, this is 6 (or perhaps 8) current carrying conductors, but in a wireway that isn't an issue.

376.22: The derating factors in 310.15(B)(2)(a) shall be applied only where the number of current-carrying conductors, including neutral conductors classified as current-carrying under the provisions of 310.15(B)(4), exceeds 30.
 

ryan_618

Senior Member
Bryan, what if you had two sets of service entrance conductors coming from outside, and they simply passed through the wireway, without splice. For example, the underground rough missed layout, and there is no way to offset the raceways fast enough to get into the enclosure. Would you still have a concern?
 

woodduder

Senior Member
Location
West Central FL.
bphgravity said:
Thanks for the comments.
These splices will require fittings and will remain accessible for the life of the equipment without any means to disconnect them.


Thanks.

Are you concerned because it is in the bldg? Services are built like this quite often on the outside where the service lateral hits a trough and then is split into 6 different meters/main disconnects.
 

tryinghard

Senior Member
Location
California
ryan_618 said:
You can't create tap condcutors from service conductors [240.2"Tap"]. This is describing a second set of service entrance conductors, meeting the rules of 230.40 via an exception.

I agree, I was thinking the person designing this application didn't know. I do notice 230.46 does allow tapping service-entrance conductors but the reasons are different than that of article 240.
 

hector pe

Member
Bryan Holland

Bryan Holland

Bryan;

Few comments:

1- The feeder cables serving the 400 amps panels should have the same ampacity.That is , cables feeding the copper busses of the 400amp panels should be 600kcm and not 300kcm. From a safety point of view, supposse we originally install a breaker of 300 amps, which will trip at 240amps. then the cable 350kcm appears to be good , since it will handle 310 amps, load of 250 amps.
Suppose in 5 years, an installer go to the 400 amp panel and say, Ok I have a 400 amp panel, lets increase the load and breaker. What happens is that the cable will be at risk for a fire.

2-Another comment is that we need to be carefull if other subpanels are to be fed from the 400amps panels.Total load cannot be exceeded from 400amps

3- I would recommend a fused disconnect switch , service entrance nema 3R rated for 600amps, at the meter location. I think it is a violation to 230.90A,


Hector Santiago
 

RUWired

Senior Member
Location
Pa.
bphgravity said:
In regard to the second question, I think we all agree the set of service entrance conductors supplying the main panelboards need to be increased in size or the service overcurrent protection reduced in size.

Thanks.
I'd like to jump in here for a few posts. Would'nt 230.90(A) exception 3 allow the service conductors to be smaller than the ocpd.The parallel feed is still larger than the calculated load of the two 400 amp panels. I agree that in design they should be equal to at least the next higher.

Exception No. 3: Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.
Rick
 
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