Help with 400 amp resi pedestal install

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jjhoward

Senior Member
Location
Northern NJ
Occupation
Owner TJ Electric
Hi Augie;
Yes I do understand that the 4/0 alum conductors are rated at 180 amps per T310.16 75 deg.C.

Can you explain why the 4/0 SEU cable will be rated on only 150 amps?

Thank you.
 

wirebender

Senior Member
okay, i see now where 230.2 allows us to call this one service for 230.40 ex. 2.

I think the Poco was wrong about being able to run a separate line to the shop since it is part of the same structure, though.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Hi Augie;
Yes I do understand that the 4/0 alum conductors are rated at 180 amps per T310.16 75 deg.C.

Can you explain why the 4/0 SEU cable will be rated on only 150 amps?

Thank you.

338.10(B)(4) ('08) references 334. 334.80 says interior NM (SE) is 60?

okay, i see now where 230.2 allows us to call this one service for 230.40 ex. 2.

I think the Poco was wrong about being able to run a separate line to the shop since it is part of the same structure, though.

One building= one service unless one of the exceptions apply
 

kwired

Electron manager
Location
NE Nebraska
I'm not sure I follow you.
He could use 4/0 AL for his service conductors to each panel, but not with one having a calculated load of 190 amps. He would have to limit the load to 180 amps.

Easy solution. Parallel the 4/0 AL then make taps to each panel. The one with 190 amps will need the taps to be 250 AL or 3/0 CU. You will likely have less voltage drop this way also. Now if total load is more than 360 then you will need larger lateral conductors.
 

jjhoward

Senior Member
Location
Northern NJ
Occupation
Owner TJ Electric
Hi Augie;
Since the cable from my trough to the main breaker panel is on the source side of the disconnect, why should it be considered a feeder or branch circuit?

Aren't feeders and branch circuits on the load side of the disconnect?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I thought you were speaking of cables after your service disconnects which must be located at the entry to the struture per 230.72(A)(1)
 

jjhoward

Senior Member
Location
Northern NJ
Occupation
Owner TJ Electric
Ok, I am sorry for the confusion, but I am happy about what you are saying!

Yes, the disconnects are on the main breaker panels which are mounted on the interior wall where the feeders enter the building.

I guess a block diagram would have eliminated a bunch of questions. I will work on that for my nxt project.

Yes, the feeder rating must be applied for my SER cable that will be running through the house to the sub panel in the shop.

And yes, 180 amps for the 4/0 alum feed to the panels.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
The whole problem stems from the SE cable being used as feeder but if it is a service conductor- which we finally realized it is- then art.338.10(B)(4) does not apply. Now the question is why shouldn't it?

It seems ludicrous that the se cable as a feeder with overcurrent protection is rated less then when it does not have overcurrent protection. Some day they will get this article right but I am afraid it won't be in my lifetime.
 

jjhoward

Senior Member
Location
Northern NJ
Occupation
Owner TJ Electric
Hi Dennis;
I always assumed that the difference in ratings between a feeder or branch circuit vs a service cable had to do with the physical attributes of the devices that the wire would be terminated to.

Service equipment is built with the expectation of high current/high heat.
Non service equipment is not built with that expectation high current/high heat.

I guess a review of the spec's for service equipment vs non service equipment would be enlightening.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
Equipment listed at suitable for use as service entrance equipment has either a factory installed or field installable Main Bonding Jumper. Current and heat have noting to do with the rating.
 
Equipment listed at suitable for use as service entrance equipment has either a factory installed or field installable Main Bonding Jumper.

Interesting question- where is the MJB (or SBJ, if you prefer)? With two sets of service conductors,would each panel need a MBJ? (and we're not suppose to have two...)

So, there are two grounded conductors from the meter into the two panels. The panel's grounding systems must be bonded to each other (both panels share the same GES). If both panels have a MBJ, then we have a parallel path- meter -> panel -> GES -> other panel -> meter. If only one panel has a MBJ, then fault current from the other has to travel up to the meter and back. Am I missing something?

(I love discussions like, you learn a lot from them.)
 

kwired

Electron manager
Location
NE Nebraska
As usual, I'm confused.
Would this not be more than one set of service entrance conductors since the meter is located at another structure?
I have a similar installation coming up is why I am so interested in this thread.

Metering equipment location does not determine the ending point of the service.
The Metering equipment is simply allowed to be installed in the supply side of the service. Sometimes metering equipment is installed at the POCO transformer or on their pole and the owner/contractor has little or nothing to do with metering equipment. The service disconnecting means is where we stop calling it service equipment and start calling everything branch circuits or feeders.

If there would be a disconnect (with overcurrent protection) at the meter then the conductors supplying the building would then be feeders. That will change what needs run to the building. For starters if you are using 2008 or 2011 code you now will need an equipment grounding conductor run with the feeder.

If the building is supplied by a feeder it is still allowed up to six disconnecting means but they must be supplied by a single feed. This can be done by installing parallel conductrors as the feeder if you wish meaning they must be tied together at the supply and load ends and then make taps to each disconnecting means.

Interesting question- where is the MJB (or SBJ, if you prefer)? With two sets of service conductors,would each panel need a MBJ? (and we're not suppose to have two...)

So, there are two grounded conductors from the meter into the two panels. The panel's grounding systems must be bonded to each other (both panels share the same GES). If both panels have a MBJ, then we have a parallel path- meter -> panel -> GES -> other panel -> meter. If only one panel has a MBJ, then fault current from the other has to travel up to the meter and back. Am I missing something?

(I love discussions like, you learn a lot from them.)

Yes all of the service disconnects need bonded together and each disconnect will have a MBJ installed.





230.2 Number of Services.
A building or other structure served shall be supplied by only one service unless permitted in 230.2(A) through (D). For the purpose of 230.40, Exception No. 2 only, underground sets of conductors, 1/0 AWG and larger, running to the same location and connected together at their supply end but not connected together at their load end shall be considered to be supplying one service.


230.40 Number of Service-Entrance Conductor Sets.
Each service drop or lateral shall supply only one set of service-entrance conductors.
.
.
Exception No. 2: Where two to six service disconnecting means in separate enclosures are grouped at one location and supply separate loads from one service drop or lateral, one set of service-entrance conductors shall be permitted to supply each or several such service equipment enclosures.

250.24
.
C) Grounded Conductor Brought to Service Equipment. Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor(s) shall be run to each service disconnecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus. A main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure. The grounded conductor(s) shall be installed in accordance with 250.24(C)(1) through (C)(3).

250.28(D)
.
(2) Main Bonding Jumper for Service with More Than One Enclosure. Where a service consists of more than a single enclosure as permitted in 230.71(A), the main bonding jumper for each enclosure shall be sized in accordance with 250.28(D)(1) based on the largest ungrounded service conductor serving that enclosure.
 
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