300A service

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electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Occupation
Electrician
Hi all, Just wanted to get confirmation that what I am planning to do is compliant, I?ve never done a 300 Amp service this way before. I plan to use a 325/400 amp meter pan which is to be mounted on a post 90 feet from the house. A 2.5 inch pvc conduit carries the service conductors into the garage of a single family dwelling, where I plan to install a 200A service panel and a 100A service panel. I plan to install two sets of service conductors in the 2.5 inch pvc, one sized for the 200A and one for the 100A (meter pan has dual load side lugs) I guess the two things I am not quite sure of are:

1. Can two sets of different sized service conductors be installed in the same pipe? They are not paralled, they just each feed their respective panels. 230.7 states that "conductors other than service conductors shall not be installed in the same raceway" so presumable there is no problem unless another article applies.

2. How is diversity interpreted when more than three current carrying conductors are installed in the same raceway? Do I have to derate 80% per table 310.15(B)(2)(a)? Obviously the chance of each panel being even close to fully loaded at he same time is minimal. I also just noticed that table 310.15(B)(2)(a) states the adjustments are for tables 310.16-310.19, but what if I am using table 310.15(B)(6) to size my conductors?

Thanks everyone, Ethan.
 
Re: 300A service

Table 310.15(B)(6) is not included in the ampacity adjustments of [.15(B)(2)(a)], because the table [.15(B)(6)] is for 3-wire dwelling services. The fact that you would like to run 2 sets of conductors may affect the ability of using this table [.15(B)(6)], and consequently the relaxing of the size of the service entrance conductors permitted by this table.

Why do you not run one set of service entrance conductors?
 
Re: 300A service

Hi pierre,

Yes I suppose I could run 250 copper from the meter to a box below or next to the panels, and tap off of that with a 2/0 and 4 AWG for the 200 and 100 Amp panels respectively (per 240.21(B)(1), taps not over 10 feet). I guess the disadvantage is I would have to get and install another piece of equipment, deal with the tapping , and keep it accessable, however maybe that approach would be safer than risking gettting bit by the inspector. Oh and I have been curious for some time, where in the code does it imply that 240.21(B), "feeder taps", can be applied to service entrance conductors? 230.46 is very brief and does not give any details on tapping.

Regards,
Ethan.
 
Re: 300A service

It appears to me that you wish to bring two service laterals to one structure which is a violation of 230.2

Also, 240.21(B) does not apply to service taps.
 
Re: 300A service

Bryan, i believe 230.40 exception 2 allows me to bring two service laterals to my disconnects. Do you agree? I am actually leaning toward running one set of service laterals and tapping off of them for each panel as this would simplify matters. Also this would allow me to size the single set of service laterals by the computed load and not the sum of the disconnect ratings (I think!), so i could use say 4/0 coppper rather than 250. I like it, anyone else?
Ethan.
 
Re: 300A service

No, I don't believe 230.40 Exception 2 does apply. This section doesn't permit you to bring two service laterals, it permits more than one set of service-entrance conductors. You are proposing bringing two service laterals to the building not service-entrance conductors, at least by definition.
 
Re: 300A service

230.2 does allow multiple sets of underground service conductors (1/0 or larger) if they are connected together on the supply end...

If you stuff them in the same conduit, you must derate according to the number of current-carrying conductors according to table 310.15(B)(2)(a)...

I like the idea of running one set of conductors sized for the load to be served and tapping at the building in a gutter and drop into each disconnect...see 366.9, 240.21(D) and 230.90 exception #3

I do agree with peirre, you can not use table 310.15(B)(6) for reduced sizing of your multiple sets of tap conductors to your disconnects. Size each according to the load to be served and select overcurrent protection according to 230.90(A)

shortcircuit2

[ March 10, 2005, 04:43 AM: Message edited by: shortcircuit2 ]
 
Re: 300A service

I'm with Allen on this one.

Wouldn't it be better to just pull the SE conductors into a 300 amp panel, and pull the 100 amp panel out of that? Why is this not being considered? :confused:
 
Re: 300A service

Thanks for all the input guys, I think the one set of conductors sized for the load, taps to the panels is the best way for me to go here. Bryan, I mistyped when I said service laterals, I meant SE conductors. The meter is not located on the structure but 75 feet away, however my interpretation of the definition is that the conductors between the remote meter and the disco would still be SE conductors. Regarding the other questions: The reason I didnt go with a 300 A service disco and use 200 and 100 amp subs is it would be more expensive (the homeowner already has the 200 A main breaker panel for one thing), and i prefer setting up mains than subs, quicker and easier. Just my preference. Where I come from, the muliple main panel method is what was always done, just seems to be the cheapest and easiest way to do services over 200A. I have just only done multiples of 200A, the different sizes threw me a bit, as well as the fact that the pipe was not run ideally for this scenario (one pipe rather than two). I have actually never seen a 300 amp panel with branch circuits, was not aware anyone made a residential panel over 200A, I suppose for a price you can get anything. Thanks again everyone, the fun begins tomorrow!

Ethan
 
Re: 300A service

electrofelon...I was curious if your local AHJ and utility company allow the...

"meter pan mounted at the post 90 feet away"

without a disconnect at the post which is a structure as defined by the NEC?

It is allowed around my area by most jurisdictions that I have worked in.

shortcircuit2
 
Re: 300A service

Ethan i did a home about 4 years ago 32,000 sq. ft.800amp ct service No mdp ,underground to ct enclosure,then a 5 ft trough to 4 200`s for interior panels and a 150 for landscape lighting and a 100 for a 8 car garage that had an office above it
 
Re: 300A service

Did an indian church in Oklahoma last year,POCO had already set the meter and a non fused disc about 150 ft from where the building was to be built.Ran 4/0 al use to a 200 amp disc that backed to backed a mlo panel.Since it was on indian land no inspections were required :D
 
Re: 300A service

Originally posted by shortcircuit2:
I was curious if your local AHJ and utility company allow the... "meter pan mounted at the post 90 feet away" without a disconnect at the post which is a structure as defined by the NEC?
Click to expand...
Don't lose sight of the fact that our meter fitting is not service equipment, think of it as a wide place in the conduit. It is no different than having a riser on a pole from an overhead service drop and then running underground to a building. All you are doing is inserting a meter fitting and changing the name of the conductors from service lateral to service entrance conductors. :D
 
Re: 300A service

charlie...I agree with you,but the code requires each building or structure to have a disconnecting means.

Would 230.70 apply to the post because it is a structure as defined by artical 100?

I'm refering to 2002NEC...

Does the wording in 230.70 "in a building or other structure" allow for omitting the disconnect for the post because no conductors enter the structure?

shortcircuit2
 
Re: 300A service

I think common sense would prevail here. Would you need a disconnecting means on a service pole that had a riser on it the went to a home? That is done all the time so why would a disconnecting means be required if a cash register was added? :D
 
Re: 300A service

Your individual taps to the 200 amp and 100 amp panels would need to be 3/0 and #3 copper respectively. Table 310.15(B)(6) only applies to the main power service and feeder. As soon as you subdivide that table no longer applies.

Your underground conductors per that table could be 250 KCM copper. Cross checking against table B.310.7 indicates that you could use 250 KCM but you would be better off using 300 KCM copper. Annex B is mandantory in Canada and some states in the U.S. The laws of heat transfer do make annex B mandantory even in the absence of legislation.

As for 2 pipes, 1 100 amp and the other 200 amp, you would need 3/0 copper and #2 copper. However, 300 KCM would give you better efficiency and voltage regulation unless you are using 1 panel for lights and the other for motors that dim the lights.

If your run was 300 feet then I would use two 200 amp lines, 1 for motors and heaters and the other for everything else..
 
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