200 amp subpanel installation

[tomgquinn]

I am installing a 200 amp subpanel in an old school building. The panel will feed a kitchen.

200 amp subpanel panel is 100 ft away from main 400 amp panel. The panel is an old GE with solid copper bussbars about 1 1/2 wide and 3/8 inch thick.

There is no snap in 200 amp breaker listed for installation in this panel... however, There are lugs on the bussbars (after the 400 amp breaker) rated to hold up to 4/0 wire.

If i understand code correctly, it would be appropriate to place a 200 amp disconnect within 6 feet (actually about 6 inches)away from the 400 amp panel, attach 3/0 copper from lugs on 400 amp bussbars to line side of 200 amp disconnect, and a 3/0 between the neutrals. A #4 copper ground conductor should also be run and at the disconnect the ground and neutral are split.

Q:: Because the 200 amp disconnect is within 6 feet of the 400 amp panel, the feeds can be sized based on the lower 200 amp overcurrent device. (3/0 instead of larger.)

Q::If I am reading UGLY book right... (no NEC available, sorry) The fourth (grounding)conductor would be #4 copper.

Then, from the disconnect, 3/0 copper and #4 ground are run (in 2" EMT) to the 200 amp subpanel and agin, the neutral and ground remain seperated.

sound ok?

 

[hornetd]

Re: 200 amp subpanel installation

For the sake of my education may I ask were you are getting the six foot distance from. I we check the tap rules the twenty five foot tap rule would seem to apply because the Over Current Protective Device that the tap supplies is more than one third of the circuit from which the tap is taken. Your installation sounds fine to me.
--
Tom

 

[iwire]

Re: 200 amp subpanel installation

As hornetd said the 25' tap rule could be used for this, and yes the grounded conductor and the grounding conductor must stay separate when you leave the main panel, at the disconnect and the panel(s) down stream you must use isolated "neutral" bars

2002 NEC

240.21(B)(2) Taps Not Over 25 ft Long Where the length of the tap conductors does not exceed 25 ft and the tap conductors comply with all of the following.

(1) The ampacity of the tap conductors is not less than one-third of the rating of the overcurrent device protecting the feeder conductors.

(2) The tap conductors terminate in a single circuit breaker or single set of fuses that will limit the load to the ampacity of the tap conductors. This device shall be permitted to supply any number of additional overcurrent devices on it's load side.

(3) The tap conductors are suitably protected from physical damage or are enclosed in a raceway.

Using 3/0 copper will be fine for the run from the 400 amp bus to the 200 amp disconnect as long as your terminals are 75C rated.

However your ground is undersized you must run a ground that is rated to trip the overcurrent device feeding the circuit.

Look at Table 250.122

Rating or Setting of Automatic Overcurrent Device in Circuit Ahead of Equipment, Conduit, etc., Not exceeding

So for a 400 amp overcurrent device you will need to run a #3 awg copper minimum, you must remember if there is a fault between the panel and the disconnect it will be the 400 amp overcurrent device that will have to trip.

Once you get to the 200 amp fused disconnect (you did not say fused but it must be) the ground can be sized for 200 amp which would be #6 awg copper minimum.

One question for you, your profile says estimator project manager, don't you think purchasing a copy of the current NEC would be a good idea?

[ April 14, 2003, 06:44 AM: Message edited by: iwire ]

 

[tomgquinn]

Re: 200 amp subpanel installation

thanks forthe help, project manager/estimator for mostly mechanical projects, (it was the best desription available on the drop down list. Helping out with a volunteer organization that can't afford a real electrician. I realize this is outside my field, thus the questions.

As far as the tap rule, i was informed of this installation technique by an obviously conservative electrician. (six vs. twnty five feet.
Appreciate the support and God Bless.

 

[tom baker]

Re: 200 amp subpanel installation

Tom, before you get too far along you should check with both your local utility and electrical inspector agency to see if there any any local codes or ordinances that apply.

 

[tomgquinn]

Re: 200 amp subpanel installation

What's a local utility or an inspector??? This is backwoods US of A.

 

[iwire]

Re: 200 amp subpanel installation

tomgquinn, Good luck with your job, I hope it all works out for you.

Bob