Installing subpanel, need advice


  #1  
Old 12-29-04, 06:49 PM
O
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Installing subpanel, need advice

Long time lurker and poster on other forums here, have recieved a lot of excellent advice that has allowed me to do a lot of DIY projects..

I am installing a subpanel in an unfinished basement to run outlets in all the rooms (7 rooms) and the lighting.

My electrical needs down there right now are not great, but its winter and we are plugging a 1500 watt heater and it keeps tripping the breaker that the outlet was run from (an upstairs bath/bedroom circuit).

The main panel doesn't have a main breaker (its a lug type), its a 150 amp 30 breaker box that is full (7 rooms on first floor, 4 rooms on second floor, and 7 rooms in basement.

I was thinking of running a 100A subpanel in the basement, there is EASY access from the main panel now to the basement, so a short 10-15 foot run with a feeder is what I planned.

Now heres where I need help: should I remove 2 single pole breakers from the main and use a 100A double pole breaker to fuse the feeder, or is there another alternative to supplying the subpanel with juice...will a 100A feeder line overload the current box I am using, or how can I figure this out.

I really dont think I need a 100A subpanel, but thought I should do it for future expandability, although I wont be living there in 2 years....

thanks a ton!

thanks,

C Scott MD
 
  #2  
Old 12-29-04, 08:31 PM
rlrct
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You can run a 100 amp subpanel and you would remove 2 single breakers and install a 100 amp, 2-pole 240v breaker to feed the subpanel. You would need a 4-wire feeder and would not bond the neutral and grounding busses in the subpanel.

If your panel doesn't have a main breaker, then you must have a seperate service disconnect. Given that, I'd expect your main panel to be wired in as a 4-wire subpanel with your Grounding Electrode System bonded at the disconnect. If that is the case, you may have a second option. If your disconnect has lugs or terminals that are rated for 2 conductors, you could install a second 150 amp rated main lug panel, in parallel with the first panel.
 
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Old 12-29-04, 08:31 PM
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You should install dedicated outlets for your space heaters, or at least not expect to run much else at all on the circuit with it. If you think you will often use space heaters, you should install baseboard heaters, a much, much, much safer alternative.

If you main panel is full, you will need to make room for your double-pole breaker somehow. The two main options are: (1) Install tandem breakers (if your panel allows them), or (2) Move two circuits to the subpanel. Since access is easy and the distance betwen the panels is short, the second alternative might be your best bet.

A 100-amp feeder line won't add any load at all to your panel. It's televisions and stoves and heaters and lights and refrigerators that add load. You might want to do a "demand load calculation" (google this term) to figure out whether your 150-amp service will handle all your load. There are lots of factors.

100 amps is a huge amount for a basement, but heck, why not? It won't hurt anything and as you say, it's good for future expandability (even if you have to upgrade your main panel to 200 amps later).
 
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Old 12-29-04, 09:30 PM
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thanks for the detailed replies....

I did a google search on demand load calculation, and wow, thats going to be fun...going to try it out friday when I have some time.

Think I'll free up 2 breakers and move the circuits to the new box and use the 100A 2 pole breaker....

Any opinion on wheather to run 12-2 with 20A breakers or 14-2 with 15A breakers...again, this is for running general outlets in the basement with basic overhead lighting.

We only need a space heater about 1-2 months out of the year, only on occasions when we go into the basement (we stay out in the colder months (Atlanta).

thanks again to both of you!!
 
  #5  
Old 12-29-04, 09:38 PM
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If it was me in my own house, I'd use all 12-gauge wire and 20-amp circuits. 14-gauge wire and 15-amp circuits is for penny-pinchers (such as electricians).
 
 

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