Replies

1. 
   Guest_ | Aug 11, 1999 08:56pm | #1

   *
   Search for "subpanel" in archives for more info.

   1) Depends on main breaker rating (safety) and length of run (voltage drop). Breaker's poles must be ganged together.

   2) Depends on main breaker rating. OK for sub's breakers to add up to more than main breaker's rating because it's unlikely you'll loadd all branch circuits to the max at once.

   A subpanel for a media room sounds a bit over the top, unless the run is quite long or you have some very powerful devices. More common use is for, say, a kitchen or where you need 240 V. But if it's more convenient, hey... I used a subpanel mostly because the old main panel was just too small. Small subpanel box is about $25, breakers $7(single)-$20(double, half-size).

   BTW, do -not- bond the subpanel neutral to ground.

1. 
   Guest_ | Aug 13, 1999 05:57pm | #2

   *I was just looking at a voltage drop table. It's pretty suprising how shorts runs have to be to insure that voltage drops are not more than 2%. These are fully loaded circuits but for 15 Amps at 120V using 14ga wire the run should be only 30 feet. For 20 Amps at 120V using 20 ga wire the run should be only 36 feet. This is not the normal situation for most circuits and it doesn't matter too much for lighting anyway but if you have any power hungry devices with motors the voltage drop could be bad. Get a book and figure out what you'll be using. It's pretty easy really. Good luck.

1. 
   Guest_ | Aug 13, 1999 08:21pm | #3

   *Lights don't care much about voltage drops -- at least incandescents don't -- but their efficiency drops fast. I think if you give an incandescent 90% of its rated current you get 70% of the rated light output. Motors, meanwhile, will overheat or refuse to start --> damage. Voltage drop can also cause annoyance, as When the lights dim every time something else switches on. I ran 10 gauge to my garage (except the undersized buried portion) to make the tools a bit happier, though it was only about 35 feet at 15 amps. Similarly, the furnace air handler called for a 15 amp breaker, which I provided on a dedicated 12 gauge 20-foot run.

1. 
   Guest_ | Aug 13, 1999 09:21pm | #4

   *You can run up to 42 breakers in any panel. I don't expect that you will buy a panel that big. More circuits mean more controll. Buy a larger panel than you possibly think you will need. Don't plan on using 1/2 size breakers. The number of circuits in the panel has nothing to do with the size of the feeder to it. Calculate your feeder size based on actual maximum load, not the number of circuits. I.e. just because you want 4 20a circuits doesn't mean you need an 80a feeder. Once you know your feeder ampacity, use a table to determine the wire size. Feeders seldom have problems with voltage drop, since they are not usually loaded up to capacity.

1. 
   Guest_ | Aug 13, 1999 09:47pm | #5

   *OK, I understand that long runs will lead to voltage drop, which may lead to an incandescent bulb dimming slightly when a motor starts up.What else may cause this? I have a de-humidifier and a refridgerator, each on different circuits, but bulbs dim in the house when they start up.(not alarmingly, but enough to notice)I checked voltage at the main breaker, and the city is giving me 108 - 110V on both feeds.Andrew, you mentioned motor damage and Jim, you mentioned 2% voltage drops as a max. target for figuring run length vs. wire gage.Please teach me: is 2% drop the established maxto avoid motor damage?I am asking because I think it might be interesting to check each of my circuits (air compressor, refridgerator,etc.) for this to confirm if I am providing a good home for my motors (voltage at breaker vs. voltage at motor during running or something like that). What do you think?

2. 
   Guest_ | Aug 13, 1999 11:35pm | #6

   *Since standard voltage these days is 120, I think that at 108-110 you already have a substantial problem. Is this an old service? You might contact your power company.

3. 
   Guest_ | Aug 14, 1999 03:27am | #7

   *Yes, I would question whether the service feed is up to snuff. A defective wire can cause this sort of thing. The dimming should be the same cause, voltage drop, except this time at the panel. Modern compressors draw SO much less current too -- if your stuff is old, that could be a problem. Replacing a 20 y.o. fridge, for example, is practically a no-brainer.Call your utility, and ask about potential damage to your appliances. They'll send someone out. I know that during brownouts people are advised to unplug these things. Don't know what voltage is called a "brownout."

4. 
   Guest_ | Aug 21, 1999 06:33am | #8

   *Norm;If my memory serves, 3% is the max permitted on a any given outlet.There is a site with an on-line V drop calculator:http://www.mikeholt.com/volt_drop.htmlI had a bad transformer and a bad neutral on the pole. Power co fixed it for free...had to convince them it was their problem. When lites dim their first, second and third response is call an electrician.I agree, 110V is way low. 115 to 120 is more desireable (110 is already 4.3% below 115)G'luckAdam

5. 
   Guest_ | Sep 01, 1999 05:19pm | #9

   *Most utilities call 103V a brownout.

2. 
   Floyd_ | Sep 01, 1999 05:39pm | #10

   *
   How is grounding treated in subpanel wiring? Isn't
   this asking for trouble?

   Very curious about this, have full main panel too. Also: any cable
   recommendations for a 50 foot run from a subpanel in garage to new
   subpanel in woodshop, different outbuilding? Does this building need a
   separate ground?

   Thanks,
   Floy

3. 
   Cadman | Sep 02, 1999 05:18am | #11

   *
   Hi All !

   Just read a thread here about 14 GA vs 12 GA wiring. I saw that in order to shorten "homeruns", a several sub panels were to be used. I am finishing my basement and constructing both a home theater and home office at the "far" end of the basement from the electrical panel (200A service). I was wondering, if I chose to install a sub panel, I ASSume I will need to install a 2 pole, (say 50A-60A), breaker in the main panel, run wire to subpanel and install appropriate breakers for circuits in the new rooms.

   Questions:

   1) wire size to run to sub panel ?

   2) total load of breakers (ie how many circuits allowed in sub panel) ?

   Hope you folks get my drift and have some answers.

   Thanks, Cadman

4. 
   Guest_ | Sep 02, 1999 05:18am | #12

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   Subpanel ground is run separate from and NOT bonded to subpanel neutral. Someone may confirm/deny this, but outbuilding can have its own ground (not required).