panel/sub panel.. total cuircuits allowed

Reply

  #1  
Old 06-02-07, 11:49 PM
Member
Thread Starter
Join Date: Sep 2003
Location: USA
Posts: 166
panel/sub panel.. total cuircuits allowed

I read today that the basic rule in figuring how many (amps) you should run on your main panel is to double the rating on it. In otherwards if it is a 125 amp service panel all the cuircuits on it should add up to no more than about 250 amps.

Is this also true for sub panels? for example if I sent 30 amps V220 to a sub panel I would be allowed to have about 60 amps worth of ciurcuits such as 4 -15 amp cuircuits in the sub panel..

Is this correct or do I have it wrong again..

Thanks in advance for the help!
 
Sponsored Links
  #2  
Old 06-03-07, 12:15 AM
Member
Join Date: Aug 2005
Location: USA
Posts: 995
Probably no rule of thumb for a subpanel as they are often run for specific areas that have specific requirements. It would vary far more often with a subpanel than with something like, say, a residential service entrance.

Where is the subpanel going and what will you be doing with the things it powers?

I've seen many 200A subpanels with 600A worth of breakers, most feeding dedicated machinery with few used at any given time.
 
  #3  
Old 06-03-07, 04:52 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
I don't know what you read, but it's not correct.
 
  #4  
Old 06-03-07, 05:05 AM
Speedy Petey's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Nov 2003
Posts: 2,455
I totally agree. That is complete hogwash.

I am VERY curious as to where this is written.
 
  #5  
Old 06-03-07, 05:21 AM
Member
Join Date: Oct 2006
Location: Wilmington
Posts: 4,219
Yep, there are specific rules for calculating the load in a service panel, 'rule of thumb' is not one of them.
 
  #6  
Old 06-03-07, 05:44 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Doubling the rating of the main breaker tells you how many amps you have available at 120 volts. If you were to run only 120 volt loads, you would not be able to exceed that many amps. (This ignores that the main breaker will allow slightly more than it's maximum for a short period of time, etc., etc.)
 
  #7  
Old 06-03-07, 09:55 AM
Member
Thread Starter
Join Date: Sep 2003
Location: USA
Posts: 166
Stanely Wiring book I believe...

"I am VERY curious as to where this is" ? by Speedy

I was down at home depot reading through there electrical books trying to get some more information on subpanels. I had 3 books out at the time but I beleive it was the wiring book put out by Stanley where they said to double your service panel as a rule of thumb. I will give you the page # and book next time I head back there. In there defense they also said to calculate your need in determining your subpanel also. Add up the individual things watts of what you would be using etc..

comment by MAC-Where is the subpanel going and what will you be doing with the things it powers?I've seen many 200A subpanels with 600A worth of breakers, most feeding dedicated machinery with few used at any given time.

----I think I get it the light bulb went on hehe... hmm okay so the key in figuring out how big a sub panel you need really comes down to whats the maximum amps that are running at one time. It doesn't really matter if you have 20 ciurcuits or 4.

so if I made it a 30 amp sub panel using 240-.. that would mean the most Amps I could use at one time should be about 30 amps before it breaks at the sub or back at the feed from the main panel... Also sounds like it doesnt hurt to have a bigger sub than you need other than grr the cost of the bigger wire to handle it... (I hope this is right)

ok I think I get it guys thanks for the help!
 
  #8  
Old 06-07-07, 07:48 AM
Member
Thread Starter
Join Date: Sep 2003
Location: USA
Posts: 166
it was stanley book I double checked

for speedy- yes I double checked it was the stanley book on electrical at home depot. grr I forget exact page I think it was 220 but not %100 sure...
 
  #9  
Old 06-07-07, 09:16 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,335
> so the key in figuring out how big a sub panel you need really comes down
> to whats the maximum amps that are running at one time

That's exactly right.

The NEC defines a procedure for figuring this out called a "demand load calculation". It takes into account many factors like lighting / sq. ft. and automatic loads like refrigerator motors which may kick on at any time. For small subpanels or for subpanels feeding specific loads a demand load calculation is typically not necessary, just add up the total watts in use at the same time.

> if I made it a 30 amp sub panel using 240

A 30A subpanel is pretty small. I generally don't think that anything less than 60A is worth the labor unless you know that you'll never need more than 30A and ~4 15A circuits and that voltage drop at the panel is not a factor.
 
  #10  
Old 06-08-07, 08:50 AM
Member
Thread Starter
Join Date: Sep 2003
Location: USA
Posts: 166
thanks for the help!

---A 30A subpanel is pretty small. I generally don't think that anything less than 60A is worth the labor unless you know that you'll never need more than 30A and ~4 15A circuits and that voltage drop at the panel is not a factor.


yah you are exactly right my plans have changed from the information on this board. I am planning on using #6 wire (100 Ft) and go with a 60 amp sub panel. I am going with 20 amp ciurcuits also (using 12 wire and maybe #10 wire for one shed thats about 45 feet away from the sub panel.
 
  #11  
Old 06-08-07, 10:11 AM
Member
Join Date: Sep 2002
Location: welland ontario
Posts: 5,599
45 feet is not far enough to require an upsize of cable. Most circuit in your house are probably already longer than that.
 
  #12  
Old 06-08-07, 11:25 PM
Member
Thread Starter
Join Date: Sep 2003
Location: USA
Posts: 166
heh good to know...

Ill just stick with #12 then thanks tip!
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'