max breakers in 200 amp panel for commerical use(school)

Status
Not open for further replies.
B

bigkev7

Member
Location
gloucester va
had an electrician tell me today that all the breakers in a panel face value can not add up to be more than 5 times the face value of the main breaker. Is this true? if so could some body give me the code number of tell me why this is wrong
 
bigkev7 said:
i know better but having trouble finding the correct codes to prove him wrong
Click to expand...
Just tell him that he is wrong and ask him to show you where it is in the code book.

Roger
 
With this being a school (or any commercial building) if you were to add up all the breakers in the facility at their face value odds are they exceed the Main Breaker size a many times over, ask him how he would handle this.

Roger
 
bigkev7 said:
i know better but having trouble finding the correct codes to prove him wrong
Click to expand...
There is no code reference to prove him wrong, just as there is no code reference to prove him right.

This issue is not addressed anywhere in the code at all. It is strictly a design issue.
I remember designing a single phase 60A main breaker panel with 42 - 15A breakers.
 
well the logic is

well the logic is

by his logic if you have a 200 amp main and you have 42- 20 amp breakers thats 840 amps by the face amps of the breakers and if you go five times the main which is 1000 amps your still bearly at the 80% mark i tried it on many panels in the school and most of them came up around 80% using this method i just wondering if anybody has ever heard of this
 
bigkev7 said:
by his logic if you have a 200 amp main and you have 42- 20 amp breakers thats 840 amps by the face amps of the breakers and if you go five times the main which is 1000 amps your still bearly at the 80% mark i tried it on many panels in the school and most of them came up around 80% using this method i just wondering if anybody has ever heard of this
Click to expand...

I've never hear of it and maybe someone might choose it as a rule of thumb. IMO it's worthless in determining anything. :)
 
Now try using this method with a panel with almost all motor loads where the breakers are all approx 2.5 times motor full load currents.

What about loads that do not run at same time?

If you do put too much load on the panel that is what the main is for whether it is in the panel or not.
 
still have not got any real answers

still have not got any real answers

well if the motors dont run at the same time where is the overload but like i said earlier this so called rule of thumb seems to work and i am not getting a whole lot of answers disproving it but just alot of people saying its wrong and not giving no real facts making it wrong
 
bigkev7 said:
well if the motors dont run at the same time where is the overload but like i said earlier this so called rule of thumb seems to work and i am not getting a whole lot of answers disproving it but just alot of people saying its wrong and not giving no real facts making it wrong
Click to expand...

Nothing about adding up breakers in 408.

III. Panelboards
408.30 General. All panelboards shall have a rating not
less than the minimum feeder capacity required for the load
calculated in accordance with Part III, IV, or V of Article
220, as applicable.

Informational Note: See 110.22 for additional requirements.

408.36 Overcurrent Protection. In addition to the requirement
of 408.30, a panelboard shall be protected by an
overcurrent protective device having a rating not greater
than that of the panelboard. This overcurrent protective device
shall be located within or at any point on the supply
side of the panelboard
 
If you want to do it, nobody is going to stop you. You asked if it was code, and we answered that question. Over current protection for feeders are given in Article 215. Overcurrent protection for panels is given in 408.36. Calculating loads are given in Article 220. There is nothing in any of these to support this rule of thumb.

In truth, it seems the rule of thumb proposed doesn't even save any time, I don't get the point.
 
Suppose I want to put 40 receptacles each on a 20 amp individual branch circuit -- because I am a nut. The calculated load for standard receptacles would be 180va. 180va * 40= 7200 va. 7200/240= 30 amps. So the electrician is saying I can't do this?

My point is the electrician needs to do a load calculation in order to determine if the panel is overloaded or not. I did a 200 amp panel 40 cir. and also fed another 40 cir. sub from that panel -- There were almost 80 circuits on that 200 amp panel.
 
bigkev7 said:
well if the motors dont run at the same time where is the overload but like i said earlier this so called rule of thumb seems to work and i am not getting a whole lot of answers disproving it but just alot of people saying its wrong and not giving no real facts making it wrong
Click to expand...

Ok, the NEC is a permisive code meaning that if there is no actual prohibition to something then it's allowed, OTOH, if something is specifically proihibited or stated (shall or shall not) then that is what has to be done or not be done and this person can not provide you an article section that states what he/she is claiming.

Many times it is not what is stated in the NEC but what is not stated that gives permission and in this case there is nothing in the NEC to substantiate your rule of thumb.

Roger
 
Last edited:
I thank you this is all i was asking for

I thank you this is all i was asking for

thank you this is was asking for is the codes to go by to prove him wrong
jumper said:
Nothing about adding up breakers in 408.

III. Panelboards
408.30 General. All panelboards shall have a rating not
less than the minimum feeder capacity required for the load
calculated in accordance with Part III, IV, or V of Article
220, as applicable.

Informational Note: See 110.22 for additional requirements.

408.36 Overcurrent Protection. In addition to the requirement
of 408.30, a panelboard shall be protected by an
overcurrent protective device having a rating not greater
than that of the panelboard. This overcurrent protective device
shall be located within or at any point on the supply
side of the panelboard
Click to expand...
 
Status
Not open for further replies.
Top