Anyone an electrician on here?

[rsalomon13]

Are any any of you electricians? I have a question regarding load capacity at 240v vs 120v. I don't want to start a heated discussion but I just want to verify what I believe to be true.

If you have a panel rated at 200amp@240v, you can technically(All balancing, 80% rule and such aside), have 20 20amp@120v breakers(Totaling 400amps@120v) running at full capacity in this panel.

Any input from those with more then basic DIY knowledge, i.e. a licensed electrician or electrical engineer, would be appreciated.

 

[EddieHunt05]

I know enough about it to get myself hurt... haha hope someone has a good answer for you

 

[IBratmanI]

Yes you can, but they won't all be running at full capacity will they?? If you actually have something drawing on each one, then something will most likely blow, but it is very common to fill the panel with breakers, and have them add up to more amps then the panel is rated for, but they can't all have a draw on them at the same time. (I worked as an electrician for over 3 years)

 

[rsalomon13]

I am not considering "the demand factor", or the 80% rule. I am talking pure concept. 200amps@240V is the same as 400amps@120V. Basic math can prove this, 240Vx200amps = 48000W, 120Vx400amps = 48000W.

What I am saying, is that a panel rated for 200amps@240v, can have 20 fully loaded 20amp@120V circuits. This is due to the fact that a dual pole(240V) breaker can carry 200amps per leg. I am 90% sure this is correct, but let me know if this is not.

 

[4WRXter]

ME. Limited Master(House wiring) Elec.

Provided you put 10 breakers on one side and 10 on the other side, you are correct in concept.

 

[wzrd]

I am not considering "the demand factor", or the 80% rule. I am talking pure concept. 200amps@240V is the same as 400amps@120V. Basic math can prove this, 240Vx200amps = 48000W, 120Vx400amps = 48000W.
What I am saying, is that a panel rated for 200amps@240v, can have 20 fully loaded 20amp@120V circuits. This is due to the fact that a dual pole(240V) breaker can carry 200amps per leg. I am 90% sure this is correct, but let me know if this is not.

why wouldnt you take into consideration the safety factor? im no master but ive wired my home and would NOT run every fully loaded ciruit in the box all at the same time ...

 

[rsalomon13]

I just got my answer from a local electrician, if any of you are wondering here is the deal.

A panel rated for 200A@240V can actually maintain a load of 400A@120V. This is only if everything is balanced, this might seem confusing but you cannot pull a SINGLE 400A@120V circuit, but you can have 2 200A@120V circuits.

To put it simply, you can supply 400A worth of 120V loads, but you cannot supply 400A at 120V.

With these big numbers it doesn't really seem relevant, here is where it becomes relevant, if you have a subpanel being fed by a 50A 2-pole breaker. You can actually have 5 20A@120V circuits running fully loaded on this panel and nothing will trip as long as the load is balanced between the two legs.

 

[rsalomon13]

why wouldnt you take into consideration the safety factor? im no master but ive wired my home and would NOT run every fully loaded ciruit in the box all at the same time ...

Simple, this is a talk of electrical theory. But also in practice, for safety as long as you have a functioning main breaker, there is no harm in running everything at full capacity. The main will trip before the amp's ever excede the capacity of your wire. This is assuming that you have used the correct gauge wire for the breaker.

Also for example 12AWG romex is rated for 20amps. This can carry 20amps all day every day. Your 20amp breaker will trip however if the CONTINUOUS load exceeds 16amps, this is way before fire or overheating ever becomes a concern

 

[wzrd]

yes sir -12 gauge wire and square d breakers and you cant go wrong.

 

[rsalomon13]

yes sir -12 gauge wire and square d breakers and you cant go wrong.

Oh, you can still go very wrong

 

[4WRXter]

Also for example 12AWG romex is rated for 20amps. This can carry 20amps all day every day. Your 20amp breaker will trip however if the CONTINUOUS load exceeds 16amps, this is way before fire or overheating ever becomes a concern

Actually, the opposite is true. The breaker is rated to trip at 20a. If the wire is subjected to a "continuous load", which is defined as a load occurring for 3 hrs or more, you must up-size the wire. Or down-size the load.

 

[rsalomon13]

Actually, the opposite is true. The breaker is rated to trip at 20a. If the wire is subjected to a "continuous load", which is defined as a load occurring for 3 hrs or more, you must up-size the wire. Or down-size the load.

Thanks for clarifying that, that actually makes more sense. So breakers are rated at 100%, but NEC dictates that they only carry 80% and this is due to the wire possibly heating under continuous load? Where I could see this getting scary is when you are up-sizing breakers. Again correct if I am wrong, but NEC says that since there are no 55A breakers, you can technically run a 60A breaker with 6-3, as long as the calculated load won't exceed 55A. What would worry me, is a homeowner coming along later and thinking they have 60A to work with(If this was say a subpanel/spa panel). Now I see why you electricians make $, a lot to remember and possibly severe consequences to forgetting something small.

 

[4WRXter]

CORRECT!!!!!!!!!!

You're right, there is a lot to know, there was initially, and there continues to be a lot of schooling. Electricians pay fees to keep licenses, and also pay to take seminars every 3 years to keep up on NEC updates.

 

[jcovey2.5]

Ya we make money when there is friggen jobs.....