So 200A /1.73= 115A for ea 3ph leg?

T310.15(b)(6) {formerly 310.16} sezs i can use #2 cu @75F

right?

:whistling2:


~CS~

 

Why are people putting 3/0 cu on a 200 amp single phase 3 wire service. They keep quoting 310.15 using 90 degree rating for copper as being 200 amp. I am questioning if they even understand what happens inside an electrical panel.

Let me explain. Each ungrounded conductor of the service carries 100 amp a piece of the 200 amp rated service. Meaning....... each conductor does not have to be rated at 200 amps. This is why table 310.15(b)(6) exists, to keep "people" from trying to tell you to do something you don't need to.

Sorry. This is just driving me crazy.

unfortunately, you have some misconceptions about how an electrical panel is rated. I suggest you read the code book or take some courses. Your statement is 90% wrong.

If the calculated load is 200A for a 200A panel, each leg must be able to carry 200A.

read that again until you understand it.

for residential single phase, you can go less than the 3/0 per code rules, but not for the reasons you stated.

 

I have never seen anywhere in the code on any course where it says that each leg is required to carry 200 amps on each leg. I also never said anything about 3 phase

 

start at article 220 and do a load calculation.

then go to article 230, and start to figure out your service. let's say it's overhead:
230.23 Size and Rating.
(A) General. Conductors shall have sufficient ampacity to
carry the current for the load as calculated in accordance
with Article 220 and shall have adequate mechanical
strength.

now, where precisely, in between your load calc in 220, and your service conductor rating in 230.23, does it say you can divide the load in half ?

It doesn't.

If you don't want to believe me, then consider this:

If what you say were true, why would the conductors have to be 2/0 ? you can get 100 amps out of #1 or #2 next size up at 60 degrees or 1/0 AL? Explain why 200 amp panels would ever need 2/0 ?

 

I can see this may be a long thread.....

~CS~

 

What would make you think think each leg only carries 50% of the rated current?

 

I sense a theory/code clash here....

~CS~

 

the allowed reductions for single phase, and neutral reductions take into account the safety factor and theory IMO Steve.

The OP has a misunderstanding of the rating of an enclosure IMO.

when you work out the watts, like most engineers do in the plans on the panel schedules, all is fairly clear.

theory be damned, we don't install by theory, we are required to install per code.

 

Take 2 sp 20 amp breakers and put them together with a handle tie. Now what amperage is each phase capable of handling without tripping. 10????? I don't think so.. LOL

 

If you have a 3000 watt heater that operates at 240V, what size circuit would you install?

I would do the math like this,
3000/240= 12.5A on each leg of the 240V circuit.

12.5*1.25 = 15.63A

So, I would run a 20A circuit to this heater.

Now, according to what you posted (at least the way I read it), you would call that a 40A circuit. It's not a 40A circuit, it's a 20A circuit.

 

Why are people putting 3/0 cu on a 200 amp single phase 3 wire service. They keep quoting 310.15 using 90 degree rating for copper as being 200 amp. I am questioning if they even understand what happens inside an electrical panel.

Let me explain. Each ungrounded conductor of the service carries 100 amp a piece of the 200 amp rated service. Meaning....... each conductor does not have to be rated at 200 amps. This is why table 310.15(b)(6) exists, to keep "people" from trying to tell you to do something you don't need to.

Sorry. This is just driving me crazy.

Wow!

 

Okay. Okay. I'm wrong. I get your point. Total misunderstanding on my part.

Don't shoot me.

 

I think your question was fair. Some things get heated pretty quick around here.
I suggest putting a post in the intro section telling us a bit about you and where you are at in your apprenticeship, experience, etc. Without doing that, usually people respond assuming you are a full-blown-know-everything-already-done-1000-homes electrician and that you should know the answer to this.

 

Let me explain. Each ungrounded conductor of the service carries 100 amp a piece of the 200 amp rated service. Meaning....... each conductor does not have to be rated at 200 amps.

Start here:

Current is equal in all parts of a series circuit. So if you had a 240 volt 200 amp load both conductors would be carrying 200 amps.

 

Perhaps they use 3/0 because they have enough on hand to do the job, as opposed to spending time & money buying more 2/0.

Jez sayin.

 

Perhaps they use 3/0 because they have enough on hand to do the job, as opposed to spending time & money buying more 2/0.



Jez sayin.


Perhaps they use 3/0 because because 2/0 is only good for 175 amps. It was never answered if it was residential

 

Perhaps they use 3/0 because they have enough on hand to do the job, as opposed to spending time & money buying more 2/0.



Jez sayin.


Perhaps they use 3/0 because because 2/0 is only good for 175 amps

Really?

Look at Table 310.15(B)(6)

 

Just edited the post. It was never stated that it was residential or not

 

Re-checked 2/0 = 175A at 75c

 

I just had this conversation/argument with my father-in-law. He was positive that a 200A service only had 100A on each leg. He is retired GTE. He should stick to telco.


He also said that all the breakers on one side of the panel was one leg, and the other was on the other side of the panel.:blink:

Stubborn, he is.

 

I just had this conversation/argument with my father-in-law. He was positive that a 200A service only had 100A on each leg. He is retired GTE. He should stick to telco.


He also said that all the breakers on one side of the panel was one leg, and the other was on the other side of the panel.:blink:

Stubborn, he is.

As long as he isn't posting on DIY chatroom he is ok :laughing:

 

I love when my customers start adding up all the breakers in the panel to do a load calculation

 

voltage drop!

 

Since the OP ruined this thread by deleting his original post and changing his profile, I will close this thread.