200 amp service, 200 or 100 per leg?

[Alwaysready]

Im a newbie
Im still trying to grasp the whole concept of 220 and have a couple of questions

1. 220v 30 amp breaker will the breaker trip when it reaches 30
amps per leg or 15 amps per leg?

2. 200 amp service Main breaker will it trip when it reaches 200 amps per leg or 100 per leg or some combiniation of 200?

3. 200 amp service is it really 400 amps, 200 on each leg to neutral?

the questions are all interrelated and to you experienced guys are simple but
as stated im a newb and had to ask
if there is another thread about this point me the way as id like to have a good handle on this
thanks in advance

 

[charlie b]

My fist bit of advice is to immediately and forever ban from your vocabulary the phrase ?per leg,? in the context of current flow. It is clear to me, from the way you are using the phrase, that you are using the word ?per? in the mathematical sense of multiplication. Example: Two dozen eggs at $1.50 PER dozen is $3.00 total. This is a multiplication problem, and that is not how current works.

The simple way of saying it (all I have time for at the present) is that, for a balanced single-phase 120/240 volt system, all the current that leaves the source on one leg is going to return to the source on the other leg. It is not 100 amps on Phase A plus 100 amps on Phase B for a total of 200 amps. Rather it is 200 amps leaves on Phase A, and the same 200 amps returns on Phase B.

Now I need to ask, before we allow this to go much further. What do you mean by ?occupation, hmmm,? and what is the nature of the electrical classes you are taking? We are not permitted to assist a person who is not employed in the electrical industry, or who is not at least studying to become employed in the electrical industry, and who intends to perform electrical installation work at home. No DIYs are allowed here.

 

[Alwaysready]

hey Charlie,
maybe i did take to many math clases in college and its stuck with me i guess that last calculus class did get to me a little so now "P-- L--" will not be spoken of

as far as my occupation I am not an electrician,currently taking a 2008 code class to educate myself more and attempt at taking the local licensing exam in the future. so the Hmm went to say id like to call my self a electrician but cant at this time i am merely a self storage building owner so clearly i dont have an occupation since i am not an employee of a company or do a particular trade on a daily basis. Rental property is not considered a business so back to Hmm, im not sure, maybe ill change it to landlord but then if i call myself a landlord i dont belong here because my occupation would then not be involved in the electrical field.

when you say that 200 amps leaves on phase A and 200 amps leave on phase B , you would be assuming that this is strictly a 220 volt system correct?
I am speaking in the terms of a standard residential panel and assuming some loads are 110 volts also

 

[LarryFine]

Al, here's a little ditty I wrote in response to a question about neutrals, but I think you'd benefit from reading it.

http://forums.mikeholt.com/showpost.php?p=708650&postcount=4

Please let me know if it helps any.

 

[infinity]

The capacity of a 200 amp is 200 amps at 240 volts or 400 amps at 120 volts. It really depends on the specifics of the question you're asking. For example, a 2400 watt load @ 120 volts will produce a load of 20 amps. A 4800 watt load @ 240 volts will produce a load of 20 amps.

Since you're learning, IMO you should try to avoid the 110/220 language when discussing voltage. The typical single phase system is 120/240 volts.

 

[derek22r]

The capacity of a 200 amp is 200 amps at 240 volts or 400 amps at 120 volts. QUOTE]

Is this what you meant to say? The capacity of a 200 amp system is 200 amps at 240V and 120V.

 

[infinity]

The capacity of a 200 amp is 200 amps at 240 volts or 400 amps at 120 volts. QUOTE]

Is this what you meant to say? The capacity of a 200 amp system is 200 amps at 240V and 120V.

Nope, the initial statement is correct. A 200 amp single phase 120/240 v service can provide 200 amps at 240 volts, or it can also provide 400 amps at 120 volts. I didn't mean to imply that it could provide both simultaneously.


If we look at this in terms of volt amps:

240v * 200a = 48000 VA
120v * 400a = 48000 VA

Either way the capacity is the same.

 

[roger]

As shown by Infinity, load each buss with single pole breakers (120 v circuits) and 200 amps per leg could be correct terminology. :wink:

If I go for a one hour drive and travel 1 mile, 1 Mile Per Hour would be an understandable description of the speed I was driving, there would not be any addition of more miles necessary or intended.

Roger

 

[jim dungar]

Nope, the initial statement is correct. A 200 amp single phase 120/240 v service can provide 200 amps at 240 volts, or it can also provide 400 amps at 120 volts.

I don't agree.

The subject panel can provide:
1 x 200A @ 240V
or
2 x 200A @ 120V

It can not provide:
1 x 400A @ 120V

It may seem like splitting hairs but the reality is that no single 120V load can be greater than 2400VA

 

[mdakxotaz]

Infinity, when you say capacity you mean available Watts or KVA able to be supplied from the transformer? If thats what you mean it makes sense, but if we're talking about what the main breaker in the service panel can handle, it doesn't..

A 200Amp 120/240Volt panel will only draw 200Amp, weather your dealing with 120Volts or 240Volts. If you draw 400Amps, the main breaker will trip.

The Amperage is going to depend on your load, so we can install a two pole 200Amp breaker and send the 240V across a load which has a resistance of 1.2Ohm or greater and not trip the breaker, but we can install a single pole 200Amp breaker using one phase of our two phase system, and only be able to connect to a load which has a resistance of .6Ohm or greater and not trip the breaker.

 

[SAC]

Here is some basic information on how single-phase power systems work.

http://www.allaboutcircuits.com/vol_2/chpt_10/1.html

 

[infinity]

I don't agree.

The subject panel can provide:
1 x 200A @ 240V
or
2 x 200A @ 120V

It can not provide:
1 x 400A @ 120V

It may seem like splitting hairs but the reality is that no single 120V load can be greater than 2400VA

Who said anything about a single load? I can install 20, single pole, 20 amp breakers with a 20 amp load on each and achieve 400 amps of load at 120 volts.

 

[infinity]

A 200Amp 120/240Volt panel will only draw 200Amp, weather your dealing with 120Volts or 240Volts. If you draw 400Amps, the main breaker will trip.

This is incorrect. You need to re-read post #7.

 

[LarryFine]

I can't believe nobody's catching that Rob is arguing semantics. (Oh, like that's never happened around here before. :roll

Yes, you can supply 400a worth of 120v loads, but no, you cannot supply 400a at 120v.

Sorry, Rob, but, because the discussion is about main breakers, the 200a side wins.

 

[roger]

I can't believe nobody's catching that Rob is arguing semantics. .

I can't believe you can't see where it was caught. :wink:

Roger

 

[jim dungar]

Who said anything about a single load? I can install 20, single pole, 20 amp breakers with a 20 amp load on each and achieve 400 amps of load at 120 volts.

If you want to install 10 1P breakers each with 30A of load and 10 1P breakers each with 10A load you had better be very careful with your load balancing.

As I said, you can supply (2) sets of 2400VA total loads. Also, you cannot feed your panel with a single 120V 2-wire 4800VA transformer.

 

[mdakxotaz]

Who said anything about a single load? I can install 20, single pole, 20 amp breakers with a 20 amp load on each and achieve 400 amps of load at 120 volts.

Right, but that is because there is a demand factor here, if all of your loads were to draw the full 20A at the same time, your main would trip. If you put a clamp on ammeter on one of the service legs, and it is drawing over 200A wouldn't you agree that the main should trip?

 

[roger]

Right, but that is because there is a demand factor here, if all of your loads were to draw the full 20A at the same time, your main would trip.

No it wouldn't, (no demand factor need be considered for the discussion at hand) each bus with ten 20 amp breakers would only see 200 amps, IOW's 200 amps per leg.

If you put a clamp on ammeter on one of the service legs, and it is drawing over 200A wouldn't you agree that the main should trip?

Yes, but with only ten single pole 20 amp breakers on a single service leg there would not be more than 200 amps.


Roger