DIYbanter - View Single Post - Load capacity of 200-amp panel

Bud--

wrote:
On Oct 26, 12:45 pm, bud-- wrote:
wrote:

....

Let me restate what I've said all along:

The arguments have gotten so twisted let me start here.

In a 200 amp service entering a house, there is a max of 200 amps of
actual current flowing. You don't count current twice on a service
cable anymore than you would on an extension cord.
Here's a simple series of questions:
1 I have a big 240V water heater that draws 200 amps and is
connected to a 200amp service via the two hot legs.
How much current is flowing in
a - Hot leg 1
b - hot leg 2
c - neutral
d - the service cable entering the house

2 Now instead of the single 240V water heater, I have two 120V water
heaters that draw 200 amps each. One is connected between hot leg 1
and neutral, the other between hot leg 2 and neutral.
How much current is flowing in:
a - Hot leg 1
b - hot leg 2
c - neutral
d - the service cable entering the house
3 Is the situation in #2 above an example of a parallel circuit or a
series circuit?
4 I now disconnect the water heater that was connected to leg 2 in
the previous example. You now have one 120V, 200 amp water heater
connected to leg 1 and neutral.
How much current is flowing in:
a - Hot leg 1
b - hot leg 2
c - neutral
d - the service cable entering the house

Everyone, I believe, has the same the answers (though I'm not sure what
"d" is).

I'm not so sure there is agreement as to the answers. And if there
is agreement, then I don't see how there can be disagreement on how
many amps are flowing on the service cable. If you have X amps
coming in and X amps going out in a circuit, then that means X amps,
no?

I don't understand Doug is saying there is 400A running in any wire.
And I am not saying there is.

The question from the OP, as I understand it, is with a panel feed at
200A 240V can you supply 200A of 120V load or 400A of 120V load.

It is case #2 above. You can supply 400A of 120V load. You can't supply
a 400A 120V load, but with the load split between the legs you can
supply a total of 400A of 120V load, half of it from each leg. In that
case the hot legs run at 200A and the neutral is zero. You don't have
400A on any wire. I assume that is not a problem for you. That is all I
read Doug as saying. I agree.

Its gotta be a point-of-view problem.

--

I don;t see it as a point of view problem at all. How many amps are
actually flowing in a 200 amp service to a house? You draw an
imaginary plane and answer the question of how many amps are flowing
in and how many are flowing out. If it is indeed 200 in, 200 out,
then that is 200 amps period. You can have 200 amps flowing between
the two hots. You can have 200 amps flowing between hot 1 and the
neutral. You can have 200 amps flowing between hot 2 hot and the
neutral, Any way you slice and dice it, it's still 200 amps.

In example #2 there is there 200A supplied to the 120V water heater on
leg 1.
And there is 200A supplied to the 120V water heater on leg 2.
Are you not supplying 400A of 120V load (split between leg 1 and leg 2)?

If you can really have 400 amps of real current flow in the service,
then maybe Doug can answer this.

I do not understand Doug ever said there was 400A in any wire. Rather
that there was 400A of total 120V load supplied - 1/2 on each leg.

Suppose I have a 120 volt load that
takes 400 amps. I connect it as a single 120V load to a 200 amp
service. What happens?

You don't connect it to one leg. You split the load in half and connect
one half leg 1 to neutral. You connect the other half from leg 2 to
neutral. (In this case you reconnect the single 400A 120V load as a 200A
240V load.)

If you have 40 - 10A 120V loads (400A total at 120V) you connect 20 of
them to leg 1 (200A). You connect the other 20 to leg 2 (200A). The
neutral current is zero. You have supplied 400A of 120V loads by
splitting it and connecting half to each leg.

A - Eveything works peechy keen, because 120V* 400amps = 48KVA, at the
service limit, so 400 amps flows just fine.

B - The service cable burns up, because the only way you can supply
that 400amps is by the load being balanced, in which case it appears
as a series load and the service is actually pulling 200amps through
one hot and back the other.

Which means that it would ONLY work if
you had two 200 amp, 120V loads connected to OPPOSIITE legs, and hence
acting as a SERIES circuit.

Which is how you connect it. I don't want to go back and reread the
thread - Doug's use of parallel may have not been the best. But I always
understood he was saying that half of a 400A load (200A) was connected
to leg 1 and the other half (200A) was connected to leg 2.

In answer to the OP's question - with a panel feed at 200A 240V can you
supply 400A of 120V load - the answer is yes.

I still think it is a point-of-view problem. You and Doug (and Smitty
and others?) all understand the underlying electrical.

--
bud--