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150 Amp Residence Service: Does It Mean 150 Amps At 115 V Or 150 Amps At 220 V ?

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Robert11

Jan 1, 1970
0
Hello:

My house has the normal 3 wires coming in from the street pole.
Two being the 220 V phase to phase, and the neutral/ground.

When they say a residence has, e.g., 150 amp service, does that mean
150 amps at 115 V, or 150 amps at 220 V ?

Thanks,
Bob
 
S

SQLit

Jan 1, 1970
0
Robert11 said:
Hello:

My house has the normal 3 wires coming in from the street pole.
Two being the 220 V phase to phase, and the neutral/ground.

When they say a residence has, e.g., 150 amp service, does that mean
150 amps at 115 V, or 150 amps at 220 V ?

Thanks,
Bob
150 amps connected load. Draw more than 150 amps either 120 or 220 and the
main breaker will open.

I had a home with 2-3 ton a/c's, 3 swamp coolers, a spa and all of the other
electrical equipment you would expect and never had a problem with the 150
amp service.
 
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Robert11

Jan 1, 1970
0
Hi,

Thanks for reply; appreciate it.

Funny, you think you understand something, and then when you think about it
a bit more, you realize you really don't.

I am still, a bit, confused over yyour explanation, even though it
is very clear. Please bear with me, as I'm a bit out of my field here:

The 120 V circuits are, of course, Phase A to neutral, and/or Phase B to
neutral.
The 220 is Phase A to Phase B.

Forgetting for a moment that the wires wouldn't take it, but as a
hypothetical only, suppose
you had 150 amps at 220 V between Phase A and Phase B.

Are you suggesting that you could "still" pull more off of either phase (to
neutral) although at 115 V ?

Thanks,
Bob
 
T

TimPerry

Jan 1, 1970
0
Robert11 said:
Hi,

Thanks for reply; appreciate it.

Funny, you think you understand something, and then when you think about it
a bit more, you realize you really don't.

I am still, a bit, confused over yyour explanation, even though it
is very clear. Please bear with me, as I'm a bit out of my field here:

The 120 V circuits are, of course, Phase A to neutral, and/or Phase B to
neutral.
The 220 is Phase A to Phase B.

Forgetting for a moment that the wires wouldn't take it, but as a
hypothetical only, suppose
you had 150 amps at 220 V between Phase A and Phase B.

Are you suggesting that you could "still" pull more off of either phase (to
neutral) although at 115 V ?

Thanks,
Bob

the 150 amp rating means that wire, connectors, busses, main breaker are all
sized to provide a peak load of 150 amps. (and probably 80% of peak load on
a continuous basis)
the object of the main breaker or fuse is to prevent excess current in the
wires up to that point. in other words from the pole to the house.
brief instantaneous peaks of current at greater then the rated value may
occur due to a time delay function depending on the type and specs of the
safety device used.

it may help to think of the 2 120V circuits as "legs" or "branches" instead
of phases because most residential service is referred to as single phase
service to distinguish it from 3 phase industrial.

the act of distributing loads between the 2 branches is called "load
balancing"

if i understand your question correctly: "how much power could i get from a
150 amp circuit if the voltage 220 instead of 120?" the answer would be
voltage times current or 220 * 150 = 33,000 watts (peak) however one would
be foolish indeed to actually attempt to run continuously at maximum. around
where i am at least the electricians and power co. use the formula 220 *
150 * .8 = 26400 watts to determine safe maximum loading. even then the
panels get warm to the touch (or hot), the breakers run hot, the
connections tend to burn up.
 
O

operator jay

Jan 1, 1970
0
Robert11 said:
Hi,

Thanks for reply; appreciate it.

Funny, you think you understand something, and then when you think about it
a bit more, you realize you really don't.

I am still, a bit, confused over yyour explanation, even though it
is very clear. Please bear with me, as I'm a bit out of my field here:

The 120 V circuits are, of course, Phase A to neutral, and/or Phase B to
neutral.
The 220 is Phase A to Phase B.

Forgetting for a moment that the wires wouldn't take it, but as a
hypothetical only, suppose
you had 150 amps at 220 V between Phase A and Phase B.

Are you suggesting that you could "still" pull more off of either phase (to
neutral) although at 115 V ?

No, he's not.

Do you now how many amps of load you have between 'Phase A' and Neutral?
Call that X. Do you know how many amps of load you have between 'Phase B'
and Neutral? Call that Y. Do you know how many amps of load you have
between 'Phase A' and 'Phase B'? Call that Z. The amps you'll see on your
incoming 'Phase A' wire will be X+Z. Keep this less than 150A. Well, keep
it less than 120A, because of the 80% factor others have mentioned. In
fact, keep it well under 120A. The amps on your incoming 'Phase B" wire
will be Y+Z. Keep this under 150A (120A) as well.

If this doesn't seem to make sense, it may be because of ac electricity and
phase angles (+ and - signs in the case of a 120/240V system where the
phases are 180 degrees apart).

The above is simplified, but for typical residential loads, it should be
adequate in terms of the math. If you're actually going to make decisions
with safety and/or monetary impact, you will want to get more info. There
are probably Code rules for determining demand. One thing that has a huge
impact is diversity. Say you had 400A worth of equipment and receptacles
hooked up on 'Phase A' in your home, you might find that the most current
you ever draw for any sustained period (say, 15 minutes) is 80A, because not
everything is on full tilt all of the time.

Hope that helps, or at least, doesn't make it worse.

j
 
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