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

• posted
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
• posted
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.
• posted
| 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 ?
In the US the nominal voltages are 120 and 240. I'll use those in the description.
The answer is either. Both phases are 150 amps capable, which means you can get 150 amps at 240 volts, or you can get 150 amps on both 120 volt circuits at the same time. Or you can do any combination such that the total current does not exceed 150 amps on either phase wire (for example 90 amps at 240 volts plus 60 amps on one 120 volt phase and 60 amps on the other 120 volt phase).
The power company typically assumes residential users won't use the full power level on a long term continuous basis. Thus they will often put in a transformer actually rated less. They can handle overloads for a while, sometimes even hours, possibly days. But if for some reason you expect to pull the 150 amps all the time, 24x7, you need to make sure the equipment is rated for continuous service at that level.
• posted
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
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• posted
150a on each leg ... 240v
• posted
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.
• posted
| 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 ?
Once you have 150 amps current flowing, that's it. If you add on a 30 amp load on just phase A, then it will be at 180 amps and that will heat up the wire even more, beyond what it's supposed to be (though it count take a little while for 180 amps to trip a 150 amp breaker). You'll have 150 amps on phase B and 30 amps on the neutral at that point.
This is assuming a normal 120/240 volt circuit. A 120/208 volt circuit derived from 2 phases of 3 phase service will behave differently.
• posted
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
• posted
It may be easier/better for you to think of this in watts, rather than amps. Your 150 amp service can provide 36,000 watts (240 volts times 150 amps). Each 120 volt half of it can provide 18,000 watts. Exceed 18,000 watts on either half, or exceed 36,000 watts total, and the breaker trips.
In the scenario you asked about, there were already 36,000 watts consumed (I changed your 220 to 240). You can't pull more without exceeding 36,000.

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