Electrical - adding AC wiring to 12 volt system - Page 2 - Fiberglass RV


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Old 08-10-2013, 02:08 PM   #15
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If we have a 30 amp service and Use a 15 amp circuit for the converter, then we only have 15 amps left. Why does it matter if a kitchen outlet pulling 5 amps is on its own circuit? Doesn't it add the same load to the power supply as it would on a shared circuit?
NO ; You are assuming that your converter is taking a full 15 amps , which it not. One of the main reason to place your converter on it's own separate circuit is not because of it's amperage draw but to help insure that another load on the same circuit does not cause the breaker to trip and in the process cause your battery to be drained . When wiring houses I always put the freezer on a separate circuit .The freezer only draws 4 amps but I would hate to come home to a freezer full of rotted food because some other piece of equipment running off the same circuit caused the breaker feeding the freezer to trip . It is the same reason home furnaces must be on their own separate circuit , again who wants their home to freeze up because another piece of equipment caused the breaker feeding the furnace to trip. We have never tripped the thirty amp main breaker feeding our trailer but have tripped the branch circuit breakers on several occasions. I have been a licensed electrician for over 40 years and have taught at the local Vo Tech for over 30 years . I am speaking from experience
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Old 08-10-2013, 02:16 PM   #16
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Ok, I am confused..

The converter will have a dedicated circuit.

And, if the circuit for the converter is 15 amps, isn't that 15 amps reserved for that circuit alone and not available to any other power draw.

Can it be smaller than 15 amps since it does not share the circuit?

If so, how would you divide the power?
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Old 08-10-2013, 02:23 PM   #17
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Steve, we are talking about multiple circuits, one for the converter and the other(s) for the remainder of the camper. My question is how many circuits can you put to carry 15 amps? A 10 and a 5? Or have I missed something (again)?
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Old 08-10-2013, 03:58 PM   #18
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Steve, we are talking about multiple circuits, one for the converter and the other(s) for the remainder of the camper. My question is how many circuits can you put to carry 15 amps? A 10 and a 5? Or have I missed something (again)?
The sub breakers do not add up to the amperage rating of the main breaker. In a house, the main may be 200 amps, but you can have as many 15 or 20 amp circuits as will fit in the box. That is because the sub breakers will trip if you exceed their rating on that circuit or the main will trip if the sum of the current draw on the sub breaker circuits exceeds the main breaker rating.
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Old 08-10-2013, 04:45 PM   #19
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Tom,

Are you saying that if, for example, our service is 30 amps we could put five 10 amp sub breakers in the box?
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Old 08-10-2013, 05:01 PM   #20
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Yes, I believe that is what he is saying. The load attached to each circuit is what determines the current drawn through the circuit (and corresponding breaker). For simplicity, think of it not so much as what current you put in, but what current you draw out. So if the current drawn by the devices attached to a particular 10A breaker exceeds 10 amps, then that breaker will trip. If the load drawn by all the devices on all the 10A breakers together exceeds 30A, then the main breaker will trip.

Does that help you to make sense of the earlier explanations?
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Old 08-10-2013, 05:14 PM   #21
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Ok, I understand that the circuit power drawn may not exceed the size of the sub breaker (it will trip) and that the total of all sub breakers my not exceed the total of the main breaker (or it will trip). In our case that is 30 amps. If we put the converter on a 15 amp breaker and the converter only pulls 6 amps, does that mean that the left over 9 amps are available to other sub circuits in the box?
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Old 08-10-2013, 05:19 PM   #22
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Yes. That is correct - the 9 A is available to other circuits.
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Old 08-10-2013, 05:24 PM   #23
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Yes, I believe that is what he is saying........
Yup

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Yes. That is correct - the 9 A is available to other circuits.
Yup
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Old 08-10-2013, 05:29 PM   #24
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Our Scamp came with a 30 amp cord and two 15 amp breakers.

We added a number of ac outlets for convenience, actually I think we have 10 ac outlet pairs and increased the breakers from two to four. That means minimally 2-3 outlets are on each breaker. The reality is that we rarely use more than a couple of outlets at any one time.

When we're home in the summer we run our trailer on 120 VAC on a standard 3 prong 20 amp circuit. We are fully capable of running the whole trailer on a single home circuit including our power convertor, refrigerator (we never shut it off) and even our air conditioner. In this configuration we have never tripped a house breaker.

This home configuration means that we use a 30 amp to 20 amp plug convertor. This is used more frequently than the 50 to 30 amp convertor though we do carry both we only use the latter about once a year.

As to running the coffee pot and the toaster simultaneously we plug them both into the same outlet and have never blown a breaker. Our coffee pot is only 600 watts and only draws sigbificant current for minutes while it brews. The toaster draws more current but again for only a couple of minutes.

We also have an in-closet air conditioner that draws about 5 amps.

When rewiring we carefully considered the assignments of circuits to breakers. Our goal was to assure that larger loads would typically be on circuits that are with typically low current or no current companions. For example our outside outlet is on the breaker that our electric heater is typically on.

The reality, at least in our trailer the only items that draw appriciable current, are the fridge and the electric heater.

In addition to our 10 AC outlets we have added 4 DC outlets.

The DC outlets, at least in our trailer are generally low current, used for our Endless Breeze fan and for running low wattage DC to AC convertors for our TV and Sat receiver.

We have no GFI breakers except on the house where the trailer plugs in. It came with none and we've added none.
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Old 08-10-2013, 05:41 PM   #25
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Hallelujah, I think I'm starting to get it. Let me just Make sure....If we have a 30 amp breaker box we can put four 20 amp sub breakers in, so that 20 amps will be available to each circuit. However if we exceed 20 amps on any breaker or 30 amps total (combined circuit usage) breakers will trip. The breaker maximums don't have to equal the 30 amp total, only the combined usage of all the circuits may not exceed 30 amps. And each circuit is limited to the breaker size.

There can be Five 20 amp breakers, each drawing 3 amps for a total of 15 amps which does not exceed the 30 amp main breaker or the individual 20 amp sub breakers. Is this correct?
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Old 08-10-2013, 05:51 PM   #26
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Yes, you have it (although you probably would choose a breaker smaller than 20A if your circuit is only drawing 3A).

And to be abundantly clear, lets change your example slightly...
There can be five circuits, each with a 20 amp breaker, each circuit actually drawing 5 amps (not exceeding the 20A breaker limit on each circuit) for a total of 25 amps which does not exceed the 30 amp main breaker.
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Old 08-10-2013, 05:55 PM   #27
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Thank you, thank you, thank you, to all. What a relief to be getting my brain around this. I am so grateful for all of the input and patience. I will inform the forum as we progress.

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Old 08-10-2013, 05:58 PM   #28
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Hallelujah, I think I'm starting to get it......
You have got it. Remember the breaker is sized to protect the wire from overheating, so the breaker size is chosen according to the gauge (size) of the wire conducting the electricity through the breaker.
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