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Old 04-24-2011, 11:44 PM   #1
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Basic (hopefully) electrical questions


Hi all,

Questions first, qualifiers at the end:

1. Any suggestions on how to determine wattage for appliances? I know about products like the Kill-A-Watt, but what about appliances that are hard wired (dishwasher, garbage disposal, sensor flood lights, etc.)?

2. I am wondering if how I am currently calculating wattage is correct:
  • looking for the wattage on the label
  • finding the amperage on the label and multiplying by the voltage (either 120v or 240v)

3. If I have properly calculated wattage of all my appliances, what will happen if I go over the wattage limit for a particular circuit breaker. For example, if a 15amp circuit breaker (1800watts) has appliances all on at the same time and wattage goes over 1800 watts, will the breaker just trip?

4. Am I correct with this thinking - one of my 30amp double-pole switches delivers 240v because it has two 120v hot wires are feeding out of the breaker, as opposed to the 15 and 20 amp breakers, which only have one 120v wire feeding out of it...

5. Is there a rule of thumb for the wire gauge to use for a specific breaker? By this, I mean should 15amp breakers use a specific gauge wire, whereas a 20amp breaker use another (smaller gauge)?

6. I recently (see below) found that all of the following appliances are connected to one 20 amp circuit breaker:
  • furnace
  • condenser
  • washer
  • microwave
  • toaster oven
  • two flood lights (sensor)
Is this too much load on one breaker? These appliances do not all run at the same time, because I'm sure I would have blown the breaker by now, but do I need to have this fixed sooner than later?

OK, so the reason for all of these questions:

I bought a house about a year and a half ago and just last week got around to mapping out the electrical system. I know I should have done this much earlier, but my motivation was to determine if I could add more lighting to my backyard. I mapped out each outlet, light and appliance to a breaker and recently started to figure out the wattage on each breaker to see what is in danger of being over and where I still had some allowance to work with.

I have been doing research on my own, including almost all of Black and Decker's guide to wiring (hoping this is a reputable book), but have not been able to grasp the ideas that generated my questions above. I do have some additional questions, but those might be answered with responses to the ones above.

Any feedback is greatly appreciated!

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Old 04-25-2011, 12:06 AM   #2
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Basic (hopefully) electrical questions


Quote:
Originally Posted by k2000lbs View Post
Hi all,

Questions first, qualifiers at the end:

1. Any suggestions on how to determine wattage for appliances? I know about products like the Kill-A-Watt, but what about appliances that are hard wired (dishwasher, garbage disposal, sensor flood lights, etc.)?

2. I am wondering if how I am currently calculating wattage is correct:
  • looking for the wattage on the label
  • finding the amperage on the label and multiplying by the voltage (either 120v or 240v)

3. If I have properly calculated wattage of all my appliances, what will happen if I go over the wattage limit for a particular circuit breaker. For example, if a 15amp circuit breaker (1800watts) has appliances all on at the same time and wattage goes over 1800 watts, will the breaker just trip?

4. Am I correct with this thinking - one of my 30amp double-pole switches delivers 240v because it has two 120v hot wires are feeding out of the breaker, as opposed to the 15 and 20 amp breakers, which only have one 120v wire feeding out of it...

5. Is there a rule of thumb for the wire gauge to use for a specific breaker? By this, I mean should 15amp breakers use a specific gauge wire, whereas a 20amp breaker use another (smaller gauge)?

6. I recently (see below) found that all of the following appliances are connected to one 20 amp circuit breaker:
  • furnace
  • condenser
  • washer
  • microwave
  • toaster oven
  • two flood lights (sensor)
Is this too much load on one breaker? These appliances do not all run at the same time, because I'm sure I would have blown the breaker by now, but do I need to have this fixed sooner than later?

OK, so the reason for all of these questions:

I bought a house about a year and a half ago and just last week got around to mapping out the electrical system. I know I should have done this much earlier, but my motivation was to determine if I could add more lighting to my backyard. I mapped out each outlet, light and appliance to a breaker and recently started to figure out the wattage on each breaker to see what is in danger of being over and where I still had some allowance to work with.

I have been doing research on my own, including almost all of Black and Decker's guide to wiring (hoping this is a reputable book), but have not been able to grasp the ideas that generated my questions above. I do have some additional questions, but those might be answered with responses to the ones above.

Any feedback is greatly appreciated!

1. the best approach would be to buy a meter that has a clamp on ammeter. I would suggest something like this
http://www.amazon.com/Fluke-Corporat.../dp/B0006Z3GZU

2. you need to keep your load calculations in amps (in this situation, where your doing breaker sizing), convert everything to amperage. Find the wattage of your appliances divide them by the voltage

3. first of all, a 15 amp circuit is only good for 15 amps if its not a constant load. For circuits that you are likely to have running everything at the same time, don't go above 80% of your breaker size. For things like lights, you don't want to get ridiculous, but most people just keep adding more lights until they are having problems with the breakers starting to trip. This probably isn't the best practice, a better practice is to periodically check you amperage of the circuit you are wondering about and see how much more load you can safely add.

4. yes, a 2 pole breaker will have 240volts and a single pole will have 120v.

5. 14g - 15 amps, 12g 20 amps, 10g 30 amp, 8g 40 amp, 6g 50 amp

6. that is definitely too much load and doesn't sound correct, are you sure they are all on one breaker? Washer should have its own 20a, microwave sometimes gets its own 20a (usually in newer houses), furnace and condenser should each have their own appropriately size breakers

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Old 04-25-2011, 12:20 AM   #3
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Thanks for the answers! Very helpful. I do have some follow-ups:

Quote:
Originally Posted by jimmy21 View Post

2. you need to keep your load calculations in amps (in this situation, where your doing breaker sizing), convert everything to amperage. Find the wattage of your appliances divide them by the voltage
Will the voltage always be either 120 or 240? I ask because I sometimes see other voltage number on some small electronics, e.g. my cable modem shows 12v--1amp. That example might not be relevant in this context, but hoping to clear up any confusion.



Quote:
Originally Posted by jimmy21 View Post

6. that is definitely too much load and doesn't sound correct, are you sure they are all on one breaker? Washer should have its own 20a, microwave sometimes gets its own 20a (usually in newer houses), furnace and condenser should each have their own appropriately size breakers
Yeah, I checked a few times to make sure. One thing that I did not mention earlier is that the condenser's power supply goes through a 60 amp breaker. That breaker is located outside, next to the condenser. However, when I flip off the 20 amp breaker inside, the one in question, the condenser shuts off too.
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Old 04-25-2011, 12:24 AM   #4
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the inside breaker could be controlling the thermostat which would kill the AC even if the power was still on.


electronics plugged in by wall warts(transformers) will be rated at their voltage.
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Old 04-25-2011, 08:44 AM   #5
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If the furnce breaker is turned off than the ac/ condensor will not work. As stated it could be controlled by the tsat, but more likely the circuit board in the furnace.
The other circuits such as microwave and toaster oven could be split so they could be on ther own circuit.
The other isue is the 20 amp breaker. Is everything fed by 12 wire or did someone changed from a 15 amp breaker to a 20 amp to cut down on overload tripping
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Old 04-25-2011, 09:37 AM   #6
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Originally Posted by NJMarine View Post
If the furnce breaker is turned off than the ac/ condensor will not work. As stated it could be controlled by the tsat, but more likely the circuit board in the furnace.
The other circuits such as microwave and toaster oven could be split so they could be on ther own circuit.
The other isue is the 20 amp breaker. Is everything fed by 12 wire or did someone changed from a 15 amp breaker to a 20 amp to cut down on overload tripping
I believe it is 12 gauge, I will have to check again. As I understand it, using a 20amp in place of a 15 amp is bad thing, right?
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Old 04-25-2011, 09:59 AM   #7
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Correct
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Old 04-25-2011, 10:05 AM   #8
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Quote:
Originally Posted by NJMarine View Post
Correct
If the wire is 12 gauge, the 20 amp breaker is correct, right? The problem would be if the wire 14 gauge or smaller wire with a 20 amp....
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Old 04-25-2011, 04:49 PM   #9
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thats right - 15a=14ga wire 20a =12ga 30a=10ga OR bigger wire
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Old 04-27-2011, 01:42 PM   #10
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So I checked everything again and it looks like this is the wiring:

-One 30 amp breaker is dedicated to the compressor. However, there is a 60amp breaker between the service panel and the actual compressor itself (the 60amp is located outside). Is this normal procedure?

-The 20 amp breaker with the furnace/thermostat, washer, microwave and toaster over does indeed use a 12 gauge wire.

Thanks for the feedback everyone!
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Old 04-27-2011, 01:59 PM   #11
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Originally Posted by k2000lbs View Post
-One 30 amp breaker is dedicated to the compressor. However, there is a 60amp breaker between the service panel and the actual compressor itself (the 60amp is located outside). Is this normal procedure?
It can be. the 60a breaker is only there for a service disconnect for the service guy. The actual protection is provided by the 30a upstream breaker. So yes that is normal. But that is a small ac

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