Amps of circuit versus appliance rating

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  #1  
Old 04-25-07, 07:24 AM
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Amps of circuit versus appliance rating

I've learned a lot from this forum, now here's something specific for my situation.

I'm wiring two electric wall fan heaters on a new 240v circuit with 10/2 wire and a ground. One heater is 1500w (6.25 amps) and one is 3000w (12.5 amps). I'm trying to decide what amperage the circuit breaker should be.

1. The total amps are beyond the 80% limit for sustained loads of a 20 amp breaker.

2. The spec sheet for the heaters say they are rated for 25 amps.

3. 25 amp breakers are not available for my breaker box (Square D QO type)

4. Through e-mail correspondence, the manufacturer's tech support people told me that I could wire both heaters on a 30 amp circuit (yet, see item 3).

Which is lower risk, a 20 amp breaker (without my 20 percent buffer for sustained loads) or a 30 amp breaker (possibly beyond the rated limits of my heaters)?

I do not have space in my breaker box to run each heater on its own circuit.
 
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  #2  
Old 04-25-07, 07:52 AM
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I can see no safety risk running 20 amp breaker, 10 awg copper wire.

Running 30 Amp on the same wire may cause a fire-risk after long time max load if wire is running in worst possible way.

The only reason for not doing this is because the code says you ned 20% extra capacity.

dsk
 
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Old 04-25-07, 08:06 AM
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There is absolutely NO fire risk in running a 30 amp breaker with #10 wire and a 19 amp load.

Please define "worst possible way". I have NO idea what this means.



Bored, unless the instructions specifically state to use a 25 amp breaker, just use the 30. The breaker protects the wire, NOT the heaters.

Yes, 25 amp breakers most certainly are available for QO panels. Just because Home Depot does not carry it does not mean it does not exist. A real supply house will have it.
 
  #4  
Old 04-25-07, 08:43 AM
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Thanks a ton guys.

Since I'll only use these two units, and since I already have a 30, I'll go ahead and use that. I'll also keep my eye out for a 25 amp replacement at some point in the future. I hate that you spotted me on my first post as a Home Depot junkie, but I appreciate the help nonetheless.

Of course, I will continue to monitor this thread and this board for other opinions and advice -- if anybody disagrees with this course.
 
  #5  
Old 04-25-07, 04:29 PM
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unless the fans have internal fuses or breakers, or you plan to install fused disconnects, you need one 15 amp circuit and one 20 amp circuit.
 
  #6  
Old 04-25-07, 04:44 PM
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1. The total amps are beyond the 80% limit for sustained loads of a 20 amp breaker.

A. if running more than 3 hours yeah it will be over the 16 amp load contounits running.

2. The spec sheet for the heaters say they are rated for 25 amps.

A. Useally when the manufacter instuction say so then you follow what the max breaker or fuse rating for this

3. 25 amp breakers are not available for my breaker box (Square D QO type)

A. sure they are avabile at electrical supply centre just ask for QO225 breaker [ they will cost little more than standard breaker size ] other wise get QO230 breaker

4. Through e-mail correspondence, the manufacturer's tech support people told me that I could wire both heaters on a 30 amp circuit (yet, see item 3).

A. see above #3 answer
Which is lower risk, a 20 amp breaker (without my 20 percent buffer for sustained loads) or a 30 amp breaker (possibly beyond the rated limits of my heaters)?

A. just run with 25 or 30 amp breaker for both heater unless the instruction say indivual heater must have it own breaker or fuse

I do not have space in my breaker box to run each heater on its own circuit.

A. I think this answer is pretty common but sure fire way is add subfeed box next to the main box it pretty straght foward work if you understand how to hook this up.
If you go this route then you can have it own circuit for each heater and use #12 -2 wires [ make sure you remark the white to red or bleu to let it know that is on 240 volt circuit ] and get QO215 breakers or QO220 breakers on this and it will work just fine as well

Merci, Marc
 
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