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docpops
10-30-2008, 09:40 PM
I'm finishing a basement, and currently have an unused 20 amp breaker once dedicated for a washer, a well as a 240V outlet for an old dryer long since moved upstairs. The 240 outlet is hooked into my main panel at a twin 30 amp breaker. My plan is to use the 20 amp for the bathroom, and then put in a subpanel where the 240V was, so I can run three circuits:
1 - spare bedroom (lights/outlets/small TV)
2 - small 120V 1000W cadet heater
3 - dedicated outlet for a treadmill (around 1100W at peak)

The electrician was out today and mentioned he could only put in a 30 amp breaker where that 240V outlet is. I already ran 2 lines of 12G romex to the area where the washer/dryer outlets were (one each for the bath and bed), and was going to run 2 more lines - one for the heater, and one for the outlets.

Something tells me I'm going about this all wrong - I couldn't quite get an answer as to why we couldn't put in more than 30 amps at that old 240 - my hope was to run three separate 20 amp circuits from it (I thought 2 30 amp breakers at the main meant I had 60 amps total - stupid of me) so I could dedicate one 20 amp breaker each to the bedroom, heater, and treadmill.

All/any input and advice appreciated.

docpops
10-30-2008, 09:47 PM
Also, I don't plan to ever be running the heater and the treadmill at the same time, or certainly not at anything near peak capacity.

Basement_Lurker
10-30-2008, 10:58 PM
You have a double 30A breaker in your main panel; which is not the same as two single breakers. The double breaker still pulls only 30A, but it uses two hots to give you 240v. I assume that the reason why you couldn't use anything larger than 30A for the sub-panel is because you plan on re-using your 3-wire dryer wire for your sub-panel. That wire is only rated at 30A; so if you wanted a larger main breaker on your sub-panel, you would have to run a larger service wire.

I think 30A should be ok for the 3 circuits you plan on wiring from the sub-panel. The bedroom sounds like a rarely used guest room, so it's hardly a factor for the small amount of power it will use, and the heater is a fixed draw at like half of a 15A circuit, and so is your treadmill, which would never be in use at the same time when one of the other two circuits would be in max use. If this is going to be inspected, you don't have to tell them that the treadmill circuit is dedicated specifically for a treadmill, it can just be normal outlet.

drick
10-30-2008, 11:31 PM
This is most likely the reason. If you are planning on reusing the dryer wire you cannot change out the 2 pole 30 to anything but a single pole 30 IF the wire is only 3 conductor (most pre 1997 dryer wires are 3 conductor instead of 4) because you don't have enough conductors to install a split phase sub panel and take advantage of both halves of the two pole 30 amp breaker.

Based on your load calculation it won't matter though. Just buy a small sub panel and feed it off of a single pole 30 at the main box. You should be fine.

-rick

docpops
10-31-2008, 05:17 AM
Thank-you so much, so far.

But, can I physically run three strands of 12G romex out of this subpanel (bedroom, heater, trdmil)? This, in my inexperienced mind, is what I'm blanking on. My associate says I have to run all of this on a single strand of 10G, but since I've got the 12 in already I was hoping there was a different way.

jadnashua
10-31-2008, 06:24 AM
If you run new wire all the way back to the original panel, remove the 30A CB, and then run new wire, as long as the wire is the proper size and you have room in the panel for the new breakers you are installing, you should be golden (assuming all of the workmanship is up to code). If you want to reuse the original wiring for the dryer for something, anything you put on it cannot exceed the original wire's power rating; so, unless that wire was oversized upon installation, what is attached to it can't exceed the original rating. But, if you use that 30A with a 30A breaker, and feed a subpanel, the total of the breakers on that subpanel can exceed the 30A (just like it likely does on your main panel). But, given what you are planning, you'd get the subpanel's breaker tripping.

Basically, no protected circuit can have an undersized wire between the source and the protection device...30A breaker, must have wire that can support 30A service. As long as all of the wires are protected properly, the aggragate total can be higher (you may have 150A worth of breakers in your main panel, but only a 100A main breaker, for example, but each branch must have the proper sized wire for its individual breaker regardless of whether if you turn everything on it doesn't overload the individual branch, but trips the main).

docpops
10-31-2008, 06:40 AM
So if I understand what you are saying, Jadnashua, I could conceivably place three separate 20 amp breakers in my subpanel, even though the main circuit is only 30 amps, and as long as the sum total load doesn't exceed 30 amps at any given time (which seems inconceivable to me) I won't be tripping the circuit?

hj
10-31-2008, 07:35 AM
If you can take care of grounding, then the dryer wire to a sub panel will give you 30 amps on each leg, in effect 60 amps at 120 v.

jadnashua
10-31-2008, 09:35 AM
A CB sets the maximum current on that individual circuit. As long as the wires feeding that CB are also properly fused or run through a CB, the weakest point must be protected...if it is exceeded, it will trip, protecting anything downstream.

An HJ's point is also correct, but needs to be done right.

jwelectric
10-31-2008, 10:40 AM
215.2 Minimum Rating and Size.
(A) Feeders Not More Than 600 Volts.
(1) General. Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220. The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

All this bull you are being told means nothing. Your asnwer lies above

Chris75
10-31-2008, 06:58 PM
215.2 Minimum Rating and Size.
(A) Feeders Not More Than 600 Volts.
(1) General. Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220. The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

All this bull you are being told means nothing. Your asnwer lies above

Why is the answer always so easy, yet so hard. :D

drick
10-31-2008, 11:15 PM
>>Why is the answer always so easy, yet so hard.

Try not to fall asleep reading article 220:) ZZZZZZZzzzzzzzzzz. Oh, sorry I accidentally flipped to page 102.

I think you skipped a math class somewhere jwelectric if you actually think the 30A breaker is going to trip.
1200W Heat +0.25 (that is your only continuous load) = 1500W
1100W for the treadmill (noncontinuous load ) = 1100W
that leaves 1000W for a single guest bedroom! You could hook up a 50 inch plasma TV and have a 500w lamp on your nightstand (better tell the guests to bring their sun shades) and that breaker will still hold!

However, if you throw in the fact that your not supposed to exceed 80% capacity on the #10 then things do start to get a little too tight. The breaker will still not trip though.


-rick

drick
10-31-2008, 11:22 PM
Thank-you so much, so far.

But, can I physically run three strands of 12G romex out of this subpanel (bedroom, heater, trdmil)? This, in my inexperienced mind, is what I'm blanking on. My associate says I have to run all of this on a single strand of 10G, but since I've got the 12 in already I was hoping there was a different way.

This is totally wrong. You can't even wire standard residential switches and outlets to 10GA wire. And yes, you can run 3 20A circuits out of the sub panel that is protected by a 30A breaker back at the main panel.

-rick

jwelectric
11-01-2008, 02:59 AM
>>Why is the answer always so easy, yet so hard.

Try not to fall asleep reading article 220:) ZZZZZZZzzzzzzzzzz. Oh, sorry I accidentally flipped to page 102.

I think you skipped a math class somewhere jwelectric if you actually think the 30A breaker is going to trip.
1200W Heat +0.25 (that is your only continuous load) = 1500W
1100W for the treadmill (noncontinuous load ) = 1100W
that leaves 1000W for a single guest bedroom! You could hook up a 50 inch plasma TV and have a 500w lamp on your nightstand (better tell the guests to bring their sun shades) and that breaker will still hold!

However, if you throw in the fact that your not supposed to exceed 80% capacity on the #10 then things do start to get a little too tight. The breaker will still not trip though.


-rick


Now wouldn't that be three watts per square foot instead of a lamp on the table and a TV?
Ain't no wonder he don't know what is going on with all these people telling him everything but how to do it the right way.

Chris75
11-01-2008, 02:26 PM
And yes, you can run 3 20A circuits out of the sub panel that is protected by a 30A breaker back at the main panel.

-rick


Yeah, sure ya can, wanna give me the code section that would allow that?

Chris75
11-01-2008, 02:27 PM
>>Why is the answer always so easy, yet so hard.

Try not to fall asleep reading article 220:) ZZZZZZZzzzzzzzzzz. Oh, sorry I accidentally flipped to page 102.

I think you skipped a math class somewhere jwelectric if you actually think the 30A breaker is going to trip.
1200W Heat +0.25 (that is your only continuous load) = 1500W
1100W for the treadmill (noncontinuous load ) = 1100W
that leaves 1000W for a single guest bedroom! You could hook up a 50 inch plasma TV and have a 500w lamp on your nightstand (better tell the guests to bring their sun shades) and that breaker will still hold!

However, if you throw in the fact that your not supposed to exceed 80% capacity on the #10 then things do start to get a little too tight. The breaker will still not trip though.


-rick

Sure... I think you skipped a few electrical classes, but what do I know?

docpops
11-01-2008, 07:16 PM
Thanks for all the help. I think I have it sorted out.

jar546
11-01-2008, 10:11 PM
215.2 Minimum Rating and Size.
(A) Feeders Not More Than 600 Volts.
(1) General. Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220. The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

All this bull you are being told means nothing. Your asnwer lies above

Best advice yet

jwelectric
11-02-2008, 03:16 PM
Best advice yet

Thank you for the kind words although now my hat wont fit my head :D:D