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Old 11-10-2010, 04:19 PM   #16
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30amp sub panel for shed??


but for what he wants is multiple ckts ckts.more than two 2 2 wire ckts 230.79(d).require 60 amps min...

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Old 11-10-2010, 04:22 PM   #17
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30amp sub panel for shed??


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but for what he wants is multiple ckts ckts.more than two 2 2 wire ckts 230.79(d).require 60 amps min...
He is not going to have more than 2 2 wire circuits, and 230.79 is only concerned with the disconnecting means, not the size of the circuit.
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Old 11-10-2010, 04:29 PM   #18
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30amp sub panel for shed??


if furnace is 120volt gas fired he will have 3 two wire ckts.this he has not said...?
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Old 11-10-2010, 04:36 PM   #19
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30amp sub panel for shed??


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if furnace is 120volt gas fired he will have 3 two wire ckts.this he has not said...?
If he runs a 30 MWBC then he will have 2 2wire circuits.
The furnace would come from the subpanel in the shed.
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Old 11-10-2010, 04:38 PM   #20
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30amp sub panel for shed??


all the ckts will come out of the sub panel..
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Old 11-10-2010, 04:47 PM   #21
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30amp sub panel for shed??


and the disconnect must be 60a...not the circuit
Breaker in main panel feeding sub is a 30a 240v
Panel in the detached building has a 60a main breaker somewhere
But the power is limited by the 30a breaker in the Main panel feeding the sub panel
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Old 11-10-2010, 05:20 PM   #22
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30amp sub panel for shed??


point al-along has been you need a 60 amp disc.i would want at least a 40 amp in main.especialy if he is running a heater.
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Old 11-10-2010, 07:03 PM   #23
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30amp sub panel for shed??


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I respectfully disagree. A double-pole 30A breaker will trip if EITHER leg pulls more than 30A (as per the trip curve).
Yes, but you can put 30A worth of 120V circuits on one leg, and 30A MORE worth of 120V circuits on the OTHER leg, totalling 60A worth of 120V circuits.

15 (lights) + 20 (receptacle circuit) + 20 (furnace) is 55.

I propose Lights + Furnace (35 MAX, but I doubt the furnace will be a continuous load) on one leg, Receptacles on the other.
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Old 11-12-2010, 11:12 AM   #24
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30amp sub panel for shed??


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Yes, but you can put 30A worth of 120V circuits on one leg, and 30A MORE worth of 120V circuits on the OTHER leg, totalling 60A worth of 120V circuits.
Maybe in the simplest of terms, but NO professional electrician would ever think of it this way. A 30A feeder is not 60A @ 120v. It is 30A @ 240v.





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15 (lights) + 20 (receptacle circuit) + 20 (furnace) is 55.
HUH??? Adding up the breaker ratings is NEVER an accurate example of anything.
In this case 15+20+20 does NOT = 55.
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Old 11-12-2010, 12:37 PM   #25
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30amp sub panel for shed??


Well thank you, as jbfan is the one who is figuring everything worst-case. My use of the breaker ratings was only to satisfy HIS insanity.

I know very well a gas or oil furnace doesn't pull 20A at 120V. HE seems to think that the furnace "using 20A" is material for his insistance that two poles of 30A is not enough!



"Maybe in the simplest of terms". Well for a person who quite clearly believes that 30A @ 240V is 3600VA (it's not. It's 7200), the simplest of terms is necessary.



I don't know a "professional electrician" who would do a load calculation resulting in 36KVA (150 amps @ 240) and proceed to spec a 400A service, unless the customer was made out of pure cash!



I already agreed, long LONG ago, that 60A would be preferred. The argument is whether or not it is NECESSARY. It is ABSOLUTELY NOT.

Seven lights and a furnace do not add up to a need for more than 30A, and can be put on one leg. IN FACT, even large multizone hydronic heating systems serving apartment buildings in my area usually run from a 15A circuit. I can't imagine a furnace to heat a "shed" actually NEEDS a 20A circuit, so let's just figure on 15A lights and 15A furnace. Two 15A circuits. Even if we do 100%, that's 30A. Why, again, do we need 60?

A 20A 'receptacles' circuit, even worst-case, fully-loaded, ALSO does not equal more than 30A, and can perfectly well be put on the other.

THERE IS NO NEED FOR 60A!
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Old 11-12-2010, 12:49 PM   #26
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30amp sub panel for shed??


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Originally Posted by emolatur View Post
Well thank you, as jbfan is the one who is figuring everything worst-case. My use of the breaker ratings was only to satisfy HIS insanity.

I know very well a gas or oil furnace doesn't pull 20A at 120V. HE seems to think that the furnace "using 20A" is material for his insistance that two poles of 30A is not enough!



"Maybe in the simplest of terms". Well for a person who quite clearly believes that 30A @ 240V is 3600VA (it's not. It's 7200), the simplest of terms is necessary.



I don't know a "professional electrician" who would do a load calculation resulting in 36KVA (150 amps @ 240) and proceed to spec a 400A service, unless the customer was made out of pure cash!



I already agreed, long LONG ago, that 60A would be preferred. The argument is whether or not it is NECESSARY. It is ABSOLUTELY NOT.

Seven lights and a furnace do not add up to a need for more than 30A, and can be put on one leg. IN FACT, even large multizone hydronic heating systems serving apartment buildings in my area usually run from a 15A circuit. I can't imagine a furnace to heat a "shed" actually NEEDS a 20A circuit, so let's just figure on 15A lights and 15A furnace. Two 15A circuits. Even if we do 100%, that's 30A. Why, again, do we need 60?

A 20A 'receptacles' circuit, even worst-case, fully-loaded, ALSO does not equal more than 30A, and can perfectly well be put on the other.

THERE IS NO NEED FOR 60A!
I think you need to reread the thread again.
I never said he needed 60 amps. I was discussing disconnect rating with oleguy74 and we came up that the disconnecting means needed to be 60 amps, not the circuit to the shed.

I don't have any trouble taking the heat for something I might have stated wrong, but I am not going to take the heat for something I never said!
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Old 11-12-2010, 02:53 PM   #27
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I think you need to reread the thread again.
I never said he needed 60 amps. I was discussing disconnect rating with oleguy74 and we came up that the disconnecting means needed to be 60 amps, not the circuit to the shed.

I don't have any trouble taking the heat for something I might have stated wrong, but I am not going to take the heat for something I never said!
I'm not going to re-read because I'm doing this at the same time as recording and don't have the spare brain cells. However, if I misunderstood your point then I apologize, and we agree.
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Old 11-12-2010, 08:07 PM   #28
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and the disconnect must be 60a...not the circuit

Panel in the detached building has a 60a main breaker somewhere
Question: Why would the disconnect in the shed need to be 60 amps for a 30 amp x 240 volt feed?

Now it could be 60 amps for futureproofing or because that's what came with the panel, although that too would be forevermore overkill unless the feed cable from the main house were 6 gauge or fatter.
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Old 11-12-2010, 08:35 PM   #29
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Question: Why would the disconnect in the shed need to be 60 amps for a 30 amp x 240 volt feed?

Now it could be 60 amps for futureproofing or because that's what came with the panel, although that too would be forevermore overkill unless the feed cable from the main house were 6 gauge or fatter.
For whatever reason a 60a disconnect is required by NEC Code
I think the proper code section has already been cited
There was another person who put in a 40a or 50a & his inspector failed it on inspection
My 60a sub in my pool cabana has a 100a main breaker
Just easier to buy it that way
I ran 60a just in case to future proof....AC in the cabana / Heat ? outdoor kitchen ? 2nd hot tub (yup) ?
Cost was not that much more
And that way you can run more then one high power tool & not worry about it
Air compressor, 18 cu ft fridge, dorm fridge, 20a 240v pool pump....no worries
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Old 11-13-2010, 08:56 AM   #30
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30amp sub panel for shed??


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Originally Posted by Speedy Petey View Post
A 30A feeder is not 60A @ 120v. It is 30A @ 240v.
A little off topic historical insight.

Way back when, some of the "services" were:
A 60 amp. service providing 60 amps x 240 volts, sometimes with as few as four screw in fuse sockets (120 volt hot to neutral) with a main pull out holder with two cartridge fuses, and a similarly sized holder with two cartridge fuses (240 volt) for an electric stove.
A 30 amp. service providing 30 amps x 120 volts, the panel containing two 15 amp fuses, the feed being one hot plus neutral coming in from the utility pole.

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Last edited by AllanJ; 11-13-2010 at 08:59 AM.
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