# 30amp sub panel for shed??



## dion11 (Nov 10, 2010)

I have a 125A main panel in my home and i want to put power to my shed. well a 30A sub panel be enough? i want a circuit of lights 15A,and a 20A circuit for plugs, and a furnace thats 20A, well a 30 amp braker sub panel be enough or should i use a 60A?? 
Thanks


----------



## lordlondis (Nov 9, 2010)

How many lights are are you putting up and what type of things will you be plugging into those outlets?


----------



## dion11 (Nov 10, 2010)

7 lights, 6 plugs wanna use 20amp cause of power tools but can probley use 15amp plugs and the furnace uses 20amps


----------



## lordlondis (Nov 9, 2010)

You might start to have problems if you have the lights on and the furnace running while using a power tool. You ae better off going with the 60 amp, this way you can always expand a little later on.


----------



## Scuba_Dave (Jan 16, 2009)

With a furnace using 20a possible out of the 30a I'd run a 60a sub
What kind of furnace ?
Actually....20a @ 120v for the furnace - that's not too bad
Unless its electric & using 240v ?
I know my boiler is on a 20a & uses far less power then that


----------



## dion11 (Nov 10, 2010)

yea thats what was thinkin, thanks for your help bud


----------



## emolatur (Nov 8, 2010)

?!

Are we talking about a 120V subpanel? Why? One more wire!

30A @ 240V? That's PLENTY for lights, one 120V 20A 'receptacles' circuit, and a furnace. Again, this is assuming the furnace is not full-electric (ie, burns oil or gas or some other non-electrical fuel).



I'm all in favor of the 60A, but let's make it quite clear that it's desirable, but NOT necessary!


----------



## secutanudu (Mar 15, 2009)

If his subpanel has 240v that does not help with the load unless the devices are also 240v. His lights and outlets are definitely not. That being said, I'd run a 60A subpanel. 

Dion, how long is the run? I bet the cost difference won't be that great.


----------



## emolatur (Nov 8, 2010)

Wrong.

30A @ 240V is TWO SEPERATE 120V hots, EACH having 30A available, for 60A total.


----------



## secutanudu (Mar 15, 2009)

emolatur said:


> Wrong.
> 
> 30A @ 240V is TWO SEPERATE 120V hots, EACH having 30A available, for 60A total.


I respectfully disagree. A double-pole 30A breaker will trip if EITHER leg pulls more than 30A (as per the trip curve).


----------



## oleguy74 (Aug 23, 2010)

article 230.79 (b) (d) 60 amp min...beacause you have more than two two-wire ckts...


----------



## lordlondis (Nov 9, 2010)

oleguy74 said:


> article 230.79 (b) (d) 60 amp min...beacause you have more than two two-wire ckts...


nevermind you are right


----------



## jbfan (Jul 1, 2004)

Service disconnecting means needs to be rated for 60 amps, but the circuit can be any size under that!


----------



## oleguy74 (Aug 23, 2010)

rating of service disconnecting means:the service disconnection means shall have a rating not less than the load to be carried,determined in accordance with article 220.in no case shall the rating be lower than specified in art.230.79(a)(b)(c) or (d).


----------



## jbfan (Jul 1, 2004)

oleguy74 said:


> rating of service disconnecting means:the service disconnection means shall have a rating not less than the load to be carried,determined in accordance with article 220.in no case shall the rating be lower than specified in art.230.79(a)(b)(c) or (d).


And the point is?

230.79(a) through (d) are talking about service disconnecting means


You can have any size service to an outbuilding you desire as long as the disconnting means are equal to or larger.


I could not charge a customer for a 60 amp service to a shed, when all that is needed is 30 amps or less.


----------



## oleguy74 (Aug 23, 2010)

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


----------



## jbfan (Jul 1, 2004)

oleguy74 said:


> 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.


----------



## oleguy74 (Aug 23, 2010)

if furnace is 120volt gas fired he will have 3 two wire ckts.this he has not said...?


----------



## jbfan (Jul 1, 2004)

oleguy74 said:


> 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.


----------



## oleguy74 (Aug 23, 2010)

all the ckts will come out of the sub panel..


----------



## Scuba_Dave (Jan 16, 2009)

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


----------



## oleguy74 (Aug 23, 2010)

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.


----------



## emolatur (Nov 8, 2010)

*load balancing*



secutanudu said:


> 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.


----------



## Speedy Petey (Feb 1, 2004)

emolatur said:


> 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.







emolatur said:


> 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. :no:


----------



## emolatur (Nov 8, 2010)

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!


----------



## jbfan (Jul 1, 2004)

emolatur said:


> 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!
> 
> ...


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!


----------



## emolatur (Nov 8, 2010)

jbfan said:


> 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.


----------



## AllanJ (Nov 24, 2007)

Scuba_Dave said:


> 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.


----------



## Scuba_Dave (Jan 16, 2009)

AllanJ said:


> 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


----------



## AllanJ (Nov 24, 2007)

Speedy Petey said:


> 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.


----------



## dion11 (Nov 10, 2010)

*Panel for a shed*

hey guys just a quick question..im wiring my shed and was gonna put a 30amp panel out there power a circuit of lights ( 5 lights ) circuit of plugs ( 6 or 8) and a oil furnace ( double poll 20A), but my question is, i got a 100 A panel of a friend to put out there but is it ok to put a 30amp breaker in that as a main breaker and run that of a 30A breaker from the house?? or any ideas on what i can do?? p.s i have a 125 am panel in my home and only want to run 30 A to the shed


----------



## rjniles (Feb 5, 2007)

30 amps is a pretty small sub panel. Since you are going to dig a trench and you have a 100 amp panel, why not go bigger?

What ever you decide you need a 4 wire feed to the shed, 2 hots, neutral and ground . UF cable or conduit with THWN cable; size (gauge) of wire depends on the size breaker (capacity) you want in the main panel. You also need 2 ground rods at the shed. Depth of bury is 18" for conduit, 2 feet for cable.


----------



## Scuba_Dave (Jan 16, 2009)

Does the 100a panel have a main breaker ?
And are the lugs rated for #10 wire ?
If so you can use a 30a breaker in the house to feed the 100a panel
The 100a breaker does not need to be removed/replaced

_2 threads on same issue merged_


----------

