Electrician Talk banner
1 - 4 of 4 Posts

·
Registered
DC Technician
Joined
·
3 Posts
Discussion Starter · #1 ·
Hello, I have two branch circuits ran in a shed and had concerns regarding the disconnecting means. The two circuits are run with 12-2 and supply several receptacles and lights, with one receptacle supplying a 5000btu AC and another one for a convenience space heater in the winter. So my questions are...

1. Would the panel in the attached link, being supplied with 240 volts through 10-3 and a 30amp breaker, be able to work safely with two 20amp breakers to protect the 12-2 fed circuits? By my load calculations one circuit would draw 15amps and the other would draw 7.5amps, around 23amps in total. Since this amount is less than 80% of the 10AWG 30amp breaker's ampacity, and not all loads will be active at any one time, will this be safe and practical?

2. If the first option is not doable will running a set of 12AWG wires for each branch circuit to two 20AMP switches inside the shed be safe? The shed is less than 50ft from the main panel in the house.

Thank You

https://www.acehardware.com/departments/lighting-and-electrical/circuit-breakers-fuses-and-panels/panels-and-load-centers/36558?store=16181&gclid=Cj0KCQjw4cOEBhDMARIsAA3XDRgeYGHcnbTdH9yiybzIfEt7xJzpKZh48D7G6hnLIhJIFaZ9Xqp-nDwaAiWnEALw_wcB&gclsrc=aw.ds
 

·
Administrator
Retired EC
Joined
·
23,358 Posts
Sure you could use that panel but there is more to it then that. Are you an electrician or a home owner? Filling out your profile would help us.
 

·
Registered
DC Technician
Joined
·
3 Posts
Discussion Starter · #3 ·
I'm a homeowner, DC Technician. I've been through 6 months of a full-time Electrical trade school program and I'm somewhat familiar with the scope of this project.
 

·
Registered
Joined
·
92 Posts
I'm a homeowner, DC Technician. I've been through 6 months of a full-time Electrical trade school program and I'm somewhat familiar with the scope of this project.
You could use that panel if, and only if, you put an enclosed switch of double pole breaker enclosure that is listed as suitable for use as service equipment in or on the shed ahead of the panel you provided the link to. That would be one hell of a way to waste materials and effort. Since you are installing a 240 volt 30 ampere feeder to that outbuilding I would suggest that you install a 6 slot panel that is listed as Suitable for use as Service Equipment. You then install a back fed breaker with a tie down kit to serve as Your Building Disconnecting Means. That leaves you 4 slots. 2 for your present circuits, and 2 for future loads. If you are willing to take the risk that you will never need additional circuits then you could use a 4 slot panel that is also listed as Suitable for use as Service Equipment. The required Building Disconnecting Means at each building is installed as if it is Service Equipment with only one exception. The Neutral Conductor of the Feeder is not bonded to the Building Disconnecting Means enclosure and is not grounded at the feeder supplied building.

That may read like the those are the same thing but they're not. There is a Main Bonding Jumper shipped with any equipment that is listed as Suitable for use as Service Equipment. That jumper, as it's full name implies only BONDS the Building Disconnecting Means enclosure to the Neutral conductor busbar. If that busbar or it's enclosure itself is not grounded You will not have grounded the Neutral Conductor at the out building. What you will have done is cross connected the Neutral Conductor of the feeder to the Equipment Grounding Conductor of the Feeder. That is not permissible at any place other that the Service Disconnecting Means. If you remove the Main Bonding Jumper from the Building Disconnecting Means you will not cross connect the Neutral Conductor of the feeder to the Equipment Grounding Conductor of the Feeder. But if you attach the required Grounding Electrode Conductor to some other point on the Neutral of the feeder; which is how it is done to the service conductors, in many places in the US, between the end of the utility's conductors and the Service Equipment; you would then have made a forbidden connection to ground on the feeder neutral.

You are required to build a Grounding Electrode System at the feeder supplied shed. If the shed has an underground metal water pipe accessible inside the building, a piece of rebar turned up out of the concrete footer, or any of the other regularly created structural Grounding Electrodes you connect them to the Grounded busbar in the Building Disconnecting Means Enclosure. That is the busbar that may or may not have come with the panel which is fastened directly to the Building Disconnecting Means cabinet using conductive hardware with at least 2 full threads in contact with the steel of the cabinet. Some panels that are listed as Suitable for use as Service Equipment will have a strap conductor between separate portions of the factory installed busbar. With such panels you remove that strap between the 2 sections of busbar making them each separate busbars. You then install the bonding screw or strap to connect one of those busbars to the BDM cabinet. That busbar is the place were all of your Equipment Grounding Conductors (EGC), Grounding Electrode Conductors (GEC), and the EGC of the feeder circuit terminate. [If you are in an area that is very prone to lightning and the feeder is in the form of overhead wire on poles you may want to connect the GEC from the ground rods to the EGC of the feeder at the point were it is first attached to the structure.]

--
Tom Horne
 
1 - 4 of 4 Posts
Top