[Joe Willie]

I'm wiring my shed for 2x120v breakers to serve 2x120v circuits. For the house subpanel I first bought a tandem 20A breaker. I learned that I could not use that because it would overload the neutral since they would both have the same phase. Someone told me I needed 2x20A with a connecting handle for some code reason. I bought one. It has 2 hot connectors. Will this give me 2x240 or 2x120? I want 120v. Do I need to exchange this for 2 single 120v breakers and will that be code:huh:? Thanks.

 

[nap]

that will give you 120 to neutral from either of the breakers and from breaker to breaker it will give you 240 volts.

and you need to stay with the 2 pole breaker/ It is current code that circuits on a shared neutral be installed so if one trips, so does the other.


the same thing can result from using to single pole breakers with a handle tie but I would use the 2 pole.

 

[AllanJ]

Use the single wide tandem breaker for two other circuits in your house and free up two adjacent breaker slots for the double wide double handle breaker for your shed.

Only one "circuit" may be run from the house to the shed; the most efficient way to do it is run 4 wires (hot, hot, neutral, ground) and the hots are connected to opposite sides of your 120/240 volt service in the main panel. THis will give you your "two 120 volt circuits" worth of power. Use 12 gauge wire for only the minimum amount of power usage; 10 gauge wire for [email protected] or [email protected] is suggested for a small shed. Use at least 8 gauge wire (or maybe even 6 gauge) for a shed large enough to become a workshop. Until a breaker bigger than 20 amps each side is put in the main panel, you don't need a subpanel in the shed although you do need a "master" on off switch out there that controls both hot wires.

 

[Joe Willie]

I learn something new every time I post on this site. Thanks. I have been trying to get straight on the 240/120 issue for a while. A few questions: 1) Can I now use 240v in my VD computation for 10-3 at 200' for 12A max load? 2) Wouldn't I have the same overloaded neutral if I replace a single pole 20A with the tandem single 20/20 at the house sub? 3) Doesn't MWBC (2X20) at the shed required sub panel? 4)Will 2x4' Cu ground rods 8' apart with a #8 bare wire to the shed subpanel grounding bar (hard ground... I know it's not code) do the job OK.

 

[nap]

1) Can I now use 240v in my VD computation for 10-3 at 200' for 12A max load?

if you will be using the supply as only a 240 volt supply or a perfectly balanced 2 X 120 v (not happening)

2) Wouldn't I have the same overloaded neutral if I replace a single pole 20A with the tandem single 20/20 at the house sub?

only if you have a shared neutral. If you use it to replace 2 breakers that feed circuits that have their own neutrals, it will not have any effect on the neutrals.

3) Doesn't MWBC (2X20) at the shed required sub panel?

no

4)Will 2x4' Cu ground rods (hard ground... I know it's not code) do the job OK.

if it's not code, it won't do the job. As to whether it would meet the same functional requirements of the proper installation; you would have to do a ground resistance test to be able to know that. and a rod is not that hard to drive until you hit pure rock. If necessary, you can install a plate electrode. If you do not have a panel in the shed, you do not need a grounding electrode system as long as you include both a neutral and a ground conductor.

I am not sure where allenJ is getting the requirement for a disconnect for the branch circuits. If they are fed as branch circuits and not a feeder, I know of no such requirement. i.e. panel= disconnect; no panel/ no disconnect

 

[Joe Willie]

NAP, Thanks for the info. If I don't need a panel for the shed, how do I treat the single neutral and ground that 10-3 UF has when running two seperate circuits (pigtails)?

 

[SD515]

I am not sure where allenJ is getting the requirement for a disconnect for the branch circuits. If they are fed as branch circuits and not a feeder, I know of no such requirement. i.e. panel= disconnect; no panel/ no disconnect

Article 225 Part II....specifically 225.31=Disconnecting means

 

[McSteve]

I usually see a double-pole 20A light switch used as a disconnect for a MWBC-fed structure around here. The switch's cover plate must be labeled "main disconnect".

 

[nap]

Article 225 Part II....specifically 225.31=Disconnecting means

I'll split it with you. While a disconnect is required, it does not have to be a single master switch and in fact, due to it being a residential installation, 2 snap switches, including 3-way or 4-way switches are allowed to be used as that means of disconnect.

 

[McSteve]

Interesting. The requirement here (MN) for a single, labeled, disconnect must be a local code thing.

 

[nap]

NAP, Thanks for the info. If I don't need a panel for the shed, how do I treat the single neutral and ground that 10-3 UF has when running two seperate circuits (pigtails)?

Not sure what you mean here. You would run the wire to a common box and (after whatever means of disconnect you use) utilize this just as you would any other MWBC.

 

[nap]

Interesting. The requirement here (MN) for a single, labeled, disconnect must be a local code thing.

there are exceptions in the code for residential use that specifically allow the use as I described. Apparently your locale has omitted those allowances from the NEC for your accepted code.

 

[SD515]

I'll split it with you. While a disconnect is required, it does not have to be a single master switch and in fact, due to it being a residential installation, 2 snap switches, including 3-way or 4-way switches are allowed to be used as that means of disconnect.

I agree with you. Not to hi-jack this thread, but 225.33(B) makes me question how can you have more than 6 operations of the hand if you only have 2 or 3 snap switches?? I guess if you had poor hand/eye co-ordination...lol

 

[nap]

I agree with you. Not to hi-jack this thread, but 225.33(B) makes me question how can you have more than 6 operations of the hand if you only have 2 or 3 snap switches?? I guess if you had poor hand/eye co-ordination...lol

I hadn't caught that before. That last sentence doesn't make any sense.

 

[Joe Willie]

The pigtail comment came from my reading about receptacle ground wiring. I was saying if I only have one ground in the 10-3 cable, but I running 2x12-2 circuits, I would have to connect the two circuit's ground wires to the one 10-3 ground wire (pigtail). I guess since they are out of phase from the house, this would be OK. I wish I could remember who told me I had to get a sub panel for for MWBC... could someone tell me why I have to ground a subpanel and not a junction box at the shed? The only difference I see is the additional breakers at the shed.

 

[nap]

with the ground wires, there is no concern of phase. You just connect all the grounds together. With the neutral, since you will be using a feed from opposite legs, you cannot overload the neutral. In fact, anytime you have load on both legs of the circuit, they will offset each other and you will actually have less current on the neutral than on either hot leg.