Multi Wire Branch Circuit Disconnect Question

[RonRock]

I am running a MWBC from my house to a newly constructed detached garage. It will have a 20 amp Double Pole Single Throw breaker in the house panel. I understand that I need a disconnect in the detached garage, can that be a small 2 breaker box wired as a sub panel? Or does it have to be a disconnect such as an AC disconnect?

I think that it will require a disconnect because of the shared neutral, but would rather use 2 breakers if approved. Would be nice to be able to break one leg to be able to work on the other.

 

[alfredeneuman]

All you need for a disconnect is a 20A 2 pole switch.
Unless both the circuits serve 120V equipment or outlets (which only requires listed handle ties) you'll have to use a 2 pole breaker. You can't use 1 circuit independently of the other because both options will shut off the circuits

 

[RonRock]

All you need for a disconnect is a 20A 2 pole switch.
Unless both the circuits serve 120V equipment or outlets (which only requires listed handle ties) you'll have to use a 2 pole breaker. You can't use 1 circuit independently of the other because both options will shut off the circuits

Thank You,

This is a garage for my daughter. I think that a "switch" could be easily misunderstood by her or someone else and mistakenly switched off. I would rather use some other disconnect in the garage for that reason. Unless there is some switch box that clearly identifies it as a disconnect. Might be the case but I am unaware of one. A small panel with 2 single 20A breakers in the garage would be best, if acceptable.

Both circuits will be 120V, lighting and receptacles in the garage. Not sure what your statement means.

Thanks,
Ron

 

[exranger06]

Use a double pole switch and use an in-use bubble cover.

Stick a label on the cover that says "Disconnect" or something to that effect. There's no way anyone is going to lift the cover without seeing the label.

 

[alfredeneuman]

A small panel with 2 single 20A breakers in the garage would be best, if acceptable.
Both circuits will be 120V

A panel would in the garage would need all grounding, such as 2 ground rods, the grounding electrode conductor, isolating the neutral busbar, and adding a ground busbar
"Both circuits will be 120V"
You couldn't shut off one without shutting off the other.

 

[sparky 1971]

Just make a label or write with a sharpie "garage power, leave on" on the switch cover. That's what I do. I also try to put the switch behind the door swing and/or about 6' off the floor to prevent inadvertent flips.

 

[PCustoms]

Do you really need a disconnect in this situation?

 

[sberry]

Just make a label or write with a sharpie "garage power, leave on" on the switch cover. That's what I do. I also try to put the switch behind the door swing and/or about 6' off the floor to prevent inadvertent flips.

I do the same.

 

[AntonLargiader]

I don't see why you'd need a single disconnect in the garage. You need a disconnecting means, but as far as I can tell a switch for the lights and another switch for the receptacles should meet the requirements of 25 part II. Falls within the "No more than six operations of the hand" thing.

 

[alfredeneuman]

Use a double pole switch and use an in-use bubble cover.Stick a label on the cover that says "Disconnect" or something to that effect. There's no way anyone is going to lift the cover without seeing the label.

A bubble cover for a switch isn't a must; just a waterproof cover. They make some with provisions for a little padlock that would be far more effective than a label.
(EDIT: They're required to be labeled too)

 

[mobetta]

they also make a little loop that screws over your switch plate so you have to think twice before hitting that switch.

 

[Chris130]

Just make a label or write with a sharpie "garage power, leave on" on the switch cover. That's what I do. I also try to put the switch behind the door swing and/or about 6' off the floor to prevent inadvertent flips.

I do the same.

^^^ This!

Edit: assuming the disco switch in inside, not exterior, then) Here's a simpler don't-mess solution to guard the switch - it still enables access to flip the switch...

https://www.amazon.com/gp/product/B082K9WTYD/?tag=atomicindus08-20

I don't see why you'd need a single disconnect in the garage.

This is a very common requirement, at least for local codes (I'm not sure how "high up" this requirement goes, but I know it's at least required by my city and neighboring cities in my metro area).

 

[AntonLargiader]

This is a very common requirement, at least for local codes (I'm not sure how "high up" this requirement goes, but I know it's at least required by my city and neighboring cities in my metro area).

Local code, OK. Maybe there are other local codes the OP needs to take into account.

Just for NEC, though, two snap switches would to the trick. Put one of those shields over the one for the receps. He can then turn one circuit off at a time. Seems to be everything he's asking for and dirt cheap.

Remember 240V loads are out of the question for him with a MWBC because he needs a dedicated circuit for receps.

Breakers mean a subpanel and next thing you know you guys will have him talked into 100A service "just in case."

 

[larry4406]

Some of our new construction homes have a detached garage. They are run with bare minimum electric.

The electrician feeds the detached garage with 12g wire. The circuit first goes to a GFI outlet and then to the lighting and garage door opener (load side of GFI). Tripping the GFI acts as the disconnect.

Not sure this will work for your MWBC with shared neutral.

 

[alfredeneuman]

Falls within the "No more than six operations of the hand" thing.

A disconnect must interrupt all energized wires of the circuit. The six throws rule is for multiple disconnects used with multiple circuits

 

[Pingel85]

I’d just screw a 1” emt one hole over the switch using the cover screw and a small washer. Low cost, switch is still operable, makes operater aware before switching. We do this for security and alarm panel disconnects frequently

 

[sberry]

Thats a slick idear.

 

[AntonLargiader]

A disconnect must interrupt all energized wires of the circuit. The six throws rule is for multiple disconnects used with multiple circuits

It seems to me that 225.33(B) is pretty clearly saying that individual circuits off a MWBC can have individual single-pole switches as the disconnect for the MWBC, just like individual circuits off a feeder can have breakers as disconnects for the feeder. Limit 6 in either case.

 

[RonRock]

Thanks guys for all of the suggestions.

Anybody care to answer the question that I asked?

Can I use a small breaker panel with 2 20A breakers as a disconnect in the garage?

 

[AntonLargiader]

If you use breakers then you have a subpanel with the additional grounding requirements. It's not that big a deal, but you get into the "Should I stay with 20A?" question.

For 20A I'd stick with the MWBC. There's just no benefit in using breakers as switches.

 

[ichabod]

Thanks guys for all of the suggestions.

Anybody care to answer the question that I asked?

Can I use a small breaker panel with 2- 20A breakers as a disconnect in the garage?

yes you can, i believe by doing this it would be considered a sub panel then you would need the grounds rods and such.

what i would do is mount a single gang box with a 2 pole 20 amp lockable switch at a height of 6 feet as your disconnect, then come out of that down to the switch box for your lights and receptacles.

 

[alfredeneuman]

It seems to me that 225.3(B)

Are you sure it's 225.3(B)? I checked 4 Code books and there is no 225.3(B)

 

[AntonLargiader]

I had edited it to the correct 33 but somehow that edit didn't save. It's 225.33(B).

 

[RonRock]

If you use breakers then you have a subpanel with the additional grounding requirements. It's not that big a deal, but you get into the "Should I stay with 20A?" question.

For 20A I'd stick with the MWBC. There's just no benefit in using breakers as switches.

The reason for using 2 separate breakers rather than a single switch is that I can break power in one leg of the MWBC and still have power to the other.

The garage has a UFER ground that should satisfy the grounding requirements I believe.


Edit,

After more thought on this I think that a switch or an AC disconnect is the only way that I can do it and pass inspection. If I do as I would prefer and install a 2 breaker sub panel then I am crossing the line of a branch circuit into a panel install. That is a whole different situation. Not worth the cost.

 

[sky jumper]

if you install the subpanel then you are not running a MWBC, you are running a 4 wire feeder to the garage. if this is really just for lighting and a 120 recepticle, then the subpanel is overkill. in fact you only need one hot. but it looks like you're a car guy... put some real power in that garage. do the subpanel with 8ga Cu feeder.

 

[AntonLargiader]

In fact you only need one hot...

If he's under NEC 2017 or later (which Iowa is), he needs two because the required receptacles can't share the circuit with the required light. Virginia and some surrounding states are still under 2014 which is why the houses Larry described can be wired that way.

 

[alfredeneuman]

It seems to me that 225.33(B) is pretty clearly saying that individual circuits off a MWBC can have individual single-pole switches as the disconnect for the MWBC, just like individual circuits off a feeder can have breakers as disconnects for the feeder. Limit 6 in either case.

.......provided they are equipped with identified handle ties or a master handle to disconnect all ungrounded conductors

 

[AntonLargiader]

.......provided they are equipped with identified handle ties or a master handle to disconnect all ungrounded conductors

"... with no more than six operations of the hand." Just to complete that sentence in the code.

 

[alfredeneuman]

"... with no more than six operations of the hand." Just to complete that sentence in the code.

They've got to have handle ties, which means that you can't turn off one without the other

 

[AntonLargiader]

The way it reads, handle ties as needed to allow shutoff with six. Same as with a subpanel, in fact it's the same paragraph that allows six with a subpanel, right? I don't think they are requiring a master disconnect for MWBC where we all agree they don't with a sub.

Let's say you have your MWBC going into your building and straight into a switch bank. One leg powers four switches and the other powers two switches and the receps (with the first being GFCI). That by itself would fail the six motions test because using the cheesy method of "disconnecting" the receps that Larry mentioned, you're at seven motions and they probably aren't even grouped (which is another failure). You would need some kind of tie to bring it down to six and still deal with the grouping. Can't be done. Use a subpanel.

But a MWBC running directly into a switch for each leg, done deal? I don't think this issue even comes up.

 

[alfredeneuman]

Like I said in post #15 "The six throws rule is for multiple disconnects used with multiple circuits"
Happy New Year!

 

[Terry D]

The way it reads, handle ties as needed to allow shutoff with six. Same as with a subpanel, in fact it's the same paragraph that allows six with a subpanel, right? I don't think they are requiring a master disconnect for MWBC where we all agree they don't with a sub.

Let's say you have your MWBC going into your building and straight into a switch bank. One leg powers four switches and the other powers two switches and the receps (with the first being GFCI). That by itself would fail the six motions test because using the cheesy method of "disconnecting" the receps that Larry mentioned, you're at seven motions and they probably aren't even grouped (which is another failure). You would need some kind of tie to bring it down to six and still deal with the grouping. Can't be done. Use a subpanel.

But a MWBC running directly into a switch for each leg, done deal? I don't think this issue even comes up.

You are reading it wrong, you must have a handle ties or a master handle to disconnect both ungrounded conductors

 

[sky jumper]

If he's under NEC 2017 or later (which Iowa is), he needs two because the required receptacles can't share the circuit with the required light. Virginia and some surrounding states are still under 2014 which is why the houses Larry described can be wired that way.

is that true if the branch circuit comes from a subpanel in the detached structure? if so then I totally violated it and didn't get caught. but I don't think my inspector would've known the difference.

 

[AntonLargiader]

You are reading it wrong, you must have a handle ties or a master handle to disconnect both ungrounded conductors

You're saying that applies to the MWBC only or to a sub also? If the former, can you tell us which code applies to the MWBC and which to the sub?

 

[AntonLargiader]

is that true if the branch circuit comes from a subpanel in the detached structure? if so then I totally violated it and didn't get caught. but I don't think my inspector would've known the difference.

From my notes: "if a garage, a receptacle for each car space on a 20A circuit (210.52 G1) that is only for receptacles (2017, 210.11 C4)"

Read the code and see how it fits your situation.

 

[sky jumper]

From my notes: "if a garage, a receptacle for each car space on a 20A circuit (210.52 G1) that is only for receptacles (2017, 210.11 C4)"

Read the code and see how it fits your situation.

wow that is a bizzare code. it absolutley does apply to me (and pretty much any garage with power). although we were on NEC 2014 when I got my permit. we are on either 2107 or 2020 now.

but why require a dedicated circuit if there's an exception for an exterior recepticle? so running my 12" miter saw and an air compressor outside on the same vehicle bay circuit is fine, but running a 60w light inside is not? huh?

 

[AntonLargiader]

If your work was permitted and inspected under 2014 then i don't see why the second part of that should apply to you.

 

[Terry D]

You're saying that applies to the MWBC only or to a sub also? If the former, can you tell us which code applies to the MWBC and which to the sub?

The way I understand it, Its the same code articles. 225.31, 225.32, 225.33

The minimum circuit you can un to a detached or attached garage these days in a jurisdiction in the 2017 NEC or later is a multiwire branch circuit. For this purpose, a MWBC is considered a single circuit.

There has to be a disconnecting means for this circuit nearest the point where it enters the building. It must disconnect all ungrounded conductors. You can accomplish this with a 2-pole switch.

The feeders to a sub panel are still a MWBC, But it changes because there are multiple circuits coming out of that sub panel, They will give you up to 6 (throws) circuits in that sub panel to open all ungrounded conductors, any more than than that you would need a main disconnect.

I personally always install garage sub panel capable of holding more than 6 circuits, so i always install a main breaker panel so there is no problems down the road if more circuits are added

 

[alfredeneuman]

You're saying that applies to the MWBC only or to a sub also? If the former, can you tell us which code applies to the MWBC and which to the sub?

It applies to both branch and feeder multiwire circuits.

 

[AntonLargiader]

It applies to both branch and feeder multiwire circuits.

Just to be clear, you are saying that multiwire feeders need a single master disconnect also, that six or fewer grouped disconnects (breakers in the case of a feeder and subpanel) to not count as a total disconnecting means for a detached structure?