BREAKERS – sizing for a garage sub panel
toolbear
| Posted in Energy, Heating & Insulation on
BREAKERS – sizing for a garage sub panel?
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This remodel is getting a 60a main lug subpanel in the detached garage via a trench. I can’t quote chapter and verse on this, but others can.
What is the protocol for sizing the breakers at the house panel and the garage for the feeder? 60A/2P house side, same garage for the disconnect? Or larger on house side.
I think a 12 space main lug enclosure might be right for the garage. A little room to grow is nice.
The ToolBear
“You can’t save the Earth unless you are willing to make other people sacrifice.” Dogbert
Replies
If it's a 60 amp panel, you can't supply it with more than 60 amps. That's a 2-pole 60 amp breaker, feeding a #6 run to the garage. Note that you need to run FOUR wires ... two hots, a neutral, AND a ground.
Then at the garage, you also get to instal a ground rod. Do not join the neutrals and grounds together at any point.
As for the circuits in the garage, size tham according to the loads they supply. Ordinary receptacles need to be GFCI protected.
If it's a 60 amp panel, you can't supply it with more than 60 amps. That's a 2-pole 60 amp breaker, feeding a #6 run to the garage. Note that you need to run FOUR wires ... two hots, a neutral, AND a ground.@@@Good to hear. That's what I had in mind - 60a breaker on both ends. garage ground rod and an isolated neutral bus bar in the garage panel.Probably run this in PVC conduit in the trench and transition to rigid where it daylights. Will suggest they run another conduit for any low voltage stuff they might think of later - while the hole is open.
The ToolBear
"You can't save the Earth unless you are willing to make other people sacrifice." Dogbert
If your subpanel is fed by a single branch circuit, you dont need the ground rod as long as you are running a ground wire. See NEC 250.32(A).
You are misreading the NEC, and confusing your terms.
The circuit that feeds a panel is a FEEDER, not a branch circuit. He most certainly needs both a ground rod and a ground wire - in addition to a neutral.
As for the four-wire feed, I will admit that this opinion was not clear until the 2008 NEC. Poor wording in the NEC left some room to argue that you didn't need all four wires. That has since been cleared up.
I am not misreading. In NEC 2008 250.32, titled "Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s)", the exception to (A) states:"A grounding electrode shall not be required where only a single branch circuit, including a multiwire branch circuit, supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the normally non-current-carrying metal parts of equipment."It sounds like his case applies.
... but this is NOT a branch circuit. Go read the definitions in article 100
In what situation are you then proposing this exception would apply?Are you saying if he wasn't installing an OCPD (and only a disconnect, which is required) in his garage, this exception would apply?Then a month later he swaps it out with an OCPD (that also can serve as a disconnect), he must install a grounding electrode to be compliant?
The exception to the electrode system in a second building was put in to make simply stringing an extension cord out there less attractive. Basically what it says is if you have one branch circuit going to some outlets in a second building you don't need a grounding electrode. You still need a means of disconnect.
It still must be made clear, if you are feeding a panel you have a feeder. A branch circuit is anything beyond the last panel.
So in your example of running one branch circuit for some outlets, you would still need a disconnect. A panel that is suitable for use as service equipment is allowed to serve as a disconnect... are we saying that in order for the exception to apply you have to use just a simple disconnect?When I wired my detached garage, I ran a 4 wires (two hots, a neutral and a ground) in a trench from my main panel, off of a 40 amp breaker to a small panel in the garage. I installed two 20 amp circuits in this panel and labeled them both service disconnect. I kept the neutral and the ground separate and did not install a grounding electrode. My inspector passed it with no questions.I understand your point with regards to the definition of a branch circuit, but if it is taken the way you are saying I don't see how you would apply the exception without saying you can't use OCPDs for your disconnecting means.Sounds like there may be some room for interpretation and that you've had it interpreted differently than I have :-)
You can't have an overcurrent device in the far building as the disconnect and call it a branch circuit. One might argue that if it was a single breaker in a box, not in a "panelboard" and the circuit went straight through (like the box that serves your AC compressor)that was simply a disconnect. It is still technically a feeder between the 2 OC devices.
In your case you have "a small panel" that splits out 40a to two 20a BRANCH circuits so there is no dispute, the wire you ran is a feeder.
Still not clear on a situation where you think this exception applies. You are forced to have a disconnect that is not an OCPD?
The moment you add any sort of overcurrent device, the wire becoms a feeder. A branch circuit is that wire between the LAST overcurrent device, and the appliance.
A multi-wire branch circuit has two hots and a neutral, and -again- there is no overcurrent devices on either 'hot' leg between the source and the appliance.
For example, one can run a light AND a receptacle circuit to the garage, and not need a ground rod for that garage.
Or, one can run 220 out to the shed for the welder, and not need a ground rod.
Add a single circuit to either of those examples, or add any form of overcurrent protection at the garage .... and you need to have a ground rod - in ADDITION to the ground wire back to the house.
The panel makes all the difference in the world. Otherwise, to use your logig, there's not a building in the country that would need a ground rod - after all, there's sure to be some sort of overcurrent protection at the power company generating plant!
I suggest that ALL users of the NEC pay particular attention to Article 90. This 'introduction' makes clear that the code presupposes that you already know the trade, and that the NEC is neither a design manual, nor an instruction manual.
The exception would apply if I ran a single circuit out to the shed, in the shed I had a switch that turned off that whole circuit (and perhaps another switch for the light).
To expand that to it's extreme, it could be a 20a 4 wire circuit with a 2 pole disconnect switch in the shed and a mix of 120 and 240 volt loads but it is still a single multiwire circuit. You are limited to 20a per leg on this circuit and it would have to be a 2 pole breaker up at the house.
Edited 2/9/2009 9:58 pm ET by gfretwell
I'm with dfret... and renos... regarding branch circuit conductors vs. feeder conductors.
Using your detached garage example (and maybe I'm beating a dead horse here), if we assume your 2 20A circuits are 120V, then the feeder breaker in the main (house) panel only needed to be a 20A breaker. If its a 40A as you say, then your FEEDER conductors between the main panel and the garage better be bigger than the 12 AWG in the 2 garage BRANCH circuits.
If I had been your electrician, you wouldn't have a small panel in the garage, the disconnect would have been a 20A rated DPST switch in a small box where the conductors enter the garage. The 2 hots would be switched. Your branch circuit conductors (from the house panel) would have been 12 AWG with a 20A (2-pole) branch circuit breaker in the house panel. You would have 1 multiwire branch circuit in the garage.
Or if you really ran larger feeders with the 40A breaker in the house panel, then I would have been pounding in ground rod(s) at your garage small panel with the 2 20A breakers. Your inspector gave you a pass.
If instead you have 1 or 2 240V circuits in the garage, then your small garage panel is a subpanel and the conductors from the main panel to the garage panel are again FEEDERS. And your inspector gave you a pass.
Does ToolBear need to consider upsizing the wire size due to voltage drop due to the distance from the house to the garage?
I believe plugs serving permemant loads like large regrigerators do not need to be GFCI, or not easily accessible ones like in the ceiling for garage door openers. Other than that, GFCI all the way, its just safer.
I believe plugs serving permemant loads like large regrigerators do not need to be GFCI@@@As I recall, no. Nor should they be - unless you want your side of beef to defrost when the GFI trips soon as you are out the door on vacation.But then you have to mount a single outlet dedicated to the fridge.The ToolBear
"You can't save the Earth unless you are willing to make other people sacrifice." Dogbert
The only exceptions in the 2008 code are ice melting systems and alarm panels.
All of those other exceptions are gone, including sump pumps and refrigerators.
Darn we are getting so safe. Are they going to make us wear heavy rubber gloves in rooms without gfci's next?For those who have fought for it Freedom has a flavor the protected will never know.
When your AHJs adopt the 2008 there really won't be any rooms without some ground fault protection since it is built into the mandated AFCIs at 30ma that will have to be virtually everywhere ... and yes NFPA is out of control.
if there is a 60 amp breaker in the main panel feeding the sub, is there a need for a main breaker in the sub panel?
"if there is a 60 amp breaker in the main panel feeding the sub, is there a need for a main breaker in the sub panel?"A service to a separate structure needs a disconnect switch. It does not need a overload protection as the feeder breaker provides that.And a main breaker in a sub-panel is the easies and cheapest way of providing the disconnect..
William the Geezer, the sequel to Billy the Kid - Shoe
Here local codes have a major effect.
The idea of running wires without overcurrent protection all the way to the new panel brings up the 'tap rules,' and I really don't like that idea at all. So, we start with a breaker feeding the wires that go to the new panel.
At this point, we don't "need' a main breaker at the new panel. Since it's a separate building, however, we need some form of main disconnect - and local rules usually require this to be on the outside of the building.
Here is my sizing suggestions on a garage sub panel.
First add up the NAMEPLATE data on the largest collection of equipment that will be used at one time. If this is a home workshop that might be a TS, DC, some lights and heat/AC.
In most cases 60 amps is fine.
Now if there is going to be a hot tub or pool off of this panel then you need to check the sizes of that equipment.
However, I recommend a 100 amp panel. Commonly available 60 amp panels are usually limited to 8 or more slots.
100 amp 20 slot pannels are common and cheap.
Now the feeder breaker can't be any larger than then SMALLEST of the ratings of the feeder wires or the sub-panel.
So I would use a 60 amp breaker and feeders, but with the 100 amp sub-panel.
The sub-panel does not need overload protection. It is already protected by the feeder breaker.
But the building does need a disconnect. And the 100 amp main breaker serves that purpose.
Now for the ground electrode. This assumes that it is a detached building. If attached it does not need one.
If this is new construction and the slab/footing are not in it should have a Ufer ground electrode. That is a copper wire burried in the concrete or a connection to the rebar.
If not then use ground rodS. Unless you have the ground rod tested and it has less than 25 ohms then yuo need 2 at least 6 ft apart. Since this uses special equipment it usually not done and just defaults to the 2 ground rods.
William the Geezer, the sequel to Billy the Kid - Shoe
First add up the NAMEPLATE data on the largest collection of equipment that will be used at one time. If this is a home workshop that might be a TS, DC, some lights and heat/AC.@@@ They want to sell the place, so we can guess. Worked on a remodel on a 6 mil four floor with elevator and miles of crown molding view home. He had one (1) outlet in the garage. We will do better.In most cases 60 amps is fine.Now if there is going to be a hot tub or pool off of this panel then you need to check the sizes of that equipment.@@@ I doubt that. Not in plans.However, I recommend a 100 amp panel. Commonly available 60 amp panels are usually limited to 8 or more slots.100 amp 20 slot pannels are common and cheap.Now the feeder breaker can't be any larger than then SMALLEST of the ratings of the feeder wires or the sub-panel.So I would use a 60 amp breaker and feeders, but with the 100 amp sub-panel. @@@ OK, makes sense and I like space in a panel. Buy 100, wire to 60.The sub-panel does not need overload protection. It is already protected by the feeder breaker.But the building does need a disconnect. And the 100 amp main breaker serves that purpose.@@@ If I follow this ... get a 100A panel with main breaker instead of a main lug panel. 60A breaker at house side feeding garage thru 100A breaker on garage panel, which serves as a disconnect.Thanks for the input.Now for the ground electrode. This assumes that it is a detached building. If attached it does not need one.If this is new construction and the slab/footing are not in it should have a Ufer ground electrode. That is a copper wire burried in the concrete or a connection to the rebar.If not then use ground rodS. Unless you have the ground rod tested and it has less than 25 ohms then yuo need 2 at least 6 ft apart. Since this uses special equipment it usually not done and just defaults to the 2 ground rods..The ToolBear
"You can't save the Earth unless you are willing to make other people sacrifice." Dogbert