Basic Wiring to Detached Garage

[fredd7924]

I recently built a detached 14x30 garage on the back of my property. I want to run electric to the garage, but am unsure the best way to do it. I am not planning on doing any large projects in the garage and am going to be selling the house within a few years, so trying to keep it basic and kinda cheap.

Basically I am thinking a set of 4 or 5 T8 lighting fixtures on a switch. Then about 5 or 6 outlets around the garage. If I ran just one 20amp circuit from the house, I'm afraid it will not be quite enough. So am I allowed to run two 20 amp circuits from the house to the garage, one for lights and one for outlets? Or at that point am i required to do a sub-panel box?

The distance from the breaker box to the garage is about 50 feet. I am going to run it under ground. What is the best way to run it under the ground and how deep? I am thinking that I will need to use something like this to enter the garage, as there is no holes in the concrete. Any recommendations?

Any good places on the internet to read up for more information?

 

[sberry]

You can run a 20A multi wire circuit, that setup you pic is good, this type of feed gives 2 20A circuits. 24 inches deep. Easiest is a 12/3 UF cable.
That is the easiest and cheapest however a 6 space panel can be had from a box store for under 20$, you need a disconnecting means anyway, it can be as simple as a double pole switch but a breaker box is just about as easy. Biggest extra expence is heavier wire and a ground rod, 60A service to it would be a great selling feature.

 

[sberry]

http://www.selfhelpandmore.com/home...o-dwellings/wiring-a-detached-garage-2002.php

 

[fredd7924]

So the basic wiring diagram would look like this?

What kind of switch should I use for the cutoff? Have 2 separate switches or one switch which incorporates both circuits?

What exactly is the type of breaker that i will be using?

 

[sberry]

You need 1 switch to cut both power legs, the breaker would be a 20A double pole breaker at the main panel. Thats a great drawing. No cheaper way to do it.

 

[Charles (in GA)]

Two words of caution about the "Edison" multiwire circuit. Be sure and use a double pole common trip breaker. This is a standard breaker used for 240V circuits, that the handles are tied together so they trip together. Its now required by code in most multiwire installations and is just plain a good idea. This allows you to know that both hots are cut off when you trip the breaker (either intentionally or by accident) and also assures you that you have both hots off separate sides (electrically) of the main panel (one off A side, and one off B side).

You cannot exceed 20amps with this circuit. If you do, it has to be set up as a feeder to a sub panel, and branch circuits from there. If you keep it to one 20 amp multiwire circuit, you do not need breakers or disconnect in the garage.

When wiring the receptacles, you should pigtail to the receptacles. That is, run a wire in, and one out, and add a short pigtail and wire nut the three together using the pigtail to connect to the receptacle. This is a must for the neutral, and a good idea for the hots. Code says the devices must be wired so if they were removed, the neutral (grounded conductor) would not be interrupted.

If you were to run a neutral to one silver/white screw on the receptacle, then continue with another wire from the other silver/white screw onward to the next receptacle, you could not remove the receptacle and keep the neutral uninterrupted, a violation of the code. Because of this, you will need to use individual GFCI receptacles at each box.

Charles

 

[sberry]

I do believe since this is a seperate building he needs a disconnect.

This is a must for the neutral, and a good idea for the hots. Code says the devices must be wired so if they were removed, the neutral (grounded conductor) would not be interrupted.

Are you refering to the N because of the multi wire circuit?

 

[Charles (in GA)]

I do believe since this is a seperate building he needs a disconnect.

Well, I was thinking that when a single BRANCH circuit supplied a detached structure, it did not have to have a disconnect, but I don't find that in the code. 225.31 requires the disconnect.

225.30 Says that you can have only ONE feeder or branch circuit supplying each building or structure on a same property, and says that a multiwire branch circuit is considered a single circuit for the purposes of that section.

225.36 exception does says that on residential property a snap switch or snap switches shall be permitted as the disconnecting means. Thus, you could use a simple 20 amp double pole snap switch (wall light switch) as a disconnect (properly labeled of course) for a simple Edison multi-wire branch circuit supplying the garage, as described above.

On detached garages supplied with electric power you are also required to have a wall switch controlled outside light that illuminates the entrance to the garage or outbuilding (roll up garage door does not count as a entrance or "mandoor") 210.70(A)(2). You are also required to have at least one receptacle in the building 210.52(G).

Are you refering to the N because of the multi wire circuit?

Yes.

Charles

 

[sberry]

For the neutrals they don't want the split of the wire where you can get in series with it, such as using the screws on a recept as a junction where the n splits, after that you could wire them any way you want. The new rule of using tied breaker removes some of this danger.
You have a much better knowledge of the "where" in the book than I do, good stuff on the disconnect.

 

[66Cyclone]

Hello, new to this forum and have just upgraded the service to my detached garage from 60 to 90 Amp.
I find the comment concerning the wiring of the receptacles interesting. Are you saying that every box should have a GFCI and each receptacle pigtailed (at least the neutrals)?
Or am I reading to much into this? Does Code accept the first receptacle in a branch circuit to be a GFCI and the rest conventional receptacles? Wouldn't the GCFI be "series wired" to accommodate how it is made - line in and load out?
I'm confused.

 

[Charles (in GA)]

Hello, new to this forum and have just upgraded the service to my detached garage from 60 to 90 Amp.
I find the comment concerning the wiring of the receptacles interesting. Are you saying that every box should have a GFCI and each receptacle pigtailed (at least the neutrals)?
Or am I reading to much into this? Does Code accept the first receptacle in a branch circuit to be a GFCI and the rest conventional receptacles? Wouldn't the GCFI be "series wired" to accommodate how it is made - line in and load out?
I'm confused.

My comment about the installation of GFCI receptacles at each location is related to the MULTI-WIRE circuit. MW is a circuit much like 240v in that it uses two circuit breakers on opposing sides of the buss (electrically) and has a neutral. Generally the only items wired from multi-wire are 120v loads, from the neutral to one of the hots. This is possible because using electrically opposite hots means the single shared neutral is not overloaded, and you can do with three wire, what ordinarily would take four wires.

However, with the shared neutral of a Multi-wire circuit, the GFCI cannot be used as a line in, load out installation.

In a typical 120v circuit, where you are stringing one wire to a receptacle and from there running another wire on to the next, a GFCI receptacle placed at the head of the circuit will protect all receptacles placed down stream of it.

In the wiring diagram above, the neutral is drawn split at the disconnect and appears as two 120v circuits, one to the lights and one to the receptacles, which have been wired line in/load out, and the GFCI would work the way it is drawn, however, NEC 300.13(B) says "Device Removal. In multiwire branch circuits, the continuity of a grounded conductor shall not depend on device connections such as lampholders, receptacles, and so forth, where the removal of such devices would interrupt the continuity." This would make the wiring diagram drawn above improper, and not in compliance with the code.

Do any of the real electricians/'lectrical engineers on the board have any comments on this.......... I don't think I'm headed down the wrong road here, but there may be an exception or other section of the code that changes this thinking.

Charles

 

[sdowney717]

I completely hid the wire inside the wall using conduit. 4 wires 2 gauge copper 100 amp. So it was 2 hots, a neutral and ground.
I drilled a hole right through the bottom wood wall plate and through a portion of the concrete footing at an angle. Ran the conduit out to the garage, pulled the wires and then covered the conduit where it sloped up to the house (underground) with concrete. So anyway it is totally invisible.
We actually ran another conduit for telephone and ethernet wires etc... and left some pull strings for some future renovator to discover.
And a hot and cold insulated PEX pipe. We got the water from the connections for the washing machine.

We used a 100 amp breaker in the main house panel, and a 100 amp breaker in the panel in the garage. The garage panel was backfed.

 

[Aceman]

Don't forget the ground rods Sdowney.

Charles that sounds right. MWBC the whole way if you use GFCI receps AT EVERY LOCATION. Otherwise, MWBC to the first GFCI's on each circuit. Then line/load out of them and split the circuits apart with 12-2 to every receptacle afterwards on each circuit.

To sum it up, you can't have a shared neutral AFTER you come out of the load side of a GFCI.

 

[66Cyclone]

Got it.
OK, thanks - I thought I was going to have to rewire there for a minute..

 

[sberry]

In multi wire branch circuits, the continuity of a grounded conductor shall not depend on device connections such as lamp holders, receptacles, and so forth, where the removal of such devices would interrupt the continuity." This would make the wiring diagram drawn above improper, and not in compliance with the code.

My explanations leave a lot to be desired but some of that was the intent of what I was trying to say,

the continuity of a grounded conductor shall not depend on device connections such as lamp holders, receptacles, and so forth, where the removal of such devices would interrupt the continuity."

The drawing is correct and meets this intent. Removal of any of the devices does not interrupt the neutral of the opposite circuit.

 

[Chris130]

Long time lurker, first time poster - thank you all for your valuable help thus far!

I would be grateful for a clarification on this discussion (I realize that I'm resurrecting an old thread here!)... It seems that Charles says the posted diagram requires some pig-tailed connections (for neutral) to be fully correct, but then sberry implies in the last post that the diagram is OK as-is (but perhaps I'm misinterpreting?)

Assuming pig-tails are indeed desirable here... Then, with respect to the diagram posted above, can some please clarify which receptacle(s) specifically would need pig-tailed neutral connections? If I'm understanding Charles' post correctly, he's saying that the FIRST GFCI receptacle (labeled "GFI" in diagram) should be pig-tailed, do I have that correct?

Next, for the 3 other "downstream" sockets shown in this diagram... First of all, should those receptacles EACH be GFCI? Or can they be regular non-GFCI sockets? In either case (GFCI or not), should EACH of those downstream receptacles pig-tailed as well? Or are regular "line-in/load-out" connections OK?

Finally, should each of the 3 lights (on the other/right-side circuit) each be pig-tailed too?

I'm sorry if these questions seem silly and basic; I'm afraid I'm perhaps making a mountain out of a molehill here by over-processing this info, but I'd like to get this right the first time!!

Thanks again to all for your help!

Cheers, Chris

 

[MTW]

About pigtails on neutral wires of a multiwire branch circuit.

Here is the code verbage.
300.13 B) Device Removal. In multiwire branch circuits, the
continuity of a grounded conductor shall not depend on
device connections such as lampholders, receptacles, and
so forth, where the removal of such devices would interrupt
the continuity.

And here is why. A 3 wire multiwire circuit is 240V + a shared neutral, split into 2) 120V 2 wire circuits. All is well when it is working and connected properly. However if the shared neutral becomes loose or disconnected the 120V circuits will become 240V circuits and anything connected to them will puff some magic smoke at a minimum, maybe belch some fire.

Actually that's an over simplification. What really happens is the 240V divides itself amongst the connected loads at the time. Some loads have low resistance and others higher, the voltage divides itself between whatever resistances are connected at the time. Some loads will get high voltage while others get low voltage. As things that are connected start to burn up and be disconnected the division ratio will change and so will the impressed voltage on the remaining connected devices.

None of this is good for your property or equipment. So the rule says not to rely on the screw connections on receptacles or lampholders. In lamen's terms this means on all your in and out cable connections must be spliced directly together with a wirenut and a pigtail from this wirenut brought out to the screw on your receptacle or lampholder.

If this is mandatory on a shared neutral conductor, it is good practice on all your box splices. Receptacle and lampholder connections will come loose over time from repeated use and thermal cycling of the metal when under load.

If a hot connection screw comes loose on a daisy chained circuit it won't affect the voltage balance of the other half of the multiwire circuit, but it will cause arcing and a possible fire. When something downstream on a circuit pulls a heavy load it will stress all the connections on the upstream side possibly causing a fire or burnt connections.

Therefore it is best practice to directly connect all circuit wiring under a wirenut, and bring a pigtail out to the device. Then if a screw connection becomes loose it will only affect that individual device. It also make it a ton easier the replace the device down the road. This should be done for the ground connections as well. To implement this you need a little more box volume that a single gang box.

 

[MTW]

A note about multiwire circuits:

The whole reason for using a multiwire circuit is to save the cost of one wire. 3 wires for 2 circuits instead of 4. And many folks use them regularly. The small savings that you get from doing this may not outweigh the disadvantages. And there are several besides the one I mentioned earlier.

One main one is GFI protected outlets may nuisance trip when connected to a shared neutral. A GFI works by measuring the current on the hot and neutral and comparing them. If the current is exactly the same, the device stays on. If there is a imbalance of more than 5 mA it shuts the device off.

This is how it protects you from electrocution. When an appliance is leaking to ground through the ground wire, water pipe, metal siding or just plain dirt, it detects that leakage and kills the power. On a shared neutral circuit there may be some stray current flowing on the neutral from the other half of the circuit and trip the GFI on this side of the circuit. This can be a pain in the **** and difficult to detect if you don't know what to look for.

Another thing that can be bad is harmonic currents from certain electronic loads. These harmonics can build up in a shared neutral and also affect the other half of the circuit.

Best practice is not to be cheap and run dedicated neutrals (separate 2 wire circuits), this is a better solution for a small price and eliminates these problems down the road.

 

[Chris130]

Many thanks for the further explanation - that all is very clear and easy to understand.

Thanks again!

Cheers, Chris