sub panel for detatched garage

[bobbyjean]

why has the code changed so many times for grounding a panel in a detached structure?
i see lots of posts on other sites about the subject and they may be posted on this site as well......whats the deal...do you need additional ground rods or not,i think i understand the reason behind keeping neutral and ground's seperate in the subpanel..but the ground rods i dont get-short answer anyone? thanks

 

[Norcal]

The only things that have changed is that 3-wire feeders to detached structures are no longer allowed, & requiring a 2nd ground rod if you can't prove 25 Ohms of resistance or less, since the testing equipment is costly & also have to be qualified to use it, driving a 2nd rod at least 6' from the 1st one is cheaper,quicker, simpler, but if someone is doing a new build, using the rebar at the bottom of the footing if it meets code requirements, as a UFER, AKA a Concrete Encased Electrode is the best way and then no driven rod(s) are required.

 

[tyme2par4]

The code hasn't really changed that much, but each jurisdiction has it's own requirements.

 

[75gmck25]

The basic requirements for wiring (4 wire connection), and ground (two ground rods is always okay, and UFER also works) have been the same for quite a while. However, you will also run into other requirements that are a little different than you needed for standard house wiring.

For example if you need to connect 2 gauge SER to 2 gauge MHF wire it requires special connectors, and the good insulated connectors are fairly expensive (about $10 each). If you need physical protection of the wire above ground, it may need to be schedule 80 PVC pipe, not the schedule 40 you find in most HD and Lowes. You will also find that when you add a separate isolated grounding bar in the sub-panel, it's holes can't handle 4 gauge wire and you will need to add a ground lug to the bar. At the main panel you will probably also need to add lugs for the ground and neutral for the sub-panel, since the ones in the panel are already used for the incoming SER. My point is that there are quite a few extra things you will need for the sub-panel connection.

Bruce

 

[ddawg16]

The only things that have changed is that 3-wire feeders to detached structures are no longer allowed, & requiring a 2nd ground rod if you can't prove 25 Ohms of resistance or less, since the testing equipment is costly & also have to be qualified to use it, driving a 2nd rod at least 6' from the 1st one is cheaper,quicker, simpler, but if someone is doing a new build, using the rebar at the bottom of the footing if it meets code requirements, as a UFER, AKA a Concrete Encased Electrode is the best way and then no driven rod(s) are required.

My inspector made me run a 20' #4 bar copper wire at the base of my footing even though I was bonded to the rebar. If that is what he wanted....that is what he got.

But I know my house is well grounded.

Bobby....don't forget your ground and neutral are NOT to be bonded together in that sub panel.

And when you're driving those ground rods in, make sure it's not through the conduit.....while your son is holding the ground rod while you bang on it....at least I know my ckt breaker works correctly.

 

[wyliesdiesels]

why has the code changed so many times for grounding a panel in a detached structure?
i see lots of posts on other sites about the subject and they may be posted on this site as well......whats the deal...do you need additional ground rods or not,i think i understand the reason behind keeping neutral and ground's seperate in the subpanel..but the ground rods i dont get-short answer anyone? thanks

Code hasnt changed in a long while on this subject so not sure what youre referring to.

Last code change on this was 2008.

The basic requirements for wiring (4 wire connection), and ground (two ground rods is always okay, and UFER also works) have been the same for quite a while. However, you will also run into other requirements that are a little different than you needed for standard house wiring.

For example if you need to connect 2 gauge SER to 2 gauge MHF wire it requires special connectors, and the good insulated connectors are fairly expensive (about $10 each). If you need physical protection of the wire above ground, it may need to be schedule 80 PVC pipe, not the schedule 40 you find in most HD and Lowes. You will also find that when you add a separate isolated grounding bar in the sub-panel, it's holes can't handle 4 gauge wire and you will need to add a ground lug to the bar. At the main panel you will probably also need to add lugs for the ground and neutral for the sub-panel, since the ones in the panel are already used for the incoming SER. My point is that there are quite a few extra things you will need for the sub-panel connection.

Bruce

The ground bar in a normal subpanel should NOT be isolated.

The only time one should be using isolated ground bars is with an ISOG wiring scheme.

My inspector made me run a 20' #4 bar copper wire at the base of my footing even though I was bonded to the rebar. If that is what he wanted....that is what he got.

But I know my house is well grounded.

Bobby....don't forget your ground and neutral are NOT to be bonded together in that sub panel.

And when you're driving those ground rods in, make sure it's not through the conduit.....while your son is holding the ground rod while you bang on it....at least I know my ckt breaker works correctly.

Grounding electrodes have absolutely NOTHING to do with breakers clearing faults.

 

[Bert_]

Grounding electrodes have absolutely NOTHING to do with breakers clearing faults.

They do when you drive it THROUGH the feeder cable

At least I'm pretty sure that's what he meant.

 

[ard]

Wow. Just saw that....talk about exciting.

 

[wyliesdiesels]

They do when you drive it THROUGH the feeder cable

At least I'm pretty sure that's what he meant.

If thats what he meant then i get what hes saying...

 

[Bolson32]

The ground bar in a normal subpanel should NOT be isolated.

The only time one should be using isolated ground bars is with an ISOG wiring scheme.

Sorry, can you expound on this? I was under the impression that ground and neutral should always use different bars in a detached sub panel with a 4 wire setup.

 

[75gmck25]

When I mentioned an "isolated ground bar" I meant was that the ground bar you added is not electrically connected to the neutral bar. However, maybe I have my terminology or description confused.

The main point I was making is that ground and neutral are separate at a sub-panel in a detached garage. This is different than a main panel, where the ground and neutral are electrically connected.

Bruce

 

[ddawg16]

They do when you drive it THROUGH the feeder cable

At least I'm pretty sure that's what he meant.

Yup.....it missed the neutral but caught the ground and one of the hots

And because the ground is bonded to the neutral buss in my main panel...it tripped.

I could not have hit the conduit more square on top.

 

[bobbyjean]

My inspector made me run a 20' #4 bar copper wire at the base of my footing even though I was bonded to the rebar. If that is what he wanted....that is what he got.

But I know my house is well grounded.

Bobby....don't forget your ground and neutral are NOT to be bonded together in that sub panel.

And when you're driving those ground rods in, make sure it's not through the conduit.....while your son is holding the ground rod while you bang on it....at least I know my ckt breaker works correctly.

thanks for the info. so if i have 25 ohms or less at ground ...i dont need additional rod's... i understand the neutral and ground isolation in the sub-panel....just wasn't clear on ground bar at sub..

 

[Norcal]

thanks for the info. so if i have 25 ohms or less at ground ...i dont need additional rod's... i understand the neutral and ground isolation in the sub-panel....just wasn't clear on ground bar at sub..

You have to have the proper testing equipment & be qualified to use it, the equipment is very expensive so it's much more sensible just drive a 2nd rod at least 6' feet away, connect them & be done with it.

 

[ddawg16]

thanks for the info. so if i have 25 ohms or less at ground ...i dont need additional rod's... i understand the neutral and ground isolation in the sub-panel....just wasn't clear on ground bar at sub..

You will spend more time and money doing the test than what a second rod will take.

Confirm with your inspector, but you should be able to bury the rods and wire.

Dig a trench as close to your house as you can....drive in the rods...connect the wire...leave it exposed for inspection....cover after you pass.

If they don't allow it to be buried....just do it close to the slab....it will be out of the way.