I have a SEU service cable going out to a detached garage that the homeowner installed. He wants me to wire the sub-panel. Although in this case it would have been proper to use a SER cable with a separate ground, would it be safe and code to install a separate ground rod at the garage and connect the ground bus directly to that? The neutral bus and ground bus will be separate and the ground bus bonded to the panel can.
Sub-panel grounding
- Thread starter grady180
- Start date
- Status
If it's an underground raceway SER is not acceptable.
Are you going to replace the SEU?
Is the project covered by your License?
Will the job be inspected and if so which Code Cycle.
The 08 requires a EGC with the structures feeders, 250.32.
You would be required to establish a GE Sys at the seperate structure. Again 250.32.
Am I missing something??
Are you going to replace the SEU?
Is the project covered by your License?
Will the job be inspected and if so which Code Cycle.
The 08 requires a EGC with the structures feeders, 250.32.
You would be required to establish a GE Sys at the seperate structure. Again 250.32.
Am I missing something??
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
I'm going to let others tackle the code issues. You appear to misunderstand the functions served by _grounding_ (the connection to an electrode actually planted in the soil) and _bonding_ (the connection made between 'ground' and 'neutral').
The installation that you describe would not be safe. In the installation that you describe, the ground bus is connected to a ground rod, but not to the electrical system neutral. This means that you don't have 'an effective fault current path'. A ground fault probably wouldn't trip the breaker, and would instead simply energize the ground rod (and all metal connected to the ground bus).
Since you are not permitted to bond to the neutral in more than one location (under current code), you must have separate equipment grounding and neutral conductors. Note that under previous versions of the code you were permitted to use the neutral as the effective ground fault path for certain detached structures.
-Jon
The installation that you describe would not be safe. In the installation that you describe, the ground bus is connected to a ground rod, but not to the electrical system neutral. This means that you don't have 'an effective fault current path'. A ground fault probably wouldn't trip the breaker, and would instead simply energize the ground rod (and all metal connected to the ground bus).
Since you are not permitted to bond to the neutral in more than one location (under current code), you must have separate equipment grounding and neutral conductors. Note that under previous versions of the code you were permitted to use the neutral as the effective ground fault path for certain detached structures.
-Jon
Thanks for the reply.
Yes the homeowner pulled it in an underground pvc conduit. Why isn't it acceptable to put SEU in an underground raceway, for temperature reasons??
I haven't decided on replacing the SEU because I wanted to look into this further and see if there was a solution to utilize the existing SEU cable.
No license is required in my state and an inspection would most likely warrant the current codes.
Are you saying all separate structure require their own GE ?
Ok, thanks. Yes I'll be honest. I have a hard time understanding this issue. If the ground and neutral are bonded at the main panel and you pull a separate ground and neutral to the sub-panel. Are they not coming from the same place? Sorry if this seems like a dumb question to you but I'm trying to comprehend it. What you've explained above doesn't sound like a good situation, thats why I wanted to look into this further.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
338.12 does not permit Type SE cable to be used underground raceway or no raceway.
No required licensing or inspections are no excuse for not doing it correctly especially if you know you are doing it wrong.
All separate structures have always required their own GEC. 2008 code has added that they now require separate Equipment grounding conductor with the feeder.
Are you running a feeder or service to the second building? That is what will make a difference of 3 or 4 conductors being required or allowed - where does it originate?
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
It's not dumb to ask, and it's easy to see why it's not easy to see why.
The basic reason is that we cannot treat conductors, as well as their terminations, as though they have no resistance. When carrying current, the voltage at one end of a conductor will not match that at the other end.
In other words, with a proper, four-wire feeder, there will be a voltage difference between the grounded (neutral) and grounding (EGC) conductors (unless there's a shared neutral and the lines' currents just happen to match).
With a three-wire feeder, that could cause energized what-should-be grounded surfaces. The same applies to the no-longer-permitted practice of allowing the neutral of a major-appliance circuit to do the grounding duties.
In a nutshell, if there are no other conductive pathways between buildings, and you're not yet under the 2008 (or later) NEC, you can still use a three-wire feeder, but there are few here who would recommend it; I wouldn't.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Well, it's easy to see why.I'm still not sure what that means
I can't see why not eitherWell, it's easy to see why.
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
Thats absolutely the case when the N/G reference is lost, and any bonded metalwork can rise to line potential, with the consequent shock hazard. Thats why I'm with Larry in saying that this arrangement is not recommended, even where allowed.
With the old school arrangement, legal in its day, and still grandfathered in, failure can lead to a properly grounded washer with an adjacent dryer whose metalwork is 120V different from the washer, in a utility room, with water sloshing about the place; this is a scary situation indeed. Why this installation practice was ever legal is something of a mystery.
Ok, its not really a call-it-what-you-will-conductor, its official term is (according to IEC 60634) is a "combined PEN conductor", which fulfills the functions of both a PE and an N conductor.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I remember ocasionally seeing jumpers installed between washers and dryers long ago, which were obviously installed in response to shocks between appliances.
We now know those jumpers were actually carrying dryer neutral currents, and imposing them on the washer EGC's (presuming no issues in the washers, of course.)
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
The code no longer allows this.
You are required to have a GE system at the garage that would connect to the ground bar of the subpanel, and you have to have seperate ground and neutral wires coming out to the garage. There can be no bonding jumper between ground and neutral in the garage subpanel.
There are some oddities with this. You could conceivably have as small as a #14 ground wire coming into the subpanel from the main. You would then need a minimum of a #6 to connect the ground bar to the GES.
Thanks for your reply. I wasn't trying to use the no license requirement as an excuse for unsafe or plain poor work at all. Hopefully I didn't come off that way. I really didn't know about the SE cable not being allowed in a raceway and was just curious as to what the NECs reasoning was behind it. I'm assuming for temperature reasons. I plan on correcting any issues after a little research and some feedback here before continuing on this project.
This will be a feeder from the main house panel(200A).
It's not dumb to ask, and it's easy to see why it's not easy to see why.
The basic reason is that we cannot treat conductors, as well as their terminations, as though they have no resistance. When carrying current, the voltage at one end of a conductor will not match that at the other end.
In other words, with a proper, four-wire feeder, there will be a voltage difference between the grounded (neutral) and grounding (EGC) conductors (unless there's a shared neutral and the lines' currents just happen to match).
With a three-wire feeder, that could cause energized what-should-be grounded surfaces. The same applies to the no-longer-permitted practice of allowing the neutral of a major-appliance circuit to do the grounding duties.
In a nutshell, if there are no other conductive pathways between buildings, and you're not yet under the 2008 (or later) NEC, you can still use a three-wire feeder, but there are few here who would recommend it; I wouldn't.
Thanks for that explanation, I appreciate that. Sometimes I forget why I'm installing things a certain way, besides the fact thats what I've always been told to do it this way. Its not that I don't want to know, just always had a tough time with the theory behind some things.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Here is what I know-- A raceway outdoor and especially underground is a wet location. Water is inevitable in most areas with a conduit in the ground. As mentioned art. 338.12(2) will confirm this. I think the real reason it is not allowed is because of the bare conductor in SE when you use aluminum wire. That bare conductor may corrode due to the minerals in the soils. Now why isn't copper SE cable allowed? Not sure but perhaps they just had to make the entire cable consistent whether copper or aluminum. Perhaps it is the bare copper conductor also but I don't think so since we have ground rods,etc wired with bare copper.
Good information, thanks. Its a 100A rated sub-panel with a 60A breaker from the main panel. Would I be correct to use at least a #10 ground wire?
That makes sense, good info. I really need a newer code book. Most of the work I do is already laid out on the drawings, panel schedules and one-line diagrams so I don't have to figure these things out everyday. Kinda spoiled I guess. I like to know though, thanks.
- Location
- Massachusetts
I really did not see the need for the change considering every grounded service in the USA uses a circuit conductor as the grounding means and that will likely never change.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Bob, I believe the main difference is that the zero-volt reference point, as far as the premises is concerned, is where the MBJ is, in the main disco enclosure. That's the origination point of the premises' EGC system.
I believe it's also why, when it was permitted, the 3-wire MA circuit had to originate at the main-disco enclousure, and not in a sub-panel. They wanted to assure the conductor was fed from the zero-voltage reference.
- Status