Conflicting info about Sub-panel with bonded ground & neutral

[teknomedic]

I've been trying to sort out when (if ever) it was acceptable to bond ground and neutral in a sub-panel in a separate building from the main service panel. Some say it's always been unacceptable since the 1923 NEC. Others give various thoughts about the NEC changing in 2008 or 1999 or sometime during/before the 1980s regarding this. It's been a bit confusing trying to sort this out.

The scenario is this:
200a main panel in a rural home (not a farm, no livestock) built in 1993. 3-wire service (2 hot, 1 neutral) then runs underground 100ft to a detached workshop. A 100a breaker in the main panel is used to run the hots which then terminate in another 100a breaker in the sub-panel. In the sub-panel the neutral is then bonded to the panel and the ground bar. This sub-panel also has a ground wire that terminates to earth. PVC was used to make the run from the home to workshop. The only other conductor connection between the two buildings is an RJ11 phone line.

I've had some people site exceptions, but suspect they're being thrown off by either the RJ11 phone line connection or the dual 100a breaker setup or perhaps local customs.

So I suppose the main questions are...
1) Was the above scenario acceptable around 1993?
2) Have bonded neutral & grounds in a detached sub-panel ever been acceptable in the NEC and if yes, what year did that change?

I appreciate any insight and education that can be shared. Thank you.

 

[roger]

#1 Yes and no. It was allowed if there were no parallel neutral paths, the phone line is the problem. Could it be removed?
#2 Yes, it was changed in the 2008 edition.

 

[winnie]

The general rule is that you must run a separate ground and neutral to a subpanel. That general rule has been around for a very long time.

A major exception is the case of detached structures. For a detached structure you were permitted to run just the neutral, and bond the ground and neutral busses at the subpanel.

The requirements for this exception have evolved over time. I believe the exception was removed in 2008. The exception was certainly available in 1993.

The phone line may violate the requirements of the exception at the time the garage was built. The key question is if there is an alternative ground path through that other system. For example a CATV cable with grounded outer conductor would mean you couldn't use the exception.

The two 100A breakers in series are not a code problem in an ordinary home.

 

[roger]

It was not an exception, it was an article section that specifically allowed it. 250.32(B)

 

[teknomedic]

I appreciate the information. Yes, the phone line can be removed easily. It's not used and we think it was installed later on by original home owner.

We're still trying to confirm the ground to earth connection though as it appears it may have had a cement slab poured over it. Heh.

 

[Seven-Delta-FortyOne]

As others have mentioned, yes, it was allowed up through the 2008 Code.

The problem arises when other conductive paths are added in the future. Probably why it’s no longer allowed.

As far as ground rods, those are less important. I’m not going to go into the details as you are not an electrician and we are not permitted to provide diy advice here. Your best option is probably an evaluation by a competent Electrical Contractor.

 

[teknomedic]

I appreciate the reply. I'm not looking for DIY advice, but to understand the code for 1993-1995 time frame as the two local electricians I've had over gave different answers (and of course different costs related to those answers). When I tried to dig up the proper information online to sort out which is correct it became murky. Unfortunately for me the previous owner was found to have cut corners on nearly all aspects of this home and I've been correcting them as I find them. I'm about to add a dedicated 240v/20a at the sub-panel, but when the sub-panel was opened we found the bonded neutral/ground situation. I've helped setup a couple sub-panels in the past, but those were new installs with 4 wire service and non-bonded neutral/ground.

That all said, I've been considering heading back to school for electrical work as I've always found this field interesting. Digging into this issue has been enjoyable for me and I think I'll be applying for the next semester.