Go Back  DoItYourself.com Community Forums > Electrical, AC & DC. Electronic Equipment and Computers > Electrical - AC & DC
Reload this Page >

Home Portable Generators -- To Bond or Not To Bond, That Is The Question.

Home Portable Generators -- To Bond or Not To Bond, That Is The Question.

Reply

  #1  
Old 06-06-14, 05:05 PM
Member
Thread Starter
Join Date: Jun 2014
Location: USA
Posts: 4
Home Portable Generators -- To Bond or Not To Bond, That Is The Question.

Hi to all ... looking for sanity in the code vs. inspector vs. contractor world. Here's the situation... caught in the middle of debate and looking for something authoritative to break the log jamb.

Situation.
- Standard home panel with 150A service. Installed panel appropriate 50A manual interlock system for portable generator to service whole home when local utility drops out.
- Have a 15kw GENERAC portable generator in an outbuilding about 50' from main house panel.
- Currently hump 80lbs 50' 6/3+8/1 molded weather tight power cable out in snow and storms every time I need to fire up due to local utility outage; getting old ... tired of the extra duty ... outages more frequent than expected.
- Renting a ditch-witch for an unrelated project, and have opportunity to bury UF-B 6/3+8/1 direct burial cable, which is ok by local code. Will go +24" deep and encase in 1-1/2" pvc conduit and concrete and run to inside pre-panel safety switch.

All above is sound ... just background.

Here's the issue....

- NEC is clear that subpanels in outbuildings fed by main panels need to separate the neutral-ground bond in the subpanel, and have their own ground to ground rods to carry stray current.

- Code isn't so clear when the home main panel becomes the subpanel, being fed by the outbuilding generator through an interlock breaker in the main panel. This is much different than use of a neutral/ground opening manual transfer switch, which is a $K solution I'd prefer to avoid.

- Key question ... do I need to bond or unbond the neutral-ground connection in the outbuilding?? And ... does the generator need to have an independent ground rod for either the power cable or permanent buried wire solution?

Please help the old fart DIY member to a peaceful solution. Appreciate any {NEC compliant} info and advice from all, who without doubt, are smarter than me!!

Thank you!!
 
Sponsored Links
  #2  
Old 06-06-14, 06:10 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,461
Welcome to the forums.

A little clarification needed. You have a 150A main panel and you are using an interlocked 50A breaker in that same panel.... correct ?

The generator line needs to connect directly to that panel.

I'm not sure where the sub panel question is coming into play here.
 
  #3  
Old 06-06-14, 07:12 PM
Justin Smith's Avatar
Member
Join Date: Dec 2010
Location: Cressona, Pa, USA
Posts: 2,546
It seems he is asking whether he needs a neutral switching transfer switch for a portable generator?
 
  #4  
Old 06-06-14, 07:18 PM
Member
Join Date: Mar 2010
Location: USA
Posts: 2,851
Neutral and ground remain unbonded at the outbuilding subpanel.

You may not use the same cable running between buildings to feed utility power from the main building to the outbuilidng and also (during utility power outage) feed generator power from the outbuilding to the main building.

You could put an interlock and backfeed breaker at the main panel to feed the outbuilding subpanel and the generator is connected directly to said outbuilding subpanel but then the outbuilding will not be eligible to receive utility power at any time.

If the generator happens to be near the outbuilding then the generator cable is not connected to anything else at the outbuilding. No changes are needed for the outbuilding subpanel or any of its appurtenances such as ground rods except that the generator frame may be connected to any existing ground rod.

The new buried generator cable is connected in the same fashion as the portable cable you have been using up until now. (I take it that the portable cable is hooked up to the generator only and directly.) The new buried generator cable is connected in the same fashion as if the generator were sitting next to the main building instead of next to the outbuilding..
 

Last edited by AllanJ; 06-06-14 at 07:48 PM.
  #5  
Old 06-07-14, 04:13 AM
Member
Join Date: Jan 2014
Location: USA
Posts: 699
My experience is mostly with larger , permanent mounted generators . Or trailer mounted generators for temporary use .

The connection involves a conductor for each phase , the neutral and earth ground . These are tied in via either a manual or automatic transfer switch . Since these are usually 3 phase , a 3 pole MTS or ATS . The neutral is kept strictly separate from the earth ground .

On permanent installations , the generator frame is is often connected to one or more ground rods .

Best I remember , if the neutral and earth ground are bonded at the generator , a 4 pole MTS or ATS is required .

Both methods are , I believe NEC legal ?

Of course , the OP is almost certainly dealing with 1 phase , so , it would be a choice between 2 and 3 pole switching .

I personally would use the 2 pole interlocked CB he refers to . And not bond the neutral and earth ground , at the generator .

God bless
Wyr
 
  #6  
Old 06-08-14, 03:15 PM
Member
Thread Starter
Join Date: Jun 2014
Location: USA
Posts: 4
Thank you all for your help and advice. Sorry I've been off line and late to respond. Also sorry for any confusion my write up caused.

The sub-panel element was just an analogy ... no sub-panels involved, and no power going from house to outbuilding.

Generator only powers the house, and only through the 50A temp power cord when deployed during utility power outages.

There's no earth ground rod at the out building, and as I understand it, the genset internally ties the neutral and frame ground wire to the ground socket in genset 14-50R connector, which takes the ground plug from the power cord 14-50P molded end, which then ties the 8/1 green wire to the earth ground in the main house panel.

For added context ... the 50A interlock breaker is set in the main house panel immediately next to the 150A main house breaker. It serves as a manual transfer switch, but only deals with the red and black hot feeds from the genset; it does not do anything with the neutral or earth ground. The interlock has a safety bar so I can only close the 50A genset supply breaker after I've opened the 150A utility main feed breaker; no way to have both closed at the same time.

Mr. Smith is correct ... that's the fundamental question. Do I need to open the neutral/earth bond in the house panel when I feed the main panel through the 50A interlock breaker.

Adding in Mr. J and Mr. Twister's thoughts, sounds like I should treat the buried UF-B just like I do the temp power cord, and should have no reason to monkey with the neutral/earth bond in the main house panel.

Again ... thanks all for your help and guidance.
 
  #7  
Old 06-08-14, 03:27 PM
Justin Smith's Avatar
Member
Join Date: Dec 2010
Location: Cressona, Pa, USA
Posts: 2,546
I would not worry about un-bonding the generator.
 
  #8  
Old 06-08-14, 05:11 PM
Member
Join Date: Mar 2010
Location: USA
Posts: 2,851
... Mr. Smith is correct ... that's the fundamental question. Do I need to open the neutral/earth bond in the house panel when I feed the main panel through the 50A interlock breaker. ...
(copied from another forum)

Technically yes, if the generator has neutral and ground bonded then a panel being fed by that generator is not supposed to ahve neutral and ground bonded.

BUT ... I would not go monkeying around with the main panel to get all the neutral wires onto one bus and all the ground wires onto another bus. (Subpanels should already have neutrals and grounds separated.) And I would not go monkeying around with the generator to unbond neutral and ground unless the instructions point out how to do that or it is easy by looking at it.

SO ... this is a situation where I say (and recommend), ignore the fact that neutral and ground might remain bonded in two places.

Psst! The extra neutral and ground bond situation here is not hazardous.

Note that substituting a whole house transfer switch that switches the neutral (has 3 poles) for the backfeed breaker and mechanical interlock will not in itself correct neutral and grounding in two places. And a neutral switching transfer switch introduces one more mechanical part that could malfunction and result in an open neutral which as a very bad situation to get into.
 

Last edited by AllanJ; 06-08-14 at 05:31 PM.
  #9  
Old 06-08-14, 07:35 PM
Member
Thread Starter
Join Date: Jun 2014
Location: USA
Posts: 4
Thumbs up

You guys are fantastic ... thanks so much!
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'