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-   -   3 vs 4 wire feed to garage (https://www.nachi.org/forum/f19/3-vs-4-wire-feed-garage-133917/)

dkostenbader 1/17/19 5:14 PM

3 vs 4 wire feed to garage
 
I was wondering if anyone could explain the need for a four wire feed to a separate building apart from the house. In the case of the house I looked at today there was a separate garage with a subpanel fed by a three wire overhead feed. The grounds and neutrals were separate. To my knowledge there wasn't any water or gas line going out to the garage. This should be a four wire feed, correct? And wasn't this a relatively recent change to the code?

Thank you as always.

dwigger 1/17/19 5:52 PM

Re: 3 vs 4 wire feed to garage
 
Sub panels require a 4-wire feed. 2 hot, neutral and ground. If only a 3-wire is present, a separate isolated ground can be used at the sub panel location. (i.e. grounding electrode with ground conductor)

rcooke 1/17/19 5:58 PM

Re: 3 vs 4 wire feed to garage
 
Quote:

Originally Posted by dwigger (Post 2043018)
Sub panels require a 4-wire feed. 2 hot, neutral and ground. If only a 3-wire is present, a separate isolated ground can be used at the sub panel location. (i.e. grounding electrode with ground conductor)


Separate ground not allowed in Canada 4 wires are required .
I do think this also a requirement in some USA places .

Robert Meier 1/17/19 6:32 PM

Re: 3 vs 4 wire feed to garage
 
Quote:

Originally Posted by dkostenbader (Post 2042983)
I was wondering if anyone could explain the need for a four wire feed to a separate building apart from the house. In the case of the house I looked at today there was a separate garage with a subpanel fed by a three wire overhead feed. The grounds and neutrals were separate. To my knowledge there wasn't any water or gas line going out to the garage. This should be a four wire feed, correct? And wasn't this a relatively recent change to the code?

Thank you as always.


Up until the 2008 NEC code cycle 3 wire feeders were permitted if there were no metallic paths between the two structures. From 2008 and beyond a 4-wire feeder is required. If there is an old 3-wire feeder you must bond the neutral just like in a service and connect the GEC from your grounding electrodes to the neutral.


With a 4-wire feeder the EGC's and neutrals are separate and the GEC goes to the EGC bus which is bonded to the enclosure, the neutral is left floating.

dwigger 1/17/19 7:12 PM

Re: 3 vs 4 wire feed to garage
 
Quote:

Originally Posted by Robert Meier (Post 2043054)
Up until the 2008 NEC code cycle 3 wire feeders were permitted if there were no metallic paths between the two structures. From 2008 and beyond a 4-wire feeder is required. If there is an old 3-wire feeder you must bond the neutral just like in a service and connect the GEC from your grounding electrodes to the neutral.


With a 4-wire feeder the EGC's and neutrals are separate and the GEC goes to the EGC bus which is bonded to the enclosure, the neutral is left floating.


Robert, thanks for the specific dates. Now I understand why I see it both ways in my neck of the woods.

Robert Meier 1/17/19 7:23 PM

Re: 3 vs 4 wire feed to garage
 
Quote:

Originally Posted by dwigger (Post 2043074)
Robert, thanks for the specific dates. Now I understand why I see it both ways in my neck of the woods.


You're welcome, and depending on when a jurisdiction adopted the 2008 NEC you might even see this on new installations beyond 2008 which may have been code compliant when installed.

dkostenbader 1/17/19 7:24 PM

Re: 3 vs 4 wire feed to garage
 
Excellent clarification. Thank you everyone. This one did have a separate ground from the panel. It looked fairly recent but I don't know when it was done exactly.

mparks2 1/22/19 5:13 PM

Re: 3 vs 4 wire feed to garage
 
Quote:

Originally Posted by dwigger (Post 2043018)
Sub panels require a 4-wire feed. 2 hot, neutral and ground. If only a 3-wire is present, a separate isolated ground can be used at the sub panel location. (i.e. grounding electrode with ground conductor)

That is dangerous! WOW!

Robert Meier 1/23/19 4:11 PM

Re: 3 vs 4 wire feed to garage
 
Quote:

Originally Posted by mparks2 (Post 2045890)
That is dangerous! WOW!


Which part?

mparks2 1/24/19 3:07 PM

Re: 3 vs 4 wire feed to garage
 
Quote:

Originally Posted by Robert Meier (Post 2046579)
Which part?

Using the earth as a conductor!

jolson8 1/25/19 10:49 AM

Re: 3 vs 4 wire feed to garage
 
Quote:

Originally Posted by Robert Meier (Post 2043054)
Up until the 2008 NEC code cycle 3 wire feeders were permitted if there were no metallic paths between the two structures. From 2008 and beyond a 4-wire feeder is required. If there is an old 3-wire feeder you must bond the neutral just like in a service and connect the GEC from your grounding electrodes to the neutral.


With a 4-wire feeder the EGC's and neutrals are separate and the GEC goes to the EGC bus which is bonded to the enclosure, the neutral is left floating.


In a 3-wire sub(distribution) panel the grounds and neutral should not be separated?

Robert Meier 1/25/19 3:55 PM

Re: 3 vs 4 wire feed to garage
 
Quote:

Originally Posted by jolson8 (Post 2047731)
In a 3-wire sub(distribution) panel the grounds and neutral should not be separated?


Actually they cannot be. If you isolate the EGC and neutral there will be no return path for the current to open an OCPD and the system will be ungrounded.


If you think of it like a service the reason that a ground fault to an EGC trips the OCPD is because the EGC's and the neutral are bonded together. With a 3-wire feeder you would also have to bond the EGC to the neutral for a ground fault to open the OCPD. For separate structures this was permitted until it changed with the 2008 NEC.

dhawley 1/27/19 2:07 PM

Re: 3 vs 4 wire feed to garage
 
Also note that a detached structure requires a grounding source (ground rod) whether it is a 3 or 4 wire remote panel. The ground rod can not be used as the only source of grounding and must be tied to the neutral if only a 3 wire feed. Best to upgrade to 4 wire but how many of us would do that.

Don Hawley CPI
Hawley Home Inspections LLC

Home Inspection Services, Termite, Radon & Sewer Scope
DonHawley575@gmail.com
Licensed Radon Professional
Licensed Home Inspector

dbowers 1/30/19 11:59 PM

Re: 3 vs 4 wire feed to garage
 
Like Robert said .............


In KC there are 81 cities or towns making up the metroplex ...... of them NONE currently use anything past the 2012 NEC.


A dozen use the 2002 NEC and 2 still use the 1999 NEC


So as a home inspector WHICH version do you quote OR do you THINK you should use IF thinking CODE is in your bucket

mparks2 1/31/19 5:10 PM

Re: 3 vs 4 wire feed to garage
 
Quote:

Originally Posted by dbowers (Post 2051684)
Like Robert said .............


In KC there are 81 cities or towns making up the metroplex ...... of them NONE currently use anything past the 2012 NEC.


A dozen use the 2002 NEC and 2 still use the 1999 NEC


So as a home inspector WHICH version do you quote OR do you THINK you should use IF thinking CODE is in your bucket


Nothing UNSAFE with a 3 wire system - as long as you do not have any paralleled conductors. (No need for a 4 wire system to an out building IMHO)


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