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.

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 .

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.

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.

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.

That is dangerous! WOW!

Which part?

Using the earth as a conductor!

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.

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
Licensed Radon Professional
Licensed Home Inspector

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)

2017 NEC would be the basis for my recommendation that it does not meet current safety standards. I dont care when it was built, wrong is wrong. My job is to point it out not to decide if it will or will not be repaired. I take this position because like Dan we have areas that dont enforce anything code wise.

Are you saying that a 3 wire system is unsafe?

I’ve approved hundreds of them and would today if Ohio wasn’t on the 2017 NEC

The question new inspectors often ask me is WHERE do you stop.

We are not code inspectors, and a 1961 house does NOT meet current building codes in hundreds of ways.

AND if you are somewhere that they are using the 2006 code … WHERE do you stop OR where do you start picking & choosing what you’re gonna say …

In Ohio, if you haven’t modified your 1961 house it IS code compliant.

Please be careful when you say not up to code!

I think that it’s more of a question as to whether or not it’s unsafe. Unless a parallel metallic path has been added between the structures IMO it’s not unsafe.