Detached garage has a 4-wire feed to a 100-amp sub-panel. Would this set up require ground rods? I thought that it would but an electrician and electrical inspector said no. He said if it were a 3-wire feed ground rods would be required. It was my understanding that this would provide lightning protection for the structure. If it does not require ground rods why not?
In Canada you can have only one Ground for a system.
Having a second ground like in an out building can cause al sorts of concern like Eddie currents
Added here is a couple … Roy
Not necessarily a “ground-rod,” but a grounding electrode is required. There are several ways to provide a grounding electrode system.
250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).
(A) Grounding Electrode. Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with Part III of Article 250. The grounding electrode conductor( s) shall be connected in accordance with 250.32(B) or ©. Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed.
Both the electrician and inspector are incorrect. Any outbuilding served by more than one circuit would require a grounding electrode system. Jeff has provided the code articles.
This requirement has been around for decades so I’m surprised that both the EI and EC got it wrong.
Question for Roy C.
Do you mean a neutral ground or are you talking a grounding electrode system? Here under the NEC you would only have one neutral connection supplied from the service panel. The additional GES at the outbuilding is for lightning etc.
Neutral to Ground only in First panel .
You still must take four wires to all out buildings .
And the neutral can not be bonded to other panels in the system .
We have some who want to take only three wires not allowed here .
Thank you all for the helpful info
Sounds the same as here Roy. Prior to the 08 NEC a 3 wire feeder was allowed with a neutral and ground re-bonding. This has been removed except for existing installations. There were also specific conditions that had to be met like no other metallic paths between buildings.
I am trying to find out what year the 2 rod grounding was introduced?
The 1940 NEC required made electrodes to have a resistance of 25 ohms or less or be supplemented by an additional electrode. My guess is that this was often not enforced or it was assumed that the electrode had a resistance of 25 ohms or less. Around here we didn’t start installing two rods until the early 90’s.